ceph/src/boost/libs/context/doc/html/context/ecv2_class.html

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  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="context.ecv2_class"></a><a name="ecv2"></a><a class="link" href="ecv2_class.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_class.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_class.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 cotnrol 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 to deallocate context'
  88       stack via the <span class="emphasis"><em>StackAllocator</em></span>. The stack walking makes
  89       the destruction of <span class="emphasis"><em>execution_context</em></span> very slow and should
  90       be prevented if possible.
  91     </p>
  92 <p>
  93       <span class="emphasis"><em>execution_context</em></span> expects a function/functor with signature
  94       <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">(</span><span class="identifier">execution_context</span> <span class="identifier">ctx</span><span class="special">,</span> <span class="keyword">void</span><span class="special">*</span>
  95       <span class="identifier">vp</span><span class="special">)</span></code>.
  96       The parameter <code class="computeroutput"><span class="identifier">ctx</span></code> represents
  97       the context from which this context was resumed (e.g. that has called <span class="emphasis"><em>execution_context::operator()</em></span>
  98       on <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>)
  99       and <code class="computeroutput"><span class="identifier">vp</span></code> is the data passed to
 100       <span class="emphasis"><em>execution_context::operator()</em></span>. The return value is the
 101       execution_context that has to be resumed, while this context terminates.
 102     </p>
 103 <h4>
 104 <a name="context.ecv2_class.h0"></a>
 105       <span><a name="context.ecv2_class.usage_of__emphasis_execution_context__emphasis_"></a></span><a class="link" href="ecv2_class.html#context.ecv2_class.usage_of__emphasis_execution_context__emphasis_">usage
 106       of <span class="emphasis"><em>execution_context</em></span></a>
 107     </h4>
 108 <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>
 109 <span class="identifier">ctx</span><span class="special">::</span><span class="identifier">execution_context</span> <span class="identifier">source</span><span class="special">(</span>
 110     <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="identifier">sink</span><span class="special">,</span><span class="keyword">void</span><span class="special">*)</span><span class="keyword">mutable</span><span class="special">{</span>
 111         <span class="keyword">int</span> <span class="identifier">a</span><span class="special">=</span><span class="number">0</span><span class="special">;</span>
 112         <span class="keyword">int</span> <span class="identifier">b</span><span class="special">=</span><span class="number">1</span><span class="special">;</span>
 113         <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>
 114             <span class="keyword">auto</span> <span class="identifier">result</span><span class="special">=</span><span class="identifier">sink</span><span class="special">(&amp;</span><span class="identifier">a</span><span class="special">);</span>
 115             <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>
 116             <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>
 117             <span class="identifier">a</span><span class="special">=</span><span class="identifier">b</span><span class="special">;</span>
 118             <span class="identifier">b</span><span class="special">=</span><span class="identifier">next</span><span class="special">;</span>
 119         <span class="special">}</span>
 120         <span class="keyword">return</span> <span class="identifier">sink</span><span class="special">;</span>
 121     <span class="special">});</span>
 122 <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>
 123     <span class="keyword">auto</span> <span class="identifier">result</span><span class="special">=</span><span class="identifier">source</span><span class="special">();</span>
 124     <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>
 125     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">&lt;&lt;*(</span><span class="keyword">int</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">)&lt;&lt;</span><span class="string">" "</span><span class="special">;</span>
 126 <span class="special">}</span>
 127
 128 <span class="identifier">output</span><span class="special">:</span>
 129     <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>
 130 </pre>
 131 <p>
 132       This simple example demonstrates the basic usage of <span class="emphasis"><em>execution_context</em></span>.
 133       The context <code class="computeroutput"><span class="identifier">sink</span></code> represents
 134       the <span class="emphasis"><em>main</em></span>-context (function <span class="emphasis"><em>main()</em></span>
 135       running). <code class="computeroutput"><span class="identifier">sink</span></code> is generated
 136       by the framework (first element of lambda's parameter list). Because the state
 137       is invalidated (== changed) by each call of <span class="emphasis"><em>execution_context::operator()</em></span>,
 138       <code class="computeroutput"><span class="identifier">sink</span></code> has to be assigned the
 139       new state of the <span class="emphasis"><em>execution_context</em></span> returned by <span class="emphasis"><em>execution_context::operator()</em></span>.
