ceph/src/boost/libs/context/doc/context.xml

   1 <?xml version="1.0" encoding="UTF-8"?>
   2 <!DOCTYPE library PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN" "http://www.boost.org/tools/boostbook/dtd/boostbook.dtd">
   3 <library id="context" name="Context" dirname="context" last-revision="$Date: 2016/03/04 17:27:33 $"
   4  xmlns:xi="http://www.w3.org/2001/XInclude">
   5   <libraryinfo>
   6     <authorgroup>
   7     <author>
   8       <firstname>Oliver</firstname> <surname>Kowalke</surname>
   9     </author>
  10     </authorgroup>
  11     <copyright>
  12       <year>2014</year> <holder>Oliver Kowalke</holder>
  13     </copyright>
  14     <legalnotice id="context.legal">
  15       <para>
  16         Distributed under the Boost Software License, Version 1.0. (See accompanying
  17         file LICENSE_1_0.txt or copy at <ulink url="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</ulink>)
  18       </para>
  19     </legalnotice>
  20     <librarypurpose>
  21       C++ Library for swiching different user ctx
  22     </librarypurpose>
  23     <librarycategory name="category:text"></librarycategory>
  24   </libraryinfo>
  25   <title>Context</title>
  26   <section id="context.overview">
  27     <title><link linkend="context.overview">Overview</link></title>
  28     <para>
  29       <emphasis role="bold">Boost.Context</emphasis> is a foundational library that
  30       provides a sort of cooperative multitasking on a single thread. By providing
  31       an abstraction of the current execution state in the current thread, including
  32       the stack (with local variables) and stack pointer, all registers and CPU flags,
  33       and the instruction pointer, a <emphasis>execution_context</emphasis> represents
  34       a specific point in the application's execution path. This is useful for building
  35       higher-level abstractions, like <emphasis>coroutines</emphasis>, <emphasis>cooperative
  36       threads (userland threads)</emphasis> or an equivalent to <ulink url="http://msdn.microsoft.com/en-us/library/9k7k7cf0%28v=vs.80%29.aspx">C#
  37       keyword <emphasis>yield</emphasis></ulink> in C++.
  38     </para>
  39     <para>
  40       <emphasis>execution_context</emphasis> provides the means to suspend the current
  41       execution path and to transfer execution control, thereby permitting another
  42       context to run on the current thread. This state full transfer mechanism enables
  43       a context to suspend execution from within nested functions and, later, to
  44       resume from where it was suspended. While the execution path represented by
  45       a <emphasis>execution_context</emphasis> only runs on a single thread, it can
  46       be migrated to another thread at any given time.
  47     </para>
  48     <para>
  49       A context switch between threads requires system calls (involving the OS kernel),
  50       which can cost more than thousand CPU cycles on x86 CPUs. By contrast, transferring
  51       control among them requires only few CPU cycles because it does not involve
  52       system calls as it is done within a single thread.
  53     </para>
  54     <para>
  55       In order to use the classes and functions described here, you can either include
  56       the specific headers specified by the descriptions of each class or function,
  57       or include the master library header:
  58     </para>
  59 <programlisting><phrase role="preprocessor">#include</phrase> <phrase role="special">&lt;</phrase><phrase role="identifier">boost</phrase><phrase role="special">/</phrase><phrase role="identifier">context</phrase><phrase role="special">/</phrase><phrase role="identifier">all</phrase><phrase role="special">.</phrase><phrase role="identifier">hpp</phrase><phrase role="special">&gt;</phrase>
  60 </programlisting>
  61     <para>
  62       which includes all the other headers in turn.
  63     </para>
  64     <para>
  65       All functions and classes are contained in the namespace <emphasis>boost::context</emphasis>.
  66     </para>
  67     <important>
  68       <para>
  69         <emphasis>execution_context</emphasis> requires C++11!
  70       </para>
  71     </important>
  72   </section>
  73   <section id="context.requirements">
  74     <title><link linkend="context.requirements">Requirements</link></title>
  75     <para>
  76       <emphasis role="bold">Boost.Context</emphasis> must be built for the particular
  77       compiler(s) and CPU architecture(s)s being targeted. <emphasis role="bold">Boost.Context</emphasis>
  78       includes assembly code and, therefore, requires GNU as and GNU preprocesspr
  79       for supported POSIX systems, MASM for Windows/x86 systems and ARMasm for Windows/arm
  80       systems.
  81     </para>
  82     <note>
  83       <para>
  84         MASM64 (ml64.exe) is a part of Microsoft's Windows Driver Kit.
  85       </para>
  86     </note>
  87     <important>
  88       <para>
  89         Please note that <code><phrase role="identifier">address</phrase><phrase
  90         role="special">-</phrase><phrase role="identifier">model</phrase><phrase
  91         role="special">=</phrase><phrase role="number">64</phrase></code> must be
  92         given to bjam command line on 64bit Windows for 64bit build; otherwise 32bit
  93         code will be generated.
  94       </para>
  95     </important>
  96     <important>
  97       <para>
  98         For cross-compiling the lib you must specify certain additional properties
  99         at bjam command line: <code><phrase role="identifier">target</phrase><phrase
 100         role="special">-</phrase><phrase role="identifier">os</phrase></code>, <code><phrase
 101         role="identifier">abi</phrase></code>, <code><phrase role="identifier">binary</phrase><phrase
 102         role="special">-</phrase><phrase role="identifier">format</phrase></code>,
 103         <code><phrase role="identifier">architecture</phrase></code> and <code><phrase
 104         role="identifier">address</phrase><phrase role="special">-</phrase><phrase
 105         role="identifier">model</phrase></code>.
 106       </para>
 107     </important>
 108     <important>
 109       <para>
 110         For safe SEH the property 'asmflags=\safeseh' must be specified at bjam command
 111         line.
 112       </para>
 113     </important>
 114   </section>
 115   <section id="context.ecv2">
 116     <title><anchor id="ecv2"/><link linkend="context.ecv2">Class execution_context
 117     (version 2)</link></title>
 118     <note>
 119       <para>
 120         This class is enabled per default.
 121       </para>
 122     </note>
 123     <para>
 124       Class <emphasis>execution_context</emphasis> encapsulates context switching
 125       and manages the associated context' stack (allocation/deallocation).
 126     </para>
 127     <para>
 128       <emphasis>execution_context</emphasis> allocates the context stack (using its
 129       <link linkend="stack"><emphasis>StackAllocator</emphasis></link> argument)
 130       and creates a control structure on top of it. This structure is responsible
 131       for managing context' stack. The address of the control structure is stored
 132       in the first frame of context' stack (e.g. it can not directly accessed from
 133       within <emphasis>execution_context</emphasis>). In contrast to <link linkend="ecv1"><emphasis>execution_context</emphasis>
 134       (v1)</link> the ownership of the control structure is not shared (no member
 135       variable to control structure in <emphasis>execution_context</emphasis>).
 136       <emphasis>execution_context</emphasis> keeps internally a state that is moved
 137       by a call of <emphasis>execution_context::operator()</emphasis> (<code><phrase
 138       role="special">*</phrase><phrase role="keyword">this</phrase></code> will be
 139       invalidated), e.g. after a calling <emphasis>execution_context::operator()</emphasis>,
 140       <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>
 141       can not be used for an additional context switch.
 142     </para>
 143     <para>
 144       <emphasis>execution_context</emphasis> is only move-constructible and move-assignable.
 145     </para>
 146     <para>
 147       The moved state is assigned to a new instance of <emphasis>execution_context</emphasis>.
 148       This object becomes the first argument of the context-function, if the context
 149       was resumed the first time, or the first element in a tuple returned by <emphasis>execution_context::operator()</emphasis>
 150       that has been called in the resumed context. In contrast to <link linkend="ecv1"><emphasis>execution_context</emphasis>
 151       (v1)</link>, the context switch is faster because no global pointer etc. is
 152       involved.
 153     </para>
 154     <important>
 155       <para>
 156         Segmented stacks are not supported by <emphasis>execution_context</emphasis>
 157         (v2).
 158       </para>
 159     </important>
 160     <para>
 161       On return the context-function of the current context has to specify an <emphasis>execution_context</emphasis>
 162       to which the execution control is transferred after termination of the current
 163       context.
 164     </para>
 165     <para>
 166       If an instance with valid state goes out of scope and the context-function
 167       has not yet returned, the stack is traversed in order to access the control
 168       structure (address stored at the first stack frame) and context' stack is deallocated
 169       via the <emphasis>StackAllocator</emphasis>. The stack walking makes the destruction
 170       of <emphasis>execution_context</emphasis> slow and should be prevented if possible.
 171     </para>
 172     <para>
 173       <emphasis>execution_context</emphasis> expects a <emphasis>context-function</emphasis>
 174       with signature <code><phrase role="identifier">execution_context</phrase><phrase
 175       role="special">(</phrase><phrase role="identifier">execution_context</phrase>
 176       <phrase role="identifier">ctx</phrase><phrase role="special">,</phrase> <phrase
 177       role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase
 178       role="identifier">args</phrase><phrase role="special">)</phrase></code>. The
 179       parameter <code><phrase role="identifier">ctx</phrase></code> represents the
 180       context from which this context was resumed (e.g. that has called <emphasis>execution_context::operator()</emphasis>
 181       on <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>)
 182       and <code><phrase role="identifier">args</phrase></code> are the data passed
 183       to <emphasis>execution_context::operator()</emphasis>. The return value represents
 184       the execution_context that has to be resumed, after termiantion of this context.
 185     </para>
 186     <para>
 187       Benefits of <link linkend="ecv2"><emphasis>execution_context</emphasis> (v2)</link>
 188       over <link linkend="ecv1"><emphasis>execution_context</emphasis> (v1)</link>
 189       are: faster context switch, type-safety of passed/returned arguments.
 190     </para>
 191     <bridgehead renderas="sect3" id="context.ecv2.h0">
 192       <phrase id="context.ecv2.usage_of__emphasis_execution_context__emphasis_"/><link
 193       linkend="context.ecv2.usage_of__emphasis_execution_context__emphasis_">usage
 194       of <emphasis>execution_context</emphasis></link>
 195     </bridgehead>
 196 <programlisting><phrase role="keyword">int</phrase> <phrase role="identifier">n</phrase><phrase role="special">=</phrase><phrase role="number">35</phrase><phrase role="special">;</phrase>
 197 <phrase role="identifier">ctx</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">source</phrase><phrase role="special">(</phrase>
 198     <phrase role="special">[</phrase><phrase role="identifier">n</phrase><phrase role="special">](</phrase><phrase role="identifier">ctx</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">sink</phrase><phrase role="special">,</phrase> <phrase role="keyword">int</phrase><phrase role="special">)</phrase> <phrase role="keyword">mutable</phrase> <phrase role="special">{</phrase>
 199         <phrase role="keyword">int</phrase> <phrase role="identifier">a</phrase><phrase role="special">=</phrase><phrase role="number">0</phrase><phrase role="special">;</phrase>
 200         <phrase role="keyword">int</phrase> <phrase role="identifier">b</phrase><phrase role="special">=</phrase><phrase role="number">1</phrase><phrase role="special">;</phrase>
 201         <phrase role="keyword">while</phrase><phrase role="special">(</phrase><phrase role="identifier">n</phrase><phrase role="special">--&gt;</phrase><phrase role="number">0</phrase><phrase role="special">){</phrase>
 202             <phrase role="keyword">auto</phrase> <phrase role="identifier">result</phrase><phrase role="special">=</phrase><phrase role="identifier">sink</phrase><phrase role="special">(</phrase><phrase role="identifier">a</phrase><phrase role="special">);</phrase>
 203             <phrase role="identifier">sink</phrase><phrase role="special">=</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">move</phrase><phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="number">0</phrase><phrase role="special">&gt;(</phrase><phrase role="identifier">result</phrase><phrase role="special">));</phrase>
 204             <phrase role="keyword">auto</phrase> <phrase role="identifier">next</phrase><phrase role="special">=</phrase><phrase role="identifier">a</phrase><phrase role="special">+</phrase><phrase role="identifier">b</phrase><phrase role="special">;</phrase>
 205             <phrase role="identifier">a</phrase><phrase role="special">=</phrase><phrase role="identifier">b</phrase><phrase role="special">;</phrase>
 206             <phrase role="identifier">b</phrase><phrase role="special">=</phrase><phrase role="identifier">next</phrase><phrase role="special">;</phrase>
 207         <phrase role="special">}</phrase>
 208         <phrase role="keyword">return</phrase> <phrase role="identifier">sink</phrase><phrase role="special">;</phrase>
 209     <phrase role="special">});</phrase>
 210 <phrase role="keyword">for</phrase><phrase role="special">(</phrase><phrase role="keyword">int</phrase> <phrase role="identifier">i</phrase><phrase role="special">=</phrase><phrase role="number">0</phrase><phrase role="special">;</phrase><phrase role="identifier">i</phrase><phrase role="special">&lt;</phrase><phrase role="number">10</phrase><phrase role="special">;++</phrase><phrase role="identifier">i</phrase><phrase role="special">){</phrase>
 211     <phrase role="keyword">auto</phrase> <phrase role="identifier">result</phrase><phrase role="special">=</phrase><phrase role="identifier">source</phrase><phrase role="special">(</phrase><phrase role="identifier">i</phrase><phrase role="special">);</phrase>
 212     <phrase role="identifier">source</phrase><phrase role="special">=</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">move</phrase><phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="number">0</phrase><phrase role="special">&gt;(</phrase><phrase role="identifier">result</phrase><phrase role="special">));</phrase>
 213     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase><phrase role="special">&lt;&lt;</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="number">1</phrase><phrase role="special">&gt;(</phrase><phrase role="identifier">result</phrase><phrase role="special">)&lt;&lt;</phrase><phrase role="string">&quot; &quot;</phrase><phrase role="special">;</phrase>
 214 <phrase role="special">}</phrase>
 215
 216 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
 217     <phrase role="number">0</phrase> <phrase role="number">1</phrase> <phrase role="number">1</phrase> <phrase role="number">2</phrase> <phrase role="number">3</phrase> <phrase role="number">5</phrase> <phrase role="number">8</phrase> <phrase role="number">13</phrase> <phrase role="number">21</phrase> <phrase role="number">34</phrase>
 218 </programlisting>
 219     <para>
 220       This simple example demonstrates the basic usage of <emphasis>execution_context</emphasis>
 221       as a generator. The context <code><phrase role="identifier">sink</phrase></code>
 222       represents the <emphasis>main</emphasis>-context (function <emphasis>main()</emphasis>
 223       running). <code><phrase role="identifier">sink</phrase></code> is generated
 224       by the framework (first element of lambda's parameter list). Because the state
 225       is invalidated (== changed) by each call of <emphasis>execution_context::operator()</emphasis>,
 226       the new state of the <emphasis>execution_context</emphasis>, returned by <emphasis>execution_context::operator()</emphasis>,
 227       needs to be assigned to <code><phrase role="identifier">sink</phrase></code>
 228       after each call.
 229     </para>
 230     <para>
 231       The lambda that calculates the Fibonacci numbers is executed inside the context
 232       represented by <code><phrase role="identifier">source</phrase></code>. Calculated
 233       Fibonacci numbers are transferred between the two context' via expression
 234       <emphasis>sink(a)</emphasis> (and returned by <emphasis>source()</emphasis>).
 235       Note that this example represents a <emphasis>generator</emphasis> thus the
 236       value transferred into the lambda via <emphasis>source()</emphasis> is not
 237       used. Using <emphasis>boost::optional&lt;&gt;</emphasis> as transferred type,
 238       might also appropriate to express this fact.
 239     </para>
 240     <para>
 241       The locale variables <code><phrase role="identifier">a</phrase></code>, <code><phrase
 242       role="identifier">b</phrase></code> and <code> <phrase role="identifier">next</phrase></code>
 243       remain their values during each context switch (<emphasis>yield(a)</emphasis>).
 244       This is possible due <code><phrase role="identifier">source</phrase></code>
 245       has its own stack and the stack is exchanged by each context switch.
 246     </para>
 247     <bridgehead renderas="sect3" id="context.ecv2.h1">
 248       <phrase id="context.ecv2.parameter_passing"/><link linkend="context.ecv2.parameter_passing">parameter
 249       passing</link>
 250     </bridgehead>
 251     <para>
 252       With <code><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase
 253       role="keyword">void</phrase><phrase role="special">&gt;</phrase></code> no
 254       data will be transferred, only the context switch is executed.
 255     </para>
 256 <programlisting><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">void</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">ctx1</phrase><phrase role="special">([](</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">void</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">ctx2</phrase><phrase role="special">){</phrase>
 257             <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">printf</phrase><phrase role="special">(</phrase><phrase role="string">&quot;inside ctx1\n&quot;</phrase><phrase role="special">);</phrase>
 258             <phrase role="keyword">return</phrase> <phrase role="identifier">ctx2</phrase><phrase role="special">();</phrase>
 259         <phrase role="special">});</phrase>
 260 <phrase role="identifier">ctx1</phrase><phrase role="special">();</phrase>
 261
 262 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
 263     <phrase role="identifier">inside</phrase> <phrase role="identifier">ctx1</phrase>
 264 </programlisting>
 265     <para>
 266       <code><phrase role="identifier">ctx1</phrase><phrase role="special">()</phrase></code>
 267       resumes <code><phrase role="identifier">ctx1</phrase></code>, e.g. the lambda
 268       passed at the constructor of <code><phrase role="identifier">ctx1</phrase></code>
 269       is entered. Argument <code><phrase role="identifier">ctx2</phrase></code> represents
 270       the context that has been suspended with the invocation of <code><phrase role="identifier">ctx1</phrase><phrase
 271       role="special">()</phrase></code>. When the lambda returns <code><phrase role="identifier">ctx2</phrase></code>,
 272       context <code><phrase role="identifier">ctx1</phrase></code> will be terminated
 273       while the context represented by <code><phrase role="identifier">ctx2</phrase></code>
 274       is resumed, hence the control of execution returns from <code><phrase role="identifier">ctx1</phrase><phrase
 275       role="special">()</phrase></code>.
 276     </para>
 277     <para>
 278       The arguments passed to <emphasis>execution_context::operator()</emphasis>,
 279       in one context, is passed as the last arguments of the <emphasis>context-function</emphasis>
 280       if the context is started for the first time. In all following invocations
 281       of <emphasis>execution_context::operator()</emphasis> the arguments passed
 282       to <emphasis>execution_context::operator()</emphasis>, in one context, is returned
 283       by <emphasis>execution_context::operator()</emphasis> in the other context.
 284     </para>
 285 <programlisting><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">ctx1</phrase><phrase role="special">([](</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">ctx2</phrase><phrase role="special">,</phrase> <phrase role="keyword">int</phrase> <phrase role="identifier">j</phrase><phrase role="special">){</phrase>
 286             <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">printf</phrase><phrase role="special">(</phrase><phrase role="string">&quot;inside ctx1, j == %d\n&quot;</phrase><phrase role="special">,</phrase> <phrase role="identifier">j</phrase><phrase role="special">);</phrase>
 287             <phrase role="keyword">return</phrase> <phrase role="identifier">ctx2</phrase><phrase role="special">(</phrase><phrase role="identifier">j</phrase><phrase role="special">+</phrase><phrase role="number">1</phrase><phrase role="special">);</phrase>
 288         <phrase role="special">});</phrase>
 289 <phrase role="keyword">int</phrase> <phrase role="identifier">i</phrase> <phrase role="special">=</phrase> <phrase role="number">1</phrase><phrase role="special">;</phrase>
 290 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tie</phrase><phrase role="special">(</phrase><phrase role="identifier">ctx1</phrase><phrase role="special">,</phrase> <phrase role="identifier">i</phrase><phrase role="special">)</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx1</phrase><phrase role="special">(</phrase><phrase role="identifier">i</phrase><phrase role="special">);</phrase>
 291 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">printf</phrase><phrase role="special">(</phrase><phrase role="string">&quot;i == %d\n&quot;</phrase><phrase role="special">,</phrase> <phrase role="identifier">i</phrase><phrase role="special">);</phrase>
 292
 293 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
 294     <phrase role="identifier">inside</phrase> <phrase role="identifier">ctx1</phrase><phrase role="special">,</phrase> <phrase role="identifier">j</phrase> <phrase role="special">==</phrase> <phrase role="number">1</phrase>
 295     <phrase role="identifier">i</phrase> <phrase role="special">==</phrase> <phrase role="number">2</phrase>
 296 </programlisting>
 297     <para>
 298       <code><phrase role="identifier">ctx1</phrase><phrase role="special">(</phrase><phrase
 299       role="identifier">i</phrase><phrase role="special">)</phrase></code> enters
 300       the lambda in context <code><phrase role="identifier">ctx1</phrase></code>
 301       with argument <code><phrase role="identifier">j</phrase><phrase role="special">=</phrase><phrase
 302       role="number">1</phrase></code>. The expression <code><phrase role="identifier">ctx2</phrase><phrase
 303       role="special">(</phrase><phrase role="identifier">j</phrase><phrase role="special">+</phrase><phrase
 304       role="number">1</phrase><phrase role="special">)</phrase></code> resumes the
 305       context represented by <code><phrase role="identifier">ctx2</phrase></code>
 306       and transfers back an integer of <code><phrase role="identifier">j</phrase><phrase
 307       role="special">+</phrase><phrase role="number">1</phrase></code>. On return
 308       of <code><phrase role="identifier">ctx1</phrase><phrase role="special">(</phrase><phrase
 309       role="identifier">i</phrase><phrase role="special">)</phrase></code>, the variable
 310       <code><phrase role="identifier">i</phrase></code> contains the value of <code><phrase
 311       role="identifier">j</phrase><phrase role="special">+</phrase><phrase role="number">1</phrase></code>.
 312     </para>
 313     <para>
 314       If more than one argument has to be transferred, the signature of the context-function
 315       is simply extended.
 316     </para>
 317 <programlisting><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">,</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">ctx1</phrase><phrase role="special">([](</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">,</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">ctx2</phrase><phrase role="special">,</phrase> <phrase role="keyword">int</phrase> <phrase role="identifier">i</phrase><phrase role="special">,</phrase> <phrase role="keyword">int</phrase> <phrase role="identifier">j</phrase><phrase role="special">){</phrase>
 318             <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">printf</phrase><phrase role="special">(</phrase><phrase role="string">&quot;inside ctx1, i == %d j == %d\n&quot;</phrase><phrase role="special">,</phrase> <phrase role="identifier">i</phrase><phrase role="special">,</phrase> <phrase role="identifier">j</phrase><phrase role="special">);</phrase>
 319             <phrase role="keyword">return</phrase> <phrase role="identifier">ctx2</phrase><phrase role="special">(</phrase><phrase role="identifier">i</phrase><phrase role="special">+</phrase><phrase role="identifier">j</phrase><phrase role="special">,</phrase><phrase role="identifier">i</phrase><phrase role="special">-</phrase><phrase role="identifier">j</phrase><phrase role="special">);</phrase>
 320         <phrase role="special">});</phrase>
 321 <phrase role="keyword">int</phrase> <phrase role="identifier">i</phrase> <phrase role="special">=</phrase> <phrase role="number">2</phrase><phrase role="special">,</phrase> <phrase role="identifier">j</phrase> <phrase role="special">=</phrase> <phrase role="number">1</phrase><phrase role="special">;</phrase>
 322 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tie</phrase><phrase role="special">(</phrase><phrase role="identifier">ctx1</phrase><phrase role="special">,</phrase> <phrase role="identifier">i</phrase><phrase role="special">,</phrase> <phrase role="identifier">j</phrase><phrase role="special">)</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx1</phrase><phrase role="special">(</phrase><phrase role="identifier">i</phrase><phrase role="special">,</phrase><phrase role="identifier">j</phrase><phrase role="special">);</phrase>
 323 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">printf</phrase><phrase role="special">(</phrase><phrase role="string">&quot;i == %d j == %d\n&quot;</phrase><phrase role="special">,</phrase> <phrase role="identifier">i</phrase><phrase role="special">,</phrase> <phrase role="identifier">j</phrase><phrase role="special">);</phrase>
 324
 325 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
 326     <phrase role="identifier">inside</phrase> <phrase role="identifier">ctx1</phrase><phrase role="special">,</phrase> <phrase role="identifier">i</phrase> <phrase role="special">==</phrase> <phrase role="number">2</phrase> <phrase role="identifier">j</phrase> <phrase role="special">==</phrase> <phrase role="number">1</phrase>
 327     <phrase role="identifier">i</phrase> <phrase role="special">==</phrase> <phrase role="number">3</phrase> <phrase role="identifier">j</phrase> <phrase role="special">==</phrase> <phrase role="number">1</phrase>
 328 </programlisting>
 329     <para>
 330       For use-cases, that require to transfer data of different type in each direction,
 331       <emphasis>boost::variant&lt;&gt;</emphasis> could be used.
