1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Context switching with fibers</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Chapter 1. Context"> 8<link rel="up" href="../index.html" title="Chapter 1. Context"> 9<link rel="prev" href="requirements.html" title="Requirements"> 10<link rel="next" href="ff/implementations__fcontext_t__ucontext_t_and_winfiber.html" title="Implementations: fcontext_t, ucontext_t and WinFiber"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<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="ff/implementations__fcontext_t__ucontext_t_and_winfiber.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="context.ff"></a><a name="ff"></a><a class="link" href="ff.html" title="Context switching with fibers">Context switching with fibers</a> 28</h2></div></div></div> 29<div class="toc"><dl class="toc"> 30<dt><span class="section"><a href="ff/implementations__fcontext_t__ucontext_t_and_winfiber.html">Implementations: 31 fcontext_t, ucontext_t and WinFiber</a></span></dt> 32<dt><span class="section"><a href="ff/class__fiber_.html">Class <code class="computeroutput"><span class="identifier">fiber</span></code></a></span></dt> 33</dl></div> 34<div class="note"><table border="0" summary="Note"> 35<tr> 36<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> 37<th align="left">Note</th> 38</tr> 39<tr><td align="left" valign="top"><p> 40 <span class="emphasis"><em>fiber</em></span> is the reference implementation of C++ proposal 41 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0876r0.pdf" target="_top">P0876R0: 42 fibers without scheduler</a>. 43 </p></td></tr> 44</table></div> 45<p> 46 A <span class="emphasis"><em>fiber</em></span> represents the state of the control flow of a 47 program at a given point in time. Fibers can be suspended and resumed later 48 in order to change the control flow of a program. 49 </p> 50<p> 51 Modern micro-processors are registers machines; the content of processor registers 52 represent a fiber of the executed program at a given point in time. Operating 53 systems simulate parallel execution of programs on a single processor by switching 54 between programs (context switch) by preserving and restoring the fiber, e.g. 55 the content of all registers. 56 </p> 57<h4> 58<a name="context.ff.h0"></a> 59 <span class="phrase"><a name="context.ff._link_linkend__ff___emphasis_fiber__emphasis___link_"></a></span><a class="link" href="ff.html#context.ff._link_linkend__ff___emphasis_fiber__emphasis___link_"><span class="emphasis"><em>fiber</em></span></a> 60 </h4> 61<p> 62 <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> captures the current fiber 63 (the rest of the computation; code after <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a>) 64 and triggers a context switch. The context switch is achieved by preserving 65 certain registers (including instruction and stack pointer), defined by the 66 calling convention of the ABI, of the current fiber and restoring those registers 67 of the resumed fiber. The control flow of the resumed fiber continues. The 68 current fiber is suspended and passed as argument to the resumed fiber. 69 </p> 70<p> 71 <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> expects a <span class="emphasis"><em>context-function</em></span> 72 with signature <code class="computeroutput"><span class="char">'fiber(fiber && f)'</span></code>. 73 The parameter <code class="computeroutput"><span class="identifier">f</span></code> represents 74 the current fiber from which this fiber was resumed (e.g. that has called 75 <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a>). 76 </p> 77<p> 78 On return the <span class="emphasis"><em>context-function</em></span> of the current fiber has 79 to specify an <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> to which 80 the execution control is transferred after termination of the current fiber. 81 </p> 82<p> 83 If an instance with valid state goes out of scope and the <span class="emphasis"><em>context-function</em></span> 84 has not yet returned, the stack is traversed in order to access the control 85 structure (address stored at the first stack frame) and fiber's stack is deallocated 86 via the <span class="emphasis"><em>StackAllocator</em></span>. 87 </p> 88<div class="note"><table border="0" summary="Note"> 89<tr> 90<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> 91<th align="left">Note</th> 92</tr> 93<tr><td align="left" valign="top"><p> 94 <a class="link" href="stack/segmented.html#segmented"><span class="emphasis"><em>Segmented stacks</em></span></a> are 95 supported by <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> using 96 <a class="link" href="ff/implementations__fcontext_t__ucontext_t_and_winfiber.html#implementation"><span class="emphasis"><em>ucontext_t</em></span></a>. 97 </p></td></tr> 98</table></div> 99<p> 100 <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> represents a <span class="emphasis"><em>fiber</em></span>; 101 it contains the content of preserved registers and manages the associated stack 102 (allocation/deallocation). <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> 103 is a one-shot fiber - it can be used only once, after calling <span class="emphasis"><em>continuation::resume()</em></span> 104 or <span class="emphasis"><em>continuation::resume_with()</em></span> it is invalidated. 