 140     </p>
 141 <p>
 142       The lambda that calculates the Fibonacci numbers is executed inside the context
 143       represented by <code class="computeroutput"><span class="identifier">source</span></code>. Calculated
 144       Fibonacci numbers are transferred between the two context' via expression
 145       <span class="emphasis"><em>sink(&amp;a)</em></span> (and returned by <span class="emphasis"><em>source()</em></span>).
 146     </p>
 147 <p>
 148       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>
 149       remain their values during each context switch (<span class="emphasis"><em>yield(a)</em></span>).
 150       This is possible due <code class="computeroutput"><span class="identifier">ctx</span></code> has
 151       its own stack and the stack is exchanged by each context switch.
 152     </p>
 153 <h4>
 154 <a name="context.ecv2_class.h1"></a>
 155       <span><a name="context.ecv2_class.inverting_the_control_flow"></a></span><a class="link" href="ecv2_class.html#context.ecv2_class.inverting_the_control_flow">inverting
 156       the control flow</a>
 157     </h4>
 158 <pre class="programlisting"><span class="comment">/*
 159  * grammar:
 160  *   P ---&gt; E '\0'
 161  *   E ---&gt; T {('+'|'-') T}
 162  *   T ---&gt; S {('*'|'/') S}
 163  *   S ---&gt; digit | '(' E ')'
 164  */</span>
 165 <span class="keyword">class</span> <span class="identifier">Parser</span><span class="special">{</span>
 166     <span class="comment">// implementation omitted; see examples directory</span>
 167 <span class="special">};</span>
 168
 169 <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>
 170 <span class="keyword">bool</span> <span class="identifier">done</span><span class="special">=</span><span class="keyword">false</span><span class="special">;</span>
 171 <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span> <span class="identifier">except</span><span class="special">;</span>
 172
 173 <span class="comment">// execute parser in new execution context</span>
 174 <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="identifier">source</span><span class="special">(</span>
 175         <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="identifier">sink</span><span class="special">,</span><span class="keyword">void</span><span class="special">*){</span>
 176         <span class="comment">// create parser with callback function</span>
 177         <span class="identifier">Parser</span> <span class="identifier">p</span><span class="special">(</span> <span class="identifier">is</span><span class="special">,</span>
 178                   <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>
 179                         <span class="comment">// resume main execution context</span>
 180                         <span class="keyword">auto</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">sink</span><span class="special">(&amp;</span><span class="identifier">ch</span><span class="special">);</span>
 181                         <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>
 182                 <span class="special">});</span>
 183             <span class="keyword">try</span> <span class="special">{</span>
 184                 <span class="comment">// start recursive parsing</span>
 185                 <span class="identifier">p</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span>
 186             <span class="special">}</span> <span class="keyword">catch</span> <span class="special">(...)</span> <span class="special">{</span>
 187                 <span class="comment">// store other exceptions in exception-pointer</span>
 188                 <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>
 189             <span class="special">}</span>
 190             <span class="comment">// set termination flag</span>
 191             <span class="identifier">done</span><span class="special">=</span><span class="keyword">true</span><span class="special">;</span>
 192             <span class="comment">// resume main execution context</span>
 193             <span class="keyword">return</span> <span class="identifier">sink</span><span class="special">;</span>
 194         <span class="special">});</span>
 195
 196 <span class="comment">// user-code pulls parsed data from parser</span>
 197 <span class="comment">// invert control flow</span>
 198 <span class="keyword">auto</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">source</span><span class="special">();</span>
 199 <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>
 200 <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">vp</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>
 201 <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">except</span><span class="special">)</span> <span class="special">{</span>
 202     <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>
 203 <span class="special">}</span>
 204 <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>
 205     <span class="identifier">printf</span><span class="special">(</span><span class="string">"Parsed: %c\n"</span><span class="special">,*</span> <span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">*&gt;(</span><span class="identifier">vp</span><span class="special">));</span>
 206     <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">vp</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">source</span><span class="special">();</span>
 207     <span class="keyword">if</span> <span class="special">(</span><span class="identifier">except</span><span class="special">)</span> <span class="special">{</span>
 208         <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>
 209     <span class="special">}</span>
 210 <span class="special">}</span>
 211
 212 <span class="identifier">output</span><span class="special">:</span>
 213     <span class="identifier">Parsed</span><span class="special">:</span> <span class="number">1</span>
 214     <span class="identifier">Parsed</span><span class="special">:</span> <span class="special">+</span>
 215     <span class="identifier">Parsed</span><span class="special">:</span> <span class="number">1</span>
 216 </pre>
 217 <p>
 218       In this example a recursive descent parser uses a callback to emit a newly
 219       passed symbol. Using <span class="emphasis"><em>execution_context</em></span> the control flow
 220       can be inverted, e.g. the user-code pulls parsed symbols from the parser -
 221       instead to get pushed from the parser (via callback).