 332     </para>
 333 <programlisting><phrase role="keyword">class</phrase> <phrase role="identifier">X</phrase><phrase role="special">{</phrase>
 334 <phrase role="keyword">private</phrase><phrase role="special">:</phrase>
 335     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">exception_ptr</phrase> <phrase role="identifier">excptr_</phrase><phrase role="special">;</phrase>
 336     <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">variant</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">,</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase><phrase role="special">&gt;&gt;</phrase> <phrase role="identifier">ctx_</phrase><phrase role="special">;</phrase>
 337
 338 <phrase role="keyword">public</phrase><phrase role="special">:</phrase>
 339     <phrase role="identifier">X</phrase><phrase role="special">():</phrase>
 340         <phrase role="identifier">excptr_</phrase><phrase role="special">(),</phrase>
 341         <phrase role="identifier">ctx_</phrase><phrase role="special">(</phrase>
 342              <phrase role="special">[=](</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">variant</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">,</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase><phrase role="special">&gt;&gt;</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">,</phrase> <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">variant</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">,</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">data</phrase><phrase role="special">){</phrase>
 343                 <phrase role="keyword">try</phrase> <phrase role="special">{</phrase>
 344                     <phrase role="keyword">for</phrase> <phrase role="special">(;;)</phrase> <phrase role="special">{</phrase>
 345                         <phrase role="keyword">int</phrase> <phrase role="identifier">i</phrase> <phrase role="special">=</phrase> <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;(</phrase><phrase role="identifier">data</phrase><phrase role="special">);</phrase>
 346                         <phrase role="identifier">data</phrase> <phrase role="special">=</phrase> <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">lexical_cast</phrase><phrase role="special">&lt;</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase><phrase role="special">&gt;(</phrase><phrase role="identifier">i</phrase><phrase role="special">);</phrase>
 347                         <phrase role="keyword">auto</phrase> <phrase role="identifier">result</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">(</phrase> <phrase role="identifier">data</phrase><phrase role="special">);</phrase>
 348                         <phrase role="identifier">ctx</phrase> <phrase role="special">=</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">move</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="number">0</phrase><phrase role="special">&gt;(</phrase> <phrase role="identifier">result</phrase><phrase role="special">)</phrase> <phrase role="special">);</phrase>
 349                         <phrase role="identifier">data</phrase> <phrase role="special">=</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="number">1</phrase><phrase role="special">&gt;(</phrase> <phrase role="identifier">result</phrase><phrase role="special">);</phrase>
 350                 <phrase role="special">}</phrase> <phrase role="keyword">catch</phrase> <phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">bad_cast</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;)</phrase> <phrase role="special">{</phrase>
 351                     <phrase role="identifier">excptr_</phrase><phrase role="special">=</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">current_exception</phrase><phrase role="special">();</phrase>
 352                 <phrase role="special">}</phrase>
 353                 <phrase role="keyword">return</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">;</phrase>
 354              <phrase role="special">})</phrase>
 355     <phrase role="special">{}</phrase>
 356
 357     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase><phrase role="keyword">int</phrase> <phrase role="identifier">i</phrase><phrase role="special">){</phrase>
 358         <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">variant</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">,</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">data</phrase> <phrase role="special">=</phrase> <phrase role="identifier">i</phrase><phrase role="special">;</phrase>
 359         <phrase role="keyword">auto</phrase> <phrase role="identifier">result</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx_</phrase><phrase role="special">(</phrase> <phrase role="identifier">data</phrase><phrase role="special">);</phrase>
 360         <phrase role="identifier">ctx_</phrase> <phrase role="special">=</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">move</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="number">0</phrase><phrase role="special">&gt;(</phrase> <phrase role="identifier">result</phrase><phrase role="special">)</phrase> <phrase role="special">);</phrase>
 361         <phrase role="identifier">data</phrase> <phrase role="special">=</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="number">1</phrase><phrase role="special">&gt;(</phrase> <phrase role="identifier">result</phrase><phrase role="special">);</phrase>
 362         <phrase role="keyword">if</phrase><phrase role="special">(</phrase><phrase role="identifier">excptr_</phrase><phrase role="special">){</phrase>
 363             <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">rethrow_exception</phrase><phrase role="special">(</phrase><phrase role="identifier">excptr_</phrase><phrase role="special">);</phrase>
 364         <phrase role="special">}</phrase>
 365         <phrase role="keyword">return</phrase> <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase><phrase role="special">&gt;(</phrase><phrase role="identifier">data</phrase><phrase role="special">);</phrase>
 366     <phrase role="special">}</phrase>
 367 <phrase role="special">};</phrase>
 368
 369 <phrase role="identifier">X</phrase> <phrase role="identifier">x</phrase><phrase role="special">;</phrase>
 370 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">x</phrase><phrase role="special">(</phrase> <phrase role="number">7</phrase><phrase role="special">)</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">endl</phrase><phrase role="special">;</phrase>
 371
 372 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
 373 <phrase role="number">7</phrase>
 374 </programlisting>
 375     <para>
 376       In the case of unidirectional transfer of data, <emphasis>boost::optional&lt;&gt;</emphasis>
 377       or a pointer are appropriate.
 378     </para>
 379     <bridgehead renderas="sect3" id="context.ecv2.h2">
 380       <phrase id="context.ecv2.exception_handling"/><link linkend="context.ecv2.exception_handling">exception
 381       handling</link>
 382     </bridgehead>
 383     <para>
 384       If the function executed inside a <emphasis>execution_context</emphasis> emits
 385       ans exception, the application is terminated by calling <emphasis>std::terminate()</emphasis>.
 386       <emphasis>std::exception_ptr</emphasis> can be used to transfer exceptions
 387       between different execution contexts.
 388     </para>
 389     <important>
 390       <para>
 391         Do not jump from inside a catch block and then re-throw the exception in
 392         another execution context.
 393       </para>
 394     </important>
 395     <anchor id="ecv2_ontop"/>
 396     <bridgehead renderas="sect3" id="context.ecv2.h3">
 397       <phrase id="context.ecv2.executing_function_on_top_of_a_context"/><link linkend="context.ecv2.executing_function_on_top_of_a_context">Executing
 398       function on top of a context</link>
 399     </bridgehead>
 400     <para>
 401       Sometimes it is useful to execute a new function on top of a resumed context.
 402       For this purpose <emphasis>execution_context::operator()</emphasis> with first
 403       argument <code><phrase role="identifier">exec_ontop_arg</phrase></code> has
 404       to be used. The function passed as argument must return a tuple of execution_context
 405       and arguments.
 406     </para>
 407 <programlisting><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">f1</phrase><phrase role="special">(</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">,</phrase><phrase role="keyword">int</phrase> <phrase role="identifier">data</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
 408     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="string">&quot;f1: entered first time: &quot;</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">data</phrase>  <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">endl</phrase><phrase role="special">;</phrase>
 409     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tie</phrase><phrase role="special">(</phrase><phrase role="identifier">ctx</phrase><phrase role="special">,</phrase><phrase role="identifier">data</phrase><phrase role="special">)</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">(</phrase><phrase role="identifier">data</phrase><phrase role="special">+</phrase><phrase role="number">1</phrase><phrase role="special">);</phrase>
 410     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="string">&quot;f1: entered second time: &quot;</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">data</phrase>  <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">endl</phrase><phrase role="special">;</phrase>
 411     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tie</phrase><phrase role="special">(</phrase><phrase role="identifier">ctx</phrase><phrase role="special">,</phrase><phrase role="identifier">data</phrase><phrase role="special">)</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">(</phrase><phrase role="identifier">data</phrase><phrase role="special">+</phrase><phrase role="number">1</phrase><phrase role="special">);</phrase>
 412     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="string">&quot;f1: entered third time: &quot;</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">data</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">endl</phrase><phrase role="special">;</phrase>
 413     <phrase role="keyword">return</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">;</phrase>
 414 <phrase role="special">}</phrase>
 415
 416 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tuple</phrase><phrase role="special">&lt;</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;,</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">f2</phrase><phrase role="special">(</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">int</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">,</phrase><phrase role="keyword">int</phrase> <phrase role="identifier">data</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
 417     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="string">&quot;f2: entered: &quot;</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">data</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">endl</phrase><phrase role="special">;</phrase>
 418     <phrase role="keyword">return</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">make_tuple</phrase><phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">move</phrase><phrase role="special">(</phrase><phrase role="identifier">ctx</phrase><phrase role="special">),-</phrase><phrase role="number">1</phrase><phrase role="special">);</phrase>
 419 <phrase role="special">}</phrase>
 420
 421 <phrase role="keyword">int</phrase> <phrase role="identifier">data</phrase> <phrase role="special">=</phrase> <phrase role="number">0</phrase><phrase role="special">;</phrase>
 422 <phrase role="identifier">ctx</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">int</phrase> <phrase role="special">&gt;</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">(</phrase><phrase role="identifier">f1</phrase><phrase role="special">);</phrase>
 423 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tie</phrase><phrase role="special">(</phrase><phrase role="identifier">ctx</phrase><phrase role="special">,</phrase><phrase role="identifier">data</phrase><phrase role="special">)</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">(</phrase><phrase role="identifier">data</phrase><phrase role="special">+</phrase><phrase role="number">1</phrase><phrase role="special">);</phrase>
 424 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="string">&quot;f1: returned first time: &quot;</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">data</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">endl</phrase><phrase role="special">;</phrase>
 425 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tie</phrase><phrase role="special">(</phrase><phrase role="identifier">ctx</phrase><phrase role="special">,</phrase><phrase role="identifier">data</phrase><phrase role="special">)</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">(</phrase><phrase role="identifier">data</phrase><phrase role="special">+</phrase><phrase role="number">1</phrase><phrase role="special">);</phrase>
 426 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="string">&quot;f1: returned second time: &quot;</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">data</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">endl</phrase><phrase role="special">;</phrase>
 427 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tie</phrase><phrase role="special">(</phrase><phrase role="identifier">ctx</phrase><phrase role="special">,</phrase><phrase role="identifier">data</phrase><phrase role="special">)</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">(</phrase><phrase role="identifier">ctx</phrase><phrase role="special">::</phrase><phrase role="identifier">exec_ontop_arg</phrase><phrase role="special">,</phrase><phrase role="identifier">f2</phrase><phrase role="special">,</phrase><phrase role="identifier">data</phrase><phrase role="special">+</phrase><phrase role="number">1</phrase><phrase role="special">);</phrase>
 428
 429 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
 430     <phrase role="identifier">f1</phrase><phrase role="special">:</phrase> <phrase role="identifier">entered</phrase> <phrase role="identifier">first</phrase> <phrase role="identifier">time</phrase><phrase role="special">:</phrase> <phrase role="number">1</phrase>
 431     <phrase role="identifier">f1</phrase><phrase role="special">:</phrase> <phrase role="identifier">returned</phrase> <phrase role="identifier">first</phrase> <phrase role="identifier">time</phrase><phrase role="special">:</phrase> <phrase role="number">2</phrase>
 432     <phrase role="identifier">f1</phrase><phrase role="special">:</phrase> <phrase role="identifier">entered</phrase> <phrase role="identifier">second</phrase> <phrase role="identifier">time</phrase><phrase role="special">:</phrase> <phrase role="number">3</phrase>
 433     <phrase role="identifier">f1</phrase><phrase role="special">:</phrase> <phrase role="identifier">returned</phrase> <phrase role="identifier">second</phrase> <phrase role="identifier">time</phrase><phrase role="special">:</phrase> <phrase role="number">4</phrase>
 434     <phrase role="identifier">f2</phrase><phrase role="special">:</phrase> <phrase role="identifier">entered</phrase><phrase role="special">:</phrase> <phrase role="number">5</phrase>
 435     <phrase role="identifier">f1</phrase><phrase role="special">:</phrase> <phrase role="identifier">entered</phrase> <phrase role="identifier">third</phrase> <phrase role="identifier">time</phrase><phrase role="special">:</phrase> <phrase role="special">-</phrase><phrase role="number">1</phrase>
 436 </programlisting>
 437     <para>
 438       The expression <code><phrase role="identifier">ctx</phrase><phrase role="special">(</phrase><phrase
 439       role="identifier">ctx</phrase><phrase role="special">::</phrase><phrase role="identifier">exec_ontop_arg</phrase><phrase
 440       role="special">,</phrase><phrase role="identifier">f2</phrase><phrase role="special">,</phrase><phrase
 441       role="identifier">data</phrase><phrase role="special">+</phrase><phrase role="number">1</phrase><phrase
 442       role="special">)</phrase></code> executes <code><phrase role="identifier">f2</phrase><phrase
 443       role="special">()</phrase></code> on top of context <code><phrase role="identifier">ctx</phrase></code>,
 444       e.g. an additional stack frame is allocated on top of the context stack (in
 445       front of <code><phrase role="identifier">f1</phrase><phrase role="special">()</phrase></code>).
 446       <code><phrase role="identifier">f2</phrase><phrase role="special">()</phrase></code>
 447       returns argument <code><phrase role="special">-</phrase><phrase role="number">1</phrase></code>
 448       that will returned by the second invocation of <code><phrase role="identifier">ctx</phrase><phrase
 449       role="special">(</phrase><phrase role="identifier">data</phrase><phrase role="special">+</phrase><phrase
 450       role="number">1</phrase><phrase role="special">)</phrase></code> in <code><phrase
 451       role="identifier">f1</phrase><phrase role="special">()</phrase></code>.
 452     </para>
 453     <para>
 454       Another option is to execute a function on top of the context that throws an
 455       exception.
 456     </para>
 457 <programlisting><phrase role="keyword">struct</phrase> <phrase role="identifier">interrupt</phrase> <phrase role="special">{</phrase>
 458     <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">void</phrase> <phrase role="special">&gt;</phrase>   <phrase role="identifier">ctx</phrase><phrase role="special">;</phrase>
 459
 460     <phrase role="identifier">interrupt</phrase><phrase role="special">(</phrase> <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">void</phrase> <phrase role="special">&gt;</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">ctx_</phrase><phrase role="special">)</phrase> <phrase role="special">:</phrase>
 461         <phrase role="identifier">ctx</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">forward</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">void</phrase> <phrase role="special">&gt;</phrase> <phrase role="special">&gt;(</phrase> <phrase role="identifier">ctx_</phrase><phrase role="special">)</phrase> <phrase role="special">)</phrase> <phrase role="special">{</phrase>
 462     <phrase role="special">}</phrase>
 463 <phrase role="special">};</phrase>
 464
 465 <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">void</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">f1</phrase><phrase role="special">(</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">void</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
 466     <phrase role="keyword">try</phrase> <phrase role="special">{</phrase>
 467         <phrase role="keyword">for</phrase> <phrase role="special">(;;)</phrase> <phrase role="special">{</phrase>
 468             <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="string">&quot;f1()&quot;</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">endl</phrase><phrase role="special">;</phrase>
 469             <phrase role="identifier">ctx</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">();</phrase>
 470         <phrase role="special">}</phrase>
 471     <phrase role="special">}</phrase> <phrase role="keyword">catch</phrase> <phrase role="special">(</phrase><phrase role="identifier">interrupt</phrase> <phrase role="special">&amp;</phrase> <phrase role="identifier">e</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
 472         <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="string">&quot;f1(): interrupted&quot;</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">endl</phrase><phrase role="special">;</phrase>
 473         <phrase role="identifier">ctx</phrase> <phrase role="special">=</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">move</phrase><phrase role="special">(</phrase> <phrase role="identifier">e</phrase><phrase role="special">.</phrase><phrase role="identifier">ctx</phrase><phrase role="special">);</phrase>
 474     <phrase role="special">}</phrase>
 475     <phrase role="keyword">return</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">;</phrase>
 476 <phrase role="special">}</phrase>
 477
 478 <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">void</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">f2</phrase><phrase role="special">(</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">void</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
 479     <phrase role="keyword">throw</phrase> <phrase role="identifier">interrupt</phrase><phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">move</phrase><phrase role="special">(</phrase><phrase role="identifier">ctx</phrase><phrase role="special">));</phrase>
 480     <phrase role="keyword">return</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">;</phrase>
 481 <phrase role="special">}</phrase>
 482
 483 <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">void</phrase> <phrase role="special">&gt;</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">(</phrase><phrase role="identifier">f1</phrase><phrase role="special">);</phrase>
 484 <phrase role="identifier">ctx</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">();</phrase>
 485 <phrase role="identifier">ctx</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">();</phrase>
 486 <phrase role="identifier">ctx</phrase> <phrase role="special">=</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">(</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">exec_ontop_arg</phrase><phrase role="special">,</phrase><phrase role="identifier">f2</phrase><phrase role="special">);</phrase>
 487
 488 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
 489     <phrase role="identifier">f1</phrase><phrase role="special">()</phrase>
 490     <phrase role="identifier">f1</phrase><phrase role="special">()</phrase>
 491     <phrase role="identifier">f1</phrase><phrase role="special">():</phrase> <phrase role="identifier">interrupted</phrase>
 492 </programlisting>
 493     <para>
 494       In this example <code><phrase role="identifier">f2</phrase><phrase role="special">()</phrase></code>
 495       is used to interrupt the <code><phrase role="keyword">for</phrase></code>-loop
 496       in <code><phrase role="identifier">f1</phrase><phrase role="special">()</phrase></code>.
 497     </para>
 498     <bridgehead renderas="sect3" id="context.ecv2.h4">
 499       <phrase id="context.ecv2.stack_destruction"/><link linkend="context.ecv2.stack_destruction">Stack
 500       destruction</link>
 501     </bridgehead>
 502     <para>
 503       On construction of <emphasis>execution_context</emphasis> a stack is allocated.
 504       If the <emphasis>context-function</emphasis> returns the stack will be destructed.
 505       If the <emphasis>context-function</emphasis> has not yet returned and the destructor
 506       of an valid <emphasis>execution_context</emphasis> instance (e.g. <emphasis>execution_context::operator
 507       bool()</emphasis> returns <code><phrase role="keyword">true</phrase></code>)
 508       is called, the stack will be destructed too.
 509     </para>
 510     <anchor id="ecv2_prealloc"/>
 511     <bridgehead renderas="sect3" id="context.ecv2.h5">
 512       <phrase id="context.ecv2.allocating_control_structures_on_top_of_stack"/><link
 513       linkend="context.ecv2.allocating_control_structures_on_top_of_stack">allocating
 514       control structures on top of stack</link>
 515     </bridgehead>
 516     <para>
 517       Allocating control structures on top of the stack requires to allocated the
 518       <emphasis>stack_context</emphasis> and create the control structure with placement
 519       new before <emphasis>execution_context</emphasis> is created.
 520     </para>
 521     <note>
 522       <para>
 523         The user is responsible for destructing the control structure at the top
 524         of the stack.
 525       </para>
 526     </note>
 527 <programlisting><phrase role="comment">// stack-allocator used for (de-)allocating stack</phrase>
 528 <phrase role="identifier">fixedsize_stack</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">(</phrase> <phrase role="number">4048</phrase><phrase role="special">);</phrase>
 529 <phrase role="comment">// allocate stack space</phrase>
 530 <phrase role="identifier">stack_context</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">(</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">.</phrase><phrase role="identifier">allocate</phrase><phrase role="special">()</phrase> <phrase role="special">);</phrase>
 531 <phrase role="comment">// reserve space for control structure on top of the stack</phrase>
 532 <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">sp</phrase> <phrase role="special">=</phrase> <phrase role="keyword">static_cast</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">char</phrase> <phrase role="special">*</phrase> <phrase role="special">&gt;(</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase role="identifier">sp</phrase><phrase role="special">)</phrase> <phrase role="special">-</phrase> <phrase role="keyword">sizeof</phrase><phrase role="special">(</phrase> <phrase role="identifier">my_control_structure</phrase><phrase role="special">);</phrase>
 533 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">size</phrase> <phrase role="special">=</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase role="identifier">size</phrase> <phrase role="special">-</phrase> <phrase role="keyword">sizeof</phrase><phrase role="special">(</phrase> <phrase role="identifier">my_control_structure</phrase><phrase role="special">);</phrase>
 534 <phrase role="comment">// placement new creates control structure on reserved space</phrase>
 535 <phrase role="identifier">my_control_structure</phrase> <phrase role="special">*</phrase> <phrase role="identifier">cs</phrase> <phrase role="special">=</phrase> <phrase role="keyword">new</phrase> <phrase role="special">(</phrase> <phrase role="identifier">sp</phrase><phrase role="special">)</phrase> <phrase role="identifier">my_control_structure</phrase><phrase role="special">(</phrase> <phrase role="identifier">sp</phrase><phrase role="special">,</phrase> <phrase role="identifier">size</phrase><phrase role="special">,</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">,</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">);</phrase>
 536 <phrase role="special">...</phrase>
 537 <phrase role="comment">// destructing the control structure</phrase>
 538 <phrase role="identifier">cs</phrase><phrase role="special">-&gt;~</phrase><phrase role="identifier">my_control_structure</phrase><phrase role="special">();</phrase>
 539 <phrase role="special">...</phrase>
 540 <phrase role="keyword">struct</phrase> <phrase role="identifier">my_control_structure</phrase>  <phrase role="special">{</phrase>
 541     <phrase role="comment">// captured context</phrase>
 542     <phrase role="identifier">execution_context</phrase> <phrase role="identifier">cctx</phrase><phrase role="special">;</phrase>
 543
 544     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">StackAllocator</phrase> <phrase role="special">&gt;</phrase>
 545     <phrase role="identifier">my_control_structure</phrase><phrase role="special">(</phrase> <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">sp</phrase><phrase role="special">,</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">size</phrase><phrase role="special">,</phrase> <phrase role="identifier">stack_context</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">,</phrase> <phrase role="identifier">StackAllocator</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">)</phrase> <phrase role="special">:</phrase>
 546         <phrase role="comment">// create captured context</phrase>
 547         <phrase role="identifier">cctx</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg</phrase><phrase role="special">,</phrase> <phrase role="identifier">preallocated</phrase><phrase role="special">(</phrase> <phrase role="identifier">sp</phrase><phrase role="special">,</phrase> <phrase role="identifier">size</phrase><phrase role="special">,</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">),</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">entry_func</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
 548     <phrase role="special">}</phrase>
 549     <phrase role="special">...</phrase>
 550 <phrase role="special">};</phrase>
 551 </programlisting>
 552     <bridgehead renderas="sect3" id="context.ecv2.h6">
 553       <phrase id="context.ecv2.inverting_the_control_flow"/><link linkend="context.ecv2.inverting_the_control_flow">inverting
 554       the control flow</link>
 555     </bridgehead>
 556 <programlisting><phrase role="comment">/*
 557  * grammar:
 558  *   P ---&gt; E '\0'
 559  *   E ---&gt; T {('+'|'-') T}
 560  *   T ---&gt; S {('*'|'/') S}
 561  *   S ---&gt; digit | '(' E ')'
 562  */</phrase>
 563 <phrase role="keyword">class</phrase> <phrase role="identifier">Parser</phrase><phrase role="special">{</phrase>
 564     <phrase role="comment">// implementation omitted; see examples directory</phrase>
 565 <phrase role="special">};</phrase>
 566
 567 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">istringstream</phrase> <phrase role="identifier">is</phrase><phrase role="special">(</phrase><phrase role="string">&quot;1+1&quot;</phrase><phrase role="special">);</phrase>
 568 <phrase role="keyword">bool</phrase> <phrase role="identifier">done</phrase><phrase role="special">=</phrase><phrase role="keyword">false</phrase><phrase role="special">;</phrase>
 569 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">exception_ptr</phrase> <phrase role="identifier">except</phrase><phrase role="special">;</phrase>
 570
 571 <phrase role="comment">// execute parser in new execution context</phrase>
 572 <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">char</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">source</phrase><phrase role="special">(</phrase>
 573         <phrase role="special">[&amp;</phrase><phrase role="identifier">is</phrase><phrase role="special">,&amp;</phrase><phrase role="identifier">done</phrase><phrase role="special">,&amp;</phrase><phrase role="identifier">except</phrase><phrase role="special">](</phrase><phrase role="identifier">ctx</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">char</phrase><phrase role="special">&gt;</phrase> <phrase role="identifier">sink</phrase><phrase role="special">,</phrase><phrase role="keyword">char</phrase><phrase role="special">){</phrase>
 574         <phrase role="comment">// create parser with callback function</phrase>
 575         <phrase role="identifier">Parser</phrase> <phrase role="identifier">p</phrase><phrase role="special">(</phrase> <phrase role="identifier">is</phrase><phrase role="special">,</phrase>
 576                   <phrase role="special">[&amp;</phrase><phrase role="identifier">sink</phrase><phrase role="special">](</phrase><phrase role="keyword">char</phrase> <phrase role="identifier">ch</phrase><phrase role="special">){</phrase>
 577                         <phrase role="comment">// resume main execution context</phrase>
 578                         <phrase role="keyword">auto</phrase> <phrase role="identifier">result</phrase> <phrase role="special">=</phrase> <phrase role="identifier">sink</phrase><phrase role="special">(</phrase><phrase role="identifier">ch</phrase><phrase role="special">);</phrase>
 579                         <phrase role="identifier">sink</phrase> <phrase role="special">=</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">move</phrase><phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="number">0</phrase><phrase role="special">&gt;(</phrase><phrase role="identifier">result</phrase><phrase role="special">));</phrase>
 580                 <phrase role="special">});</phrase>
 581             <phrase role="keyword">try</phrase> <phrase role="special">{</phrase>
 582                 <phrase role="comment">// start recursive parsing</phrase>
 583                 <phrase role="identifier">p</phrase><phrase role="special">.</phrase><phrase role="identifier">run</phrase><phrase role="special">();</phrase>
 584             <phrase role="special">}</phrase> <phrase role="keyword">catch</phrase> <phrase role="special">(...)</phrase> <phrase role="special">{</phrase>
 585                 <phrase role="comment">// store other exceptions in exception-pointer</phrase>
 586                 <phrase role="identifier">except</phrase> <phrase role="special">=</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">current_exception</phrase><phrase role="special">();</phrase>
 587             <phrase role="special">}</phrase>
 588             <phrase role="comment">// set termination flag</phrase>
 589             <phrase role="identifier">done</phrase><phrase role="special">=</phrase><phrase role="keyword">true</phrase><phrase role="special">;</phrase>
 590             <phrase role="comment">// resume main execution context</phrase>
 591             <phrase role="keyword">return</phrase> <phrase role="identifier">sink</phrase><phrase role="special">;</phrase>
 592         <phrase role="special">});</phrase>
 593
 594 <phrase role="comment">// user-code pulls parsed data from parser</phrase>
 595 <phrase role="comment">// invert control flow</phrase>
 596 <phrase role="keyword">auto</phrase> <phrase role="identifier">result</phrase> <phrase role="special">=</phrase> <phrase role="identifier">source</phrase><phrase role="special">(</phrase><phrase role="char">'\0'</phrase><phrase role="special">);</phrase>
 597 <phrase role="identifier">source</phrase> <phrase role="special">=</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">move</phrase><phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="number">0</phrase><phrase role="special">&gt;(</phrase><phrase role="identifier">result</phrase><phrase role="special">));</phrase>
 598 <phrase role="keyword">char</phrase> <phrase role="identifier">c</phrase> <phrase role="special">=</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">get</phrase><phrase role="special">&lt;</phrase><phrase role="number">1</phrase><phrase role="special">&gt;(</phrase><phrase role="identifier">result</phrase><phrase role="special">);</phrase>
 599 <phrase role="keyword">if</phrase> <phrase role="special">(</phrase> <phrase role="identifier">except</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
 600     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">rethrow_exception</phrase><phrase role="special">(</phrase><phrase role="identifier">except</phrase><phrase role="special">);</phrase>
 601 <phrase role="special">}</phrase>
 602 <phrase role="keyword">while</phrase><phrase role="special">(</phrase> <phrase role="special">!</phrase> <phrase role="identifier">done</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
 603     <phrase role="identifier">printf</phrase><phrase role="special">(</phrase><phrase role="string">&quot;Parsed: %c\n&quot;</phrase><phrase role="special">,</phrase><phrase role="identifier">c</phrase><phrase role="special">);</phrase>
 604     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tie</phrase><phrase role="special">(</phrase><phrase role="identifier">source</phrase><phrase role="special">,</phrase><phrase role="identifier">c</phrase><phrase role="special">)</phrase> <phrase role="special">=</phrase> <phrase role="identifier">source</phrase><phrase role="special">(</phrase><phrase role="char">'\0'</phrase><phrase role="special">);</phrase>
 605     <phrase role="keyword">if</phrase> <phrase role="special">(</phrase><phrase role="identifier">except</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
 606         <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">rethrow_exception</phrase><phrase role="special">(</phrase><phrase role="identifier">except</phrase><phrase role="special">);</phrase>
 607     <phrase role="special">}</phrase>
 608 <phrase role="special">}</phrase>
 609
 610 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
 611     <phrase role="identifier">Parsed</phrase><phrase role="special">:</phrase> <phrase role="number">1</phrase>
 612     <phrase role="identifier">Parsed</phrase><phrase role="special">:</phrase> <phrase role="special">+</phrase>
 613     <phrase role="identifier">Parsed</phrase><phrase role="special">:</phrase> <phrase role="number">1</phrase>
 614 </programlisting>
 615     <para>
 616       In this example a recursive descent parser uses a callback to emit a newly
 617       passed symbol. Using <emphasis>execution_context</emphasis> the control flow
 618       can be inverted, e.g. the user-code pulls parsed symbols from the parser -
 619       instead to get pushed from the parser (via callback).
