ceph/src/boost/libs/context/doc/html/context/ecv2.html

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  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="context.ecv2"></a><a name="ecv2"></a><a class="link" href="ecv2.html" title="Class execution_context (version 2)">Class execution_context
  28     (version 2)</a>
  29 </h2></div></div></div>
  30 <div class="note"><table border="0" summary="Note">
  31 <tr>
  32 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
  33 <th align="left">Note</th>
  34 </tr>
  35 <tr><td align="left" valign="top"><p>
  36         This class is enabled per default.
  37       </p></td></tr>
  38 </table></div>
  39 <p>
  40       Class <span class="emphasis"><em>execution_context</em></span> encapsulates context switching
  41       and manages the associated context' stack (allocation/deallocation).
  42     </p>
  43 <p>
  44       <span class="emphasis"><em>execution_context</em></span> allocates the context stack (using its
  45       <a class="link" href="stack.html#stack"><span class="emphasis"><em>StackAllocator</em></span></a> argument)
  46       and creates a control structure on top of it. This structure is responsible
  47       for managing context' stack. The address of the control structure is stored
  48       in the first frame of context' stack (e.g. it can not directly accessed from
  49       within <span class="emphasis"><em>execution_context</em></span>). In contrast to <a class="link" href="ecv1.html#ecv1"><span class="emphasis"><em>execution_context</em></span>
  50       (v1)</a> the ownership of the control structure is not shared (no member
  51       variable to control structure in <span class="emphasis"><em>execution_context</em></span>).
  52       <span class="emphasis"><em>execution_context</em></span> keeps internally a state that is moved
  53       by a call of <span class="emphasis"><em>execution_context::operator()</em></span> (<code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> will be
  54       invalidated), e.g. after a calling <span class="emphasis"><em>execution_context::operator()</em></span>,
  55       <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
  56       can not be used for an additional context switch.
  57     </p>
  58 <p>
  59       <span class="emphasis"><em>execution_context</em></span> is only move-constructible and move-assignable.
  60     </p>
  61 <p>
  62       The moved state is assigned to a new instance of <span class="emphasis"><em>execution_context</em></span>.
  63       This object becomes the first argument of the context-function, if the context
  64       was resumed the first time, or the first element in a tuple returned by <span class="emphasis"><em>execution_context::operator()</em></span>
  65       that has been called in the resumed context. In contrast to <a class="link" href="ecv1.html#ecv1"><span class="emphasis"><em>execution_context</em></span>
  66       (v1)</a>, the context switch is faster because no global pointer etc. is
  67       involved.
  68     </p>
  69 <div class="important"><table border="0" summary="Important">
  70 <tr>
  71 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td>
  72 <th align="left">Important</th>
  73 </tr>
  74 <tr><td align="left" valign="top"><p>
  75         Segmented stacks are not supported by <span class="emphasis"><em>execution_context</em></span>
  76         (v2).
  77       </p></td></tr>
  78 </table></div>
  79 <p>
  80       On return the context-function of the current context has to specify an <span class="emphasis"><em>execution_context</em></span>
  81       to which the execution control is transferred after termination of the current
  82       context.
  83     </p>
  84 <p>
  85       If an instance with valid state goes out of scope and the context-function
  86       has not yet returned, the stack is traversed in order to access the control
  87       structure (address stored at the first stack frame) and context' stack is deallocated
  88       via the <span class="emphasis"><em>StackAllocator</em></span>. The stack walking makes the destruction
  89       of <span class="emphasis"><em>execution_context</em></span> slow and should be prevented if possible.
  90     </p>
  91 <p>
  92       <span class="emphasis"><em>execution_context</em></span> expects a <span class="emphasis"><em>context-function</em></span>
  93       with signature <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">(</span><span class="identifier">execution_context</span>
  94       <span class="identifier">ctx</span><span class="special">,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">)</span></code>. The
  95       parameter <code class="computeroutput"><span class="identifier">ctx</span></code> represents the
  96       context from which this context was resumed (e.g. that has called <span class="emphasis"><em>execution_context::operator()</em></span>
  97       on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>)
  98       and <code class="computeroutput"><span class="identifier">args</span></code> are the data passed
  99       to <span class="emphasis"><em>execution_context::operator()</em></span>. The return value represents
 100       the execution_context that has to be resumed, after termiantion of this context.
 101     </p>
 102 <p>
 103       Benefits of <a class="link" href="ecv2.html#ecv2"><span class="emphasis"><em>execution_context</em></span> (v2)</a>
 104       over <a class="link" href="ecv1.html#ecv1"><span class="emphasis"><em>execution_context</em></span> (v1)</a>
 105       are: faster context switch, type-safety of passed/returned arguments.
 106     </p>
 107 <h4>
 108 <a name="context.ecv2.h0"></a>
 109       <span><a name="context.ecv2.usage_of__emphasis_execution_context__emphasis_"></a></span><a class="link" href="ecv2.html#context.ecv2.usage_of__emphasis_execution_context__emphasis_">usage
 110       of <span class="emphasis"><em>execution_context</em></span></a>
 111     </h4>
 112 <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">n</span><span class="special">=</span><span class="number">35</span><span class="special">;</span>
 113 <span class="identifier">ctx</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">source</span><span class="special">(</span>
 114     <span class="special">[</span><span class="identifier">n</span><span class="special">](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">sink</span><span class="special">,</span> <span class="keyword">int</span><span class="special">)</span> <span class="keyword">mutable</span> <span class="special">{</span>
 115         <span class="keyword">int</span> <span class="identifier">a</span><span class="special">=</span><span class="number">0</span><span class="special">;</span>
 116         <span class="keyword">int</span> <span class="identifier">b</span><span class="special">=</span><span class="number">1</span><span class="special">;</span>
 117         <span class="keyword">while</span><span class="special">(</span><span class="identifier">n</span><span class="special">--&gt;</span><span class="number">0</span><span class="special">){</span>
 118             <span class="keyword">auto</span> <span class="identifier">result</span><span class="special">=</span><span class="identifier">sink</span><span class="special">(</span><span class="identifier">a</span><span class="special">);</span>
 119             <span class="identifier">sink</span><span class="special">=</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">));</span>
 120             <span class="keyword">auto</span> <span class="identifier">next</span><span class="special">=</span><span class="identifier">a</span><span class="special">+</span><span class="identifier">b</span><span class="special">;</span>
 121             <span class="identifier">a</span><span class="special">=</span><span class="identifier">b</span><span class="special">;</span>
 122             <span class="identifier">b</span><span class="special">=</span><span class="identifier">next</span><span class="special">;</span>
 123         <span class="special">}</span>
 124         <span class="keyword">return</span> <span class="identifier">sink</span><span class="special">;</span>
 125     <span class="special">});</span>
 126 <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">=</span><span class="number">0</span><span class="special">;</span><span class="identifier">i</span><span class="special">&lt;</span><span class="number">10</span><span class="special">;++</span><span class="identifier">i</span><span class="special">){</span>
 127     <span class="keyword">auto</span> <span class="identifier">result</span><span class="special">=</span><span class="identifier">source</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>
 128     <span class="identifier">source</span><span class="special">=</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">));</span>
 129     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">&lt;&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">)&lt;&lt;</span><span class="string">" "</span><span class="special">;</span>
 130 <span class="special">}</span>
 131
 132 <span class="identifier">output</span><span class="special">:</span>
 133     <span class="number">0</span> <span class="number">1</span> <span class="number">1</span> <span class="number">2</span> <span class="number">3</span> <span class="number">5</span> <span class="number">8</span> <span class="number">13</span> <span class="number">21</span> <span class="number">34</span>
 134 </pre>
 135 <p>
 136       This simple example demonstrates the basic usage of <span class="emphasis"><em>execution_context</em></span>
 137       as a generator. The context <code class="computeroutput"><span class="identifier">sink</span></code>
 138       represents the <span class="emphasis"><em>main</em></span>-context (function <span class="emphasis"><em>main()</em></span>
 139       running). <code class="computeroutput"><span class="identifier">sink</span></code> is generated
 140       by the framework (first element of lambda's parameter list). Because the state
 141       is invalidated (== changed) by each call of <span class="emphasis"><em>execution_context::operator()</em></span>,
 142       the new state of the <span class="emphasis"><em>execution_context</em></span>, returned by <span class="emphasis"><em>execution_context::operator()</em></span>,
 143       needs to be assigned to <code class="computeroutput"><span class="identifier">sink</span></code>
 144       after each call.