 222     </p>
 223 <p>
 224       The data (character) is transferred between the two <span class="emphasis"><em>execution_context</em></span>.
 225     </p>
 226 <p>
 227       If the code executed by <span class="emphasis"><em>execution_context</em></span> emits an exception,
 228       the application is terminated. <span class="emphasis"><em>std::exception_ptr</em></span> can
 229       be used to transfer exceptions between different execution contexts.
 230     </p>
 231 <p>
 232       Sometimes it is necessary to unwind the stack of an unfinished context to destroy
 233       local stack variables so they can release allocated resources (RAII pattern).
 234       The user is responsible for this task.
 235     </p>
 236 <a name="ecv2_prealloc"></a><h4>
 237 <a name="context.ecv2_class.h2"></a>
 238       <span><a name="context.ecv2_class.allocating_control_structures_on_top_of_stack"></a></span><a class="link" href="ecv2_class.html#context.ecv2_class.allocating_control_structures_on_top_of_stack">allocating
 239       control structures on top of stack</a>
 240     </h4>
 241 <p>
 242       Allocating control structures on top of the stack requires to allocated the
 243       <span class="emphasis"><em>stack_context</em></span> and create the control structure with placement
 244       new before <span class="emphasis"><em>execution_context</em></span> is created.
 245     </p>
 246 <div class="note"><table border="0" summary="Note">
 247 <tr>
 248 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
 249 <th align="left">Note</th>
 250 </tr>
 251 <tr><td align="left" valign="top"><p>
 252         The user is responsible for destructing the control structure at the top
 253         of the stack.
 254       </p></td></tr>
 255 </table></div>
 256 <pre class="programlisting"><span class="comment">// stack-allocator used for (de-)allocating stack</span>
 257 <span class="identifier">fixedsize_stack</span> <span class="identifier">salloc</span><span class="special">(</span> <span class="number">4048</span><span class="special">);</span>
 258 <span class="comment">// allocate stack space</span>
 259 <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>
 260 <span class="comment">// reserve space for control structure on top of the stack</span>
 261 <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>
 262 <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>
 263 <span class="comment">// placement new creates control structure on reserved space</span>
 264 <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>
 265 <span class="special">...</span>
 266 <span class="comment">// destructing the control structure</span>
 267 <span class="identifier">cs</span><span class="special">-&gt;~</span><span class="identifier">my_control_structure</span><span class="special">();</span>
 268 <span class="special">...</span>
 269 <span class="keyword">struct</span> <span class="identifier">my_control_structure</span>  <span class="special">{</span>
 270     <span class="comment">// captured context</span>
 271     <span class="identifier">execution_context</span> <span class="identifier">cctx</span><span class="special">;</span>
 272
 273     <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>
 274     <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>
 275         <span class="comment">// create captured context</span>
 276         <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>
 277     <span class="special">}</span>
 278     <span class="special">...</span>
 279 <span class="special">};</span>
 280 </pre>
 281 <h4>
 282 <a name="context.ecv2_class.h3"></a>
 283       <span><a name="context.ecv2_class.exception_handling"></a></span><a class="link" href="ecv2_class.html#context.ecv2_class.exception_handling">exception
 284       handling</a>
 285     </h4>
 286 <p>
 287       If the function executed inside a <span class="emphasis"><em>execution_context</em></span> emits
 288       ans exception, the application is terminated by calling <span class="emphasis"><em>std::terminate()</em></span>.
 289       <span class="emphasis"><em>std::exception_ptr</em></span> can be used to transfer exceptions
 290       between different execution contexts.