 620     </para>
 621     <para>
 622       The data (character) is transferred between the two <emphasis>execution_context</emphasis>.
 623     </para>
 624     <para>
 625       If the code executed by <emphasis>execution_context</emphasis> emits an exception,
 626       the application is terminated. <emphasis>std::exception_ptr</emphasis> can
 627       be used to transfer exceptions between different execution contexts.
 628     </para>
 629     <para>
 630       Sometimes it is necessary to unwind the stack of an unfinished context to destroy
 631       local stack variables so they can release allocated resources (RAII pattern).
 632       The user is responsible for this task.
 633     </para>
 634     <bridgehead renderas="sect3" id="context.ecv2.h7">
 635       <phrase id="context.ecv2.class__code__phrase_role__identifier__execution_context__phrase___code_"/><link
 636       linkend="context.ecv2.class__code__phrase_role__identifier__execution_context__phrase___code_">Class
 637       <code><phrase role="identifier">execution_context</phrase></code></link>
 638     </bridgehead>
 639 <programlisting><phrase role="keyword">struct</phrase> <phrase role="identifier">exec_ontop_arg_t</phrase> <phrase role="special">{};</phrase>
 640 <phrase role="keyword">const</phrase> <phrase role="identifier">exec_ontop_arg_t</phrase> <phrase role="identifier">exec_ontop_arg</phrase><phrase role="special">{};</phrase>
 641
 642 <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&gt;</phrase>
 643 <phrase role="keyword">class</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="special">{</phrase>
 644 <phrase role="keyword">public</phrase><phrase role="special">:</phrase>
 645     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&gt;</phrase>
 646     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">params</phrase><phrase role="special">);</phrase>
 647
 648     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">StackAlloc</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&gt;</phrase>
 649     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">StackAlloc</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">params</phrase><phrase role="special">);</phrase>
 650
 651     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">StackAlloc</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&gt;</phrase>
 652     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">preallocated</phrase> <phrase role="identifier">palloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">StackAlloc</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">params</phrase><phrase role="special">);</phrase>
 653
 654     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&gt;</phrase>
 655     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">segemented_stack</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">params</phrase><phrase role="special">)</phrase> <phrase role="special">=</phrase> <phrase role="keyword">delete</phrase><phrase role="special">;</phrase>
 656
 657     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&gt;</phrase>
 658     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">preallocated</phrase> <phrase role="identifier">palloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">segmented</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">params</phrase><phrase role="special">)=</phrase> <phrase role="keyword">delete</phrase><phrase role="special">;</phrase>
 659
 660     <phrase role="special">~</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">();</phrase>
 661
 662     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 663     <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 664
 665     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase> <phrase role="special">=</phrase> <phrase role="keyword">delete</phrase><phrase role="special">;</phrase>
 666     <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase> <phrase role="special">=</phrase> <phrase role="keyword">delete</phrase><phrase role="special">;</phrase>
 667
 668     <phrase role="keyword">explicit</phrase> <phrase role="keyword">operator</phrase> <phrase role="keyword">bool</phrase><phrase role="special">()</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 669     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">!()</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 670
 671     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tuple</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">execution_context</phrase><phrase role="special">,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase role="special">&gt;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase role="identifier">args</phrase><phrase role="special">);</phrase>
 672
 673     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&gt;</phrase>
 674     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tuple</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">execution_context</phrase><phrase role="special">,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase role="special">&gt;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase> <phrase role="identifier">exec_ontop_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase role="identifier">args</phrase><phrase role="special">);</phrase>
 675
 676     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">==(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 677
 678     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">!=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 679
 680     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&lt;(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 681
 682     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&gt;(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 683
 684     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&lt;=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 685
 686     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&gt;=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 687
 688     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="keyword">class</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase>
 689     <phrase role="keyword">friend</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">basic_ostream</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase> <phrase role="special">&amp;</phrase>
 690     <phrase role="keyword">operator</phrase><phrase role="special">&lt;&lt;(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">basic_ostream</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase> <phrase role="special">&amp;</phrase> <phrase role="identifier">os</phrase><phrase role="special">,</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">);</phrase>
 691 <phrase role="special">};</phrase>
 692 </programlisting>
 693     <para>
 694       <bridgehead renderas="sect4" id="ecv2_constructor_bridgehead">
 695   <phrase id="ecv2_constructor"/>
 696   <link linkend="ecv2_constructor">Constructor</link>
 697 </bridgehead>
 698     </para>
 699 <programlisting><phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&gt;</phrase>
 700 <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">params</phrase><phrase role="special">);</phrase>
 701
 702 <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">StackAlloc</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&gt;</phrase>
 703 <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">StackAlloc</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">params</phrase><phrase role="special">);</phrase>
 704
 705 <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">StackAlloc</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&gt;</phrase>
 706 <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">preallocated</phrase> <phrase role="identifier">palloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">StackAlloc</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Params</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">params</phrase><phrase role="special">);</phrase>
 707 </programlisting>
 708     <variablelist>
 709       <title></title>
 710       <varlistentry>
 711         <term>Effects:</term>
 712         <listitem>
 713           <para>
 714             Creates a new execution context and prepares the context to execute
 715             <code><phrase role="identifier">fn</phrase></code>. <code><phrase role="identifier">fixedsize_stack</phrase></code>
 716             is used as default stack allocator (stack size == fixedsize_stack::traits::default_size()).
 717             The constructor with argument type <code><phrase role="identifier">preallocated</phrase></code>,
 718             is used to create a user defined data <link linkend="ecv2_prealloc">(for
 719             instance additional control structures)</link> on top of the stack.
 720           </para>
 721         </listitem>
 722       </varlistentry>
 723     </variablelist>
 724     <para>
 725       <bridgehead renderas="sect4" id="ecv2_destructor destructor_bridgehead">
 726   <phrase id="ecv2_destructor destructor"/>
 727   <link linkend="ecv2_destructor
 728       destructor">Destructor</link>
 729 </bridgehead>
 730     </para>
 731 <programlisting><phrase role="special">~</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">();</phrase>
 732 </programlisting>
 733     <variablelist>
 734       <title></title>
 735       <varlistentry>
 736         <term>Effects:</term>
 737         <listitem>
 738           <para>
 739             Destructs the associated stack if <code><phrase role="special">*</phrase><phrase
 740             role="keyword">this</phrase></code> is a valid context, e.g. <emphasis>execution_context::operator
 741             bool()</emphasis> returns <code><phrase role="keyword">true</phrase></code>.
 742           </para>
 743         </listitem>
 744       </varlistentry>
 745       <varlistentry>
 746         <term>Throws:</term>
 747         <listitem>
 748           <para>
 749             Nothing.
 750           </para>
 751         </listitem>
 752       </varlistentry>
 753     </variablelist>
 754     <para>
 755       <bridgehead renderas="sect4" id="ecv2_move constructor_bridgehead">
 756   <phrase id="ecv2_move constructor"/>
 757   <link linkend="ecv2_move constructor">Move
 758       constructor</link>
 759 </bridgehead>
 760     </para>
 761 <programlisting><phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 762 </programlisting>
 763     <variablelist>
 764       <title></title>
 765       <varlistentry>
 766         <term>Effects:</term>
 767         <listitem>
 768           <para>
 769             Moves underlying capture record to <code><phrase role="special">*</phrase><phrase
 770             role="keyword">this</phrase></code>.
 771           </para>
 772         </listitem>
 773       </varlistentry>
 774       <varlistentry>
 775         <term>Throws:</term>
 776         <listitem>
 777           <para>
 778             Nothing.
 779           </para>
 780         </listitem>
 781       </varlistentry>
 782     </variablelist>
 783     <para>
 784       <bridgehead renderas="sect4" id="ecv2_move assignment_bridgehead">
 785   <phrase id="ecv2_move assignment"/>
 786   <link linkend="ecv2_move assignment">Move
 787       assignment operator</link>
 788 </bridgehead>
 789     </para>
 790 <programlisting><phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 791 </programlisting>
 792     <variablelist>
 793       <title></title>
 794       <varlistentry>
 795         <term>Effects:</term>
 796         <listitem>
 797           <para>
 798             Moves the state of <code><phrase role="identifier">other</phrase></code>
 799             to <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>
 800             using move semantics.
 801           </para>
 802         </listitem>
 803       </varlistentry>
 804       <varlistentry>
 805         <term>Throws:</term>
 806         <listitem>
 807           <para>
 808             Nothing.
 809           </para>
 810         </listitem>
 811       </varlistentry>
 812     </variablelist>
 813     <para>
 814       <bridgehead renderas="sect4" id="ecv2_operator_bool_bridgehead">
 815   <phrase id="ecv2_operator_bool"/>
 816   <link linkend="ecv2_operator_bool">Member function
 817       <code>operator bool</code>()</link>
 818 </bridgehead>
 819     </para>
 820 <programlisting><phrase role="keyword">explicit</phrase> <phrase role="keyword">operator</phrase> <phrase role="keyword">bool</phrase><phrase role="special">()</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 821 </programlisting>
 822     <variablelist>
 823       <title></title>
 824       <varlistentry>
 825         <term>Returns:</term>
 826         <listitem>
 827           <para>
 828             <code><phrase role="keyword">true</phrase></code> if <code><phrase role="special">*</phrase><phrase
 829             role="keyword">this</phrase></code> points to a capture record.
 830           </para>
 831         </listitem>
 832       </varlistentry>
 833       <varlistentry>
 834         <term>Throws:</term>
 835         <listitem>
 836           <para>
 837             Nothing.
 838           </para>
 839         </listitem>
 840       </varlistentry>
 841     </variablelist>
 842     <para>
 843       <bridgehead renderas="sect4" id="ecv2_operator_not_bridgehead">
 844   <phrase id="ecv2_operator_not"/>
 845   <link linkend="ecv2_operator_not">Member function
 846       <code>operator!</code>()</link>
 847 </bridgehead>
 848     </para>
 849 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">!()</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
 850 </programlisting>
 851     <variablelist>
 852       <title></title>
 853       <varlistentry>
 854         <term>Returns:</term>
 855         <listitem>
 856           <para>
 857             <code><phrase role="keyword">true</phrase></code> if <code><phrase role="special">*</phrase><phrase
 858             role="keyword">this</phrase></code> does not point to a capture record.
 859           </para>
 860         </listitem>
 861       </varlistentry>
 862       <varlistentry>
 863         <term>Throws:</term>
 864         <listitem>
 865           <para>
 866             Nothing.
 867           </para>
 868         </listitem>
 869       </varlistentry>
 870     </variablelist>
 871     <para>
 872       <bridgehead renderas="sect4" id="ecv2_operator_call_bridgehead">
 873   <phrase id="ecv2_operator_call"/>
 874   <link linkend="ecv2_operator_call">Member function
 875       <code>operator()</code>()</link>
 876 </bridgehead>
 877     </para>
 878 <programlisting><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tuple</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase role="special">&gt;,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase role="special">&gt;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase role="identifier">args</phrase><phrase role="special">);</phrase> <phrase role="comment">// member of generic execution_context template</phrase>
 879
 880 <phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">void</phrase> <phrase role="special">&gt;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()();</phrase> <phrase role="comment">// member of execution_context&lt; void &gt;</phrase>
 881 </programlisting>
 882     <variablelist>
 883       <title></title>
 884       <varlistentry>
 885         <term>Effects:</term>
 886         <listitem>
 887           <para>
 888             Stores internally the current context data (stack pointer, instruction
 889             pointer, and CPU registers) of the current active context and restores
 890             the context data from <code><phrase role="special">*</phrase><phrase
 891             role="keyword">this</phrase></code>, which implies jumping to <code><phrase
 892             role="special">*</phrase><phrase role="keyword">this</phrase></code>'s
 893             context. The arguments, <code><phrase role="special">...</phrase> <phrase
 894             role="identifier">args</phrase></code>, are passed to the current context
 895             to be returned by the most recent call to <code><phrase role="identifier">execution_context</phrase><phrase
 896             role="special">::</phrase><phrase role="keyword">operator</phrase><phrase
 897             role="special">()</phrase></code> in the same thread.
 898           </para>
 899         </listitem>
 900       </varlistentry>
 901       <varlistentry>
 902         <term>Returns:</term>
 903         <listitem>
 904           <para>
 905             The tuple of execution_context and returned arguments passed to the most
 906             recent call to <code><phrase role="identifier">execution_context</phrase><phrase
 907             role="special">::</phrase><phrase role="keyword">operator</phrase><phrase
 908             role="special">()</phrase></code>, if any and a execution_context representing
 909             the context that has been suspended.
 910           </para>
 911         </listitem>
 912       </varlistentry>
 913       <varlistentry>
 914         <term>Note:</term>
 915         <listitem>
 916           <para>
 917             The returned execution_context indicates if the suspended context has
 918             terminated (return from context-function) via <code><phrase role="keyword">bool</phrase>
 919             <phrase role="keyword">operator</phrase><phrase role="special">()</phrase></code>.
 920             If the returned execution_context has terminated no data are transferred
 921             in the returned tuple.
 922           </para>
 923         </listitem>
 924       </varlistentry>
 925     </variablelist>
 926     <para>
 927       <bridgehead renderas="sect4" id="ecv2_operator_call_ontop_bridgehead">
 928   <phrase id="ecv2_operator_call_ontop"/>
 929   <link linkend="ecv2_operator_call_ontop">Member
 930       function <code>operator()</code>()</link>
 931 </bridgehead>
 932     </para>
 933 <programlisting><phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&gt;</phrase>
 934 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">tuple</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase role="special">&gt;,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase role="special">&gt;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase> <phrase role="identifier">exec_ontop_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">...</phrase> <phrase role="identifier">args</phrase><phrase role="special">);</phrase> <phrase role="comment">// member of generic execution_context</phrase>
 935
 936 <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&gt;</phrase>
 937 <phrase role="identifier">execution_context</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">void</phrase> <phrase role="special">&gt;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase> <phrase role="identifier">exec_ontop_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">);</phrase> <phrase role="comment">// member of execution_context&lt; void &gt;</phrase>
 938 </programlisting>
 939     <variablelist>
 940       <title></title>
 941       <varlistentry>
 942         <term>Effects:</term>
 943         <listitem>
 944           <para>
 945             Same as <emphasis>execution_context::operator()</emphasis>. Additionally,
 946             function <code><phrase role="identifier">fn</phrase></code> is executed
 947             in the context of <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>
 948             (e.g. the stack frame of <code><phrase role="identifier">fn</phrase></code>
 949             is allocated on stack of <code><phrase role="special">*</phrase><phrase
 950             role="keyword">this</phrase></code>).
 951           </para>
 952         </listitem>
 953       </varlistentry>
 954       <varlistentry>
 955         <term>Returns:</term>
 956         <listitem>
 957           <para>
 958             The tuple of execution_context and returned arguments passed to the most
 959             recent call to <code><phrase role="identifier">execution_context</phrase><phrase
 960             role="special">::</phrase><phrase role="keyword">operator</phrase><phrase
 961             role="special">()</phrase></code>, if any and a execution_context representing
 962             the context that has been suspended .
 963           </para>
 964         </listitem>
 965       </varlistentry>
 966       <varlistentry>
 967         <term>Note:</term>
 968         <listitem>
 969           <para>
 970             The tuple of execution_context and returned arguments from <code><phrase
 971             role="identifier">fn</phrase></code> are passed as arguments to the context-function
 972             of resumed context (if the context is entered the first time) or those
 973             arguments are returned from <code><phrase role="identifier">execution_context</phrase><phrase
 974             role="special">::</phrase><phrase role="keyword">operator</phrase><phrase
 975             role="special">()</phrase></code> within the resumed context.
 976           </para>
 977         </listitem>
 978       </varlistentry>
 979       <varlistentry>
 980         <term>Note:</term>
 981         <listitem>
 982           <para>
 983             Function <code><phrase role="identifier">fn</phrase></code> needs to
 984             return a tuple of execution_context and arguments (<link linkend="ecv2_ontop">see
 985             description</link>).
 986           </para>
 987         </listitem>
 988       </varlistentry>
 989       <varlistentry>
 990         <term>Note:</term>
 991         <listitem>
 992           <para>
 993             The context calling this function must not be destroyed before the arguments,
 994             that will be returned from <code><phrase role="identifier">fn</phrase></code>,
 995             are preserved at least in the stack frame of the resumed context.
 996           </para>
 997         </listitem>
 998       </varlistentry>
 999       <varlistentry>
1000         <term>Note:</term>
1001         <listitem>
1002           <para>
1003             The returned execution_context indicates if the suspended context has
1004             terminated (return from context-function) via <code><phrase role="keyword">bool</phrase>
1005             <phrase role="keyword">operator</phrase><phrase role="special">()</phrase></code>.
1006             If the returned execution_context has terminated no data are transferred
1007             in the returned tuple.
1008           </para>
1009         </listitem>
1010       </varlistentry>
1011     </variablelist>
1012     <para>
1013       <bridgehead renderas="sect4" id="ecv2_operator_equal_bridgehead">
1014   <phrase id="ecv2_operator_equal"/>
1015   <link linkend="ecv2_operator_equal">Member
1016       function <code>operator==</code>()</link>
1017 </bridgehead>
1018     </para>
1019 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">==(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1020 </programlisting>
1021     <variablelist>
1022       <title></title>
1023       <varlistentry>
1024         <term>Returns:</term>
1025         <listitem>
1026           <para>
1027             <code><phrase role="keyword">true</phrase></code> if <code><phrase role="special">*</phrase><phrase
1028             role="keyword">this</phrase></code> and <code><phrase role="identifier">other</phrase></code>
1029             represent the same execution context, <code><phrase role="keyword">false</phrase></code>
1030             otherwise.
1031           </para>
1032         </listitem>
1033       </varlistentry>
1034       <varlistentry>
1035         <term>Throws:</term>
1036         <listitem>
1037           <para>
1038             Nothing.
1039           </para>
1040         </listitem>
1041       </varlistentry>
1042     </variablelist>
1043     <para>
1044       <bridgehead renderas="sect4" id="ecv2_operator_notequal_bridgehead">
1045   <phrase id="ecv2_operator_notequal"/>
1046   <link linkend="ecv2_operator_notequal">Member
1047       function <code>operator!=</code>()</link>
1048 </bridgehead>
1049     </para>
1050 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">!=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1051 </programlisting>
1052     <variablelist>
1053       <title></title>
1054       <varlistentry>
1055         <term>Returns:</term>
1056         <listitem>
1057           <para>
1058             <code>! (other == * this)</code>
1059           </para>
1060         </listitem>
1061       </varlistentry>
1062       <varlistentry>
1063         <term>Throws:</term>
1064         <listitem>
1065           <para>
1066             Nothing.
1067           </para>
1068         </listitem>
1069       </varlistentry>
1070     </variablelist>
1071     <para>
1072       <bridgehead renderas="sect4" id="ecv2_operator_less_bridgehead">
1073   <phrase id="ecv2_operator_less"/>
1074   <link linkend="ecv2_operator_less">Member function
1075       <code>operator&lt;</code>()</link>
1076 </bridgehead>
1077     </para>
1078 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&lt;(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1079 </programlisting>
1080     <variablelist>
1081       <title></title>
1082       <varlistentry>
1083         <term>Returns:</term>
1084         <listitem>
1085           <para>
1086             <code><phrase role="keyword">true</phrase></code> if <code><phrase role="special">*</phrase><phrase
1087             role="keyword">this</phrase> <phrase role="special">!=</phrase> <phrase
1088             role="identifier">other</phrase></code> is true and the implementation-defined
1089             total order of <code><phrase role="identifier">execution_context</phrase></code>
1090             values places <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>
1091             before <code><phrase role="identifier">other</phrase></code>, false otherwise.