 145     </p>
 146 <p>
 147       The lambda that calculates the Fibonacci numbers is executed inside the context
 148       represented by <code class="computeroutput"><span class="identifier">source</span></code>. Calculated
 149       Fibonacci numbers are transferred between the two context' via expression
 150       <span class="emphasis"><em>sink(a)</em></span> (and returned by <span class="emphasis"><em>source()</em></span>).
 151       Note that this example represents a <span class="emphasis"><em>generator</em></span> thus the
 152       value transferred into the lambda via <span class="emphasis"><em>source()</em></span> is not
 153       used. Using <span class="emphasis"><em>boost::optional&lt;&gt;</em></span> as transferred type,
 154       might also appropriate to express this fact.
 155     </p>
 156 <p>
 157       The locale variables <code class="computeroutput"><span class="identifier">a</span></code>, <code class="computeroutput"><span class="identifier">b</span></code> and <code class="computeroutput"> <span class="identifier">next</span></code>
 158       remain their values during each context switch (<span class="emphasis"><em>yield(a)</em></span>).
 159       This is possible due <code class="computeroutput"><span class="identifier">source</span></code>
 160       has its own stack and the stack is exchanged by each context switch.
 161     </p>
 162 <h4>
 163 <a name="context.ecv2.h1"></a>
 164       <span><a name="context.ecv2.parameter_passing"></a></span><a class="link" href="ecv2.html#context.ecv2.parameter_passing">parameter
 165       passing</a>
 166     </h4>
 167 <p>
 168       With <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span></code> no
 169       data will be transferred, only the context switch is executed.
 170     </p>
 171 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">ctx1</span><span class="special">([](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">ctx2</span><span class="special">){</span>
 172             <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"inside ctx1\n"</span><span class="special">);</span>
 173             <span class="keyword">return</span> <span class="identifier">ctx2</span><span class="special">();</span>
 174         <span class="special">});</span>
 175 <span class="identifier">ctx1</span><span class="special">();</span>
 176
 177 <span class="identifier">output</span><span class="special">:</span>
 178     <span class="identifier">inside</span> <span class="identifier">ctx1</span>
 179 </pre>
 180 <p>
 181       <code class="computeroutput"><span class="identifier">ctx1</span><span class="special">()</span></code>
 182       resumes <code class="computeroutput"><span class="identifier">ctx1</span></code>, e.g. the lambda
 183       passed at the constructor of <code class="computeroutput"><span class="identifier">ctx1</span></code>
 184       is entered. Argument <code class="computeroutput"><span class="identifier">ctx2</span></code> represents
 185       the context that has been suspended with the invocation of <code class="computeroutput"><span class="identifier">ctx1</span><span class="special">()</span></code>. When the lambda returns <code class="computeroutput"><span class="identifier">ctx2</span></code>,
 186       context <code class="computeroutput"><span class="identifier">ctx1</span></code> will be terminated
 187       while the context represented by <code class="computeroutput"><span class="identifier">ctx2</span></code>
 188       is resumed, hence the control of execution returns from <code class="computeroutput"><span class="identifier">ctx1</span><span class="special">()</span></code>.
 189     </p>
 190 <p>
 191       The arguments passed to <span class="emphasis"><em>execution_context::operator()</em></span>,
 192       in one context, is passed as the last arguments of the <span class="emphasis"><em>context-function</em></span>
 193       if the context is started for the first time. In all following invocations
 194       of <span class="emphasis"><em>execution_context::operator()</em></span> the arguments passed
 195       to <span class="emphasis"><em>execution_context::operator()</em></span>, in one context, is returned
 196       by <span class="emphasis"><em>execution_context::operator()</em></span> in the other context.
 197     </p>
 198 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">ctx1</span><span class="special">([](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">ctx2</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">j</span><span class="special">){</span>
 199             <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"inside ctx1, j == %d\n"</span><span class="special">,</span> <span class="identifier">j</span><span class="special">);</span>
 200             <span class="keyword">return</span> <span class="identifier">ctx2</span><span class="special">(</span><span class="identifier">j</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 201         <span class="special">});</span>
 202 <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>
 203 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx1</span><span class="special">,</span> <span class="identifier">i</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">ctx1</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>
 204 <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"i == %d\n"</span><span class="special">,</span> <span class="identifier">i</span><span class="special">);</span>
 205
 206 <span class="identifier">output</span><span class="special">:</span>
 207     <span class="identifier">inside</span> <span class="identifier">ctx1</span><span class="special">,</span> <span class="identifier">j</span> <span class="special">==</span> <span class="number">1</span>
 208     <span class="identifier">i</span> <span class="special">==</span> <span class="number">2</span>
 209 </pre>
 210 <p>
 211       <code class="computeroutput"><span class="identifier">ctx1</span><span class="special">(</span><span class="identifier">i</span><span class="special">)</span></code> enters
 212       the lambda in context <code class="computeroutput"><span class="identifier">ctx1</span></code>
 213       with argument <code class="computeroutput"><span class="identifier">j</span><span class="special">=</span><span class="number">1</span></code>. The expression <code class="computeroutput"><span class="identifier">ctx2</span><span class="special">(</span><span class="identifier">j</span><span class="special">+</span><span class="number">1</span><span class="special">)</span></code> resumes the
 214       context represented by <code class="computeroutput"><span class="identifier">ctx2</span></code>
 215       and transfers back an integer of <code class="computeroutput"><span class="identifier">j</span><span class="special">+</span><span class="number">1</span></code>. On return
 216       of <code class="computeroutput"><span class="identifier">ctx1</span><span class="special">(</span><span class="identifier">i</span><span class="special">)</span></code>, the variable
 217       <code class="computeroutput"><span class="identifier">i</span></code> contains the value of <code class="computeroutput"><span class="identifier">j</span><span class="special">+</span><span class="number">1</span></code>.
 218     </p>
 219 <p>
 220       If more than one argument has to be transferred, the signature of the context-function
 221       is simply extended.
 222     </p>
 223 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">ctx1</span><span class="special">([](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">ctx2</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">i</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">j</span><span class="special">){</span>
 224             <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"inside ctx1, i == %d j == %d\n"</span><span class="special">,</span> <span class="identifier">i</span><span class="special">,</span> <span class="identifier">j</span><span class="special">);</span>
 225             <span class="keyword">return</span> <span class="identifier">ctx2</span><span class="special">(</span><span class="identifier">i</span><span class="special">+</span><span class="identifier">j</span><span class="special">,</span><span class="identifier">i</span><span class="special">-</span><span class="identifier">j</span><span class="special">);</span>
 226         <span class="special">});</span>
 227 <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">2</span><span class="special">,</span> <span class="identifier">j</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>
 228 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx1</span><span class="special">,</span> <span class="identifier">i</span><span class="special">,</span> <span class="identifier">j</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">ctx1</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span><span class="identifier">j</span><span class="special">);</span>
 229 <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"i == %d j == %d\n"</span><span class="special">,</span> <span class="identifier">i</span><span class="special">,</span> <span class="identifier">j</span><span class="special">);</span>
 230
 231 <span class="identifier">output</span><span class="special">:</span>
 232     <span class="identifier">inside</span> <span class="identifier">ctx1</span><span class="special">,</span> <span class="identifier">i</span> <span class="special">==</span> <span class="number">2</span> <span class="identifier">j</span> <span class="special">==</span> <span class="number">1</span>
 233     <span class="identifier">i</span> <span class="special">==</span> <span class="number">3</span> <span class="identifier">j</span> <span class="special">==</span> <span class="number">1</span>
 234 </pre>
 235 <p>
 236       For use-cases, that require to transfer data of different type in each direction,
 237       <span class="emphasis"><em>boost::variant&lt;&gt;</em></span> could be used.