105 </p> 106<p> 107 <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> is only move-constructible 108 and move-assignable. 109 </p> 110<p> 111 As a first-class object <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> 112 can be applied to and returned from a function, assigned to a variable or stored 113 in a container. 114 </p> 115<p> 116 A fiber is continued by calling <code class="computeroutput"><span class="identifier">resume</span><span class="special">()</span></code>/<code class="computeroutput"><span class="identifier">resume_with</span><span class="special">()</span></code>. 117 </p> 118<h4> 119<a name="context.ff.h1"></a> 120 <span class="phrase"><a name="context.ff.usage"></a></span><a class="link" href="ff.html#context.ff.usage">Usage</a> 121 </h4> 122<pre class="programlisting"><span class="keyword">namespace</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> 123<span class="keyword">int</span> <span class="identifier">a</span><span class="special">;</span> 124<span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="identifier">source</span><span class="special">{[&</span><span class="identifier">a</span><span class="special">](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span><span class="special">&&</span> <span class="identifier">sink</span><span class="special">){</span> 125 <span class="identifier">a</span><span class="special">=</span><span class="number">0</span><span class="special">;</span> 126 <span class="keyword">int</span> <span class="identifier">b</span><span class="special">=</span><span class="number">1</span><span class="special">;</span> 127 <span class="keyword">for</span><span class="special">(;;){</span> 128 <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">sink</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 129 <span class="keyword">int</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> 130 <span class="identifier">a</span><span class="special">=</span><span class="identifier">b</span><span class="special">;</span> 131 <span class="identifier">b</span><span class="special">=</span><span class="identifier">next</span><span class="special">;</span> 132 <span class="special">}</span> 133 <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">sink</span><span class="special">);</span> 134<span class="special">}};</span> 135<span class="keyword">for</span> <span class="special">(</span><span class="keyword">int</span> <span class="identifier">j</span><span class="special">=</span><span class="number">0</span><span class="special">;</span><span class="identifier">j</span><span class="special"><</span><span class="number">10</span><span class="special">;++</span><span class="identifier">j</span><span class="special">)</span> <span class="special">{</span> 136 <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">source</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 137 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">a</span> <span class="special"><<</span> <span class="string">" "</span><span class="special">;</span> 138<span class="special">}</span> 139 140<span class="identifier">output</span><span class="special">:</span> 141 <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> 142</pre> 143<p> 144 This simple example demonstrates the basic usage of <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> 145 as a <span class="emphasis"><em>generator</em></span>. The fiber <code class="computeroutput"><span class="identifier">sink</span></code> 146 represents the <span class="emphasis"><em>main</em></span>-fiber (function <code class="computeroutput"><span class="identifier">main</span><span class="special">()</span></code>). <code class="computeroutput"><span class="identifier">sink</span></code> 147 is captured (current-fiber) by invoking <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> 148 and passed as parameter to the lambda. 149 </p> 150<p> 151 Because the state is invalidated (one-shot fiber) by each call of <span class="emphasis"><em>continuation::resume()</em></span>, 152 the new state of the <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a>, 153 returned by <span class="emphasis"><em>continuation::resume()</em></span>, needs to be assigned 154 to <code class="computeroutput"><span class="identifier">sink</span></code> after each call. In 155 order to express the invalidation of the resumed fiber, the member functions 156 <code class="computeroutput"><span class="identifier">resume</span><span class="special">()</span></code> 157 and <code class="computeroutput"><span class="identifier">resume_with</span><span class="special">()</span></code> 158 are rvalue-ref qualified. Both functions bind only to rvalues. Thus an lvalue 159 fiber must be casted to an rvalue via <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">()</span></code>. 160 </p> 161<p> 162 The lambda that calculates the Fibonacci numbers is executed inside the fiber 163 represented by <code class="computeroutput"><span class="identifier">source</span></code>. Calculated 164 Fibonacci numbers are transferred between the two fibers via variable <code class="computeroutput"><span class="identifier">a</span></code> (lambda capture reference). 