1092           </para>
1093         </listitem>
1094       </varlistentry>
1095       <varlistentry>
1096         <term>Throws:</term>
1097         <listitem>
1098           <para>
1099             Nothing.
1100           </para>
1101         </listitem>
1102       </varlistentry>
1103     </variablelist>
1104     <para>
1105       <bridgehead renderas="sect4" id="ecv2_operator_greater_bridgehead">
1106   <phrase id="ecv2_operator_greater"/>
1107   <link linkend="ecv2_operator_greater">Member
1108       function <code>operator&gt;</code>()</link>
1109 </bridgehead>
1110     </para>
1111 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&gt;(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1112 </programlisting>
1113     <variablelist>
1114       <title></title>
1115       <varlistentry>
1116         <term>Returns:</term>
1117         <listitem>
1118           <para>
1119             <code><phrase role="identifier">other</phrase> <phrase role="special">&lt;</phrase>
1120             <phrase role="special">*</phrase> <phrase role="keyword">this</phrase></code>
1121           </para>
1122         </listitem>
1123       </varlistentry>
1124       <varlistentry>
1125         <term>Throws:</term>
1126         <listitem>
1127           <para>
1128             Nothing.
1129           </para>
1130         </listitem>
1131       </varlistentry>
1132     </variablelist>
1133     <para>
1134       <bridgehead renderas="sect4" id="ecv2_operator_lesseq_bridgehead">
1135   <phrase id="ecv2_operator_lesseq"/>
1136   <link linkend="ecv2_operator_lesseq">Member
1137       function <code>operator&lt;=</code>()</link>
1138 </bridgehead>
1139     </para>
1140 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&lt;=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1141 </programlisting>
1142     <variablelist>
1143       <title></title>
1144       <varlistentry>
1145         <term>Returns:</term>
1146         <listitem>
1147           <para>
1148             <code><phrase role="special">!</phrase> <phrase role="special">(</phrase><phrase
1149             role="identifier">other</phrase> <phrase role="special">&lt;</phrase>
1150             <phrase role="special">*</phrase> <phrase role="keyword">this</phrase><phrase
1151             role="special">)</phrase></code>
1152           </para>
1153         </listitem>
1154       </varlistentry>
1155       <varlistentry>
1156         <term>Throws:</term>
1157         <listitem>
1158           <para>
1159             Nothing.
1160           </para>
1161         </listitem>
1162       </varlistentry>
1163     </variablelist>
1164     <para>
1165       <bridgehead renderas="sect4" id="ecv2_operator_greatereq_bridgehead">
1166   <phrase id="ecv2_operator_greatereq"/>
1167   <link linkend="ecv2_operator_greatereq">Member
1168       function <code>operator&gt;=</code>()</link>
1169 </bridgehead>
1170     </para>
1171 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&gt;=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1172 </programlisting>
1173     <variablelist>
1174       <title></title>
1175       <varlistentry>
1176         <term>Returns:</term>
1177         <listitem>
1178           <para>
1179             <code><phrase role="special">!</phrase> <phrase role="special">(*</phrase>
1180             <phrase role="keyword">this</phrase> <phrase role="special">&lt;</phrase>
1181             <phrase role="identifier">other</phrase><phrase role="special">)</phrase></code>
1182           </para>
1183         </listitem>
1184       </varlistentry>
1185       <varlistentry>
1186         <term>Throws:</term>
1187         <listitem>
1188           <para>
1189             Nothing.
1190           </para>
1191         </listitem>
1192       </varlistentry>
1193     </variablelist>
1194     <para>
1195       <bridgehead renderas="sect4" id="ecv2__bridgehead">
1196   <phrase id="ecv2_"/>
1197   <link linkend="ecv2_">Non-member function <code>operator&lt;&lt;()</code></link>
1198 </bridgehead>
1199     </para>
1200 <programlisting><phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="keyword">class</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase>
1201 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">basic_ostream</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase> <phrase role="special">&amp;</phrase>
1202 <phrase role="keyword">operator</phrase><phrase role="special">&lt;&lt;(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">basic_ostream</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase> <phrase role="special">&amp;</phrase> <phrase role="identifier">os</phrase><phrase role="special">,</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">);</phrase>
1203 </programlisting>
1204     <variablelist>
1205       <title></title>
1206       <varlistentry>
1207         <term>Efects:</term>
1208         <listitem>
1209           <para>
1210             Writes the representation of <code><phrase role="identifier">other</phrase></code>
1211             to stream <code><phrase role="identifier">os</phrase></code>.
1212           </para>
1213         </listitem>
1214       </varlistentry>
1215       <varlistentry>
1216         <term>Returns:</term>
1217         <listitem>
1218           <para>
1219             <code><phrase role="identifier">os</phrase></code>
1220           </para>
1221         </listitem>
1222       </varlistentry>
1223     </variablelist>
1224   </section>
1225   <section id="context.ecv1">
1226     <title><anchor id="ecv1"/><link linkend="context.ecv1">Class execution_context
1227     (version 1)</link></title>
1228     <note>
1229       <para>
1230         This class is only enabled if property <emphasis>segmented-stacks=on</emphasis>
1231         (enables segmented stacks) or compiler flag <emphasis>BOOST_EXECUTION_CONTEXT=1</emphasis>
1232         is specified at b2-commandline.
1233       </para>
1234     </note>
1235     <para>
1236       Class <emphasis>execution_context</emphasis> encapsulates context switching
1237       and manages the associated context' stack (allocation/deallocation).
1238     </para>
1239     <para>
1240       <emphasis>execution_context</emphasis> allocates the context stack (using its
1241       <link linkend="stack"><emphasis>StackAllocator</emphasis></link> argument)
1242       and creates a control structure on top of it. This structure is responsible
1243       for managing context' stack. Instances of <emphasis>execution_context</emphasis>,
1244       associated with a specific context, share the ownership of the control structure.
1245       If the last reference goes out of scope, the control structure is destroyed
1246       and the stack gets deallocated via the <emphasis>StackAllocator</emphasis>.
1247     </para>
1248     <para>
1249       <emphasis>execution_context</emphasis> is copy-constructible, move-constructible,
1250       copy-assignable and move-assignable.
1251     </para>
1252     <para>
1253       <emphasis>execution_context</emphasis> maintains a static (thread-local) pointer,
1254       accessed by <emphasis>execution_context::current()</emphasis>, pointing to
1255       the active context. On each context switch the pointer is updated. The usage
1256       of this global pointer makes the context switch a little bit slower (due access
1257       of thread local storage) but has some advantages. It allows to access the control
1258       structure of the current active context from arbitrary code paths required
1259       in order to support segmented stacks, which require to call certain maintenance
1260       functions (like __splitstack_getcontext() etc.) before each context switch
1261       (each context switch exchanges the stack).
1262     </para>
1263     <para>
1264       <emphasis>execution_context</emphasis> expects a function/functor with signature
1265       <code><phrase role="keyword">void</phrase><phrase role="special">(</phrase><phrase
1266       role="keyword">void</phrase><phrase role="special">*</phrase> <phrase role="identifier">vp</phrase><phrase
1267       role="special">)</phrase></code> (<code><phrase role="identifier">vp</phrase></code>
1268       is the data passed at the first invocation of <link linkend="ecv1_operator_call"> <code>ecv1::operator()()</code></link>).
1269     </para>
1270     <bridgehead renderas="sect3" id="context.ecv1.h0">
1271       <phrase id="context.ecv1.usage_of__emphasis_execution_context__emphasis_"/><link
1272       linkend="context.ecv1.usage_of__emphasis_execution_context__emphasis_">usage
1273       of <emphasis>execution_context</emphasis></link>
1274     </bridgehead>
1275 <programlisting><phrase role="keyword">int</phrase> <phrase role="identifier">n</phrase><phrase role="special">=</phrase><phrase role="number">35</phrase><phrase role="special">;</phrase>
1276 <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase> <phrase role="identifier">sink</phrase><phrase role="special">(</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">::</phrase><phrase role="identifier">current</phrase><phrase role="special">());</phrase>
1277 <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase> <phrase role="identifier">source</phrase><phrase role="special">(</phrase>
1278     <phrase role="special">[</phrase><phrase role="identifier">n</phrase><phrase role="special">,&amp;</phrase><phrase role="identifier">sink</phrase><phrase role="special">](</phrase><phrase role="keyword">void</phrase><phrase role="special">*)</phrase><phrase role="keyword">mutable</phrase><phrase role="special">{</phrase>
1279         <phrase role="keyword">int</phrase> <phrase role="identifier">a</phrase><phrase role="special">=</phrase><phrase role="number">0</phrase><phrase role="special">;</phrase>
1280         <phrase role="keyword">int</phrase> <phrase role="identifier">b</phrase><phrase role="special">=</phrase><phrase role="number">1</phrase><phrase role="special">;</phrase>
1281         <phrase role="keyword">while</phrase><phrase role="special">(</phrase><phrase role="identifier">n</phrase><phrase role="special">--&gt;</phrase><phrase role="number">0</phrase><phrase role="special">){</phrase>
1282             <phrase role="identifier">sink</phrase><phrase role="special">(&amp;</phrase><phrase role="identifier">a</phrase><phrase role="special">);</phrase>
1283             <phrase role="keyword">auto</phrase> <phrase role="identifier">next</phrase><phrase role="special">=</phrase><phrase role="identifier">a</phrase><phrase role="special">+</phrase><phrase role="identifier">b</phrase><phrase role="special">;</phrase>
1284             <phrase role="identifier">a</phrase><phrase role="special">=</phrase><phrase role="identifier">b</phrase><phrase role="special">;</phrase>
1285             <phrase role="identifier">b</phrase><phrase role="special">=</phrase><phrase role="identifier">next</phrase><phrase role="special">;</phrase>
1286         <phrase role="special">}</phrase>
1287     <phrase role="special">});</phrase>
1288 <phrase role="keyword">for</phrase><phrase role="special">(</phrase><phrase role="keyword">int</phrase> <phrase role="identifier">i</phrase><phrase role="special">=</phrase><phrase role="number">0</phrase><phrase role="special">;</phrase><phrase role="identifier">i</phrase><phrase role="special">&lt;</phrase><phrase role="number">10</phrase><phrase role="special">;++</phrase><phrase role="identifier">i</phrase><phrase role="special">){</phrase>
1289     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase><phrase role="special">&lt;&lt;*(</phrase><phrase role="keyword">int</phrase><phrase role="special">*)</phrase><phrase role="identifier">source</phrase><phrase role="special">()&lt;&lt;</phrase><phrase role="string">&quot; &quot;</phrase><phrase role="special">;</phrase>
1290 <phrase role="special">}</phrase>
1291
1292 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
1293     <phrase role="number">0</phrase> <phrase role="number">1</phrase> <phrase role="number">1</phrase> <phrase role="number">2</phrase> <phrase role="number">3</phrase> <phrase role="number">5</phrase> <phrase role="number">8</phrase> <phrase role="number">13</phrase> <phrase role="number">21</phrase> <phrase role="number">34</phrase>
1294 </programlisting>
1295     <para>
1296       This simple example demonstrates the basic usage of <emphasis>execution_context</emphasis>.
1297       The context <code><phrase role="identifier">sink</phrase></code>, returned
1298       by <emphasis>execution_context::current()</emphasis>, represents the <emphasis>main</emphasis>-context
1299       (function <emphasis>main()</emphasis> running) and is one of the captured parameters
1300       in the lambda expression. The lambda that calculates the Fibonacci numbers
1301       is executed inside the context represented by <code><phrase role="identifier">source</phrase></code>.
1302       Calculated Fibonacci numbers are transferred between the two context' via expression
1303       <emphasis>sink(&amp;a)</emphasis> (and returned by <emphasis>source()</emphasis>).
1304     </para>
1305     <para>
1306       The locale variables <code><phrase role="identifier">a</phrase></code>, <code><phrase
1307       role="identifier">b</phrase></code> and <code> <phrase role="identifier">next</phrase></code>
1308       remain their values during each context switch (<emphasis>yield(a)</emphasis>).
1309       This is possible because <code><phrase role="identifier">ctx</phrase></code>
1310       owns a stack (exchanged by context switch).
1311     </para>
1312     <bridgehead renderas="sect3" id="context.ecv1.h1">
1313       <phrase id="context.ecv1.inverting_the_control_flow"/><link linkend="context.ecv1.inverting_the_control_flow">inverting
1314       the control flow</link>
1315     </bridgehead>
1316 <programlisting><phrase role="comment">/*
1317  * grammar:
1318  *   P ---&gt; E '\0'
1319  *   E ---&gt; T {('+'|'-') T}
1320  *   T ---&gt; S {('*'|'/') S}
1321  *   S ---&gt; digit | '(' E ')'
1322  */</phrase>
1323 <phrase role="keyword">class</phrase> <phrase role="identifier">Parser</phrase><phrase role="special">{</phrase>
1324     <phrase role="comment">// implementation omitted; see examples directory</phrase>
1325 <phrase role="special">};</phrase>
1326
1327 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">istringstream</phrase> <phrase role="identifier">is</phrase><phrase role="special">(</phrase><phrase role="string">&quot;1+1&quot;</phrase><phrase role="special">);</phrase>
1328 <phrase role="keyword">bool</phrase> <phrase role="identifier">done</phrase><phrase role="special">=</phrase><phrase role="keyword">false</phrase><phrase role="special">;</phrase>
1329 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">exception_ptr</phrase> <phrase role="identifier">except</phrase><phrase role="special">;</phrase>
1330
1331 <phrase role="comment">// create handle to main execution context</phrase>
1332 <phrase role="keyword">auto</phrase> <phrase role="identifier">main_ctx</phrase><phrase role="special">(</phrase><phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">::</phrase><phrase role="identifier">current</phrase><phrase role="special">());</phrase>
1333 <phrase role="comment">// execute parser in new execution context</phrase>
1334 <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase> <phrase role="identifier">source</phrase><phrase role="special">(</phrase>
1335         <phrase role="special">[&amp;</phrase><phrase role="identifier">sink</phrase><phrase role="special">,&amp;</phrase><phrase role="identifier">is</phrase><phrase role="special">,&amp;</phrase><phrase role="identifier">done</phrase><phrase role="special">,&amp;</phrase><phrase role="identifier">except</phrase><phrase role="special">](</phrase><phrase role="keyword">void</phrase><phrase role="special">*){</phrase>
1336         <phrase role="comment">// create parser with callback function</phrase>
1337         <phrase role="identifier">Parser</phrase> <phrase role="identifier">p</phrase><phrase role="special">(</phrase><phrase role="identifier">is</phrase><phrase role="special">,</phrase>
1338                  <phrase role="special">[&amp;</phrase><phrase role="identifier">sink</phrase><phrase role="special">](</phrase><phrase role="keyword">char</phrase> <phrase role="identifier">ch</phrase><phrase role="special">){</phrase>
1339                         <phrase role="comment">// resume main execution context</phrase>
1340                         <phrase role="identifier">sink</phrase><phrase role="special">(&amp;</phrase><phrase role="identifier">ch</phrase><phrase role="special">);</phrase>
1341                 <phrase role="special">});</phrase>
1342             <phrase role="keyword">try</phrase> <phrase role="special">{</phrase>
1343                 <phrase role="comment">// start recursive parsing</phrase>
1344                 <phrase role="identifier">p</phrase><phrase role="special">.</phrase><phrase role="identifier">run</phrase><phrase role="special">();</phrase>
1345             <phrase role="special">}</phrase> <phrase role="keyword">catch</phrase> <phrase role="special">(...)</phrase> <phrase role="special">{</phrase>
1346                 <phrase role="comment">// store other exceptions in exception-pointer</phrase>
1347                 <phrase role="identifier">except</phrase> <phrase role="special">=</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">current_exception</phrase><phrase role="special">();</phrase>
1348             <phrase role="special">}</phrase>
1349             <phrase role="comment">// set termination flag</phrase>
1350             <phrase role="identifier">done</phrase><phrase role="special">=</phrase><phrase role="keyword">true</phrase><phrase role="special">;</phrase>
1351             <phrase role="comment">// resume main execution context</phrase>
1352             <phrase role="identifier">sink</phrase><phrase role="special">();</phrase>
1353         <phrase role="special">});</phrase>
1354
1355 <phrase role="comment">// user-code pulls parsed data from parser</phrase>
1356 <phrase role="comment">// invert control flow</phrase>
1357 <phrase role="keyword">void</phrase><phrase role="special">*</phrase> <phrase role="identifier">vp</phrase> <phrase role="special">=</phrase> <phrase role="identifier">source</phrase><phrase role="special">();</phrase>
1358 <phrase role="keyword">if</phrase> <phrase role="special">(</phrase><phrase role="identifier">except</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
1359     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">rethrow_exception</phrase><phrase role="special">(</phrase><phrase role="identifier">except</phrase><phrase role="special">);</phrase>
1360 <phrase role="special">}</phrase>
1361 <phrase role="keyword">while</phrase><phrase role="special">(</phrase> <phrase role="special">!</phrase> <phrase role="identifier">done</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
1362     <phrase role="identifier">printf</phrase><phrase role="special">(</phrase><phrase role="string">&quot;Parsed: %c\n&quot;</phrase><phrase role="special">,*</phrase> <phrase role="keyword">static_cast</phrase><phrase role="special">&lt;</phrase><phrase role="keyword">char</phrase><phrase role="special">*&gt;(</phrase><phrase role="identifier">vp</phrase><phrase role="special">));</phrase>
1363     <phrase role="identifier">vp</phrase> <phrase role="special">=</phrase> <phrase role="identifier">source</phrase><phrase role="special">();</phrase>
1364     <phrase role="keyword">if</phrase> <phrase role="special">(</phrase><phrase role="identifier">except</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
1365         <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">rethrow_exception</phrase><phrase role="special">(</phrase><phrase role="identifier">except</phrase><phrase role="special">);</phrase>
1366     <phrase role="special">}</phrase>
1367 <phrase role="special">}</phrase>
1368
1369 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
1370     <phrase role="identifier">Parsed</phrase><phrase role="special">:</phrase> <phrase role="number">1</phrase>
1371     <phrase role="identifier">Parsed</phrase><phrase role="special">:</phrase> <phrase role="special">+</phrase>
1372     <phrase role="identifier">Parsed</phrase><phrase role="special">:</phrase> <phrase role="number">1</phrase>
1373 </programlisting>
1374     <para>
1375       In this example a recursive descent parser uses a callback to emit a newly
1376       passed symbol. Using <emphasis>execution_context</emphasis> the control flow
1377       can be inverted, e.g. the user-code pulls parsed symbols from the parser -
1378       instead to get pushed from the parser (via callback).
1379     </para>
1380     <para>
1381       The data (character) is transferred between the two <emphasis>execution_context</emphasis>.
1382     </para>
1383     <para>
1384       If the code executed by <emphasis>execution_context</emphasis> emits an exception,
1385       the application is terminated. <emphasis>std::exception_ptr</emphasis> can
1386       be used to transfer exceptions between different execution contexts.
1387     </para>
1388     <para>
1389       Sometimes it is necessary to unwind the stack of an unfinished context to destroy
1390       local stack variables so they can release allocated resources (RAII pattern).
1391       The user is responsible for this task.
1392     </para>
1393     <anchor id="ecv1_prealloc"/>
1394     <bridgehead renderas="sect3" id="context.ecv1.h2">
1395       <phrase id="context.ecv1.allocating_control_structures_on_top_of_stack"/><link
1396       linkend="context.ecv1.allocating_control_structures_on_top_of_stack">allocating
1397       control structures on top of stack</link>
1398     </bridgehead>
1399     <para>
1400       Allocating control structures on top of the stack requires to allocated the
1401       <emphasis>stack_context</emphasis> and create the control structure with placement
1402       new before <emphasis>execution_context</emphasis> is created.
1403     </para>
1404     <note>
1405       <para>
1406         The user is responsible for destructing the control structure at the top
1407         of the stack.
1408       </para>
1409     </note>
1410 <programlisting><phrase role="comment">// stack-allocator used for (de-)allocating stack</phrase>
1411 <phrase role="identifier">fixedsize_stack</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">(</phrase> <phrase role="number">4048</phrase><phrase role="special">);</phrase>
1412 <phrase role="comment">// allocate stack space</phrase>
1413 <phrase role="identifier">stack_context</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">(</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">.</phrase><phrase role="identifier">allocate</phrase><phrase role="special">()</phrase> <phrase role="special">);</phrase>
1414 <phrase role="comment">// reserve space for control structure on top of the stack</phrase>
1415 <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">sp</phrase> <phrase role="special">=</phrase> <phrase role="keyword">static_cast</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">char</phrase> <phrase role="special">*</phrase> <phrase role="special">&gt;(</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase role="identifier">sp</phrase><phrase role="special">)</phrase> <phrase role="special">-</phrase> <phrase role="keyword">sizeof</phrase><phrase role="special">(</phrase> <phrase role="identifier">my_control_structure</phrase><phrase role="special">);</phrase>
1416 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">size</phrase> <phrase role="special">=</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase role="identifier">size</phrase> <phrase role="special">-</phrase> <phrase role="keyword">sizeof</phrase><phrase role="special">(</phrase> <phrase role="identifier">my_control_structure</phrase><phrase role="special">);</phrase>
1417 <phrase role="comment">// placement new creates control structure on reserved space</phrase>
1418 <phrase role="identifier">my_control_structure</phrase> <phrase role="special">*</phrase> <phrase role="identifier">cs</phrase> <phrase role="special">=</phrase> <phrase role="keyword">new</phrase> <phrase role="special">(</phrase> <phrase role="identifier">sp</phrase><phrase role="special">)</phrase> <phrase role="identifier">my_control_structure</phrase><phrase role="special">(</phrase> <phrase role="identifier">sp</phrase><phrase role="special">,</phrase> <phrase role="identifier">size</phrase><phrase role="special">,</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">,</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">);</phrase>
1419 <phrase role="special">...</phrase>
1420 <phrase role="comment">// destructing the control structure</phrase>
1421 <phrase role="identifier">cs</phrase><phrase role="special">-&gt;~</phrase><phrase role="identifier">my_control_structure</phrase><phrase role="special">();</phrase>
1422 <phrase role="special">...</phrase>
1423 <phrase role="keyword">struct</phrase> <phrase role="identifier">my_control_structure</phrase>  <phrase role="special">{</phrase>
1424     <phrase role="comment">// execution context</phrase>
1425     <phrase role="identifier">execution_context</phrase> <phrase role="identifier">ectx</phrase><phrase role="special">;</phrase>
1426
1427     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">StackAllocator</phrase> <phrase role="special">&gt;</phrase>
1428     <phrase role="identifier">my_control_structure</phrase><phrase role="special">(</phrase> <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">sp</phrase><phrase role="special">,</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">size</phrase><phrase role="special">,</phrase> <phrase role="identifier">stack_context</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">,</phrase> <phrase role="identifier">StackAllocator</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">)</phrase> <phrase role="special">:</phrase>
1429         <phrase role="comment">// create execution context</phrase>
1430         <phrase role="identifier">ectx</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg</phrase><phrase role="special">,</phrase> <phrase role="identifier">preallocated</phrase><phrase role="special">(</phrase> <phrase role="identifier">sp</phrase><phrase role="special">,</phrase> <phrase role="identifier">size</phrase><phrase role="special">,</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">),</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">entry_func</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
1431     <phrase role="special">}</phrase>
1432     <phrase role="special">...</phrase>
1433 <phrase role="special">};</phrase>
1434 </programlisting>
1435     <bridgehead renderas="sect3" id="context.ecv1.h3">
1436       <phrase id="context.ecv1.exception_handling"/><link linkend="context.ecv1.exception_handling">exception
1437       handling</link>
1438     </bridgehead>
1439     <para>
1440       If the function executed inside a <emphasis>execution_context</emphasis> emits
1441       ans exception, the application is terminated by calling <emphasis>std::terminate()</emphasis>.
1442       <emphasis>std::exception_ptr</emphasis> can be used to transfer exceptions
1443       between different execution contexts.
1444     </para>
1445     <important>
1446       <para>
1447         Do not jump from inside a catch block and then re-throw the exception in
1448         another execution context.
1449       </para>
1450     </important>
1451     <bridgehead renderas="sect3" id="context.ecv1.h4">
1452       <phrase id="context.ecv1.parameter_passing"/><link linkend="context.ecv1.parameter_passing">parameter
1453       passing</link>
1454     </bridgehead>
1455     <para>
1456       The void pointer argument passed to <emphasis>execution_context::operator()</emphasis>,
1457       in one context, is passed as the last argument of the <emphasis>context-function</emphasis>
1458       if the context is started for the first time. In all following invocations
1459       of <emphasis>execution_context::operator()</emphasis> the void pointer passed
1460       to <emphasis>execution_context::operator()</emphasis>, in one context, is returned
1461       by <emphasis>execution_context::operator()</emphasis> in the other context.