 291     </p>
 292 <h4>
 293 <a name="context.ecv2_class.h4"></a>
 294       <span><a name="context.ecv2_class.parameter_passing"></a></span><a class="link" href="ecv2_class.html#context.ecv2_class.parameter_passing">parameter
 295       passing</a>
 296     </h4>
 297 <p>
 298       The void pointer argument passed to <span class="emphasis"><em>execution_context::operator()</em></span>,
 299       in one context, is passed as the last argument of the <span class="emphasis"><em>context-function</em></span>
 300       if the context is started for the first time. In all following invocations
 301       of <span class="emphasis"><em>execution_context::operator()</em></span> the void pointer passed
 302       to <span class="emphasis"><em>execution_context::operator()</em></span>, in one context, is returned
 303       by <span class="emphasis"><em>execution_context::operator()</em></span> in the other context.
 304     </p>
 305 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">X</span> <span class="special">{</span>
 306 <span class="keyword">private</span><span class="special">:</span>
 307     <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span> <span class="identifier">excptr_</span><span class="special">;</span>
 308     <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="identifier">ctx_</span><span class="special">;</span>
 309
 310 <span class="keyword">public</span><span class="special">:</span>
 311     <span class="identifier">X</span><span class="special">()</span> <span class="special">:</span>
 312         <span class="identifier">excptr_</span><span class="special">(),</span>
 313         <span class="identifier">ctx_</span><span class="special">([=](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">execution_context</span> <span class="identifier">ctx</span><span class="special">,</span> <span class="keyword">void</span><span class="special">*</span> <span class="identifier">vp</span><span class="special">)</span><span class="keyword">mutable</span><span class="special">{</span>
 314                     <span class="keyword">try</span> <span class="special">{</span>
 315                         <span class="keyword">for</span> <span class="special">(;;)</span> <span class="special">{</span>
 316                             <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">*</span> <span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">*&gt;(</span><span class="identifier">vp</span><span class="special">);</span>
 317                             <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">str</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>
 318                             <span class="keyword">auto</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">ctx</span><span class="special">(&amp;</span> <span class="identifier">str</span><span class="special">);</span>
 319                             <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>
 320                             <span class="identifier">vp</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>
 321                         <span class="special">}</span>
 322                     <span class="special">}</span> <span class="keyword">catch</span> <span class="special">(</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">forced_unwind</span> <span class="keyword">const</span><span class="special">&amp;)</span> <span class="special">{</span>
 323                         <span class="keyword">throw</span><span class="special">;</span>
 324                     <span class="special">}</span> <span class="keyword">catch</span> <span class="special">(...)</span> <span class="special">{</span>
 325                         <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>
 326                     <span class="special">}</span>
 327                     <span class="keyword">return</span> <span class="identifier">ctx</span><span class="special">;</span>
 328              <span class="special">})</span>
 329     <span class="special">{}</span>
 330
 331     <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> <span class="special">{</span>
 332         <span class="keyword">auto</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">ctx_</span><span class="special">(&amp;</span><span class="identifier">i</span><span class="special">);</span>
 333         <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>
 334         <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">ret</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>
 335         <span class="keyword">if</span><span class="special">(</span><span class="identifier">excptr_</span><span class="special">){</span>
 336             <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>
 337         <span class="special">}</span>
 338         <span class="keyword">return</span> <span class="special">*</span> <span class="keyword">static_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">ret</span><span class="special">);</span>
 339     <span class="special">}</span>
 340 <span class="special">};</span>
 341
 342 <span class="identifier">X</span> <span class="identifier">x</span><span class="special">;</span>
 343 <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>
 344
 345 <span class="identifier">output</span><span class="special">:</span>
 346 <span class="number">7</span>
 347 </pre>
 348 <h4>
 349 <a name="context.ecv2_class.h5"></a>
 350       <span><a name="context.ecv2_class.class__code__phrase_role__identifier__execution_context__phrase___code_"></a></span><a class="link" href="ecv2_class.html#context.ecv2_class.class__code__phrase_role__identifier__execution_context__phrase___code_">Class
 351       <code class="computeroutput"><span class="identifier">execution_context</span></code></a>
 352     </h4>
 353 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">execution_context</span> <span class="special">{</span>
 354 <span class="keyword">public</span><span class="special">:</span>
 355     <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">Args</span> <span class="special">&gt;</span>
 356     <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">Args</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 357
 358     <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">Args</span> <span class="special">&gt;</span>