165 </p> 166<p> 167 The locale variables <code class="computeroutput"><span class="identifier">b</span></code> and 168 <code class="computeroutput"> <span class="identifier">next</span></code> remain their values during 169 each context switch. This is possible due <code class="computeroutput"><span class="identifier">source</span></code> 170 has its own stack and the stack is exchanged by each context switch. 171 </p> 172<h4> 173<a name="context.ff.h2"></a> 174 <span class="phrase"><a name="context.ff.parameter_passing"></a></span><a class="link" href="ff.html#context.ff.parameter_passing">Parameter 175 passing</a> 176 </h4> 177<p> 178 Data can be transferred between two fibers via global pointers, calling wrappers 179 (like <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">bind</span></code>) or lambda captures. 180 </p> 181<pre class="programlisting"><span class="keyword">namespace</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> 182<span class="keyword">int</span> <span class="identifier">i</span><span class="special">=</span><span class="number">1</span><span class="special">;</span> 183<span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="identifier">f1</span><span class="special">{[&</span><span class="identifier">i</span><span class="special">](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span><span class="special">&&</span> <span class="identifier">f2</span><span class="special">){</span> 184 <span class="identifier">std</span><span class="special">::</span><span class="identifier">printf</span><span class="special">(</span><span class="string">"inside f1,i==%d\n"</span><span class="special">,</span><span class="identifier">i</span><span class="special">);</span> 185 <span class="identifier">i</span><span class="special">+=</span><span class="number">1</span><span class="special">;</span> 186 <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">f2</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 187<span class="special">}};</span> 188<span class="identifier">f1</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">f1</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 189<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> 190 191<span class="identifier">output</span><span class="special">:</span> 192 <span class="identifier">inside</span> <span class="identifier">c1</span><span class="special">,</span><span class="identifier">i</span><span class="special">==</span><span class="number">1</span> 193 <span class="identifier">i</span><span class="special">==</span><span class="number">2</span> 194</pre> 195<p> 196 <code class="computeroutput"><span class="identifier">f1</span><span class="special">.</span><span class="identifier">resume</span><span class="special">()</span></code> 197 enters the lambda in fiber represented by <code class="computeroutput"><span class="identifier">f1</span></code> 198 with lambda capture reference <code class="computeroutput"><span class="identifier">i</span><span class="special">=</span><span class="number">1</span></code>. The expression 199 <code class="computeroutput"><span class="identifier">f2</span><span class="special">.</span><span class="identifier">resume</span><span class="special">()</span></code> 200 resumes the fiber <code class="computeroutput"><span class="identifier">f2</span></code>. On return 201 of <code class="computeroutput"><span class="identifier">f1</span><span class="special">.</span><span class="identifier">resume</span><span class="special">()</span></code>, 202 the variable <code class="computeroutput"><span class="identifier">i</span></code> has the value 203 of <code class="computeroutput"><span class="identifier">i</span><span class="special">+</span><span class="number">1</span></code>. 204 </p> 205<h4> 206<a name="context.ff.h3"></a> 207 <span class="phrase"><a name="context.ff.exception_handling"></a></span><a class="link" href="ff.html#context.ff.exception_handling">Exception 208 handling</a> 209 </h4> 210<p> 211 If the function executed inside a <span class="emphasis"><em>context-function</em></span> emits 212 ans exception, the application is terminated by calling <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">terminate</span><span class="special">()</span></code>. <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span></code> 213 can be used to transfer exceptions between different fibers. 214 </p> 215<div class="important"><table border="0" summary="Important"> 216<tr> 217<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td> 218<th align="left">Important</th> 219</tr> 220<tr><td align="left" valign="top"><p> 221 Do not jump from inside a catch block and then re-throw the exception in 222 another fiber. 223 </p></td></tr> 224</table></div> 225<a name="ff_ontop"></a><h4> 226<a name="context.ff.h4"></a> 227 <span class="phrase"><a name="context.ff.executing_function_on_top_of_a_fiber"></a></span><a class="link" href="ff.html#context.ff.executing_function_on_top_of_a_fiber">Executing 228 function on top of a fiber</a> 229 </h4> 230<p> 231 Sometimes it is useful to execute a new function on top of a resumed fiber. 232 For this purpose <span class="emphasis"><em>continuation::resume_with()</em></span> has to be 233 used. The function passed as argument must accept a rvalue reference to <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> and return <code class="computeroutput"><span class="keyword">void</span></code>. 