 238     </p>
 239 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">X</span><span class="special">{</span>
 240 <span class="keyword">private</span><span class="special">:</span>
 241     <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span> <span class="identifier">excptr_</span><span class="special">;</span>
 242     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;&gt;</span> <span class="identifier">ctx_</span><span class="special">;</span>
 243
 244 <span class="keyword">public</span><span class="special">:</span>
 245     <span class="identifier">X</span><span class="special">():</span>
 246         <span class="identifier">excptr_</span><span class="special">(),</span>
 247         <span class="identifier">ctx_</span><span class="special">(</span>
 248              <span class="special">[=](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;&gt;</span> <span class="identifier">ctx</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">data</span><span class="special">){</span>
 249                 <span class="keyword">try</span> <span class="special">{</span>
 250                     <span class="keyword">for</span> <span class="special">(;;)</span> <span class="special">{</span>
 251                         <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="identifier">data</span><span class="special">);</span>
 252                         <span class="identifier">data</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;(</span><span class="identifier">i</span><span class="special">);</span>
 253                         <span class="keyword">auto</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">(</span> <span class="identifier">data</span><span class="special">);</span>
 254                         <span class="identifier">ctx</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span> <span class="identifier">result</span><span class="special">)</span> <span class="special">);</span>
 255                         <span class="identifier">data</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;(</span> <span class="identifier">result</span><span class="special">);</span>
 256                 <span class="special">}</span> <span class="keyword">catch</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">bad_cast</span> <span class="keyword">const</span><span class="special">&amp;)</span> <span class="special">{</span>
 257                     <span class="identifier">excptr_</span><span class="special">=</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">current_exception</span><span class="special">();</span>
 258                 <span class="special">}</span>
 259                 <span class="keyword">return</span> <span class="identifier">ctx</span><span class="special">;</span>
 260              <span class="special">})</span>
 261     <span class="special">{}</span>
 262
 263     <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">){</span>
 264         <span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">data</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>
 265         <span class="keyword">auto</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">ctx_</span><span class="special">(</span> <span class="identifier">data</span><span class="special">);</span>
 266         <span class="identifier">ctx_</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span> <span class="identifier">result</span><span class="special">)</span> <span class="special">);</span>
 267         <span class="identifier">data</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;(</span> <span class="identifier">result</span><span class="special">);</span>
 268         <span class="keyword">if</span><span class="special">(</span><span class="identifier">excptr_</span><span class="special">){</span>
 269             <span class="identifier">std</span><span class="special">::</span><span class="identifier">rethrow_exception</span><span class="special">(</span><span class="identifier">excptr_</span><span class="special">);</span>
 270         <span class="special">}</span>
 271         <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;(</span><span class="identifier">data</span><span class="special">);</span>
 272     <span class="special">}</span>
 273 <span class="special">};</span>
 274
 275 <span class="identifier">X</span> <span class="identifier">x</span><span class="special">;</span>
 276 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">x</span><span class="special">(</span> <span class="number">7</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 277
 278 <span class="identifier">output</span><span class="special">:</span>
 279 <span class="number">7</span>
 280 </pre>
 281 <p>
 282       In the case of unidirectional transfer of data, <span class="emphasis"><em>boost::optional&lt;&gt;</em></span>
 283       or a pointer are appropriate.
 284     </p>
 285 <h4>
 286 <a name="context.ecv2.h2"></a>
 287       <span><a name="context.ecv2.exception_handling"></a></span><a class="link" href="ecv2.html#context.ecv2.exception_handling">exception
 288       handling</a>
 289     </h4>
 290 <p>
 291       If the function executed inside a <span class="emphasis"><em>execution_context</em></span> emits
 292       ans exception, the application is terminated by calling <span class="emphasis"><em>std::terminate()</em></span>.
 293       <span class="emphasis"><em>std::exception_ptr</em></span> can be used to transfer exceptions
 294       between different execution contexts.
 295     </p>
 296 <div class="important"><table border="0" summary="Important">
 297 <tr>
 298 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td>
 299 <th align="left">Important</th>
 300 </tr>
 301 <tr><td align="left" valign="top"><p>
 302         Do not jump from inside a catch block and then re-throw the exception in
 303         another execution context.
 304       </p></td></tr>
 305 </table></div>
 306 <a name="ecv2_ontop"></a><h4>
 307 <a name="context.ecv2.h3"></a>
 308       <span><a name="context.ecv2.executing_function_on_top_of_a_context"></a></span><a class="link" href="ecv2.html#context.ecv2.executing_function_on_top_of_a_context">Executing
 309       function on top of a context</a>
 310     </h4>
 311 <p>
 312       Sometimes it is useful to execute a new function on top of a resumed context.
 313       For this purpose <span class="emphasis"><em>execution_context::operator()</em></span> with first
 314       argument <code class="computeroutput"><span class="identifier">exec_ontop_arg</span></code> has
 315       to be used. The function passed as argument must return a tuple of execution_context
 316       and arguments.
 317     </p>
 318 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">f1</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">ctx</span><span class="special">,</span><span class="keyword">int</span> <span class="identifier">data</span><span class="special">)</span> <span class="special">{</span>
 319     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1: entered first time: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span>  <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 320     <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span><span class="identifier">data</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 321     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1: entered second time: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span>  <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 322     <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span><span class="identifier">data</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 323     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1: entered third time: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 324     <span class="keyword">return</span> <span class="identifier">ctx</span><span class="special">;</span>
 325 <span class="special">}</span>
 326
 327 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;,</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">f2</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">ctx</span><span class="special">,</span><span class="keyword">int</span> <span class="identifier">data</span><span class="special">)</span> <span class="special">{</span>
 328     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f2: entered: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 329     <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_tuple</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">),-</span><span class="number">1</span><span class="special">);</span>
 330 <span class="special">}</span>
 331
 332 <span class="keyword">int</span> <span class="identifier">data</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
 333 <span class="identifier">ctx</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="keyword">int</span> <span class="special">&gt;</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">f1</span><span class="special">);</span>
 334 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span><span class="identifier">data</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 335 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1: returned first time: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 336 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span><span class="identifier">data</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 337 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1: returned second time: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">data</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 338 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span><span class="identifier">data</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">exec_ontop_arg</span><span class="special">,</span><span class="identifier">f2</span><span class="special">,</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">);</span>
 339
 340 <span class="identifier">output</span><span class="special">:</span>
 341     <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">entered</span> <span class="identifier">first</span> <span class="identifier">time</span><span class="special">:</span> <span class="number">1</span>
 342     <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">returned</span> <span class="identifier">first</span> <span class="identifier">time</span><span class="special">:</span> <span class="number">2</span>
 343     <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">entered</span> <span class="identifier">second</span> <span class="identifier">time</span><span class="special">:</span> <span class="number">3</span>
 344     <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">returned</span> <span class="identifier">second</span> <span class="identifier">time</span><span class="special">:</span> <span class="number">4</span>
 345     <span class="identifier">f2</span><span class="special">:</span> <span class="identifier">entered</span><span class="special">:</span> <span class="number">5</span>
 346     <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">entered</span> <span class="identifier">third</span> <span class="identifier">time</span><span class="special">:</span> <span class="special">-</span><span class="number">1</span>
 347 </pre>
 348 <p>
 349       The expression <code class="computeroutput"><span class="identifier">ctx</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">exec_ontop_arg</span><span class="special">,</span><span class="identifier">f2</span><span class="special">,</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">)</span></code> executes <code class="computeroutput"><span class="identifier">f2</span><span class="special">()</span></code> on top of context <code class="computeroutput"><span class="identifier">ctx</span></code>,
 350       e.g. an additional stack frame is allocated on top of the context stack (in
 351       front of <code class="computeroutput"><span class="identifier">f1</span><span class="special">()</span></code>).