 359     <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">Args</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 360
 361     <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">Args</span> <span class="special">&gt;</span>
 362     <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">Args</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 363
 364
 365     <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">Args</span> <span class="special">&gt;</span>
 366     <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">Args</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
 367
 368     <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">Args</span> <span class="special">&gt;</span>
 369     <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">Args</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">)=</span> <span class="keyword">delete</span><span class="special">;</span>
 370     <span class="special">~</span><span class="identifier">execution_context</span><span class="special">();</span>
 371
 372     <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>
 373     <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>
 374
 375     <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>
 376     <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>
 377
 378     <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>
 379     <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>
 380
 381     <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="keyword">void</span> <span class="special">*</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">data</span> <span class="special">=</span> <span class="keyword">nullptr</span><span class="special">);</span>
 382
 383     <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">Args</span> <span class="special">&gt;</span>
 384     <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="keyword">void</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">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 385
 386     <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">Args</span> <span class="special">&gt;</span>
 387     <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="keyword">void</span> <span class="special">*</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">data</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">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 388
 389     <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>
 390
 391     <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>
 392
 393     <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>
 394
 395     <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>
 396
 397     <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>
 398
 399     <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>
 400
 401     <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>
 402     <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>
 403     <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>
 404 <span class="special">};</span>
 405 </pre>
 406 <p>
 407       </p>
 408 <h5>
 409 <a name="ecv2_constructor_bridgehead"></a>
 410   <span><a name="ecv2_constructor"></a></span>
 411   <a class="link" href="ecv2_class.html#ecv2_constructor">Constructor</a>
 412 </h5>
 413 <p>
 414     </p>
 415 <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">Args</span> <span class="special">&gt;</span>
 416 <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">Args</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 417
 418 <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">Args</span> <span class="special">&gt;</span>
 419 <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">Args</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 420
 421 <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">Args</span> <span class="special">&gt;</span>
 422 <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">Args</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 423 </pre>
 424 <div class="variablelist">
 425 <p class="title"><b></b></p>
 426 <dl>
 427 <dt><span class="term">Effects:</span></dt>
 428 <dd><p>
 429             Creates a new execution context and prepares the context to execute
 430             <code class="computeroutput"><span class="identifier">fn</span></code>. <code class="computeroutput"><span class="identifier">fixedsize_stack</span></code>
 431             is used as default stack allocator (stack size == fixedsize_stack::traits::default_size()).
 432             The constructor with argument type <code class="computeroutput"><span class="identifier">preallocated</span></code>,
 433             is used to create a user defined data <a class="link" href="../">(for
 434             instance additional control structures)</a> on top of the stack.
 435           </p></dd>
 436 </dl>
 437 </div>
 438 <p>
 439       </p>
 440 <h5>
 441 <a name="ecv2_move%20constructor_bridgehead"></a>
 442   <span><a name="ecv2_move%20constructor"></a></span>
 443   <a class="link" href="ecv2_class.html#ecv2_move%20constructor">Move
 444       constructor</a>
 445 </h5>
 446 <p>
 447     </p>
 448 <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>
 449 </pre>
 450 <div class="variablelist">
 451 <p class="title"><b></b></p>
 452 <dl>
 453 <dt><span class="term">Effects:</span></dt>
 454 <dd><p>
 455             Moves underlying capture record to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
 456           </p></dd>
 457 <dt><span class="term">Throws:</span></dt>
 458 <dd><p>
 459             Nothing.
 460           </p></dd>
 461 </dl>
 462 </div>
 463 <p>
 464       </p>
 465 <h5>
 466 <a name="ecv2_move%20assignment_bridgehead"></a>
 467   <span><a name="ecv2_move%20assignment"></a></span>
 468   <a class="link" href="ecv2_class.html#ecv2_move%20assignment">Move
 469       assignment operator</a>
 470 </h5>
 471 <p>
 472     </p>
 473 <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>
 474 </pre>
 475 <div class="variablelist">
 476 <p class="title"><b></b></p>
 477 <dl>
 478 <dt><span class="term">Effects:</span></dt>
 479 <dd><p>
 480             Moves the state of <code class="computeroutput"><span class="identifier">other</span></code>
 481             to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 482             using move semantics.