1462     </para>
1463 <programlisting><phrase role="keyword">class</phrase> <phrase role="identifier">X</phrase> <phrase role="special">{</phrase>
1464 <phrase role="keyword">private</phrase><phrase role="special">:</phrase>
1465     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">exception_ptr</phrase> <phrase role="identifier">excptr_</phrase><phrase role="special">;</phrase>
1466     <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase> <phrase role="identifier">caller_</phrase><phrase role="special">;</phrase>
1467     <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase> <phrase role="identifier">callee_</phrase><phrase role="special">;</phrase>
1468
1469 <phrase role="keyword">public</phrase><phrase role="special">:</phrase>
1470     <phrase role="identifier">X</phrase><phrase role="special">()</phrase> <phrase role="special">:</phrase>
1471         <phrase role="identifier">excptr_</phrase><phrase role="special">(),</phrase>
1472         <phrase role="identifier">caller_</phrase><phrase role="special">(</phrase> <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">context</phrase><phrase role="special">::</phrase><phrase role="identifier">execution_context</phrase><phrase role="special">::</phrase><phrase role="identifier">current</phrase><phrase role="special">()</phrase> <phrase role="special">),</phrase>
1473         <phrase role="identifier">callee_</phrase><phrase role="special">(</phrase> <phrase role="special">[=]</phrase> <phrase role="special">(</phrase><phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">vp</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
1474                     <phrase role="keyword">try</phrase> <phrase role="special">{</phrase>
1475                         <phrase role="keyword">int</phrase> <phrase role="identifier">i</phrase> <phrase role="special">=</phrase> <phrase role="special">*</phrase> <phrase role="keyword">static_cast</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">int</phrase> <phrase role="special">*</phrase> <phrase role="special">&gt;(</phrase> <phrase role="identifier">vp</phrase><phrase role="special">);</phrase>
1476                         <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase> <phrase role="identifier">str</phrase> <phrase role="special">=</phrase> <phrase role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">lexical_cast</phrase><phrase role="special">&lt;</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase><phrase role="special">&gt;(</phrase><phrase role="identifier">i</phrase><phrase role="special">);</phrase>
1477                         <phrase role="identifier">caller_</phrase><phrase role="special">(</phrase> <phrase role="special">&amp;</phrase> <phrase role="identifier">str</phrase><phrase role="special">);</phrase>
1478                     <phrase role="special">}</phrase> <phrase role="keyword">catch</phrase> <phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">bad_cast</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;)</phrase> <phrase role="special">{</phrase>
1479                         <phrase role="identifier">excptr_</phrase><phrase role="special">=</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">current_exception</phrase><phrase role="special">();</phrase>
1480                     <phrase role="special">}</phrase>
1481                  <phrase role="special">})</phrase>
1482     <phrase role="special">{}</phrase>
1483
1484     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase> <phrase role="keyword">int</phrase> <phrase role="identifier">i</phrase><phrase role="special">)</phrase> <phrase role="special">{</phrase>
1485         <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">ret</phrase> <phrase role="special">=</phrase> <phrase role="identifier">callee_</phrase><phrase role="special">(</phrase> <phrase role="special">&amp;</phrase> <phrase role="identifier">i</phrase><phrase role="special">);</phrase>
1486         <phrase role="keyword">if</phrase><phrase role="special">(</phrase><phrase role="identifier">excptr_</phrase><phrase role="special">){</phrase>
1487             <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">rethrow_exception</phrase><phrase role="special">(</phrase><phrase role="identifier">excptr_</phrase><phrase role="special">);</phrase>
1488         <phrase role="special">}</phrase>
1489         <phrase role="keyword">return</phrase> <phrase role="special">*</phrase> <phrase role="keyword">static_cast</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">string</phrase> <phrase role="special">*</phrase> <phrase role="special">&gt;(</phrase> <phrase role="identifier">ret</phrase><phrase role="special">);</phrase>
1490     <phrase role="special">}</phrase>
1491 <phrase role="special">};</phrase>
1492
1493 <phrase role="identifier">X</phrase> <phrase role="identifier">x</phrase><phrase role="special">;</phrase>
1494 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">cout</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">x</phrase><phrase role="special">(</phrase> <phrase role="number">7</phrase><phrase role="special">)</phrase> <phrase role="special">&lt;&lt;</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">endl</phrase><phrase role="special">;</phrase>
1495
1496 <phrase role="identifier">output</phrase><phrase role="special">:</phrase>
1497     <phrase role="number">7</phrase>
1498 </programlisting>
1499     <bridgehead renderas="sect3" id="context.ecv1.h5">
1500       <phrase id="context.ecv1.class__code__phrase_role__identifier__execution_context__phrase___code_"/><link
1501       linkend="context.ecv1.class__code__phrase_role__identifier__execution_context__phrase___code_">Class
1502       <code><phrase role="identifier">execution_context</phrase></code></link>
1503     </bridgehead>
1504 <programlisting><phrase role="keyword">class</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="special">{</phrase>
1505 <phrase role="keyword">public</phrase><phrase role="special">:</phrase>
1506     <phrase role="keyword">static</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="identifier">current</phrase><phrase role="special">()</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1507
1508     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&gt;</phrase>
1509     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">args</phrase><phrase role="special">);</phrase>
1510
1511     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">StackAlloc</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&gt;</phrase>
1512     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">StackAlloc</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">args</phrase><phrase role="special">);</phrase>
1513
1514     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">StackAlloc</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&gt;</phrase>
1515     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">preallocated</phrase> <phrase role="identifier">palloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">StackAlloc</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">args</phrase><phrase role="special">);</phrase>
1516
1517     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1518     <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1519
1520     <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1521     <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1522
1523     <phrase role="keyword">explicit</phrase> <phrase role="keyword">operator</phrase> <phrase role="keyword">bool</phrase><phrase role="special">()</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1524     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">!()</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1525
1526     <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase> <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">vp</phrase> <phrase role="special">=</phrase> <phrase role="keyword">nullptr</phrase><phrase role="special">);</phrase>
1527
1528     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&gt;</phrase>
1529     <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase> <phrase role="identifier">exec_ontop_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">vp</phrase> <phrase role="special">=</phrase> <phrase role="keyword">nullptr</phrase><phrase role="special">);</phrase>
1530
1531     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">==(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1532
1533     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">!=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1534
1535     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&lt;(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1536
1537     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&gt;(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1538
1539     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&lt;=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1540
1541     <phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&gt;=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1542
1543     <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="keyword">class</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase>
1544     <phrase role="keyword">friend</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">basic_ostream</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase> <phrase role="special">&amp;</phrase>
1545     <phrase role="keyword">operator</phrase><phrase role="special">&lt;&lt;(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">basic_ostream</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase> <phrase role="special">&amp;</phrase> <phrase role="identifier">os</phrase><phrase role="special">,</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">);</phrase>
1546 <phrase role="special">};</phrase>
1547 </programlisting>
1548     <para>
1549       <bridgehead renderas="sect4" id="ecv1_current_bridgehead">
1550   <phrase id="ecv1_current"/>
1551   <link linkend="ecv1_current">Static member function <code>current</code>()</link>
1552 </bridgehead>
1553     </para>
1554 <programlisting><phrase role="keyword">static</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="identifier">current</phrase><phrase role="special">()</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1555 </programlisting>
1556     <variablelist>
1557       <title></title>
1558       <varlistentry>
1559         <term>Returns:</term>
1560         <listitem>
1561           <para>
1562             Returns an instance of excution_context pointing to the active execution
1563             context.
1564           </para>
1565         </listitem>
1566       </varlistentry>
1567       <varlistentry>
1568         <term>Throws:</term>
1569         <listitem>
1570           <para>
1571             Nothing.
1572           </para>
1573         </listitem>
1574       </varlistentry>
1575     </variablelist>
1576     <para>
1577       <bridgehead renderas="sect4" id="ecv1_constructor_bridgehead">
1578   <phrase id="ecv1_constructor"/>
1579   <link linkend="ecv1_constructor">Constructor</link>
1580 </bridgehead>
1581     </para>
1582 <programlisting><phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&gt;</phrase>
1583 <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">args</phrase><phrase role="special">);</phrase>
1584
1585 <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">StackAlloc</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&gt;</phrase>
1586 <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">StackAlloc</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">args</phrase><phrase role="special">);</phrase>
1587
1588 <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">StackAlloc</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">typename</phrase> <phrase role="special">...</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&gt;</phrase>
1589 <phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">allocator_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">preallocated</phrase> <phrase role="identifier">palloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">StackAlloc</phrase> <phrase role="identifier">salloc</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="identifier">Args</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="special">...</phrase> <phrase role="identifier">args</phrase><phrase role="special">);</phrase>
1590 </programlisting>
1591     <variablelist>
1592       <title></title>
1593       <varlistentry>
1594         <term>Effects:</term>
1595         <listitem>
1596           <para>
1597             Creates a new execution context and prepares the context to execute
1598             <code><phrase role="identifier">fn</phrase></code>. <code><phrase role="identifier">fixedsize_stack</phrase></code>
1599             is used as default stack allocator (stack size == fixedsize_stack::traits::default_size()).
1600             The constructor with argument type <code><phrase role="identifier">preallocated</phrase></code>,
1601             is used to create a user defined data <link linkend="ecv1_prealloc">(for
1602             instance additional control structures)</link> on top of the stack.
1603           </para>
1604         </listitem>
1605       </varlistentry>
1606     </variablelist>
1607     <para>
1608       <bridgehead renderas="sect4" id="ecv1_copy constructor_bridgehead">
1609   <phrase id="ecv1_copy constructor"/>
1610   <link linkend="ecv1_copy constructor">Copy
1611       constructor</link>
1612 </bridgehead>
1613     </para>
1614 <programlisting><phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1615 </programlisting>
1616     <variablelist>
1617       <title></title>
1618       <varlistentry>
1619         <term>Effects:</term>
1620         <listitem>
1621           <para>
1622             Copies <code><phrase role="identifier">other</phrase></code>, e.g. underlying
1623             control structure is shared with <code><phrase role="special">*</phrase><phrase
1624             role="keyword">this</phrase></code>.
1625           </para>
1626         </listitem>
1627       </varlistentry>
1628       <varlistentry>
1629         <term>Throws:</term>
1630         <listitem>
1631           <para>
1632             Nothing.
1633           </para>
1634         </listitem>
1635       </varlistentry>
1636     </variablelist>
1637     <para>
1638       <bridgehead renderas="sect4" id="ecv1_move constructor_bridgehead">
1639   <phrase id="ecv1_move constructor"/>
1640   <link linkend="ecv1_move constructor">Move
1641       constructor</link>
1642 </bridgehead>
1643     </para>
1644 <programlisting><phrase role="identifier">execution_context</phrase><phrase role="special">(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1645 </programlisting>
1646     <variablelist>
1647       <title></title>
1648       <varlistentry>
1649         <term>Effects:</term>
1650         <listitem>
1651           <para>
1652             Moves underlying control structure to <code><phrase role="special">*</phrase><phrase
1653             role="keyword">this</phrase></code>.
1654           </para>
1655         </listitem>
1656       </varlistentry>
1657       <varlistentry>
1658         <term>Throws:</term>
1659         <listitem>
1660           <para>
1661             Nothing.
1662           </para>
1663         </listitem>
1664       </varlistentry>
1665     </variablelist>
1666     <para>
1667       <bridgehead renderas="sect4" id="ecv1_copy assignment_bridgehead">
1668   <phrase id="ecv1_copy assignment"/>
1669   <link linkend="ecv1_copy assignment">Copy
1670       assignment operator</link>
1671 </bridgehead>
1672     </para>
1673 <programlisting><phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1674 </programlisting>
1675     <variablelist>
1676       <title></title>
1677       <varlistentry>
1678         <term>Effects:</term>
1679         <listitem>
1680           <para>
1681             Copies the state of <code><phrase role="identifier">other</phrase></code>
1682             to <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>,
1683             control structure is shared.
1684           </para>
1685         </listitem>
1686       </varlistentry>
1687       <varlistentry>
1688         <term>Throws:</term>
1689         <listitem>
1690           <para>
1691             Nothing.
1692           </para>
1693         </listitem>
1694       </varlistentry>
1695     </variablelist>
1696     <para>
1697       <bridgehead renderas="sect4" id="ecv1_move assignment_bridgehead">
1698   <phrase id="ecv1_move assignment"/>
1699   <link linkend="ecv1_move assignment">Move
1700       assignment operator</link>
1701 </bridgehead>
1702     </para>
1703 <programlisting><phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;</phrase> <phrase role="keyword">operator</phrase><phrase role="special">=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1704 </programlisting>
1705     <variablelist>
1706       <title></title>
1707       <varlistentry>
1708         <term>Effects:</term>
1709         <listitem>
1710           <para>
1711             Moves the control structure of <code><phrase role="identifier">other</phrase></code>
1712             to <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>
1713             using move semantics.
1714           </para>
1715         </listitem>
1716       </varlistentry>
1717       <varlistentry>
1718         <term>Throws:</term>
1719         <listitem>
1720           <para>
1721             Nothing.
1722           </para>
1723         </listitem>
1724       </varlistentry>
1725     </variablelist>
1726     <para>
1727       <bridgehead renderas="sect4" id="ecv1_operator_bool_bridgehead">
1728   <phrase id="ecv1_operator_bool"/>
1729   <link linkend="ecv1_operator_bool">Member function
1730       <code>operator bool</code>()</link>
1731 </bridgehead>
1732     </para>
1733 <programlisting><phrase role="keyword">explicit</phrase> <phrase role="keyword">operator</phrase> <phrase role="keyword">bool</phrase><phrase role="special">()</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1734 </programlisting>
1735     <variablelist>
1736       <title></title>
1737       <varlistentry>
1738         <term>Returns:</term>
1739         <listitem>
1740           <para>
1741             <code><phrase role="keyword">true</phrase></code> if <code><phrase role="special">*</phrase><phrase
1742             role="keyword">this</phrase></code> points to a control structure.
1743           </para>
1744         </listitem>
1745       </varlistentry>
1746       <varlistentry>
1747         <term>Throws:</term>
1748         <listitem>
1749           <para>
1750             Nothing.
1751           </para>
1752         </listitem>
1753       </varlistentry>
1754     </variablelist>
1755     <para>
1756       <bridgehead renderas="sect4" id="ecv1_operator_not_bridgehead">
1757   <phrase id="ecv1_operator_not"/>
1758   <link linkend="ecv1_operator_not">Member function
1759       <code>operator!</code>()</link>
1760 </bridgehead>
1761     </para>
1762 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">!()</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1763 </programlisting>
1764     <variablelist>
1765       <title></title>
1766       <varlistentry>
1767         <term>Returns:</term>
1768         <listitem>
1769           <para>
1770             <code><phrase role="keyword">true</phrase></code> if <code><phrase role="special">*</phrase><phrase
1771             role="keyword">this</phrase></code> does not point to a control structure.
1772           </para>
1773         </listitem>
1774       </varlistentry>
1775       <varlistentry>
1776         <term>Throws:</term>
1777         <listitem>
1778           <para>
1779             Nothing.
1780           </para>
1781         </listitem>
1782       </varlistentry>
1783     </variablelist>
1784     <para>
1785       <bridgehead renderas="sect4" id="ecv1_operator_call_bridgehead">
1786   <phrase id="ecv1_operator_call"/>
1787   <link linkend="ecv1_operator_call">Member function
1788       <code>operator()</code>()</link>
1789 </bridgehead>
1790     </para>
1791 <programlisting><phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase> <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">vp</phrase> <phrase role="special">=</phrase> <phrase role="keyword">nullptr</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1792 </programlisting>
1793     <variablelist>
1794       <title></title>
1795       <varlistentry>
1796         <term>Effects:</term>
1797         <listitem>
1798           <para>
1799             Stores internally the current context data (stack pointer, instruction
1800             pointer, and CPU registers) of the current active context and restores
1801             the context data from <code><phrase role="special">*</phrase><phrase
1802             role="keyword">this</phrase></code>, which implies jumping to <code><phrase
1803             role="special">*</phrase><phrase role="keyword">this</phrase></code>'s
1804             context. The void pointer argument, <code><phrase role="identifier">vp</phrase></code>,
1805             is passed to the current context to be returned by the most recent call
1806             to <code><phrase role="identifier">execution_context</phrase><phrase
1807             role="special">::</phrase><phrase role="keyword">operator</phrase><phrase
1808             role="special">()</phrase></code> in the same thread. <code><phrase role="identifier">fn</phrase></code>
1809             is executed with arguments <code><phrase role="identifier">args</phrase></code>
1810             on top of the stack of <code><phrase role="keyword">this</phrase></code>.
1811           </para>
1812         </listitem>
1813       </varlistentry>
1814       <varlistentry>
1815         <term>Note:</term>
1816         <listitem>
1817           <para>
1818             The behaviour is undefined if <code><phrase role="keyword">operator</phrase><phrase
1819             role="special">()()</phrase></code> is called while <emphasis>execution_context::current()</emphasis>
1820             returns <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>
1821             (e.g. resuming an already running context). If the top-level context
1822             function returns, <code><phrase role="identifier">std</phrase><phrase
1823             role="special">::</phrase><phrase role="identifier">exit</phrase><phrase
1824             role="special">()</phrase></code> is called.
1825           </para>
1826         </listitem>
1827       </varlistentry>
1828       <varlistentry>
1829         <term>Returns:</term>
1830         <listitem>
1831           <para>
1832             The void pointer argument passed to the most recent call to <emphasis>execution_context::operator()</emphasis>,
1833             if any.
1834           </para>
1835         </listitem>
1836       </varlistentry>
1837     </variablelist>
1838     <para>
1839       <bridgehead renderas="sect4" id="ecv1_operator_call_ontop_bridgehead">
1840   <phrase id="ecv1_operator_call_ontop"/>
1841   <link linkend="ecv1_operator_call_ontop">Member
1842       function <code>operator(exec_ontop_arg_t)</code>()</link>
1843 </bridgehead>
1844     </para>
1845 <programlisting><phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&gt;</phrase>
1846 <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="keyword">operator</phrase><phrase role="special">()(</phrase> <phrase role="identifier">exec_ontop_arg_t</phrase><phrase role="special">,</phrase> <phrase role="identifier">Fn</phrase> <phrase role="special">&amp;&amp;</phrase> <phrase role="identifier">fn</phrase><phrase role="special">,</phrase> <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">vp</phrase> <phrase role="special">=</phrase> <phrase role="keyword">nullptr</phrase><phrase role="special">);</phrase>
1847 </programlisting>
1848     <variablelist>
1849       <title></title>
1850       <varlistentry>
1851         <term>Effects:</term>
1852         <listitem>
1853           <para>
1854             Same as <emphasis>execution_context::operator()</emphasis>. Additionally,
1855             function <code><phrase role="identifier">fn</phrase></code> is executed
1856             with arguments <code><phrase role="identifier">vp</phrase></code> in
1857             the context of <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>
1858             (e.g. the stack frame of <code><phrase role="identifier">fn</phrase></code>
1859             is allocated on stack of <code><phrase role="special">*</phrase><phrase
1860             role="keyword">this</phrase></code>).
1861           </para>
1862         </listitem>
1863       </varlistentry>
1864       <varlistentry>
1865         <term>Returns:</term>
1866         <listitem>
1867           <para>
1868             The void pointer argument passed to the most recent call to <emphasis>execution_context::operator()</emphasis>,
1869             if any.
1870           </para>
1871         </listitem>
1872       </varlistentry>
1873     </variablelist>
1874     <para>
1875       <bridgehead renderas="sect4" id="ecv1_operator_equal_bridgehead">
1876   <phrase id="ecv1_operator_equal"/>
1877   <link linkend="ecv1_operator_equal">Member
1878       function <code>operator==</code>()</link>
1879 </bridgehead>
1880     </para>
1881 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">==(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1882 </programlisting>
1883     <variablelist>
1884       <title></title>
1885       <varlistentry>
1886         <term>Returns:</term>
1887         <listitem>
1888           <para>
1889             <code><phrase role="keyword">true</phrase></code> if <code><phrase role="special">*</phrase><phrase
1890             role="keyword">this</phrase></code> and <code><phrase role="identifier">other</phrase></code>
1891             represent the same execution context, <code><phrase role="keyword">false</phrase></code>
1892             otherwise.
1893           </para>
1894         </listitem>
1895       </varlistentry>
1896       <varlistentry>
1897         <term>Throws:</term>
1898         <listitem>
1899           <para>
1900             Nothing.
1901           </para>
1902         </listitem>
1903       </varlistentry>
1904     </variablelist>
1905     <para>
1906       <bridgehead renderas="sect4" id="ecv1_operator_notequal_bridgehead">
1907   <phrase id="ecv1_operator_notequal"/>
1908   <link linkend="ecv1_operator_notequal">Member
1909       function <code>operator!=</code>()</link>
1910 </bridgehead>
1911     </para>
1912 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">!=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1913 </programlisting>
1914     <variablelist>
1915       <title></title>
1916       <varlistentry>
1917         <term>Returns:</term>
1918         <listitem>
1919           <para>
1920             <code>! (other == * this)</code>
1921           </para>
1922         </listitem>
1923       </varlistentry>
1924       <varlistentry>
1925         <term>Throws:</term>
1926         <listitem>
1927           <para>
1928             Nothing.
1929           </para>
1930         </listitem>
1931       </varlistentry>
1932     </variablelist>
1933     <para>
1934       <bridgehead renderas="sect4" id="ecv1_operator_less_bridgehead">
1935   <phrase id="ecv1_operator_less"/>
1936   <link linkend="ecv1_operator_less">Member function
1937       <code>operator&lt;</code>()</link>
1938 </bridgehead>
1939     </para>
1940 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&lt;(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1941 </programlisting>
1942     <variablelist>
1943       <title></title>
1944       <varlistentry>
1945         <term>Returns:</term>
1946         <listitem>
1947           <para>
1948             <code><phrase role="keyword">true</phrase></code> if <code><phrase role="special">*</phrase><phrase
1949             role="keyword">this</phrase> <phrase role="special">!=</phrase> <phrase
1950             role="identifier">other</phrase></code> is true and the implementation-defined
1951             total order of <code><phrase role="identifier">execution_context</phrase></code>
1952             values places <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>
1953             before <code><phrase role="identifier">other</phrase></code>, false otherwise.
1954           </para>
1955         </listitem>
1956       </varlistentry>
1957       <varlistentry>
1958         <term>Throws:</term>
1959         <listitem>
1960           <para>
1961             Nothing.
1962           </para>
1963         </listitem>
1964       </varlistentry>
1965     </variablelist>
1966     <para>
1967       <bridgehead renderas="sect4" id="ecv1_operator_greater_bridgehead">
1968   <phrase id="ecv1_operator_greater"/>
1969   <link linkend="ecv1_operator_greater">Member
1970       function <code>operator&gt;</code>()</link>
1971 </bridgehead>
1972     </para>
1973 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&gt;(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
1974 </programlisting>
1975     <variablelist>
1976       <title></title>
1977       <varlistentry>
1978         <term>Returns:</term>
1979         <listitem>
1980           <para>
1981             <code><phrase role="identifier">other</phrase> <phrase role="special">&lt;</phrase>
1982             <phrase role="special">*</phrase> <phrase role="keyword">this</phrase></code>
1983           </para>
1984         </listitem>
1985       </varlistentry>
1986       <varlistentry>
1987         <term>Throws:</term>
1988         <listitem>
1989           <para>
1990             Nothing.
1991           </para>
1992         </listitem>
1993       </varlistentry>
1994     </variablelist>
1995     <para>
1996       <bridgehead renderas="sect4" id="ecv1_operator_lesseq_bridgehead">
1997   <phrase id="ecv1_operator_lesseq"/>
1998   <link linkend="ecv1_operator_lesseq">Member
1999       function <code>operator&lt;=</code>()</link>
2000 </bridgehead>
2001     </para>
2002 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&lt;=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
2003 </programlisting>
2004     <variablelist>
2005       <title></title>
2006       <varlistentry>
2007         <term>Returns:</term>
2008         <listitem>
2009           <para>
2010             <code><phrase role="special">!</phrase> <phrase role="special">(</phrase><phrase
2011             role="identifier">other</phrase> <phrase role="special">&lt;</phrase>
2012             <phrase role="special">*</phrase> <phrase role="keyword">this</phrase><phrase
2013             role="special">)</phrase></code>
2014           </para>
2015         </listitem>
2016       </varlistentry>
2017       <varlistentry>
2018         <term>Throws:</term>
2019         <listitem>
2020           <para>
2021             Nothing.
2022           </para>
2023         </listitem>
2024       </varlistentry>
2025     </variablelist>
2026     <para>
2027       <bridgehead renderas="sect4" id="ecv1_operator_greatereq_bridgehead">
2028   <phrase id="ecv1_operator_greatereq"/>
2029   <link linkend="ecv1_operator_greatereq">Member
2030       function <code>operator&gt;=</code>()</link>
2031 </bridgehead>
2032     </para>
2033 <programlisting><phrase role="keyword">bool</phrase> <phrase role="keyword">operator</phrase><phrase role="special">&gt;=(</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">)</phrase> <phrase role="keyword">const</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
2034 </programlisting>
2035     <variablelist>
2036       <title></title>
2037       <varlistentry>
2038         <term>Returns:</term>
2039         <listitem>
2040           <para>
2041             <code><phrase role="special">!</phrase> <phrase role="special">(*</phrase>
2042             <phrase role="keyword">this</phrase> <phrase role="special">&lt;</phrase>
2043             <phrase role="identifier">other</phrase><phrase role="special">)</phrase></code>
2044           </para>
2045         </listitem>
2046       </varlistentry>
2047       <varlistentry>
2048         <term>Throws:</term>
2049         <listitem>
2050           <para>
2051             Nothing.
2052           </para>
2053         </listitem>
2054       </varlistentry>
2055     </variablelist>
2056     <para>
2057       <bridgehead renderas="sect4" id="ecv1__bridgehead">
2058   <phrase id="ecv1_"/>
2059   <link linkend="ecv1_">Non-member function <code>operator&lt;&lt;()</code></link>
2060 </bridgehead>
2061     </para>
2062 <programlisting><phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="keyword">class</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase>
2063 <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">basic_ostream</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase> <phrase role="special">&amp;</phrase>
2064 <phrase role="keyword">operator</phrase><phrase role="special">&lt;&lt;(</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">basic_ostream</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">charT</phrase><phrase role="special">,</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase> <phrase role="special">&amp;</phrase> <phrase role="identifier">os</phrase><phrase role="special">,</phrase> <phrase role="identifier">execution_context</phrase> <phrase role="keyword">const</phrase><phrase role="special">&amp;</phrase> <phrase role="identifier">other</phrase><phrase role="special">);</phrase>
2065 </programlisting>
2066     <variablelist>
2067       <title></title>
2068       <varlistentry>
2069         <term>Efects:</term>
2070         <listitem>
2071           <para>
2072             Writes the representation of <code><phrase role="identifier">other</phrase></code>
2073             to stream <code><phrase role="identifier">os</phrase></code>.
2074           </para>
2075         </listitem>
2076       </varlistentry>
2077       <varlistentry>
2078         <term>Returns:</term>
2079         <listitem>
2080           <para>
2081             <code><phrase role="identifier">os</phrase></code>
2082           </para>
2083         </listitem>
2084       </varlistentry>
2085     </variablelist>
2086   </section>
2087   <section id="context.stack">
2088     <title><anchor id="stack"/><link linkend="context.stack">Stack allocation</link></title>
2089     <para>
2090       The memory used by the stack is allocated/deallocated via a <emphasis>StackAllocator</emphasis>
2091       which is required to model a <emphasis>stack-allocator concept</emphasis>.