 352       <code class="computeroutput"><span class="identifier">f2</span><span class="special">()</span></code>
 353       returns argument <code class="computeroutput"><span class="special">-</span><span class="number">1</span></code>
 354       that will returned by the second invocation of <code class="computeroutput"><span class="identifier">ctx</span><span class="special">(</span><span class="identifier">data</span><span class="special">+</span><span class="number">1</span><span class="special">)</span></code> in <code class="computeroutput"><span class="identifier">f1</span><span class="special">()</span></code>.
 355     </p>
 356 <p>
 357       Another option is to execute a function on top of the context that throws an
 358       exception.
 359     </p>
 360 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">interrupt</span> <span class="special">{</span>
 361     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="keyword">void</span> <span class="special">&gt;</span>   <span class="identifier">ctx</span><span class="special">;</span>
 362
 363     <span class="identifier">interrupt</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="keyword">void</span> <span class="special">&gt;</span> <span class="special">&amp;&amp;</span> <span class="identifier">ctx_</span><span class="special">)</span> <span class="special">:</span>
 364         <span class="identifier">ctx</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special">&lt;</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="keyword">void</span> <span class="special">&gt;</span> <span class="special">&gt;(</span> <span class="identifier">ctx_</span><span class="special">)</span> <span class="special">)</span> <span class="special">{</span>
 365     <span class="special">}</span>
 366 <span class="special">};</span>
 367
 368 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">f1</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">ctx</span><span class="special">)</span> <span class="special">{</span>
 369     <span class="keyword">try</span> <span class="special">{</span>
 370         <span class="keyword">for</span> <span class="special">(;;)</span> <span class="special">{</span>
 371             <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1()"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 372             <span class="identifier">ctx</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">();</span>
 373         <span class="special">}</span>
 374     <span class="special">}</span> <span class="keyword">catch</span> <span class="special">(</span><span class="identifier">interrupt</span> <span class="special">&amp;</span> <span class="identifier">e</span><span class="special">)</span> <span class="special">{</span>
 375         <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"f1(): interrupted"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 376         <span class="identifier">ctx</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">ctx</span><span class="special">);</span>
 377     <span class="special">}</span>
 378     <span class="keyword">return</span> <span class="identifier">ctx</span><span class="special">;</span>
 379 <span class="special">}</span>
 380
 381 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">f2</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">ctx</span><span class="special">)</span> <span class="special">{</span>
 382     <span class="keyword">throw</span> <span class="identifier">interrupt</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">));</span>
 383     <span class="keyword">return</span> <span class="identifier">ctx</span><span class="special">;</span>
 384 <span class="special">}</span>
 385
 386 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="keyword">void</span> <span class="special">&gt;</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">f1</span><span class="special">);</span>
 387 <span class="identifier">ctx</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">();</span>
 388 <span class="identifier">ctx</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">();</span>
 389 <span class="identifier">ctx</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">exec_ontop_arg</span><span class="special">,</span><span class="identifier">f2</span><span class="special">);</span>
 390
 391 <span class="identifier">output</span><span class="special">:</span>
 392     <span class="identifier">f1</span><span class="special">()</span>
 393     <span class="identifier">f1</span><span class="special">()</span>
 394     <span class="identifier">f1</span><span class="special">():</span> <span class="identifier">interrupted</span>
 395 </pre>
 396 <p>
 397       In this example <code class="computeroutput"><span class="identifier">f2</span><span class="special">()</span></code>
 398       is used to interrupt the <code class="computeroutput"><span class="keyword">for</span></code>-loop
 399       in <code class="computeroutput"><span class="identifier">f1</span><span class="special">()</span></code>.
 400     </p>
 401 <h4>
 402 <a name="context.ecv2.h4"></a>
 403       <span><a name="context.ecv2.stack_destruction"></a></span><a class="link" href="ecv2.html#context.ecv2.stack_destruction">Stack
 404       destruction</a>
 405     </h4>
 406 <p>
 407       On construction of <span class="emphasis"><em>execution_context</em></span> a stack is allocated.
 408       If the <span class="emphasis"><em>context-function</em></span> returns the stack will be destructed.
 409       If the <span class="emphasis"><em>context-function</em></span> has not yet returned and the destructor
 410       of an valid <span class="emphasis"><em>execution_context</em></span> instance (e.g. <span class="emphasis"><em>execution_context::operator
 411       bool()</em></span> returns <code class="computeroutput"><span class="keyword">true</span></code>)
 412       is called, the stack will be destructed too.
 413     </p>
 414 <a name="ecv2_prealloc"></a><h4>
 415 <a name="context.ecv2.h5"></a>
 416       <span><a name="context.ecv2.allocating_control_structures_on_top_of_stack"></a></span><a class="link" href="ecv2.html#context.ecv2.allocating_control_structures_on_top_of_stack">allocating
 417       control structures on top of stack</a>
 418     </h4>
 419 <p>
 420       Allocating control structures on top of the stack requires to allocated the
 421       <span class="emphasis"><em>stack_context</em></span> and create the control structure with placement
 422       new before <span class="emphasis"><em>execution_context</em></span> is created.
 423     </p>
 424 <div class="note"><table border="0" summary="Note">
 425 <tr>
 426 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
 427 <th align="left">Note</th>
 428 </tr>
 429 <tr><td align="left" valign="top"><p>
 430         The user is responsible for destructing the control structure at the top
 431         of the stack.