 483           </p></dd>
 484 <dt><span class="term">Throws:</span></dt>
 485 <dd><p>
 486             Nothing.
 487           </p></dd>
 488 </dl>
 489 </div>
 490 <p>
 491       </p>
 492 <h5>
 493 <a name="ecv2_operator_bool_bridgehead"></a>
 494   <span><a name="ecv2_operator_bool"></a></span>
 495   <a class="link" href="ecv2_class.html#ecv2_operator_bool">Member function
 496       <code class="computeroutput">operator bool</code>()</a>
 497 </h5>
 498 <p>
 499     </p>
 500 <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>
 501 </pre>
 502 <div class="variablelist">
 503 <p class="title"><b></b></p>
 504 <dl>
 505 <dt><span class="term">Returns:</span></dt>
 506 <dd><p>
 507             <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.
 508           </p></dd>
 509 <dt><span class="term">Throws:</span></dt>
 510 <dd><p>
 511             Nothing.
 512           </p></dd>
 513 </dl>
 514 </div>
 515 <p>
 516       </p>
 517 <h5>
 518 <a name="ecv2_operator_not_bridgehead"></a>
 519   <span><a name="ecv2_operator_not"></a></span>
 520   <a class="link" href="ecv2_class.html#ecv2_operator_not">Member function
 521       <code class="computeroutput">operator!</code>()</a>
 522 </h5>
 523 <p>
 524     </p>
 525 <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>
 526 </pre>
 527 <div class="variablelist">
 528 <p class="title"><b></b></p>
 529 <dl>
 530 <dt><span class="term">Returns:</span></dt>
 531 <dd><p>
 532             <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.
 533           </p></dd>
 534 <dt><span class="term">Throws:</span></dt>
 535 <dd><p>
 536             Nothing.
 537           </p></dd>
 538 </dl>
 539 </div>
 540 <p>
 541       </p>
 542 <h5>
 543 <a name="ecv2_operator_call_bridgehead"></a>
 544   <span><a name="ecv2_operator_call"></a></span>
 545   <a class="link" href="ecv2_class.html#ecv2_operator_call">Member function
 546       <code class="computeroutput">operator()</code>()</a>
 547 </h5>
 548 <p>
 549     </p>
 550 <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">,</span> <span class="keyword">void</span> <span class="special">*</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">data</span> <span class="special">=</span> <span class="keyword">nullptr</span><span class="special">);</span>
 551 </pre>
 552 <div class="variablelist">
 553 <p class="title"><b></b></p>
 554 <dl>
 555 <dt><span class="term">Effects:</span></dt>
 556 <dd><p>
 557             Stores internally the current context data (stack pointer, instruction
 558             pointer, and CPU registers) of the current active context and restores
 559             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
 560             context. The void pointer argument, <code class="computeroutput"><span class="identifier">vp</span></code>,
 561             is passed to the current context to be returned by the most recent call
 562             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. <code class="computeroutput"><span class="identifier">fn</span></code>
 563             is executed with arguments <code class="computeroutput"><span class="identifier">args</span></code>
 564             on top of the stack of <code class="computeroutput"><span class="keyword">this</span></code>.
 565           </p></dd>
 566 <dt><span class="term">Note:</span></dt>
 567 <dd><p>
 568             The behaviour is undefined if <code class="computeroutput"><span class="keyword">operator</span><span class="special">()()</span></code> is called while <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="identifier">current</span><span class="special">()</span></code> returns <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> (e.g. resuming an already running
 569             context). If the top-level context function returns, <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">exit</span><span class="special">()</span></code> is called.
 570           </p></dd>
 571 <dt><span class="term">Returns:</span></dt>
 572 <dd><p>
 573             The tuple of void pointer argument passed to the most recent call to
 574             <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code>,
 575             if any and a execution_context representing the context that has been
 576             suspended .