2092     </para>
2093     <bridgehead renderas="sect3" id="context.stack.h0">
2094       <phrase id="context.stack._emphasis_stack_allocator_concept__emphasis_"/><link
2095       linkend="context.stack._emphasis_stack_allocator_concept__emphasis_"><emphasis>stack-allocator
2096       concept</emphasis></link>
2097     </bridgehead>
2098     <para>
2099       A <emphasis>StackAllocator</emphasis> must satisfy the <emphasis>stack-allocator
2100       concept</emphasis> requirements shown in the following table, in which <code><phrase
2101       role="identifier">a</phrase></code> is an object of a <emphasis>StackAllocator</emphasis>
2102       type, <code><phrase role="identifier">sctx</phrase></code> is a <code><phrase
2103       role="identifier">stack_context</phrase></code>, and <code><phrase role="identifier">size</phrase></code>
2104       is a <code><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase
2105       role="identifier">size_t</phrase></code>:
2106     </para>
2107     <informaltable frame="all">
2108       <tgroup cols="3">
2109         <thead>
2110           <row>
2111             <entry>
2112               <para>
2113                 expression
2114               </para>
2115             </entry>
2116             <entry>
2117               <para>
2118                 return type
2119               </para>
2120             </entry>
2121             <entry>
2122               <para>
2123                 notes
2124               </para>
2125             </entry>
2126           </row>
2127         </thead>
2128         <tbody>
2129           <row>
2130             <entry>
2131               <para>
2132                 <code><phrase role="identifier">a</phrase><phrase role="special">(</phrase><phrase
2133                 role="identifier">size</phrase><phrase role="special">)</phrase></code>
2134               </para>
2135             </entry>
2136             <entry>
2137             </entry>
2138             <entry>
2139               <para>
2140                 creates a stack allocator
2141               </para>
2142             </entry>
2143           </row>
2144           <row>
2145             <entry>
2146               <para>
2147                 <code><phrase role="identifier">a</phrase><phrase role="special">.</phrase><phrase
2148                 role="identifier">allocate</phrase><phrase role="special">()</phrase></code>
2149               </para>
2150             </entry>
2151             <entry>
2152               <para>
2153                 <code><phrase role="identifier">stack_context</phrase></code>
2154               </para>
2155             </entry>
2156             <entry>
2157               <para>
2158                 creates a stack
2159               </para>
2160             </entry>
2161           </row>
2162           <row>
2163             <entry>
2164               <para>
2165                 <code><phrase role="identifier">a</phrase><phrase role="special">.</phrase><phrase
2166                 role="identifier">deallocate</phrase><phrase role="special">(</phrase>
2167                 <phrase role="identifier">sctx</phrase><phrase role="special">)</phrase></code>
2168               </para>
2169             </entry>
2170             <entry>
2171               <para>
2172                 <code><phrase role="keyword">void</phrase></code>
2173               </para>
2174             </entry>
2175             <entry>
2176               <para>
2177                 deallocates the stack created by <code><phrase role="identifier">a</phrase><phrase
2178                 role="special">.</phrase><phrase role="identifier">allocate</phrase><phrase
2179                 role="special">()</phrase></code>
2180               </para>
2181             </entry>
2182           </row>
2183         </tbody>
2184       </tgroup>
2185     </informaltable>
2186     <important>
2187       <para>
2188         The implementation of <code><phrase role="identifier">allocate</phrase><phrase
2189         role="special">()</phrase></code> might include logic to protect against
2190         exceeding the context's available stack size rather than leaving it as undefined
2191         behaviour.
2192       </para>
2193     </important>
2194     <important>
2195       <para>
2196         Calling <code><phrase role="identifier">deallocate</phrase><phrase role="special">()</phrase></code>
2197         with a <code><phrase role="identifier">stack_context</phrase></code> not
2198         set by <code><phrase role="identifier">allocate</phrase><phrase role="special">()</phrase></code>
2199         results in undefined behaviour.
2200       </para>
2201     </important>
2202     <note>
2203       <para>
2204         The stack is not required to be aligned; alignment takes place inside <emphasis>execution_context</emphasis>.
2205       </para>
2206     </note>
2207     <note>
2208       <para>
2209         Depending on the architecture <code><phrase role="identifier">allocate</phrase><phrase
2210         role="special">()</phrase></code> stores an address from the top of the stack
2211         (growing downwards) or the bottom of the stack (growing upwards).
2212       </para>
2213     </note>
2214     <section id="context.stack.protected_fixedsize">
2215       <title><link linkend="context.stack.protected_fixedsize">Class <emphasis>protected_fixedsize</emphasis></link></title>
2216       <para>
2217         <emphasis role="bold">Boost.Context</emphasis> provides the class <emphasis>protected_fixedsize_stack</emphasis>
2218         which models the <emphasis>stack-allocator concept</emphasis>. It appends
2219         a guard page at the end of each stack to protect against exceeding the stack.
2220         If the guard page is accessed (read or write operation) a segmentation fault/access
2221         violation is generated by the operating system.
2222       </para>
2223       <important>
2224         <para>
2225           Using <emphasis>protected_fixedsize_stack</emphasis> is expensive. That
2226           is, launching a new coroutine with a new stack is expensive; the allocated
2227           stack is just as efficient to use as any other stack.
2228         </para>
2229       </important>
2230       <note>
2231         <para>
2232           The appended <code><phrase role="identifier">guard</phrase> <phrase role="identifier">page</phrase></code>
2233           is <emphasis role="bold">not</emphasis> mapped to physical memory, only
2234           virtual addresses are used.
2235         </para>
2236       </note>
2237 <programlisting><phrase role="preprocessor">#include</phrase> <phrase role="special">&lt;</phrase><phrase role="identifier">boost</phrase><phrase role="special">/</phrase><phrase role="identifier">context</phrase><phrase role="special">/</phrase><phrase role="identifier">protected_fixedsize</phrase><phrase role="special">.</phrase><phrase role="identifier">hpp</phrase><phrase role="special">&gt;</phrase>
2238
2239 <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase>
2240 <phrase role="keyword">struct</phrase> <phrase role="identifier">basic_protected_fixedsize</phrase> <phrase role="special">{</phrase>
2241     <phrase role="keyword">typedef</phrase> <phrase role="identifier">traitT</phrase>  <phrase role="identifier">traits_type</phrase><phrase role="special">;</phrase>
2242
2243     <phrase role="identifier">basic_protected_fixesize</phrase><phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">size</phrase> <phrase role="special">=</phrase> <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase role="identifier">default_size</phrase><phrase role="special">());</phrase>
2244
2245     <phrase role="identifier">stack_context</phrase> <phrase role="identifier">allocate</phrase><phrase role="special">();</phrase>
2246
2247     <phrase role="keyword">void</phrase> <phrase role="identifier">deallocate</phrase><phrase role="special">(</phrase> <phrase role="identifier">stack_context</phrase> <phrase role="special">&amp;);</phrase>
2248 <phrase role="special">}</phrase>
2249
2250 <phrase role="keyword">typedef</phrase> <phrase role="identifier">basic_protected_fixedsize</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">stack_traits</phrase> <phrase role="special">&gt;</phrase> <phrase role="identifier">protected_fixedsize</phrase>
2251 </programlisting>
2252       <bridgehead renderas="sect4" id="context.stack.protected_fixedsize.h0">
2253         <phrase id="context.stack.protected_fixedsize._code__phrase_role__identifier__stack_context__phrase___phrase_role__identifier__allocate__phrase__phrase_role__special______phrase___code_"/><link
2254         linkend="context.stack.protected_fixedsize._code__phrase_role__identifier__stack_context__phrase___phrase_role__identifier__allocate__phrase__phrase_role__special______phrase___code_"><code><phrase
2255         role="identifier">stack_context</phrase> <phrase role="identifier">allocate</phrase><phrase
2256         role="special">()</phrase></code></link>
2257       </bridgehead>
2258       <variablelist>
2259         <title></title>
2260         <varlistentry>
2261           <term>Preconditions:</term>
2262           <listitem>
2263             <para>
2264               <code><phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2265               role="identifier">minimum</phrase><phrase role="special">:</phrase><phrase
2266               role="identifier">size</phrase><phrase role="special">()</phrase>
2267               <phrase role="special">&lt;=</phrase> <phrase role="identifier">size</phrase></code>
2268               and <code><phrase role="special">!</phrase> <phrase role="identifier">traits_type</phrase><phrase
2269               role="special">::</phrase><phrase role="identifier">is_unbounded</phrase><phrase
2270               role="special">()</phrase> <phrase role="special">&amp;&amp;</phrase>
2271               <phrase role="special">(</phrase> <phrase role="identifier">traits_type</phrase><phrase
2272               role="special">::</phrase><phrase role="identifier">maximum</phrase><phrase
2273               role="special">:</phrase><phrase role="identifier">size</phrase><phrase
2274               role="special">()</phrase> <phrase role="special">&gt;=</phrase> <phrase
2275               role="identifier">size</phrase><phrase role="special">)</phrase></code>.
2276             </para>
2277           </listitem>
2278         </varlistentry>
2279         <varlistentry>
2280           <term>Effects:</term>
2281           <listitem>
2282             <para>
2283               Allocates memory of at least <code><phrase role="identifier">size</phrase></code>
2284               Bytes and stores a pointer to the stack and its actual size in <code><phrase
2285               role="identifier">sctx</phrase></code>. Depending on the architecture
2286               (the stack grows downwards/upwards) the stored address is the highest/lowest
2287               address of the stack.
2288             </para>
2289           </listitem>
2290         </varlistentry>
2291       </variablelist>
2292       <bridgehead renderas="sect4" id="context.stack.protected_fixedsize.h1">
2293         <phrase id="context.stack.protected_fixedsize._code__phrase_role__keyword__void__phrase___phrase_role__identifier__deallocate__phrase__phrase_role__special_____phrase___phrase_role__identifier__stack_context__phrase___phrase_role__special___amp___phrase___phrase_role__identifier__sctx__phrase__phrase_role__special_____phrase___code_"/><link
2294         linkend="context.stack.protected_fixedsize._code__phrase_role__keyword__void__phrase___phrase_role__identifier__deallocate__phrase__phrase_role__special_____phrase___phrase_role__identifier__stack_context__phrase___phrase_role__special___amp___phrase___phrase_role__identifier__sctx__phrase__phrase_role__special_____phrase___code_"><code><phrase
2295         role="keyword">void</phrase> <phrase role="identifier">deallocate</phrase><phrase
2296         role="special">(</phrase> <phrase role="identifier">stack_context</phrase>
2297         <phrase role="special">&amp;</phrase> <phrase role="identifier">sctx</phrase><phrase
2298         role="special">)</phrase></code></link>
2299       </bridgehead>
2300       <variablelist>
2301         <title></title>
2302         <varlistentry>
2303           <term>Preconditions:</term>
2304           <listitem>
2305             <para>
2306               <code><phrase role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase
2307               role="identifier">sp</phrase></code> is valid, <code><phrase role="identifier">traits_type</phrase><phrase
2308               role="special">::</phrase><phrase role="identifier">minimum</phrase><phrase
2309               role="special">:</phrase><phrase role="identifier">size</phrase><phrase
2310               role="special">()</phrase> <phrase role="special">&lt;=</phrase> <phrase
2311               role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase
2312               role="identifier">size</phrase></code> and <code><phrase role="special">!</phrase>
2313               <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2314               role="identifier">is_unbounded</phrase><phrase role="special">()</phrase>
2315               <phrase role="special">&amp;&amp;</phrase> <phrase role="special">(</phrase>
2316               <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2317               role="identifier">maximum</phrase><phrase role="special">:</phrase><phrase
2318               role="identifier">size</phrase><phrase role="special">()</phrase>
2319               <phrase role="special">&gt;=</phrase> <phrase role="identifier">sctx</phrase><phrase
2320               role="special">.</phrase><phrase role="identifier">size</phrase><phrase
2321               role="special">)</phrase></code>.
2322             </para>
2323           </listitem>
2324         </varlistentry>
2325         <varlistentry>
2326           <term>Effects:</term>
2327           <listitem>
2328             <para>
2329               Deallocates the stack space.
2330             </para>
2331           </listitem>
2332         </varlistentry>
2333       </variablelist>
2334     </section>
2335     <section id="context.stack.pooled_fixedsize">
2336       <title><link linkend="context.stack.pooled_fixedsize">Class <emphasis>pooled_fixedsize_stack</emphasis></link></title>
2337       <para>
2338         <emphasis role="bold">Boost.Context</emphasis> provides the class <emphasis>pooled_fixedsize_stack</emphasis>
2339         which models the <emphasis>stack-allocator concept</emphasis>. In contrast
2340         to <emphasis>protected_fixedsize_stack</emphasis> it does not append a guard
2341         page at the end of each stack. The memory is managed internally by <ulink
2342         url="http://www.boost.org/doc/libs/release/libs/pool/doc/html/boost/pool.html"><code><phrase
2343         role="identifier">boost</phrase><phrase role="special">::</phrase><phrase
2344         role="identifier">pool</phrase><phrase role="special">&lt;&gt;</phrase></code></ulink>.
2345       </para>
2346 <programlisting><phrase role="preprocessor">#include</phrase> <phrase role="special">&lt;</phrase><phrase role="identifier">boost</phrase><phrase role="special">/</phrase><phrase role="identifier">context</phrase><phrase role="special">/</phrase><phrase role="identifier">pooled_fixedsize_stack</phrase><phrase role="special">.</phrase><phrase role="identifier">hpp</phrase><phrase role="special">&gt;</phrase>
2347
2348 <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase>
2349 <phrase role="keyword">struct</phrase> <phrase role="identifier">basic_pooled_fixedsize_stack</phrase> <phrase role="special">{</phrase>
2350     <phrase role="keyword">typedef</phrase> <phrase role="identifier">traitT</phrase>  <phrase role="identifier">traits_type</phrase><phrase role="special">;</phrase>
2351
2352     <phrase role="identifier">basic_pooled_fixedsize_stack</phrase><phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">stack_size</phrase> <phrase role="special">=</phrase> <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase role="identifier">default_size</phrase><phrase role="special">(),</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">next_size</phrase> <phrase role="special">=</phrase> <phrase role="number">32</phrase><phrase role="special">,</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">max_size</phrase> <phrase role="special">=</phrase> <phrase role="number">0</phrase><phrase role="special">);</phrase>
2353
2354     <phrase role="identifier">stack_context</phrase> <phrase role="identifier">allocate</phrase><phrase role="special">();</phrase>
2355
2356     <phrase role="keyword">void</phrase> <phrase role="identifier">deallocate</phrase><phrase role="special">(</phrase> <phrase role="identifier">stack_context</phrase> <phrase role="special">&amp;);</phrase>
2357 <phrase role="special">}</phrase>
2358
2359 <phrase role="keyword">typedef</phrase> <phrase role="identifier">basic_pooled_fixedsize_stack</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">stack_traits</phrase> <phrase role="special">&gt;</phrase> <phrase role="identifier">pooled_fixedsize_stack</phrase><phrase role="special">;</phrase>
2360 </programlisting>
2361       <bridgehead renderas="sect4" id="context.stack.pooled_fixedsize.h0">
2362         <phrase id="context.stack.pooled_fixedsize._code__phrase_role__identifier__basic_pooled_fixedsize_stack__phrase__phrase_role__special_____phrase__phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__stack_size__phrase__phrase_role__special_____phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__next_size__phrase__phrase_role__special_____phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__max_size__phrase__phrase_role__special_____phrase___code_"/><link
2363         linkend="context.stack.pooled_fixedsize._code__phrase_role__identifier__basic_pooled_fixedsize_stack__phrase__phrase_role__special_____phrase__phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__stack_size__phrase__phrase_role__special_____phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__next_size__phrase__phrase_role__special_____phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__max_size__phrase__phrase_role__special_____phrase___code_"><code><phrase
2364         role="identifier">basic_pooled_fixedsize_stack</phrase><phrase role="special">(</phrase><phrase
2365         role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase>
2366         <phrase role="identifier">stack_size</phrase><phrase role="special">,</phrase>
2367         <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase
2368         role="identifier">size_t</phrase> <phrase role="identifier">next_size</phrase><phrase
2369         role="special">,</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase
2370         role="identifier">size_t</phrase> <phrase role="identifier">max_size</phrase><phrase
2371         role="special">)</phrase></code></link>
2372       </bridgehead>
2373       <variablelist>
2374         <title></title>
2375         <varlistentry>
2376           <term>Preconditions:</term>
2377           <listitem>
2378             <para>
2379               <code><phrase role="special">!</phrase> <phrase role="identifier">traits_type</phrase><phrase
2380               role="special">::</phrase><phrase role="identifier">is_unbounded</phrase><phrase
2381               role="special">()</phrase> <phrase role="special">&amp;&amp;</phrase>
2382               <phrase role="special">(</phrase> <phrase role="identifier">traits_type</phrase><phrase
2383               role="special">::</phrase><phrase role="identifier">maximum</phrase><phrase
2384               role="special">:</phrase><phrase role="identifier">size</phrase><phrase
2385               role="special">()</phrase> <phrase role="special">&gt;=</phrase> <phrase
2386               role="identifier">stack_size</phrase><phrase role="special">)</phrase></code>
2387               and <code><phrase role="number">0</phrase> <phrase role="special">&lt;</phrase>
2388               <phrase role="identifier">nest_size</phrase></code>.
2389             </para>
2390           </listitem>
2391         </varlistentry>
2392         <varlistentry>
2393           <term>Effects:</term>
2394           <listitem>
2395             <para>
2396               Allocates memory of at least <code><phrase role="identifier">stack_size</phrase></code>
2397               Bytes and stores a pointer to the stack and its actual size in <code><phrase
2398               role="identifier">sctx</phrase></code>. Depending on the architecture
2399               (the stack grows downwards/upwards) the stored address is the highest/lowest
2400               address of the stack. Argument <code><phrase role="identifier">next_size</phrase></code>
2401               determines the number of stacks to request from the system the first
2402               time that <code><phrase role="special">*</phrase><phrase role="keyword">this</phrase></code>
2403               needs to allocate system memory. The third argument <code><phrase role="identifier">max_size</phrase></code>
2404               controls how many memory might be allocated for stacks - a value of
2405               zero means no uper limit.
2406             </para>
2407           </listitem>
2408         </varlistentry>
2409       </variablelist>
2410       <bridgehead renderas="sect4" id="context.stack.pooled_fixedsize.h1">
2411         <phrase id="context.stack.pooled_fixedsize._code__phrase_role__identifier__stack_context__phrase___phrase_role__identifier__allocate__phrase__phrase_role__special______phrase___code_"/><link
2412         linkend="context.stack.pooled_fixedsize._code__phrase_role__identifier__stack_context__phrase___phrase_role__identifier__allocate__phrase__phrase_role__special______phrase___code_"><code><phrase
2413         role="identifier">stack_context</phrase> <phrase role="identifier">allocate</phrase><phrase
2414         role="special">()</phrase></code></link>
2415       </bridgehead>
2416       <variablelist>
2417         <title></title>
2418         <varlistentry>
2419           <term>Preconditions:</term>
2420           <listitem>
2421             <para>
2422               <code><phrase role="special">!</phrase> <phrase role="identifier">traits_type</phrase><phrase
2423               role="special">::</phrase><phrase role="identifier">is_unbounded</phrase><phrase
2424               role="special">()</phrase> <phrase role="special">&amp;&amp;</phrase>
2425               <phrase role="special">(</phrase> <phrase role="identifier">traits_type</phrase><phrase
2426               role="special">::</phrase><phrase role="identifier">maximum</phrase><phrase
2427               role="special">:</phrase><phrase role="identifier">size</phrase><phrase
2428               role="special">()</phrase> <phrase role="special">&gt;=</phrase> <phrase
2429               role="identifier">stack_size</phrase><phrase role="special">)</phrase></code>.
2430             </para>
2431           </listitem>
2432         </varlistentry>
2433         <varlistentry>
2434           <term>Effects:</term>
2435           <listitem>
2436             <para>
2437               Allocates memory of at least <code><phrase role="identifier">stack_size</phrase></code>
2438               Bytes and stores a pointer to the stack and its actual size in <code><phrase
2439               role="identifier">sctx</phrase></code>. Depending on the architecture
2440               (the stack grows downwards/upwards) the stored address is the highest/lowest
2441               address of the stack.
2442             </para>
2443           </listitem>
2444         </varlistentry>
2445       </variablelist>
2446       <bridgehead renderas="sect4" id="context.stack.pooled_fixedsize.h2">
2447         <phrase id="context.stack.pooled_fixedsize._code__phrase_role__keyword__void__phrase___phrase_role__identifier__deallocate__phrase__phrase_role__special_____phrase___phrase_role__identifier__stack_context__phrase___phrase_role__special___amp___phrase___phrase_role__identifier__sctx__phrase__phrase_role__special_____phrase___code_"/><link
2448         linkend="context.stack.pooled_fixedsize._code__phrase_role__keyword__void__phrase___phrase_role__identifier__deallocate__phrase__phrase_role__special_____phrase___phrase_role__identifier__stack_context__phrase___phrase_role__special___amp___phrase___phrase_role__identifier__sctx__phrase__phrase_role__special_____phrase___code_"><code><phrase
2449         role="keyword">void</phrase> <phrase role="identifier">deallocate</phrase><phrase
2450         role="special">(</phrase> <phrase role="identifier">stack_context</phrase>
2451         <phrase role="special">&amp;</phrase> <phrase role="identifier">sctx</phrase><phrase
2452         role="special">)</phrase></code></link>
2453       </bridgehead>
2454       <variablelist>
2455         <title></title>
2456         <varlistentry>
2457           <term>Preconditions:</term>
2458           <listitem>
2459             <para>
2460               <code><phrase role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase
2461               role="identifier">sp</phrase></code> is valid, <code><phrase role="special">!</phrase>
2462               <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2463               role="identifier">is_unbounded</phrase><phrase role="special">()</phrase>
2464               <phrase role="special">&amp;&amp;</phrase> <phrase role="special">(</phrase>
2465               <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2466               role="identifier">maximum</phrase><phrase role="special">:</phrase><phrase
2467               role="identifier">size</phrase><phrase role="special">()</phrase>
2468               <phrase role="special">&gt;=</phrase> <phrase role="identifier">sctx</phrase><phrase
2469               role="special">.</phrase><phrase role="identifier">size</phrase><phrase
2470               role="special">)</phrase></code>.
2471             </para>
2472           </listitem>
2473         </varlistentry>
2474         <varlistentry>
2475           <term>Effects:</term>
2476           <listitem>
2477             <para>
2478               Deallocates the stack space.
2479             </para>
2480           </listitem>
2481         </varlistentry>
2482       </variablelist>
2483     </section>
2484     <section id="context.stack.fixedsize">
2485       <title><link linkend="context.stack.fixedsize">Class <emphasis>fixedsize_stack</emphasis></link></title>
2486       <para>
2487         <emphasis role="bold">Boost.Context</emphasis> provides the class <emphasis>fixedsize_stack</emphasis>
2488         which models the <emphasis>stack-allocator concept</emphasis>. In contrast
2489         to <emphasis>protected_fixedsize_stack</emphasis> it does not append a guard
2490         page at the end of each stack. The memory is simply managed by <code><phrase
2491         role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">malloc</phrase><phrase
2492         role="special">()</phrase></code> and <code><phrase role="identifier">std</phrase><phrase
2493         role="special">::</phrase><phrase role="identifier">free</phrase><phrase
2494         role="special">()</phrase></code>.
2495       </para>
2496 <programlisting><phrase role="preprocessor">#include</phrase> <phrase role="special">&lt;</phrase><phrase role="identifier">boost</phrase><phrase role="special">/</phrase><phrase role="identifier">context</phrase><phrase role="special">/</phrase><phrase role="identifier">fixedsize_stack</phrase><phrase role="special">.</phrase><phrase role="identifier">hpp</phrase><phrase role="special">&gt;</phrase>
2497
2498 <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase>
2499 <phrase role="keyword">struct</phrase> <phrase role="identifier">basic_fixedsize_stack</phrase> <phrase role="special">{</phrase>
2500     <phrase role="keyword">typedef</phrase> <phrase role="identifier">traitT</phrase>  <phrase role="identifier">traits_type</phrase><phrase role="special">;</phrase>
2501
2502     <phrase role="identifier">basic_fixesize_stack</phrase><phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">size</phrase> <phrase role="special">=</phrase> <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase role="identifier">default_size</phrase><phrase role="special">());</phrase>
2503
2504     <phrase role="identifier">stack_context</phrase> <phrase role="identifier">allocate</phrase><phrase role="special">();</phrase>
2505
2506     <phrase role="keyword">void</phrase> <phrase role="identifier">deallocate</phrase><phrase role="special">(</phrase> <phrase role="identifier">stack_context</phrase> <phrase role="special">&amp;);</phrase>
2507 <phrase role="special">}</phrase>
2508
2509 <phrase role="keyword">typedef</phrase> <phrase role="identifier">basic_fixedsize_stack</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">stack_traits</phrase> <phrase role="special">&gt;</phrase> <phrase role="identifier">fixedsize_stack</phrase><phrase role="special">;</phrase>
2510 </programlisting>
2511       <bridgehead renderas="sect4" id="context.stack.fixedsize.h0">
2512         <phrase id="context.stack.fixedsize._code__phrase_role__identifier__stack_context__phrase___phrase_role__identifier__allocate__phrase__phrase_role__special______phrase___code_"/><link
2513         linkend="context.stack.fixedsize._code__phrase_role__identifier__stack_context__phrase___phrase_role__identifier__allocate__phrase__phrase_role__special______phrase___code_"><code><phrase
2514         role="identifier">stack_context</phrase> <phrase role="identifier">allocate</phrase><phrase
2515         role="special">()</phrase></code></link>
2516       </bridgehead>
2517       <variablelist>
2518         <title></title>
2519         <varlistentry>
2520           <term>Preconditions:</term>
2521           <listitem>
2522             <para>
2523               <code><phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2524               role="identifier">minimum</phrase><phrase role="special">:</phrase><phrase
2525               role="identifier">size</phrase><phrase role="special">()</phrase>
2526               <phrase role="special">&lt;=</phrase> <phrase role="identifier">size</phrase></code>
2527               and <code><phrase role="special">!</phrase> <phrase role="identifier">traits_type</phrase><phrase
2528               role="special">::</phrase><phrase role="identifier">is_unbounded</phrase><phrase
2529               role="special">()</phrase> <phrase role="special">&amp;&amp;</phrase>
2530               <phrase role="special">(</phrase> <phrase role="identifier">traits_type</phrase><phrase
2531               role="special">::</phrase><phrase role="identifier">maximum</phrase><phrase
2532               role="special">:</phrase><phrase role="identifier">size</phrase><phrase
2533               role="special">()</phrase> <phrase role="special">&gt;=</phrase> <phrase
2534               role="identifier">size</phrase><phrase role="special">)</phrase></code>.