 432       </p></td></tr>
 433 </table></div>
 434 <pre class="programlisting"><span class="comment">// stack-allocator used for (de-)allocating stack</span>
 435 <span class="identifier">fixedsize_stack</span> <span class="identifier">salloc</span><span class="special">(</span> <span class="number">4048</span><span class="special">);</span>
 436 <span class="comment">// allocate stack space</span>
 437 <span class="identifier">stack_context</span> <span class="identifier">sctx</span><span class="special">(</span> <span class="identifier">salloc</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">()</span> <span class="special">);</span>
 438 <span class="comment">// reserve space for control structure on top of the stack</span>
 439 <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">sp</span> <span class="special">=</span> <span class="keyword">static_cast</span><span class="special">&lt;</span> <span class="keyword">char</span> <span class="special">*</span> <span class="special">&gt;(</span> <span class="identifier">sctx</span><span class="special">.</span><span class="identifier">sp</span><span class="special">)</span> <span class="special">-</span> <span class="keyword">sizeof</span><span class="special">(</span> <span class="identifier">my_control_structure</span><span class="special">);</span>
 440 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">size</span> <span class="special">=</span> <span class="identifier">sctx</span><span class="special">.</span><span class="identifier">size</span> <span class="special">-</span> <span class="keyword">sizeof</span><span class="special">(</span> <span class="identifier">my_control_structure</span><span class="special">);</span>
 441 <span class="comment">// placement new creates control structure on reserved space</span>
 442 <span class="identifier">my_control_structure</span> <span class="special">*</span> <span class="identifier">cs</span> <span class="special">=</span> <span class="keyword">new</span> <span class="special">(</span> <span class="identifier">sp</span><span class="special">)</span> <span class="identifier">my_control_structure</span><span class="special">(</span> <span class="identifier">sp</span><span class="special">,</span> <span class="identifier">size</span><span class="special">,</span> <span class="identifier">sctx</span><span class="special">,</span> <span class="identifier">salloc</span><span class="special">);</span>
 443 <span class="special">...</span>
 444 <span class="comment">// destructing the control structure</span>
 445 <span class="identifier">cs</span><span class="special">-&gt;~</span><span class="identifier">my_control_structure</span><span class="special">();</span>
 446 <span class="special">...</span>
 447 <span class="keyword">struct</span> <span class="identifier">my_control_structure</span>  <span class="special">{</span>
 448     <span class="comment">// captured context</span>
 449     <span class="identifier">execution_context</span> <span class="identifier">cctx</span><span class="special">;</span>
 450
 451     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">StackAllocator</span> <span class="special">&gt;</span>
 452     <span class="identifier">my_control_structure</span><span class="special">(</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">sp</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">size</span><span class="special">,</span> <span class="identifier">stack_context</span> <span class="identifier">sctx</span><span class="special">,</span> <span class="identifier">StackAllocator</span> <span class="identifier">salloc</span><span class="special">)</span> <span class="special">:</span>
 453         <span class="comment">// create captured context</span>
 454         <span class="identifier">cctx</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg</span><span class="special">,</span> <span class="identifier">preallocated</span><span class="special">(</span> <span class="identifier">sp</span><span class="special">,</span> <span class="identifier">size</span><span class="special">,</span> <span class="identifier">sctx</span><span class="special">),</span> <span class="identifier">salloc</span><span class="special">,</span> <span class="identifier">entry_func</span><span class="special">)</span> <span class="special">{</span>
 455     <span class="special">}</span>
 456     <span class="special">...</span>
 457 <span class="special">};</span>
 458 </pre>
 459 <h4>
 460 <a name="context.ecv2.h6"></a>
 461       <span><a name="context.ecv2.inverting_the_control_flow"></a></span><a class="link" href="ecv2.html#context.ecv2.inverting_the_control_flow">inverting
 462       the control flow</a>
 463     </h4>
 464 <pre class="programlisting"><span class="comment">/*
 465  * grammar:
 466  *   P ---&gt; E '\0'
 467  *   E ---&gt; T {('+'|'-') T}
 468  *   T ---&gt; S {('*'|'/') S}
 469  *   S ---&gt; digit | '(' E ')'
 470  */</span>
 471 <span class="keyword">class</span> <span class="identifier">Parser</span><span class="special">{</span>
 472     <span class="comment">// implementation omitted; see examples directory</span>
 473 <span class="special">};</span>
 474
 475 <span class="identifier">std</span><span class="special">::</span><span class="identifier">istringstream</span> <span class="identifier">is</span><span class="special">(</span><span class="string">"1+1"</span><span class="special">);</span>
 476 <span class="keyword">bool</span> <span class="identifier">done</span><span class="special">=</span><span class="keyword">false</span><span class="special">;</span>
 477 <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span> <span class="identifier">except</span><span class="special">;</span>
 478
 479 <span class="comment">// execute parser in new execution context</span>
 480 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span> <span class="identifier">source</span><span class="special">(</span>
 481         <span class="special">[&amp;</span><span class="identifier">is</span><span class="special">,&amp;</span><span class="identifier">done</span><span class="special">,&amp;</span><span class="identifier">except</span><span class="special">](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">execution_context</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span> <span class="identifier">sink</span><span class="special">,</span><span class="keyword">char</span><span class="special">){</span>
 482         <span class="comment">// create parser with callback function</span>
 483         <span class="identifier">Parser</span> <span class="identifier">p</span><span class="special">(</span> <span class="identifier">is</span><span class="special">,</span>
 484                   <span class="special">[&amp;</span><span class="identifier">sink</span><span class="special">](</span><span class="keyword">char</span> <span class="identifier">ch</span><span class="special">){</span>
 485                         <span class="comment">// resume main execution context</span>
 486                         <span class="keyword">auto</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">sink</span><span class="special">(</span><span class="identifier">ch</span><span class="special">);</span>
 487                         <span class="identifier">sink</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">));</span>
 488                 <span class="special">});</span>
 489             <span class="keyword">try</span> <span class="special">{</span>
 490                 <span class="comment">// start recursive parsing</span>
 491                 <span class="identifier">p</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span>
 492             <span class="special">}</span> <span class="keyword">catch</span> <span class="special">(...)</span> <span class="special">{</span>
 493                 <span class="comment">// store other exceptions in exception-pointer</span>
 494                 <span class="identifier">except</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">current_exception</span><span class="special">();</span>
 495             <span class="special">}</span>
 496             <span class="comment">// set termination flag</span>
 497             <span class="identifier">done</span><span class="special">=</span><span class="keyword">true</span><span class="special">;</span>
 498             <span class="comment">// resume main execution context</span>
 499             <span class="keyword">return</span> <span class="identifier">sink</span><span class="special">;</span>
 500         <span class="special">});</span>
 501
 502 <span class="comment">// user-code pulls parsed data from parser</span>
 503 <span class="comment">// invert control flow</span>
 504 <span class="keyword">auto</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">source</span><span class="special">(</span><span class="char">'\0'</span><span class="special">);</span>
 505 <span class="identifier">source</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">));</span>
 506 <span class="keyword">char</span> <span class="identifier">c</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;(</span><span class="identifier">result</span><span class="special">);</span>
 507 <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">except</span><span class="special">)</span> <span class="special">{</span>
 508     <span class="identifier">std</span><span class="special">::</span><span class="identifier">rethrow_exception</span><span class="special">(</span><span class="identifier">except</span><span class="special">);</span>
 509 <span class="special">}</span>
 510 <span class="keyword">while</span><span class="special">(</span> <span class="special">!</span> <span class="identifier">done</span><span class="special">)</span> <span class="special">{</span>
 511     <span class="identifier">printf</span><span class="special">(</span><span class="string">"Parsed: %c\n"</span><span class="special">,</span><span class="identifier">c</span><span class="special">);</span>
 512     <span class="identifier">std</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">source</span><span class="special">,</span><span class="identifier">c</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">source</span><span class="special">(</span><span class="char">'\0'</span><span class="special">);</span>
 513     <span class="keyword">if</span> <span class="special">(</span><span class="identifier">except</span><span class="special">)</span> <span class="special">{</span>
 514         <span class="identifier">std</span><span class="special">::</span><span class="identifier">rethrow_exception</span><span class="special">(</span><span class="identifier">except</span><span class="special">);</span>
 515     <span class="special">}</span>
 516 <span class="special">}</span>
 517
 518 <span class="identifier">output</span><span class="special">:</span>
 519     <span class="identifier">Parsed</span><span class="special">:</span> <span class="number">1</span>
 520     <span class="identifier">Parsed</span><span class="special">:</span> <span class="special">+</span>
 521     <span class="identifier">Parsed</span><span class="special">:</span> <span class="number">1</span>
 522 </pre>
 523 <p>
 524       In this example a recursive descent parser uses a callback to emit a newly
 525       passed symbol. Using <span class="emphasis"><em>execution_context</em></span> the control flow
 526       can be inverted, e.g. the user-code pulls parsed symbols from the parser -
 527       instead to get pushed from the parser (via callback).
 528     </p>
 529 <p>
 530       The data (character) is transferred between the two <span class="emphasis"><em>execution_context</em></span>.
 531     </p>
 532 <p>
 533       If the code executed by <span class="emphasis"><em>execution_context</em></span> emits an exception,
 534       the application is terminated. <span class="emphasis"><em>std::exception_ptr</em></span> can
 535       be used to transfer exceptions between different execution contexts.
 536     </p>
 537 <p>
 538       Sometimes it is necessary to unwind the stack of an unfinished context to destroy
 539       local stack variables so they can release allocated resources (RAII pattern).