 577           </p></dd>
 578 </dl>
 579 </div>
 580 <p>
 581       </p>
 582 <h5>
 583 <a name="ecv2_operator_call_ontop_bridgehead"></a>
 584   <span><a name="ecv2_operator_call_ontop"></a></span>
 585   <a class="link" href="ecv2_class.html#ecv2_operator_call_ontop">Member
 586       function <code class="computeroutput">operator()</code>()</a>
 587 </h5>
 588 <p>
 589     </p>
 590 <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">Args</span> <span class="special">&gt;</span>
 591 <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="keyword">void</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">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 592
 593 <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">Args</span> <span class="special">&gt;</span>
 594 <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="keyword">void</span> <span class="special">*</span> <span class="special">&gt;</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">data</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">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 595 </pre>
 596 <div class="variablelist">
 597 <p class="title"><b></b></p>
 598 <dl>
 599 <dt><span class="term">Effects:</span></dt>
 600 <dd><p>
 601             Same as <span class="emphasis"><em>execution_context::operator()</em></span>. Additionally,
 602             function <code class="computeroutput"><span class="identifier">fn</span></code> is executed
 603             with arguments <code class="computeroutput"><span class="identifier">args</span></code> in
 604             the context of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 605             (e.g. the stack frame of <code class="computeroutput"><span class="identifier">fn</span></code>
 606             is allocated on stack of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>).
 607           </p></dd>
 608 <dt><span class="term">Returns:</span></dt>
 609 <dd><p>
 610             The tuple of void pointer argument passed to the most recent call to
 611             <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code>,
 612             if any and a execution_context representing the context that has been
 613             suspended .
 614           </p></dd>
 615 </dl>
 616 </div>
 617 <p>
 618       </p>
 619 <h5>
 620 <a name="ecv2_operator_equal_bridgehead"></a>
 621   <span><a name="ecv2_operator_equal"></a></span>
 622   <a class="link" href="ecv2_class.html#ecv2_operator_equal">Member
 623       function <code class="computeroutput">operator==</code>()</a>
 624 </h5>
 625 <p>
 626     </p>
 627 <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>
 628 </pre>
 629 <div class="variablelist">
 630 <p class="title"><b></b></p>
 631 <dl>
 632 <dt><span class="term">Returns:</span></dt>
 633 <dd><p>
 634             <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>
 635             represent the same execution context, <code class="computeroutput"><span class="keyword">false</span></code>
 636             otherwise.
 637           </p></dd>
 638 <dt><span class="term">Throws:</span></dt>
 639 <dd><p>
 640             Nothing.
 641           </p></dd>
 642 </dl>
 643 </div>
 644 <p>
 645       </p>
 646 <h5>
 647 <a name="ecv2_operator_notequal_bridgehead"></a>
 648   <span><a name="ecv2_operator_notequal"></a></span>
 649   <a class="link" href="ecv2_class.html#ecv2_operator_notequal">Member
 650       function <code class="computeroutput">operator!=</code>()</a>
 651 </h5>
 652 <p>
 653     </p>
 654 <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>
 655 </pre>
 656 <div class="variablelist">
 657 <p class="title"><b></b></p>
 658 <dl>
 659 <dt><span class="term">Returns:</span></dt>
 660 <dd><p>
 661             <code class="computeroutput">! (other == * this)</code>
 662           </p></dd>
 663 <dt><span class="term">Throws:</span></dt>
 664 <dd><p>
 665             Nothing.
 666           </p></dd>
 667 </dl>
 668 </div>
 669 <p>
 670       </p>
 671 <h5>
 672 <a name="ecv2_operator_less_bridgehead"></a>
 673   <span><a name="ecv2_operator_less"></a></span>
 674   <a class="link" href="ecv2_class.html#ecv2_operator_less">Member function
 675       <code class="computeroutput">operator&lt;</code>()</a>
 676 </h5>
 677 <p>
 678     </p>
 679 <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>
 680 </pre>
 681 <div class="variablelist">
 682 <p class="title"><b></b></p>
 683 <dl>
 684 <dt><span class="term">Returns:</span></dt>
 685 <dd><p>
 686             <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
 687             total order of <code class="computeroutput"><span class="identifier">execution_context</span></code>
 688             values places <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 689             before <code class="computeroutput"><span class="identifier">other</span></code>, false otherwise.