2535             </para>
2536           </listitem>
2537         </varlistentry>
2538         <varlistentry>
2539           <term>Effects:</term>
2540           <listitem>
2541             <para>
2542               Allocates memory of at least <code><phrase role="identifier">size</phrase></code>
2543               Bytes and stores a pointer to the stack and its actual size in <code><phrase
2544               role="identifier">sctx</phrase></code>. Depending on the architecture
2545               (the stack grows downwards/upwards) the stored address is the highest/lowest
2546               address of the stack.
2547             </para>
2548           </listitem>
2549         </varlistentry>
2550       </variablelist>
2551       <bridgehead renderas="sect4" id="context.stack.fixedsize.h1">
2552         <phrase id="context.stack.fixedsize._code__phrase_role__keyword__void__phrase___phrase_role__identifier__deallocate__phrase__phrase_role__special_____phrase___phrase_role__identifier__stack_context__phrase___phrase_role__special___amp___phrase___phrase_role__identifier__sctx__phrase__phrase_role__special_____phrase___code_"/><link
2553         linkend="context.stack.fixedsize._code__phrase_role__keyword__void__phrase___phrase_role__identifier__deallocate__phrase__phrase_role__special_____phrase___phrase_role__identifier__stack_context__phrase___phrase_role__special___amp___phrase___phrase_role__identifier__sctx__phrase__phrase_role__special_____phrase___code_"><code><phrase
2554         role="keyword">void</phrase> <phrase role="identifier">deallocate</phrase><phrase
2555         role="special">(</phrase> <phrase role="identifier">stack_context</phrase>
2556         <phrase role="special">&amp;</phrase> <phrase role="identifier">sctx</phrase><phrase
2557         role="special">)</phrase></code></link>
2558       </bridgehead>
2559       <variablelist>
2560         <title></title>
2561         <varlistentry>
2562           <term>Preconditions:</term>
2563           <listitem>
2564             <para>
2565               <code><phrase role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase
2566               role="identifier">sp</phrase></code> is valid, <code><phrase role="identifier">traits_type</phrase><phrase
2567               role="special">::</phrase><phrase role="identifier">minimum</phrase><phrase
2568               role="special">:</phrase><phrase role="identifier">size</phrase><phrase
2569               role="special">()</phrase> <phrase role="special">&lt;=</phrase> <phrase
2570               role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase
2571               role="identifier">size</phrase></code> and <code><phrase role="special">!</phrase>
2572               <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2573               role="identifier">is_unbounded</phrase><phrase role="special">()</phrase>
2574               <phrase role="special">&amp;&amp;</phrase> <phrase role="special">(</phrase>
2575               <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2576               role="identifier">maximum</phrase><phrase role="special">:</phrase><phrase
2577               role="identifier">size</phrase><phrase role="special">()</phrase>
2578               <phrase role="special">&gt;=</phrase> <phrase role="identifier">sctx</phrase><phrase
2579               role="special">.</phrase><phrase role="identifier">size</phrase><phrase
2580               role="special">)</phrase></code>.
2581             </para>
2582           </listitem>
2583         </varlistentry>
2584         <varlistentry>
2585           <term>Effects:</term>
2586           <listitem>
2587             <para>
2588               Deallocates the stack space.
2589             </para>
2590           </listitem>
2591         </varlistentry>
2592       </variablelist>
2593     </section>
2594     <section id="context.stack.segmented">
2595       <title><link linkend="context.stack.segmented">Class <emphasis>segmented_stack</emphasis></link></title>
2596       <para>
2597         <emphasis role="bold">Boost.Context</emphasis> supports usage of a <emphasis>segmented_stack</emphasis>,
2598         e. g. the size of the stack grows on demand. The coroutine is created with
2599         a minimal stack size and will be increased as required. Class <emphasis>segmented_stack</emphasis>
2600         models the <emphasis>stack-allocator concept</emphasis>. In contrast to
2601         <emphasis>protected_fixedsize_stack</emphasis> and <emphasis>fixedsize_stack</emphasis>
2602         it creates a stack which grows on demand.
2603       </para>
2604       <note>
2605         <para>
2606           Segmented stacks are currently only supported by <emphasis role="bold">gcc</emphasis>
2607           from version <emphasis role="bold">4.7</emphasis> <emphasis role="bold">clang</emphasis>
2608           from version <emphasis role="bold">3.4</emphasis> onwards. In order to
2609           use a __segmented_stack__ <emphasis role="bold">Boost.Context</emphasis>
2610           must be built with property <code><phrase role="identifier">segmented</phrase><phrase
2611           role="special">-</phrase><phrase role="identifier">stacks</phrase></code>,
2612           e.g. <emphasis role="bold">toolset=gcc segmented-stacks=on</emphasis> at
2613           b2/bjam command line.
2614         </para>
2615       </note>
2616 <programlisting><phrase role="preprocessor">#include</phrase> <phrase role="special">&lt;</phrase><phrase role="identifier">boost</phrase><phrase role="special">/</phrase><phrase role="identifier">context</phrase><phrase role="special">/</phrase><phrase role="identifier">segmented_stack</phrase><phrase role="special">.</phrase><phrase role="identifier">hpp</phrase><phrase role="special">&gt;</phrase>
2617
2618 <phrase role="keyword">template</phrase><phrase role="special">&lt;</phrase> <phrase role="keyword">typename</phrase> <phrase role="identifier">traitsT</phrase> <phrase role="special">&gt;</phrase>
2619 <phrase role="keyword">struct</phrase> <phrase role="identifier">basic_segmented_stack</phrase> <phrase role="special">{</phrase>
2620     <phrase role="keyword">typedef</phrase> <phrase role="identifier">traitT</phrase>  <phrase role="identifier">traits_type</phrase><phrase role="special">;</phrase>
2621
2622     <phrase role="identifier">basic_segmented_stack</phrase><phrase role="special">(</phrase><phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">size</phrase> <phrase role="special">=</phrase> <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase role="identifier">default_size</phrase><phrase role="special">());</phrase>
2623
2624     <phrase role="identifier">stack_context</phrase> <phrase role="identifier">allocate</phrase><phrase role="special">();</phrase>
2625
2626     <phrase role="keyword">void</phrase> <phrase role="identifier">deallocate</phrase><phrase role="special">(</phrase> <phrase role="identifier">stack_context</phrase> <phrase role="special">&amp;);</phrase>
2627 <phrase role="special">}</phrase>
2628
2629 <phrase role="keyword">typedef</phrase> <phrase role="identifier">basic_segmented_stack</phrase><phrase role="special">&lt;</phrase> <phrase role="identifier">stack_traits</phrase> <phrase role="special">&gt;</phrase> <phrase role="identifier">segmented_stack</phrase><phrase role="special">;</phrase>
2630 </programlisting>
2631       <bridgehead renderas="sect4" id="context.stack.segmented.h0">
2632         <phrase id="context.stack.segmented._code__phrase_role__identifier__stack_context__phrase___phrase_role__identifier__allocate__phrase__phrase_role__special______phrase___code_"/><link
2633         linkend="context.stack.segmented._code__phrase_role__identifier__stack_context__phrase___phrase_role__identifier__allocate__phrase__phrase_role__special______phrase___code_"><code><phrase
2634         role="identifier">stack_context</phrase> <phrase role="identifier">allocate</phrase><phrase
2635         role="special">()</phrase></code></link>
2636       </bridgehead>
2637       <variablelist>
2638         <title></title>
2639         <varlistentry>
2640           <term>Preconditions:</term>
2641           <listitem>
2642             <para>
2643               <code><phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2644               role="identifier">minimum</phrase><phrase role="special">:</phrase><phrase
2645               role="identifier">size</phrase><phrase role="special">()</phrase>
2646               <phrase role="special">&lt;=</phrase> <phrase role="identifier">size</phrase></code>
2647               and <code><phrase role="special">!</phrase> <phrase role="identifier">traits_type</phrase><phrase
2648               role="special">::</phrase><phrase role="identifier">is_unbounded</phrase><phrase
2649               role="special">()</phrase> <phrase role="special">&amp;&amp;</phrase>
2650               <phrase role="special">(</phrase> <phrase role="identifier">traits_type</phrase><phrase
2651               role="special">::</phrase><phrase role="identifier">maximum</phrase><phrase
2652               role="special">:</phrase><phrase role="identifier">size</phrase><phrase
2653               role="special">()</phrase> <phrase role="special">&gt;=</phrase> <phrase
2654               role="identifier">size</phrase><phrase role="special">)</phrase></code>.
2655             </para>
2656           </listitem>
2657         </varlistentry>
2658         <varlistentry>
2659           <term>Effects:</term>
2660           <listitem>
2661             <para>
2662               Allocates memory of at least <code><phrase role="identifier">size</phrase></code>
2663               Bytes and stores a pointer to the stack and its actual size in <code><phrase
2664               role="identifier">sctx</phrase></code>. Depending on the architecture
2665               (the stack grows downwards/upwards) the stored address is the highest/lowest
2666               address of the stack.
2667             </para>
2668           </listitem>
2669         </varlistentry>
2670       </variablelist>
2671       <bridgehead renderas="sect4" id="context.stack.segmented.h1">
2672         <phrase id="context.stack.segmented._code__phrase_role__keyword__void__phrase___phrase_role__identifier__deallocate__phrase__phrase_role__special_____phrase___phrase_role__identifier__stack_context__phrase___phrase_role__special___amp___phrase___phrase_role__identifier__sctx__phrase__phrase_role__special_____phrase___code_"/><link
2673         linkend="context.stack.segmented._code__phrase_role__keyword__void__phrase___phrase_role__identifier__deallocate__phrase__phrase_role__special_____phrase___phrase_role__identifier__stack_context__phrase___phrase_role__special___amp___phrase___phrase_role__identifier__sctx__phrase__phrase_role__special_____phrase___code_"><code><phrase
2674         role="keyword">void</phrase> <phrase role="identifier">deallocate</phrase><phrase
2675         role="special">(</phrase> <phrase role="identifier">stack_context</phrase>
2676         <phrase role="special">&amp;</phrase> <phrase role="identifier">sctx</phrase><phrase
2677         role="special">)</phrase></code></link>
2678       </bridgehead>
2679       <variablelist>
2680         <title></title>
2681         <varlistentry>
2682           <term>Preconditions:</term>
2683           <listitem>
2684             <para>
2685               <code><phrase role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase
2686               role="identifier">sp</phrase></code> is valid, <code><phrase role="identifier">traits_type</phrase><phrase
2687               role="special">::</phrase><phrase role="identifier">minimum</phrase><phrase
2688               role="special">:</phrase><phrase role="identifier">size</phrase><phrase
2689               role="special">()</phrase> <phrase role="special">&lt;=</phrase> <phrase
2690               role="identifier">sctx</phrase><phrase role="special">.</phrase><phrase
2691               role="identifier">size</phrase></code> and <code><phrase role="special">!</phrase>
2692               <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2693               role="identifier">is_unbounded</phrase><phrase role="special">()</phrase>
2694               <phrase role="special">&amp;&amp;</phrase> <phrase role="special">(</phrase>
2695               <phrase role="identifier">traits_type</phrase><phrase role="special">::</phrase><phrase
2696               role="identifier">maximum</phrase><phrase role="special">:</phrase><phrase
2697               role="identifier">size</phrase><phrase role="special">()</phrase>
2698               <phrase role="special">&gt;=</phrase> <phrase role="identifier">sctx</phrase><phrase
2699               role="special">.</phrase><phrase role="identifier">size</phrase><phrase
2700               role="special">)</phrase></code>.
2701             </para>
2702           </listitem>
2703         </varlistentry>
2704         <varlistentry>
2705           <term>Effects:</term>
2706           <listitem>
2707             <para>
2708               Deallocates the stack space.
2709             </para>
2710           </listitem>
2711         </varlistentry>
2712       </variablelist>
2713       <note>
2714         <para>
2715           If the library is compiled for segmented stacks, __segmented_stack__ is
2716           the only available stack allocator.
2717         </para>
2718       </note>
2719     </section>
2720     <section id="context.stack.stack_traits">
2721       <title><link linkend="context.stack.stack_traits">Class <emphasis>stack_traits</emphasis></link></title>
2722       <para>
2723         <emphasis>stack_traits</emphasis> models a <emphasis>stack-traits</emphasis>
2724         providing a way to access certain properites defined by the enironment. Stack
2725         allocators use <emphasis>stack-traits</emphasis> to allocate stacks.
2726       </para>
2727 <programlisting><phrase role="preprocessor">#include</phrase> <phrase role="special">&lt;</phrase><phrase role="identifier">boost</phrase><phrase role="special">/</phrase><phrase role="identifier">context</phrase><phrase role="special">/</phrase><phrase role="identifier">stack_traits</phrase><phrase role="special">.</phrase><phrase role="identifier">hpp</phrase><phrase role="special">&gt;</phrase>
2728
2729 <phrase role="keyword">struct</phrase> <phrase role="identifier">stack_traits</phrase> <phrase role="special">{</phrase>
2730     <phrase role="keyword">static</phrase> <phrase role="keyword">bool</phrase> <phrase role="identifier">is_unbounded</phrase><phrase role="special">()</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
2731
2732     <phrase role="keyword">static</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">page_size</phrase><phrase role="special">()</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
2733
2734     <phrase role="keyword">static</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">default_size</phrase><phrase role="special">()</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
2735
2736     <phrase role="keyword">static</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">minimum_size</phrase><phrase role="special">()</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
2737
2738     <phrase role="keyword">static</phrase> <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">maximum_size</phrase><phrase role="special">()</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
2739 <phrase role="special">}</phrase>
2740 </programlisting>
2741       <bridgehead renderas="sect4" id="context.stack.stack_traits.h0">
2742         <phrase id="context.stack.stack_traits._code__phrase_role__keyword__static__phrase___phrase_role__keyword__bool__phrase___phrase_role__identifier__is_unbounded__phrase__phrase_role__special______phrase___code_"/><link
2743         linkend="context.stack.stack_traits._code__phrase_role__keyword__static__phrase___phrase_role__keyword__bool__phrase___phrase_role__identifier__is_unbounded__phrase__phrase_role__special______phrase___code_"><code><phrase
2744         role="keyword">static</phrase> <phrase role="keyword">bool</phrase> <phrase
2745         role="identifier">is_unbounded</phrase><phrase role="special">()</phrase></code></link>
2746       </bridgehead>
2747       <variablelist>
2748         <title></title>
2749         <varlistentry>
2750           <term>Returns:</term>
2751           <listitem>
2752             <para>
2753               Returns <code><phrase role="keyword">true</phrase></code> if the environment
2754               defines no limit for the size of a stack.
2755             </para>
2756           </listitem>
2757         </varlistentry>
2758         <varlistentry>
2759           <term>Throws:</term>
2760           <listitem>
2761             <para>
2762               Nothing.
2763             </para>
2764           </listitem>
2765         </varlistentry>
2766       </variablelist>
2767       <bridgehead renderas="sect4" id="context.stack.stack_traits.h1">
2768         <phrase id="context.stack.stack_traits._code__phrase_role__keyword__static__phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__page_size__phrase__phrase_role__special______phrase___code_"/><link
2769         linkend="context.stack.stack_traits._code__phrase_role__keyword__static__phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__page_size__phrase__phrase_role__special______phrase___code_"><code><phrase
2770         role="keyword">static</phrase> <phrase role="identifier">std</phrase><phrase
2771         role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase
2772         role="identifier">page_size</phrase><phrase role="special">()</phrase></code></link>
2773       </bridgehead>
2774       <variablelist>
2775         <title></title>
2776         <varlistentry>
2777           <term>Returns:</term>
2778           <listitem>
2779             <para>
2780               Returns the page size in bytes.
2781             </para>
2782           </listitem>
2783         </varlistentry>
2784         <varlistentry>
2785           <term>Throws:</term>
2786           <listitem>
2787             <para>
2788               Nothing.
2789             </para>
2790           </listitem>
2791         </varlistentry>
2792       </variablelist>
2793       <bridgehead renderas="sect4" id="context.stack.stack_traits.h2">
2794         <phrase id="context.stack.stack_traits._code__phrase_role__keyword__static__phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__default_size__phrase__phrase_role__special______phrase___code_"/><link
2795         linkend="context.stack.stack_traits._code__phrase_role__keyword__static__phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__default_size__phrase__phrase_role__special______phrase___code_"><code><phrase
2796         role="keyword">static</phrase> <phrase role="identifier">std</phrase><phrase
2797         role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase
2798         role="identifier">default_size</phrase><phrase role="special">()</phrase></code></link>
2799       </bridgehead>
2800       <variablelist>
2801         <title></title>
2802         <varlistentry>
2803           <term>Returns:</term>
2804           <listitem>
2805             <para>
2806               Returns a default stack size, which may be platform specific. If the
2807               stack is unbounded then the present implementation returns the maximum
2808               of <code><phrase role="number">64</phrase> <phrase role="identifier">kB</phrase></code>
2809               and <code><phrase role="identifier">minimum_size</phrase><phrase role="special">()</phrase></code>.
2810             </para>
2811           </listitem>
2812         </varlistentry>
2813         <varlistentry>
2814           <term>Throws:</term>
2815           <listitem>
2816             <para>
2817               Nothing.
2818             </para>
2819           </listitem>
2820         </varlistentry>
2821       </variablelist>
2822       <bridgehead renderas="sect4" id="context.stack.stack_traits.h3">
2823         <phrase id="context.stack.stack_traits._code__phrase_role__keyword__static__phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__minimum_size__phrase__phrase_role__special______phrase___code_"/><link
2824         linkend="context.stack.stack_traits._code__phrase_role__keyword__static__phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__minimum_size__phrase__phrase_role__special______phrase___code_"><code><phrase
2825         role="keyword">static</phrase> <phrase role="identifier">std</phrase><phrase
2826         role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase
2827         role="identifier">minimum_size</phrase><phrase role="special">()</phrase></code></link>
2828       </bridgehead>
2829       <variablelist>
2830         <title></title>
2831         <varlistentry>
2832           <term>Returns:</term>
2833           <listitem>
2834             <para>
2835               Returns the minimum size in bytes of stack defined by the environment
2836               (Win32 4kB/Win64 8kB, defined by rlimit on POSIX).
2837             </para>
2838           </listitem>
2839         </varlistentry>
2840         <varlistentry>
2841           <term>Throws:</term>
2842           <listitem>
2843             <para>
2844               Nothing.
2845             </para>
2846           </listitem>
2847         </varlistentry>
2848       </variablelist>
2849       <bridgehead renderas="sect4" id="context.stack.stack_traits.h4">
2850         <phrase id="context.stack.stack_traits._code__phrase_role__keyword__static__phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__maximum_size__phrase__phrase_role__special______phrase___code_"/><link
2851         linkend="context.stack.stack_traits._code__phrase_role__keyword__static__phrase___phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__maximum_size__phrase__phrase_role__special______phrase___code_"><code><phrase
2852         role="keyword">static</phrase> <phrase role="identifier">std</phrase><phrase
2853         role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase
2854         role="identifier">maximum_size</phrase><phrase role="special">()</phrase></code></link>
2855       </bridgehead>
2856       <variablelist>
2857         <title></title>
2858         <varlistentry>
2859           <term>Preconditions:</term>
2860           <listitem>
2861             <para>
2862               <code><phrase role="identifier">is_unbounded</phrase><phrase role="special">()</phrase></code>
2863               returns <code><phrase role="keyword">false</phrase></code>.
2864             </para>
2865           </listitem>
2866         </varlistentry>
2867         <varlistentry>
2868           <term>Returns:</term>
2869           <listitem>
2870             <para>
2871               Returns the maximum size in bytes of stack defined by the environment.
2872             </para>
2873           </listitem>
2874         </varlistentry>
2875         <varlistentry>
2876           <term>Throws:</term>
2877           <listitem>
2878             <para>
2879               Nothing.
2880             </para>
2881           </listitem>
2882         </varlistentry>
2883       </variablelist>
2884     </section>
2885     <section id="context.stack.stack_context">
2886       <title><link linkend="context.stack.stack_context">Class <emphasis>stack_context</emphasis></link></title>
2887       <para>
2888         <emphasis role="bold">Boost.Context</emphasis> provides the class <emphasis>stack_context</emphasis>
2889         which will contain the stack pointer and the size of the stack. In case of
2890         a <emphasis>segmented_stack</emphasis>, <emphasis>stack_context</emphasis>
2891         contains some extra control structures.
2892       </para>
2893 <programlisting><phrase role="keyword">struct</phrase> <phrase role="identifier">stack_context</phrase> <phrase role="special">{</phrase>
2894     <phrase role="keyword">void</phrase>    <phrase role="special">*</phrase>   <phrase role="identifier">sp</phrase><phrase role="special">;</phrase>
2895     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">size</phrase><phrase role="special">;</phrase>
2896
2897     <phrase role="comment">// might contain additional control structures</phrase>
2898     <phrase role="comment">// for segmented stacks</phrase>
2899 <phrase role="special">}</phrase>
2900 </programlisting>
2901       <bridgehead renderas="sect4" id="context.stack.stack_context.h0">
2902         <phrase id="context.stack.stack_context._code__phrase_role__keyword__void__phrase___phrase_role__special_____phrase___phrase_role__identifier__sp__phrase___code_"/><link
2903         linkend="context.stack.stack_context._code__phrase_role__keyword__void__phrase___phrase_role__special_____phrase___phrase_role__identifier__sp__phrase___code_"><code><phrase
2904         role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">sp</phrase></code></link>
2905       </bridgehead>
2906       <variablelist>
2907         <title></title>
2908         <varlistentry>
2909           <term>Value:</term>
2910           <listitem>
2911             <para>
2912               Pointer to the beginning of the stack.
2913             </para>
2914           </listitem>
2915         </varlistentry>
2916       </variablelist>
2917       <bridgehead renderas="sect4" id="context.stack.stack_context.h1">
2918         <phrase id="context.stack.stack_context._code__phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__size__phrase___code_"/><link
2919         linkend="context.stack.stack_context._code__phrase_role__identifier__std__phrase__phrase_role__special______phrase__phrase_role__identifier__size_t__phrase___phrase_role__identifier__size__phrase___code_"><code><phrase
2920         role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase>
2921         <phrase role="identifier">size</phrase></code></link>
2922       </bridgehead>
2923       <variablelist>
2924         <title></title>
2925         <varlistentry>
2926           <term>Value:</term>
2927           <listitem>
2928             <para>
2929               Actual size of the stack.
2930             </para>
2931           </listitem>
2932         </varlistentry>
2933       </variablelist>
2934     </section>
2935     <section id="context.stack.valgrind">
2936       <title><link linkend="context.stack.valgrind">Support for valgrind</link></title>
2937       <para>
2938         Running programs that switch stacks under valgrind causes problems. Property
2939         (b2 command-line) <code><phrase role="identifier">valgrind</phrase><phrase
2940         role="special">=</phrase><phrase role="identifier">on</phrase></code> let
2941         valgrind treat the memory regions as stack space which suppresses the errors.