 540       The user is responsible for this task.
 541     </p>
 542 <h4>
 543 <a name="context.ecv2.h7"></a>
 544       <span><a name="context.ecv2.class__code__phrase_role__identifier__execution_context__phrase___code_"></a></span><a class="link" href="ecv2.html#context.ecv2.class__code__phrase_role__identifier__execution_context__phrase___code_">Class
 545       <code class="computeroutput"><span class="identifier">execution_context</span></code></a>
 546     </h4>
 547 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">exec_ontop_arg_t</span> <span class="special">{};</span>
 548 <span class="keyword">const</span> <span class="identifier">exec_ontop_arg_t</span> <span class="identifier">exec_ontop_arg</span><span class="special">{};</span>
 549
 550 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="special">...</span> <span class="identifier">Args</span> <span class="special">&gt;</span>
 551 <span class="keyword">class</span> <span class="identifier">execution_context</span> <span class="special">{</span>
 552 <span class="keyword">public</span><span class="special">:</span>
 553     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">typename</span> <span class="special">...</span> <span class="identifier">Params</span> <span class="special">&gt;</span>
 554     <span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Params</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">params</span><span class="special">);</span>
 555
 556     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">StackAlloc</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">typename</span> <span class="special">...</span> <span class="identifier">Params</span> <span class="special">&gt;</span>
 557     <span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span><span class="special">,</span> <span class="identifier">StackAlloc</span> <span class="identifier">salloc</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Params</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">params</span><span class="special">);</span>
 558
 559     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">StackAlloc</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">typename</span> <span class="special">...</span> <span class="identifier">Params</span> <span class="special">&gt;</span>
 560     <span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span><span class="special">,</span> <span class="identifier">preallocated</span> <span class="identifier">palloc</span><span class="special">,</span> <span class="identifier">StackAlloc</span> <span class="identifier">salloc</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Params</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">params</span><span class="special">);</span>
 561
 562     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">typename</span> <span class="special">...</span> <span class="identifier">Params</span> <span class="special">&gt;</span>
 563     <span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span><span class="special">,</span> <span class="identifier">segemented_stack</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Params</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">params</span><span class="special">)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
 564
 565     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">typename</span> <span class="special">...</span> <span class="identifier">Params</span> <span class="special">&gt;</span>
 566     <span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span><span class="special">,</span> <span class="identifier">preallocated</span> <span class="identifier">palloc</span><span class="special">,</span> <span class="identifier">segmented</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Params</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">params</span><span class="special">)=</span> <span class="keyword">delete</span><span class="special">;</span>
 567
 568     <span class="special">~</span><span class="identifier">execution_context</span><span class="special">();</span>
 569
 570     <span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">execution_context</span> <span class="special">&amp;&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 571     <span class="identifier">execution_context</span> <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">execution_context</span> <span class="special">&amp;&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 572
 573     <span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
 574     <span class="identifier">execution_context</span> <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
 575
 576     <span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 577     <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 578
 579     <span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span> <span class="identifier">execution_context</span><span class="special">,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 580
 581     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">&gt;</span>
 582     <span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span> <span class="identifier">execution_context</span><span class="special">,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="identifier">exec_ontop_arg_t</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 583
 584     <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">==(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 585
 586     <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 587
 588     <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&lt;(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 589
 590     <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&gt;(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 591
 592     <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&lt;=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 593
 594     <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&gt;=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 595
 596     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">charT</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">traitsT</span> <span class="special">&gt;</span>
 597     <span class="keyword">friend</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span> <span class="identifier">charT</span><span class="special">,</span> <span class="identifier">traitsT</span> <span class="special">&gt;</span> <span class="special">&amp;</span>
 598     <span class="keyword">operator</span><span class="special">&lt;&lt;(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span> <span class="identifier">charT</span><span class="special">,</span> <span class="identifier">traitsT</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">os</span><span class="special">,</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">);</span>
 599 <span class="special">};</span>
 600 </pre>
 601 <p>
 602       </p>
 603 <h5>
 604 <a name="ecv2_constructor_bridgehead"></a>
 605   <span><a name="ecv2_constructor"></a></span>
 606   <a class="link" href="ecv2.html#ecv2_constructor">Constructor</a>
 607 </h5>
 608 <p>
 609     </p>
 610 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">typename</span> <span class="special">...</span> <span class="identifier">Params</span> <span class="special">&gt;</span>
 611 <span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Params</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">params</span><span class="special">);</span>
 612
 613 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">StackAlloc</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">typename</span> <span class="special">...</span> <span class="identifier">Params</span> <span class="special">&gt;</span>
 614 <span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span><span class="special">,</span> <span class="identifier">StackAlloc</span> <span class="identifier">salloc</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Params</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">params</span><span class="special">);</span>
 615
 616 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">StackAlloc</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">typename</span> <span class="special">...</span> <span class="identifier">Params</span> <span class="special">&gt;</span>
 617 <span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span><span class="special">,</span> <span class="identifier">preallocated</span> <span class="identifier">palloc</span><span class="special">,</span> <span class="identifier">StackAlloc</span> <span class="identifier">salloc</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Params</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">params</span><span class="special">);</span>
 618 </pre>
 619 <div class="variablelist">
 620 <p class="title"><b></b></p>
 621 <dl>
 622 <dt><span class="term">Effects:</span></dt>
 623 <dd><p>
 624             Creates a new execution context and prepares the context to execute
 625             <code class="computeroutput"><span class="identifier">fn</span></code>. <code class="computeroutput"><span class="identifier">fixedsize_stack</span></code>
 626             is used as default stack allocator (stack size == fixedsize_stack::traits::default_size()).
 627             The constructor with argument type <code class="computeroutput"><span class="identifier">preallocated</span></code>,
 628             is used to create a user defined data <a class="link" href="ecv2.html#ecv2_prealloc">(for
 629             instance additional control structures)</a> on top of the stack.
 630           </p></dd>
 631 </dl>
 632 </div>
 633 <p>
 634       </p>
 635 <h5>
 636 <a name="ecv2_destructor%20destructor_bridgehead"></a>
 637   <span><a name="ecv2_destructor%20destructor"></a></span>
 638   <a class="link" href="ecv2.html#ecv2_destructor%20destructor">Destructor</a>
 639 </h5>
 640 <p>
 641     </p>
 642 <pre class="programlisting"><span class="special">~</span><span class="identifier">execution_context</span><span class="special">();</span>
 643 </pre>
 644 <div class="variablelist">
 645 <p class="title"><b></b></p>
 646 <dl>
 647 <dt><span class="term">Effects:</span></dt>
 648 <dd><p>
 649             Destructs the associated stack if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is a valid context, e.g. <span class="emphasis"><em>execution_context::operator
 650             bool()</em></span> returns <code class="computeroutput"><span class="keyword">true</span></code>.
 651           </p></dd>
 652 <dt><span class="term">Throws:</span></dt>
 653 <dd><p>
 654             Nothing.
 655           </p></dd>
 656 </dl>
 657 </div>
 658 <p>
 659       </p>
 660 <h5>
 661 <a name="ecv2_move%20constructor_bridgehead"></a>
 662   <span><a name="ecv2_move%20constructor"></a></span>
 663   <a class="link" href="ecv2.html#ecv2_move%20constructor">Move
 664       constructor</a>
 665 </h5>
 666 <p>
 667     </p>
 668 <pre class="programlisting"><span class="identifier">execution_context</span><span class="special">(</span> <span class="identifier">execution_context</span> <span class="special">&amp;&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 669 </pre>
 670 <div class="variablelist">
 671 <p class="title"><b></b></p>
 672 <dl>
 673 <dt><span class="term">Effects:</span></dt>
 674 <dd><p>
 675             Moves underlying capture record to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
 676           </p></dd>
 677 <dt><span class="term">Throws:</span></dt>
 678 <dd><p>
 679             Nothing.
 680           </p></dd>
 681 </dl>
 682 </div>
 683 <p>
 684       </p>
 685 <h5>
 686 <a name="ecv2_move%20assignment_bridgehead"></a>
 687   <span><a name="ecv2_move%20assignment"></a></span>
 688   <a class="link" href="ecv2.html#ecv2_move%20assignment">Move
 689       assignment operator</a>
 690 </h5>
 691 <p>
 692     </p>
 693 <pre class="programlisting"><span class="identifier">execution_context</span> <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">execution_context</span> <span class="special">&amp;&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 694 </pre>
 695 <div class="variablelist">
 696 <p class="title"><b></b></p>
 697 <dl>
 698 <dt><span class="term">Effects:</span></dt>
 699 <dd><p>
 700             Moves the state of <code class="computeroutput"><span class="identifier">other</span></code>
 701             to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 702             using move semantics.