 690           </p></dd>
 691 <dt><span class="term">Throws:</span></dt>
 692 <dd><p>
 693             Nothing.
 694           </p></dd>
 695 </dl>
 696 </div>
 697 <p>
 698       </p>
 699 <h5>
 700 <a name="ecv2_operator_greater_bridgehead"></a>
 701   <span><a name="ecv2_operator_greater"></a></span>
 702   <a class="link" href="ecv2_class.html#ecv2_operator_greater">Member
 703       function <code class="computeroutput">operator&gt;</code>()</a>
 704 </h5>
 705 <p>
 706     </p>
 707 <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>
 708 </pre>
 709 <div class="variablelist">
 710 <p class="title"><b></b></p>
 711 <dl>
 712 <dt><span class="term">Returns:</span></dt>
 713 <dd><p>
 714             <code class="computeroutput"><span class="identifier">other</span> <span class="special">&lt;</span>
 715             <span class="special">*</span> <span class="keyword">this</span></code>
 716           </p></dd>
 717 <dt><span class="term">Throws:</span></dt>
 718 <dd><p>
 719             Nothing.
 720           </p></dd>
 721 </dl>
 722 </div>
 723 <p>
 724       </p>
 725 <h5>
 726 <a name="ecv2_operator_lesseq_bridgehead"></a>
 727   <span><a name="ecv2_operator_lesseq"></a></span>
 728   <a class="link" href="ecv2_class.html#ecv2_operator_lesseq">Member
 729       function <code class="computeroutput">operator&lt;=</code>()</a>
 730 </h5>
 731 <p>
 732     </p>
 733 <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>
 734 </pre>
 735 <div class="variablelist">
 736 <p class="title"><b></b></p>
 737 <dl>
 738 <dt><span class="term">Returns:</span></dt>
 739 <dd><p>
 740             <code class="computeroutput"><span class="special">!</span> <span class="special">(</span><span class="identifier">other</span> <span class="special">&lt;</span>
 741             <span class="special">*</span> <span class="keyword">this</span><span class="special">)</span></code>
 742           </p></dd>
 743 <dt><span class="term">Throws:</span></dt>
 744 <dd><p>
 745             Nothing.
 746           </p></dd>
 747 </dl>
 748 </div>
 749 <p>
 750       </p>
 751 <h5>
 752 <a name="ecv2_operator_greatereq_bridgehead"></a>
 753   <span><a name="ecv2_operator_greatereq"></a></span>
 754   <a class="link" href="ecv2_class.html#ecv2_operator_greatereq">Member
 755       function <code class="computeroutput">operator&gt;=</code>()</a>
 756 </h5>
 757 <p>
 758     </p>
 759 <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>
 760 </pre>
 761 <div class="variablelist">
 762 <p class="title"><b></b></p>
 763 <dl>
 764 <dt><span class="term">Returns:</span></dt>
 765 <dd><p>
 766             <code class="computeroutput"><span class="special">!</span> <span class="special">(*</span>
 767             <span class="keyword">this</span> <span class="special">&lt;</span>
 768             <span class="identifier">other</span><span class="special">)</span></code>
 769           </p></dd>
 770 <dt><span class="term">Throws:</span></dt>
 771 <dd><p>
 772             Nothing.
 773           </p></dd>
 774 </dl>
 775 </div>
 776 <p>
 777       </p>
 778 <h5>
 779 <a name="ecv2_bridgehead"></a>
 780   <span><a name="ecv2"></a></span>
 781   <a class="link" href="ecv2_class.html#ecv2">Non-member function <code class="computeroutput">operator&lt;&lt;()</code></a>
 782 </h5>
 783 <p>
 784     </p>
 785 <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>
 786 <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>
 787 <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>
 788 </pre>
 789 <div class="variablelist">
 790 <p class="title"><b></b></p>
 791 <dl>
 792 <dt><span class="term">Efects:</span></dt>
 793 <dd><p>
 794             Writes the representation of <code class="computeroutput"><span class="identifier">other</span></code>
 795             to stream <code class="computeroutput"><span class="identifier">os</span></code>.
 796           </p></dd>
 797 <dt><span class="term">Returns:</span></dt>
 798 <dd><p>
 799             <code class="computeroutput"><span class="identifier">os</span></code>
 800           </p></dd>
 801 </dl>
 802 </div>
 803 </div>
 804 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 805 <td align="left"></td>
 806 <td align="right"><div class="copyright-footer">Copyright &#169; 2014 Oliver Kowalke<p>
 807         Distributed under the Boost Software License, Version 1.0. (See accompanying
 808         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>)
 809       </p>
 810 </div></td>
 811 </tr></table>
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