234 </p> 235<pre class="programlisting"><span class="keyword">namespace</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> 236<span class="keyword">int</span> <span class="identifier">data</span><span class="special">=</span><span class="number">0</span><span class="special">;</span> 237<span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="identifier">f1</span><span class="special">{[&</span><span class="identifier">data</span><span class="special">](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span><span class="special">&&</span> <span class="identifier">f2</span><span class="special">)</span> <span class="special">{</span> 238 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"f1: entered first time: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 239 <span class="identifier">data</span><span class="special">+=</span><span class="number">1</span><span class="special">;</span> 240 <span class="identifier">f2</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">f2</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 241 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"f1: entered second time: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 242 <span class="identifier">data</span><span class="special">+=</span><span class="number">1</span><span class="special">;</span> 243 <span class="identifier">f2</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">f2</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 244 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"f1: entered third time: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 245 <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">f2</span><span class="special">);</span> 246<span class="special">}};</span> 247<span class="identifier">f1</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">f1</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 248<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"f1: returned first time: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 249<span class="identifier">data</span><span class="special">+=</span><span class="number">1</span><span class="special">;</span> 250<span class="identifier">f1</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">f1</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 251<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"f1: returned second time: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 252<span class="identifier">data</span><span class="special">+=</span><span class="number">1</span><span class="special">;</span> 253<span class="identifier">f1</span><span class="special">=</span><span class="identifier">f1</span><span class="special">.</span><span class="identifier">resume_with</span><span class="special">([&</span><span class="identifier">data</span><span class="special">](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span><span class="special">&&</span> <span class="identifier">f2</span><span class="special">){</span> 254 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"f2: entered: "</span> <span class="special"><<</span> <span class="identifier">data</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 255 <span class="identifier">data</span><span class="special">=-</span><span class="number">1</span><span class="special">;</span> 256 <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">f2</span><span class="special">);</span> 257<span class="special">});</span> 258<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"f1: returned third time"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 259 260<span class="identifier">output</span><span class="special">:</span> 261 <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">0</span> 262 <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">1</span> 263 <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">2</span> 264 <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">3</span> 265 <span class="identifier">f2</span><span class="special">:</span> <span class="identifier">entered</span><span class="special">:</span> <span class="number">4</span> 266 <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> 267 <span class="identifier">f1</span><span class="special">:</span> <span class="identifier">returned</span> <span class="identifier">third</span> <span class="identifier">time</span> 268</pre> 269<p> 270 The expression <code class="computeroutput"><span class="identifier">f1</span><span class="special">.</span><span class="identifier">resume_with</span><span class="special">(...)</span></code> 271 executes a lambda on top of fiber <code class="computeroutput"><span class="identifier">f1</span></code>, 272 e.g. an additional stack frame is allocated on top of the stack. This lambda 273 assigns <code class="computeroutput"><span class="special">-</span><span class="number">1</span></code> 274 to <code class="computeroutput"><span class="identifier">data</span></code> and returns to the 275 second invocation of <code class="computeroutput"><span class="identifier">f1</span><span class="special">.</span><span class="identifier">resume</span><span class="special">()</span></code>. 276 </p> 277<p> 278 Another option is to execute a function on top of the fiber that throws an 279 exception. 