 703           </p></dd>
 704 <dt><span class="term">Throws:</span></dt>
 705 <dd><p>
 706             Nothing.
 707           </p></dd>
 708 </dl>
 709 </div>
 710 <p>
 711       </p>
 712 <h5>
 713 <a name="ecv2_operator_bool_bridgehead"></a>
 714   <span><a name="ecv2_operator_bool"></a></span>
 715   <a class="link" href="ecv2.html#ecv2_operator_bool">Member function
 716       <code class="computeroutput">operator bool</code>()</a>
 717 </h5>
 718 <p>
 719     </p>
 720 <pre class="programlisting"><span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 721 </pre>
 722 <div class="variablelist">
 723 <p class="title"><b></b></p>
 724 <dl>
 725 <dt><span class="term">Returns:</span></dt>
 726 <dd><p>
 727             <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> points to a capture record.
 728           </p></dd>
 729 <dt><span class="term">Throws:</span></dt>
 730 <dd><p>
 731             Nothing.
 732           </p></dd>
 733 </dl>
 734 </div>
 735 <p>
 736       </p>
 737 <h5>
 738 <a name="ecv2_operator_not_bridgehead"></a>
 739   <span><a name="ecv2_operator_not"></a></span>
 740   <a class="link" href="ecv2.html#ecv2_operator_not">Member function
 741       <code class="computeroutput">operator!</code>()</a>
 742 </h5>
 743 <p>
 744     </p>
 745 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 746 </pre>
 747 <div class="variablelist">
 748 <p class="title"><b></b></p>
 749 <dl>
 750 <dt><span class="term">Returns:</span></dt>
 751 <dd><p>
 752             <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not point to a capture record.
 753           </p></dd>
 754 <dt><span class="term">Throws:</span></dt>
 755 <dd><p>
 756             Nothing.
 757           </p></dd>
 758 </dl>
 759 </div>
 760 <p>
 761       </p>
 762 <h5>
 763 <a name="ecv2_operator_call_bridgehead"></a>
 764   <span><a name="ecv2_operator_call"></a></span>
 765   <a class="link" href="ecv2.html#ecv2_operator_call">Member function
 766       <code class="computeroutput">operator()</code>()</a>
 767 </h5>
 768 <p>
 769     </p>
 770 <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span> <span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">&gt;,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span> <span class="comment">// member of generic execution_context template</span>
 771
 772 <span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="keyword">void</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()();</span> <span class="comment">// member of execution_context&lt; void &gt;</span>
 773 </pre>
 774 <div class="variablelist">
 775 <p class="title"><b></b></p>
 776 <dl>
 777 <dt><span class="term">Effects:</span></dt>
 778 <dd><p>
 779             Stores internally the current context data (stack pointer, instruction
 780             pointer, and CPU registers) of the current active context and restores
 781             the context data from <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>, which implies jumping to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>'s
 782             context. The arguments, <code class="computeroutput"><span class="special">...</span> <span class="identifier">args</span></code>, are passed to the current context
 783             to be returned by the most recent call to <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code> in the same thread.
 784           </p></dd>
 785 <dt><span class="term">Returns:</span></dt>
 786 <dd><p>
 787             The tuple of execution_context and returned arguments passed to the most
 788             recent call to <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code>, if any and a execution_context representing
 789             the context that has been suspended.
 790           </p></dd>
 791 <dt><span class="term">Note:</span></dt>
 792 <dd><p>
 793             The returned execution_context indicates if the suspended context has
 794             terminated (return from context-function) via <code class="computeroutput"><span class="keyword">bool</span>
 795             <span class="keyword">operator</span><span class="special">()</span></code>.
 796             If the returned execution_context has terminated no data are transferred
 797             in the returned tuple.
 798           </p></dd>
 799 </dl>
 800 </div>
 801 <p>
 802       </p>
 803 <h5>
 804 <a name="ecv2_operator_call_ontop_bridgehead"></a>
 805   <span><a name="ecv2_operator_call_ontop"></a></span>
 806   <a class="link" href="ecv2.html#ecv2_operator_call_ontop">Member
 807       function <code class="computeroutput">operator()</code>()</a>
 808 </h5>
 809 <p>
 810     </p>
 811 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">&gt;</span>
 812 <span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span> <span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">&gt;,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="identifier">exec_ontop_arg_t</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">,</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span> <span class="comment">// member of generic execution_context</span>
 813
 814 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">&gt;</span>
 815 <span class="identifier">execution_context</span><span class="special">&lt;</span> <span class="keyword">void</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="identifier">exec_ontop_arg_t</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">);</span> <span class="comment">// member of execution_context&lt; void &gt;</span>
 816 </pre>
 817 <div class="variablelist">
 818 <p class="title"><b></b></p>
 819 <dl>
 820 <dt><span class="term">Effects:</span></dt>
 821 <dd><p>
 822             Same as <span class="emphasis"><em>execution_context::operator()</em></span>. Additionally,
 823             function <code class="computeroutput"><span class="identifier">fn</span></code> is executed
 824             in the context of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 825             (e.g. the stack frame of <code class="computeroutput"><span class="identifier">fn</span></code>
 826             is allocated on stack of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>).
 827           </p></dd>
 828 <dt><span class="term">Returns:</span></dt>
 829 <dd><p>
 830             The tuple of execution_context and returned arguments passed to the most
 831             recent call to <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code>, if any and a execution_context representing
 832             the context that has been suspended .
 833           </p></dd>
 834 <dt><span class="term">Note:</span></dt>
 835 <dd><p>
 836             The tuple of execution_context and returned arguments from <code class="computeroutput"><span class="identifier">fn</span></code> are passed as arguments to the context-function
 837             of resumed context (if the context is entered the first time) or those
 838             arguments are returned from <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code> within the resumed context.
 839           </p></dd>
 840 <dt><span class="term">Note:</span></dt>
 841 <dd><p>
 842             Function <code class="computeroutput"><span class="identifier">fn</span></code> needs to
 843             return a tuple of execution_context and arguments (<a class="link" href="ecv2.html#ecv2_ontop">see
 844             description</a>).
 845           </p></dd>
 846 <dt><span class="term">Note:</span></dt>
 847 <dd><p>
 848             The context calling this function must not be destroyed before the arguments,
 849             that will be returned from <code class="computeroutput"><span class="identifier">fn</span></code>,
 850             are preserved at least in the stack frame of the resumed context.
 851           </p></dd>
 852 <dt><span class="term">Note:</span></dt>
 853 <dd><p>
 854             The returned execution_context indicates if the suspended context has
 855             terminated (return from context-function) via <code class="computeroutput"><span class="keyword">bool</span>
 856             <span class="keyword">operator</span><span class="special">()</span></code>.
 857             If the returned execution_context has terminated no data are transferred
 858             in the returned tuple.