2942       </para>
2943     </section>
2944   </section>
2945   <section id="context.struct__preallocated_">
2946     <title><link linkend="context.struct__preallocated_">Struct <code><phrase role="identifier">preallocated</phrase></code></link></title>
2947 <programlisting><phrase role="keyword">struct</phrase> <phrase role="identifier">preallocated</phrase> <phrase role="special">{</phrase>
2948     <phrase role="keyword">void</phrase>        <phrase role="special">*</phrase>   <phrase role="identifier">sp</phrase><phrase role="special">;</phrase>
2949     <phrase role="identifier">std</phrase><phrase role="special">::</phrase><phrase role="identifier">size_t</phrase>     <phrase role="identifier">size</phrase><phrase role="special">;</phrase>
2950     <phrase role="identifier">stack_context</phrase>   <phrase role="identifier">sctx</phrase><phrase role="special">;</phrase>
2951
2952     <phrase role="identifier">preallocated</phrase><phrase role="special">(</phrase> <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">sp</phrase><phrase role="special">,</phrase> <phrase role="identifier">std</phrase><phrase role="special">:</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">size</phrase><phrase role="special">,</phrase> <phrase role="identifier">stack_allocator</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
2953 <phrase role="special">};</phrase>
2954 </programlisting>
2955     <bridgehead renderas="sect3" id="context.struct__preallocated_.h0">
2956       <phrase id="context.struct__preallocated_.constructor"/><link linkend="context.struct__preallocated_.constructor">Constructor</link>
2957     </bridgehead>
2958 <programlisting><phrase role="identifier">preallocated</phrase><phrase role="special">(</phrase> <phrase role="keyword">void</phrase> <phrase role="special">*</phrase> <phrase role="identifier">sp</phrase><phrase role="special">,</phrase> <phrase role="identifier">std</phrase><phrase role="special">:</phrase><phrase role="identifier">size_t</phrase> <phrase role="identifier">size</phrase><phrase role="special">,</phrase> <phrase role="identifier">stack_allocator</phrase> <phrase role="identifier">sctx</phrase><phrase role="special">)</phrase> <phrase role="keyword">noexcept</phrase><phrase role="special">;</phrase>
2959 </programlisting>
2960     <variablelist>
2961       <title></title>
2962       <varlistentry>
2963         <term>Effects:</term>
2964         <listitem>
2965           <para>
2966             Creates an object of preallocated.
2967           </para>
2968         </listitem>
2969       </varlistentry>
2970     </variablelist>
2971   </section>
2972   <section id="context.performance">
2973     <title><link linkend="context.performance">Performance</link></title>
2974     <para>
2975       Performance of <emphasis role="bold">Boost.Context</emphasis> was measured
2976       on the platforms shown in the following table. Performance measurements were
2977       taken using <code><phrase role="identifier">rdtsc</phrase></code> and <code><phrase
2978       role="identifier">boost</phrase><phrase role="special">::</phrase><phrase role="identifier">chrono</phrase><phrase
2979       role="special">::</phrase><phrase role="identifier">high_resolution_clock</phrase></code>,
2980       with overhead corrections, on x86 platforms. In each case, cache warm-up was
2981       accounted for, and the one running thread was pinned to a single CPU. The code
2982       was compiled using the build options, 'variant = release cxxflags = -DBOOST_DISABLE_ASSERTS'.
2983     </para>
2984     <table frame="all" id="context.performance.performance_of_context_switch">
2985       <title>Performance of context switch</title>
2986       <tgroup cols="4">
2987         <thead>
2988           <row>
2989             <entry>
2990               <para>
2991                 Platform
2992               </para>
2993             </entry>
2994             <entry>
2995               <para>
2996                 ucontext_t
2997               </para>
2998             </entry>
2999             <entry>
3000               <para>
3001                 execution_context (v1)
3002               </para>
3003             </entry>
3004             <entry>
3005               <para>
3006                 execution_context (v2)
3007               </para>
3008             </entry>
3009           </row>
3010         </thead>
3011         <tbody>
3012           <row>
3013             <entry>
3014               <para>
3015                 x86_64 <footnote id="context.performance.f0">
3016                 <para>
3017                   Intel Core2 Q6700
3018                 </para>
3019                 </footnote>
3020               </para>
3021             </entry>
3022             <entry>
3023               <para>
3024                 547 ns / 1433 cycles
3025               </para>
3026             </entry>
3027             <entry>
3028               <para>
3029                 51 ns / 141 cycles
3030               </para>
3031             </entry>
3032             <entry>
3033               <para>
3034                 7 ns / 18 cycles
3035               </para>
3036             </entry>
3037           </row>
3038         </tbody>
3039       </tgroup>
3040     </table>
3041   </section>
3042   <section id="context.architectures">
3043     <title><link linkend="context.architectures">Architectures</link></title>
3044     <para>
3045       <emphasis role="bold">Boost.Context</emphasis> supports following architectures:
3046     </para>
3047     <table frame="all" id="context.architectures.supported_architectures___abi_binary_format__">
3048       <title>Supported architectures (&lt;ABI|binary format&gt;)</title>
3049       <tgroup cols="5">
3050         <thead>
3051           <row>
3052             <entry>
3053               <para>
3054                 Architecture
3055               </para>
3056             </entry>
3057             <entry>
3058               <para>
3059                 LINUX (UNIX)
3060               </para>
3061             </entry>
3062             <entry>
3063               <para>
3064                 Windows
3065               </para>
3066             </entry>
3067             <entry>
3068               <para>
3069                 MacOS X
3070               </para>
3071             </entry>
3072             <entry>
3073               <para>
3074                 iOS
3075               </para>
3076             </entry>
3077           </row>
3078         </thead>
3079         <tbody>
3080           <row>
3081             <entry>
3082               <para>
3083                 arm (aarch32)
3084               </para>
3085             </entry>
3086             <entry>
3087               <para>
3088                 AAPCS|ELF
3089               </para>
3090             </entry>
3091             <entry>
3092               <para>
3093                 AAPCS|PE
3094               </para>
3095             </entry>
3096             <entry>
3097               <para>
3098                 -
3099               </para>
3100             </entry>
3101             <entry>
3102               <para>
3103                 AAPCS|MACH-O
3104               </para>
3105             </entry>
3106           </row>
3107           <row>
3108             <entry>
3109               <para>
3110                 arm (aarch64)
3111               </para>
3112             </entry>
3113             <entry>
3114               <para>
3115                 AAPCS|ELF
3116               </para>
3117             </entry>
3118             <entry>
3119               <para>
3120                 -
3121               </para>
3122             </entry>
3123             <entry>
3124               <para>
3125                 -
3126               </para>
3127             </entry>
3128             <entry>
3129               <para>
3130                 AAPCS|MACH-O
3131               </para>
3132             </entry>
3133           </row>
3134           <row>
3135             <entry>
3136               <para>
3137                 i386
3138               </para>
3139             </entry>
3140             <entry>
3141               <para>
3142                 SYSV|ELF
3143               </para>
3144             </entry>
3145             <entry>
3146               <para>
3147                 MS|PE
3148               </para>
3149             </entry>
3150             <entry>
3151               <para>
3152                 SYSV|MACH-O
3153               </para>
3154             </entry>
3155             <entry>
3156               <para>
3157                 -
3158               </para>
3159             </entry>
3160           </row>
3161           <row>
3162             <entry>
3163               <para>
3164                 mips1
3165               </para>
3166             </entry>
3167             <entry>
3168               <para>
3169                 O32|ELF
3170               </para>
3171             </entry>
3172             <entry>
3173               <para>
3174                 -
3175               </para>
3176             </entry>
3177             <entry>
3178               <para>
3179                 -
3180               </para>
3181             </entry>
3182             <entry>
3183               <para>
3184                 -
3185               </para>
3186             </entry>
3187           </row>
3188           <row>
3189             <entry>
3190               <para>
3191                 ppc32
3192               </para>
3193             </entry>
3194             <entry>
3195               <para>
3196                 SYSV|ELF,XCOFF
3197               </para>
3198             </entry>
3199             <entry>
3200               <para>
3201                 -
3202               </para>
3203             </entry>
3204             <entry>
3205               <para>
3206                 SYSV|MACH-O
3207               </para>
3208             </entry>
3209             <entry>
3210               <para>
3211                 -
3212               </para>
3213             </entry>
3214           </row>
3215           <row>
3216             <entry>
3217               <para>
3218                 ppc64
3219               </para>
3220             </entry>
3221             <entry>
3222               <para>
3223                 SYSV|ELF,XCOFF
3224               </para>
3225             </entry>
3226             <entry>
3227               <para>
3228                 -
3229               </para>
3230             </entry>
3231             <entry>
3232               <para>
3233                 SYSV|MACH-O
3234               </para>
3235             </entry>
3236             <entry>
3237               <para>
3238                 -
3239               </para>
3240             </entry>
3241           </row>
3242           <row>
3243             <entry>
3244               <para>
3245                 sparc
3246               </para>
3247             </entry>
3248             <entry>
3249               <para>
3250                 -
3251               </para>
3252             </entry>
3253             <entry>
3254               <para>
3255                 -
3256               </para>
3257             </entry>
3258             <entry>
3259               <para>
3260                 -
3261               </para>
3262             </entry>
3263             <entry>
3264               <para>
3265                 -
3266               </para>
3267             </entry>
3268           </row>
3269           <row>
3270             <entry>
3271               <para>
3272                 x86_64
3273               </para>
3274             </entry>
3275             <entry>
3276               <para>
3277                 SYSV,X32|ELF
3278               </para>
3279             </entry>
3280             <entry>
3281               <para>
3282                 MS|PE
3283               </para>
3284             </entry>
3285             <entry>
3286               <para>
3287                 SYSV|MACH-O
3288               </para>
3289             </entry>
3290             <entry>
3291               <para>
3292                 -
3293               </para>
3294             </entry>
3295           </row>
3296         </tbody>
3297       </tgroup>
3298     </table>
3299     <section id="context.architectures.crosscompiling">
3300       <title><link linkend="context.architectures.crosscompiling">Cross compiling</link></title>
3301       <para>
3302         Cross compiling the library requires to specify the build properties &lt;architecture&gt;,
3303         &lt;address-model&gt;, &lt;binary-format&gt; and &lt;abi&gt; at b2 command
3304         line.
3305       </para>
3306     </section>
3307   </section>
3308   <section id="context.rationale">
3309     <title><link linkend="context.rationale">Rationale</link></title>
3310     <bridgehead renderas="sect3" id="context.rationale.h0">
3311       <phrase id="context.rationale.no_inline_assembler"/><link linkend="context.rationale.no_inline_assembler">No
3312       inline-assembler</link>
3313     </bridgehead>
3314     <para>
3315       Some newer compiler (for instance MSVC 10 for x86_64 and itanium) do not support
3316       inline assembler. <footnote id="context.rationale.f0">
3317       <para>
3318         <ulink url="http://msdn.microsoft.com/en-us/library/4ks26t93.aspx">MSDN article
3319         'Inline Assembler'</ulink>
3320       </para>
3321       </footnote>. Inlined assembler generates code bloating which is not welcome
3322       on embedded systems.
3323     </para>
3324     <bridgehead renderas="sect3" id="context.rationale.h1">
3325       <phrase id="context.rationale.fcontext_t"/><link linkend="context.rationale.fcontext_t">fcontext_t</link>
3326     </bridgehead>
3327     <para>
3328       <emphasis role="bold">Boost.Context</emphasis> provides the low level API fcontext_t
3329       which is implemented in assembler to provide context swapping operations. fcontext_t
3330       is the part to port to new platforms.
3331     </para>
3332     <note>
3333       <para>
3334         Context switches do not preserve the signal mask on UNIX systems.
3335       </para>
3336     </note>
3337     <para>
3338       <emphasis>fcontext_t</emphasis> is an opaque pointer.
3339     </para>
3340     <section id="context.rationale.other_apis_">
3341       <title><link linkend="context.rationale.other_apis_">Other APIs </link></title>
3342       <bridgehead renderas="sect4" id="context.rationale.other_apis_.h0">
3343         <phrase id="context.rationale.other_apis_.setjmp___longjmp__"/><link linkend="context.rationale.other_apis_.setjmp___longjmp__">setjmp()/longjmp()</link>
3344       </bridgehead>
3345       <para>
3346         C99 defines <code><phrase role="identifier">setjmp</phrase><phrase role="special">()</phrase></code>/<code><phrase
3347         role="identifier">longjmp</phrase><phrase role="special">()</phrase></code>
3348         to provide non-local jumps but it does not require that <emphasis>longjmp()</emphasis>
3349         preserves the current stack frame. Therefore, jumping into a function which
3350         was exited via a call to <emphasis>longjmp()</emphasis> is undefined <footnote
3351         id="context.rationale.other_apis_.f0">
3352         <para>
3353           ISO/IEC 9899:1999, 2005, 7.13.2.1:2
3354         </para>
3355         </footnote>.
3356       </para>
3357       <bridgehead renderas="sect4" id="context.rationale.other_apis_.h1">
3358         <phrase id="context.rationale.other_apis_.ucontext_t"/><link linkend="context.rationale.other_apis_.ucontext_t">ucontext_t</link>
3359       </bridgehead>
3360       <para>
3361         Since POSIX.1-2003 <code><phrase role="identifier">ucontext_t</phrase></code>
3362         is deprecated and was removed in POSIX.1-2008! The function signature of
3363         <code><phrase role="identifier">makecontext</phrase><phrase role="special">()</phrase></code>
3364         is:
3365       </para>
3366 <programlisting><phrase role="keyword">void</phrase> <phrase role="identifier">makecontext</phrase><phrase role="special">(</phrase><phrase role="identifier">ucontext_t</phrase> <phrase role="special">*</phrase><phrase role="identifier">ucp</phrase><phrase role="special">,</phrase> <phrase role="keyword">void</phrase> <phrase role="special">(*</phrase><phrase role="identifier">func</phrase><phrase role="special">)(),</phrase> <phrase role="keyword">int</phrase> <phrase role="identifier">argc</phrase><phrase role="special">,</phrase> <phrase role="special">...);</phrase>
3367 </programlisting>
3368       <para>
3369         The third argument of <code><phrase role="identifier">makecontext</phrase><phrase
3370         role="special">()</phrase></code> specifies the number of integer arguments
3371         that follow which will require function pointer cast if <code><phrase role="identifier">func</phrase></code>
3372         will accept those arguments which is undefined in C99 <footnote id="context.rationale.other_apis_.f1">
3373         <para>
3374           ISO/IEC 9899:1999, 2005, J.2
3375         </para>
3376         </footnote>.
3377       </para>
3378       <para>
3379         The arguments in the var-arg list are required to be integers, passing pointers
3380         in var-arg list is not guaranteed to work, especially it will fail for architectures
3381         where pointers are larger than integers.
3382       </para>
3383       <para>
3384         <code><phrase role="identifier">ucontext_t</phrase></code> preserves signal
3385         mask between context switches which involves system calls consuming a lot
3386         of CPU cycles (ucontext_t is slower by perfomance_link[factor 13x] relative
3387         to <code><phrase role="identifier">fcontext_t</phrase></code>).
3388       </para>
3389       <bridgehead renderas="sect4" id="context.rationale.other_apis_.h2">
3390         <phrase id="context.rationale.other_apis_.windows_fibers"/><link linkend="context.rationale.other_apis_.windows_fibers">Windows
3391         fibers</link>
3392       </bridgehead>
3393       <para>
3394         A drawback of Windows Fiber API is that <code><phrase role="identifier">CreateFiber</phrase><phrase
3395         role="special">()</phrase></code> does not accept a pointer to user allocated
3396         stack space preventing the reuse of stacks for other context instances. Because
3397         the Windows Fiber API requires to call <code><phrase role="identifier">ConvertThreadToFiber</phrase><phrase
3398         role="special">()</phrase></code> if <code><phrase role="identifier">SwitchFiber</phrase><phrase
3399         role="special">()</phrase></code> is called for a thread which has not been
3400         converted to a fiber. For the same reason <code><phrase role="identifier">ConvertFiberToThread</phrase><phrase
3401         role="special">()</phrase></code> must be called after return from <code><phrase
3402         role="identifier">SwitchFiber</phrase><phrase role="special">()</phrase></code>
3403         if the thread was forced to be converted to a fiber before (which is inefficient).
3404       </para>
3405 <programlisting><phrase role="keyword">if</phrase> <phrase role="special">(</phrase> <phrase role="special">!</phrase> <phrase role="identifier">is_a_fiber</phrase><phrase role="special">()</phrase> <phrase role="special">)</phrase>
3406 <phrase role="special">{</phrase>
3407     <phrase role="identifier">ConvertThreadToFiber</phrase><phrase role="special">(</phrase> <phrase role="number">0</phrase><phrase role="special">);</phrase>
3408     <phrase role="identifier">SwitchToFiber</phrase><phrase role="special">(</phrase> <phrase role="identifier">ctx</phrase><phrase role="special">);</phrase>
3409     <phrase role="identifier">ConvertFiberToThread</phrase><phrase role="special">();</phrase>
3410 <phrase role="special">}</phrase>
3411 </programlisting>
3412       <para>
3413         If the condition <code><phrase role="identifier">_WIN32_WINNT</phrase> <phrase
3414         role="special">&gt;=</phrase> <phrase role="identifier">_WIN32_WINNT_VISTA</phrase></code>
3415         is met function <code><phrase role="identifier">IsThreadAFiber</phrase><phrase
3416         role="special">()</phrase></code> is provided in order to detect if the current
3417         thread was already converted. Unfortunately Windows XP + SP 2/3 defines
3418         <code><phrase role="identifier">_WIN32_WINNT</phrase> <phrase role="special">&gt;=</phrase>
3419         <phrase role="identifier">_WIN32_WINNT_VISTA</phrase></code> without providing
3420         <code><phrase role="identifier">IsThreadAFiber</phrase><phrase role="special">()</phrase></code>.
3421       </para>
3422     </section>
3423     <section id="context.rationale.x86_and_floating_point_env">
3424       <title><link linkend="context.rationale.x86_and_floating_point_env">x86 and
3425       floating-point env</link></title>
3426       <bridgehead renderas="sect4" id="context.rationale.x86_and_floating_point_env.h0">
3427         <phrase id="context.rationale.x86_and_floating_point_env.i386"/><link linkend="context.rationale.x86_and_floating_point_env.i386">i386</link>
3428       </bridgehead>
3429       <para>
3430         &quot;The FpCsr and the MxCsr register must be saved and restored before
3431         any call or return by any procedure that needs to modify them ...&quot;
3432         <footnote id="context.rationale.x86_and_floating_point_env.f0">
3433         <para>
3434           'Calling Conventions', Agner Fog
3435         </para>
3436         </footnote>.
3437       </para>
3438       <bridgehead renderas="sect4" id="context.rationale.x86_and_floating_point_env.h1">
3439         <phrase id="context.rationale.x86_and_floating_point_env.x86_64"/><link linkend="context.rationale.x86_and_floating_point_env.x86_64">x86_64</link>
3440       </bridgehead>
3441       <bridgehead renderas="sect4" id="context.rationale.x86_and_floating_point_env.h2">
3442         <phrase id="context.rationale.x86_and_floating_point_env.windows"/><link
3443         linkend="context.rationale.x86_and_floating_point_env.windows">Windows</link>
3444       </bridgehead>
3445       <para>
3446         MxCsr - &quot;A callee that modifies any of the non-volatile fields within
3447         MxCsr must restore them before returning to its caller. Furthermore, a caller
3448         that has modified any of these fields must restore them to their standard
3449         values before invoking a callee ...&quot; <footnote id="context.rationale.x86_and_floating_point_env.f1">
3450         <para>
3451           <ulink url="http://http://msdn.microsoft.com/en-us/library/yxty7t75.aspx">MSDN
3452           article 'MxCsr'</ulink>
3453         </para>
3454         </footnote>.
3455       </para>
3456       <para>
3457         FpCsr - &quot;A callee that modifies any of the fields within FpCsr must
3458         restore them before returning to its caller. Furthermore, a caller that has
3459         modified any of these fields must restore them to their standard values before
3460         invoking a callee ...&quot; <footnote id="context.rationale.x86_and_floating_point_env.f2">
3461         <para>
3462           <ulink url="http://http://msdn.microsoft.com/en-us/library/ms235300.aspx">MSDN
3463           article 'FpCsr'</ulink>
3464         </para>
3465         </footnote>.
3466       </para>
3467       <para>
3468         &quot;The MMX and floating-point stack registers (MM0-MM7/ST0-ST7) are preserved
3469         across context switches. There is no explicit calling convention for these
3470         registers.&quot; <footnote id="context.rationale.x86_and_floating_point_env.f3">
3471         <para>
3472           <ulink url="http://msdn.microsoft.com/en-us/library/a32tsf7t%28VS.80%29.aspx">MSDN
3473           article 'Legacy Floating-Point Support'</ulink>
3474         </para>
3475         </footnote>.
3476       </para>
3477       <para>
3478         &quot;The 64-bit Microsoft compiler does not use ST(0)-ST(7)/MM0-MM7&quot;.
3479         <footnote id="context.rationale.x86_and_floating_point_env.f4">
3480         <para>
3481           'Calling Conventions', Agner Fog
3482         </para>
3483         </footnote>.
3484       </para>
3485       <para>
3486         &quot;XMM6-XMM15 must be preserved&quot; <footnote id="context.rationale.x86_and_floating_point_env.f5">
3487         <para>
3488           <ulink url="http://msdn.microsoft.com/en-us/library/9z1stfyw%28v=vs.100%29.aspx">MSDN
3489           article 'Register Usage'</ulink>
3490         </para>
3491         </footnote>
3492       </para>
3493       <bridgehead renderas="sect4" id="context.rationale.x86_and_floating_point_env.h3">
3494         <phrase id="context.rationale.x86_and_floating_point_env.sysv"/><link linkend="context.rationale.x86_and_floating_point_env.sysv">SysV</link>
3495       </bridgehead>
3496       <para>
3497         &quot;The control bits of the MxCsr register are callee-saved (preserved
3498         across calls), while the status bits are caller-saved (not preserved). The
3499         x87 status word register is caller-saved, whereas the x87 control word (FpCsr)
3500         is callee-saved.&quot; <footnote id="context.rationale.x86_and_floating_point_env.f6">
3501         <para>
3502           SysV ABI AMD64 Architecture Processor Supplement Draft Version 0.99.4,
3503           3.2.1
3504         </para>
3505         </footnote>.
3506       </para>
3507     </section>
3508   </section>
3509   <section id="context.reference">
3510     <title><link linkend="context.reference">Reference</link></title>
3511     <bridgehead renderas="sect3" id="context.reference.h0">
3512       <phrase id="context.reference.arm"/><link linkend="context.reference.arm">ARM</link>
3513     </bridgehead>
3514     <itemizedlist>
3515       <listitem>
3516         <simpara>
3517           AAPCS ABI: Procedure Call Standard for the ARM Architecture
3518         </simpara>
3519       </listitem>
3520       <listitem>
3521         <simpara>
3522           AAPCS/LINUX: ARM GNU/Linux Application Binary Interface Supplement
3523         </simpara>
3524       </listitem>
3525     </itemizedlist>
3526     <bridgehead renderas="sect3" id="context.reference.h1">
3527       <phrase id="context.reference.mips"/><link linkend="context.reference.mips">MIPS</link>
3528     </bridgehead>
3529     <itemizedlist>
3530       <listitem>
3531         <simpara>
3532           O32 ABI: SYSTEM V APPLICATION BINARY INTERFACE, MIPS RISC Processor Supplement
3533         </simpara>
3534       </listitem>
3535     </itemizedlist>
3536     <bridgehead renderas="sect3" id="context.reference.h2">
3537       <phrase id="context.reference.powerpc32"/><link linkend="context.reference.powerpc32">PowerPC32</link>
3538     </bridgehead>
3539     <itemizedlist>
3540       <listitem>
3541         <simpara>
3542           SYSV ABI: SYSTEM V APPLICATION BINARY INTERFACE PowerPC Processor Supplement
3543         </simpara>
3544       </listitem>
3545     </itemizedlist>
3546     <bridgehead renderas="sect3" id="context.reference.h3">
3547       <phrase id="context.reference.powerpc64"/><link linkend="context.reference.powerpc64">PowerPC64</link>
3548     </bridgehead>
3549     <itemizedlist>
3550       <listitem>
3551         <simpara>
3552           SYSV ABI: PowerPC User Instruction Set Architecture, Book I
3553         </simpara>
3554       </listitem>
3555     </itemizedlist>
3556     <bridgehead renderas="sect3" id="context.reference.h4">
3557       <phrase id="context.reference.x86_32"/><link linkend="context.reference.x86_32">X86-32</link>
3558     </bridgehead>
3559     <itemizedlist>
3560       <listitem>
3561         <simpara>
3562           SYSV ABI: SYSTEM V APPLICATION BINARY INTERFACE, Intel386TM Architecture
3563           Processor Supplement
3564         </simpara>
3565       </listitem>
3566       <listitem>
3567         <simpara>
3568           MS PE: <ulink url="http://msdn.microsoft.com/en-us/library/k2b2ssfy.aspx">Calling
3569           Conventions</ulink>
3570         </simpara>
3571       </listitem>
3572     </itemizedlist>
3573     <bridgehead renderas="sect3" id="context.reference.h5">
3574       <phrase id="context.reference.x86_64"/><link linkend="context.reference.x86_64">X86-64</link>
3575     </bridgehead>
3576     <itemizedlist>
3577       <listitem>
3578         <simpara>
3579           SYSV ABI: System V Application Binary Interface, AMD64 Architecture Processor
3580           Supplement
3581         </simpara>
3582       </listitem>
3583       <listitem>
3584         <simpara>
3585           MS PE: <ulink url="http://msdn.microsoft.com/en-us/library/7kcdt6fy%28VS.80%29.aspx">x64
3586           Software Conventions</ulink>
3587         </simpara>
3588       </listitem>
3589     </itemizedlist>
3590   </section>
3591   <section id="context.acknowledgements">
3592     <title><link linkend="context.acknowledgements">Acknowledgments</link></title>
3593     <para>
3594       I'd like to thank Adreas Fett, Artyom Beilis, Daniel Larimer, David Deakins,
3595       Evgeny Shapovalov, Fernando Pelliccioni, Giovanni Piero Deretta, Gordon Woodhull,
3596       Helge Bahmann, Holger Grund, Jeffrey Lee Hellrung (Jr.), Keith Jeffery, Martin
3597       Husemann, Phil Endecott, Robert Stewart, Sergey Cheban, Steven Watanabe, Vicente
3598       J. Botet Escriba, Wayne Piekarski.
3599     </para>
3600   </section>
3601 </library>