 859           </p></dd>
 860 </dl>
 861 </div>
 862 <p>
 863       </p>
 864 <h5>
 865 <a name="ecv2_operator_equal_bridgehead"></a>
 866   <span><a name="ecv2_operator_equal"></a></span>
 867   <a class="link" href="ecv2.html#ecv2_operator_equal">Member
 868       function <code class="computeroutput">operator==</code>()</a>
 869 </h5>
 870 <p>
 871     </p>
 872 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">==(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 873 </pre>
 874 <div class="variablelist">
 875 <p class="title"><b></b></p>
 876 <dl>
 877 <dt><span class="term">Returns:</span></dt>
 878 <dd><p>
 879             <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">other</span></code>
 880             represent the same execution context, <code class="computeroutput"><span class="keyword">false</span></code>
 881             otherwise.
 882           </p></dd>
 883 <dt><span class="term">Throws:</span></dt>
 884 <dd><p>
 885             Nothing.
 886           </p></dd>
 887 </dl>
 888 </div>
 889 <p>
 890       </p>
 891 <h5>
 892 <a name="ecv2_operator_notequal_bridgehead"></a>
 893   <span><a name="ecv2_operator_notequal"></a></span>
 894   <a class="link" href="ecv2.html#ecv2_operator_notequal">Member
 895       function <code class="computeroutput">operator!=</code>()</a>
 896 </h5>
 897 <p>
 898     </p>
 899 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 900 </pre>
 901 <div class="variablelist">
 902 <p class="title"><b></b></p>
 903 <dl>
 904 <dt><span class="term">Returns:</span></dt>
 905 <dd><p>
 906             <code class="computeroutput">! (other == * this)</code>
 907           </p></dd>
 908 <dt><span class="term">Throws:</span></dt>
 909 <dd><p>
 910             Nothing.
 911           </p></dd>
 912 </dl>
 913 </div>
 914 <p>
 915       </p>
 916 <h5>
 917 <a name="ecv2_operator_less_bridgehead"></a>
 918   <span><a name="ecv2_operator_less"></a></span>
 919   <a class="link" href="ecv2.html#ecv2_operator_less">Member function
 920       <code class="computeroutput">operator&lt;</code>()</a>
 921 </h5>
 922 <p>
 923     </p>
 924 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&lt;(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 925 </pre>
 926 <div class="variablelist">
 927 <p class="title"><b></b></p>
 928 <dl>
 929 <dt><span class="term">Returns:</span></dt>
 930 <dd><p>
 931             <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">!=</span> <span class="identifier">other</span></code> is true and the implementation-defined
 932             total order of <code class="computeroutput"><span class="identifier">execution_context</span></code>
 933             values places <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 934             before <code class="computeroutput"><span class="identifier">other</span></code>, false otherwise.
 935           </p></dd>
 936 <dt><span class="term">Throws:</span></dt>
 937 <dd><p>
 938             Nothing.
 939           </p></dd>
 940 </dl>
 941 </div>
 942 <p>
 943       </p>
 944 <h5>
 945 <a name="ecv2_operator_greater_bridgehead"></a>
 946   <span><a name="ecv2_operator_greater"></a></span>
 947   <a class="link" href="ecv2.html#ecv2_operator_greater">Member
 948       function <code class="computeroutput">operator&gt;</code>()</a>
 949 </h5>
 950 <p>
 951     </p>
 952 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&gt;(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 953 </pre>
 954 <div class="variablelist">
 955 <p class="title"><b></b></p>
 956 <dl>
 957 <dt><span class="term">Returns:</span></dt>
 958 <dd><p>
 959             <code class="computeroutput"><span class="identifier">other</span> <span class="special">&lt;</span>
 960             <span class="special">*</span> <span class="keyword">this</span></code>
 961           </p></dd>
 962 <dt><span class="term">Throws:</span></dt>
 963 <dd><p>
 964             Nothing.
 965           </p></dd>
 966 </dl>
 967 </div>
 968 <p>
 969       </p>
 970 <h5>
 971 <a name="ecv2_operator_lesseq_bridgehead"></a>
 972   <span><a name="ecv2_operator_lesseq"></a></span>
 973   <a class="link" href="ecv2.html#ecv2_operator_lesseq">Member
 974       function <code class="computeroutput">operator&lt;=</code>()</a>
 975 </h5>
 976 <p>
 977     </p>
 978 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&lt;=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 979 </pre>
 980 <div class="variablelist">
 981 <p class="title"><b></b></p>
 982 <dl>
 983 <dt><span class="term">Returns:</span></dt>
 984 <dd><p>
 985             <code class="computeroutput"><span class="special">!</span> <span class="special">(</span><span class="identifier">other</span> <span class="special">&lt;</span>
 986             <span class="special">*</span> <span class="keyword">this</span><span class="special">)</span></code>
 987           </p></dd>
 988 <dt><span class="term">Throws:</span></dt>
 989 <dd><p>
 990             Nothing.
 991           </p></dd>
 992 </dl>
 993 </div>
 994 <p>
 995       </p>
 996 <h5>
 997 <a name="ecv2_operator_greatereq_bridgehead"></a>
 998   <span><a name="ecv2_operator_greatereq"></a></span>
 999   <a class="link" href="ecv2.html#ecv2_operator_greatereq">Member
1000       function <code class="computeroutput">operator&gt;=</code>()</a>
1001 </h5>
1002 <p>
1003     </p>
1004 <pre class="programlisting"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&gt;=(</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
1005 </pre>
1006 <div class="variablelist">
1007 <p class="title"><b></b></p>
1008 <dl>
1009 <dt><span class="term">Returns:</span></dt>
1010 <dd><p>
1011             <code class="computeroutput"><span class="special">!</span> <span class="special">(*</span>
1012             <span class="keyword">this</span> <span class="special">&lt;</span>
1013             <span class="identifier">other</span><span class="special">)</span></code>
1014           </p></dd>
1015 <dt><span class="term">Throws:</span></dt>
1016 <dd><p>
1017             Nothing.
1018           </p></dd>
1019 </dl>
1020 </div>
1021 <p>
1022       </p>
1023 <h5>
1024 <a name="ecv2__bridgehead"></a>
1025   <span><a name="ecv2_"></a></span>
1026   <a class="link" href="ecv2.html#ecv2_">Non-member function <code class="computeroutput">operator&lt;&lt;()</code></a>
1027 </h5>
1028 <p>
1029     </p>
1030 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">charT</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">traitsT</span> <span class="special">&gt;</span>
1031 <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span> <span class="identifier">charT</span><span class="special">,</span> <span class="identifier">traitsT</span> <span class="special">&gt;</span> <span class="special">&amp;</span>
1032 <span class="keyword">operator</span><span class="special">&lt;&lt;(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span> <span class="identifier">charT</span><span class="special">,</span> <span class="identifier">traitsT</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">os</span><span class="special">,</span> <span class="identifier">execution_context</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">);</span>
1033 </pre>
1034 <div class="variablelist">
1035 <p class="title"><b></b></p>
1036 <dl>
1037 <dt><span class="term">Efects:</span></dt>
1038 <dd><p>
1039             Writes the representation of <code class="computeroutput"><span class="identifier">other</span></code>
1040             to stream <code class="computeroutput"><span class="identifier">os</span></code>.
1041           </p></dd>
1042 <dt><span class="term">Returns:</span></dt>
1043 <dd><p>
1044             <code class="computeroutput"><span class="identifier">os</span></code>
1045           </p></dd>
1046 </dl>
1047 </div>
1048 </div>
1049 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
1050 <td align="left"></td>
1051 <td align="right"><div class="copyright-footer">Copyright &#169; 2014 Oliver Kowalke<p>
1052         Distributed under the Boost Software License, Version 1.0. (See accompanying
1053         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
1054       </p>
1055 </div></td>
1056 </tr></table>
1057 <hr>
1058 <div class="spirit-nav">
1059 <a accesskey="p" href="requirements.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="ecv1.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
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