280 </p> 281<pre class="programlisting"><span class="keyword">namespace</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> 282<span class="keyword">struct</span> <span class="identifier">my_exception</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span> <span class="special">{</span> 283 <span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="identifier">f</span><span class="special">;</span> 284 <span class="identifier">my_exception</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span><span class="special">&&</span> <span class="identifier">f_</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">what</span><span class="special">)</span> <span class="special">:</span> 285 <span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span><span class="special">{</span> <span class="identifier">what</span> <span class="special">},</span> 286 <span class="identifier">f</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">f_</span><span class="special">)</span> <span class="special">}</span> <span class="special">{</span> 287 <span class="special">}</span> 288<span class="special">};</span> 289 290<span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="identifier">f</span><span class="special">{[](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="special">&&</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">-></span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="special">{</span> 291 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"entered"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 292 <span class="keyword">try</span> <span class="special">{</span> 293 <span class="identifier">f</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">f</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 294 <span class="special">}</span> <span class="keyword">catch</span> <span class="special">(</span><span class="identifier">my_exception</span> <span class="special">&</span> <span class="identifier">ex</span><span class="special">)</span> <span class="special">{</span> 295 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="string">"my_exception: "</span> <span class="special"><<</span> <span class="identifier">ex</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 296 <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">ex</span><span class="special">.</span><span class="identifier">f</span><span class="special">);</span> 297 <span class="special">}</span> 298 <span class="keyword">return</span> <span class="special">{};</span> 299<span class="special">});</span> 300<span class="identifier">f</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">f</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 301<span class="identifier">f</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">f</span><span class="special">).</span><span class="identifier">resume_with</span><span class="special">([](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="special">&&</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">-></span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="special">{</span> 302 <span class="keyword">throw</span> <span class="identifier">my_exception</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">f</span><span class="special">),</span><span class="string">"abc"</span><span class="special">);</span> 303 <span class="keyword">return</span> <span class="special">{};</span> 304<span class="special">});</span> 305 306<span class="identifier">output</span><span class="special">:</span> 307 <span class="identifier">entered</span> 308 <span class="identifier">my_exception</span><span class="special">:</span> <span class="identifier">abc</span> 309</pre> 310<p> 311 In this exception <code class="computeroutput"><span class="identifier">my_exception</span></code> 312 is throw from a function invoked on-top of fiber <code class="computeroutput"><span class="identifier">f</span></code> 313 and catched inside the <code class="computeroutput"><span class="keyword">for</span></code>-loop. 314 </p> 315<h4> 316<a name="context.ff.h5"></a> 317 <span class="phrase"><a name="context.ff.stack_unwinding"></a></span><a class="link" href="ff.html#context.ff.stack_unwinding">Stack 318 unwinding</a> 319 </h4> 320<p> 321 On construction of <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> a stack 322 is allocated. If the <span class="emphasis"><em>context-function</em></span> returns the stack 323 will be destructed. If the <span class="emphasis"><em>context-function</em></span> has not yet 324 returned and the destructor of an valid <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> 325 instance (e.g. <span class="emphasis"><em>fiber::operator bool()</em></span> returns <code class="computeroutput"><span class="keyword">true</span></code>) is called, the stack will be destructed 326 too. 327 </p> 328<div class="important"><table border="0" summary="Important"> 329<tr> 330<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td> 331<th align="left">Important</th> 332</tr> 333<tr><td align="left" valign="top"><p> 334 Code executed by <span class="emphasis"><em>context-function</em></span> must not prevent the 335 propagation ofs the <span class="emphasis"><em>detail::forced_unwind</em></span> exception. 336 Absorbing that exception will cause stack unwinding to fail. Thus, any code 337 that catches all exceptions must re-throw any pending <span class="emphasis"><em>detail::forced_unwind</em></span> 338 exception. 339 </p></td></tr> 340</table></div> 341<a name="ff_prealloc"></a><h4> 342<a name="context.ff.h6"></a> 343 <span class="phrase"><a name="context.ff.allocating_control_structures_on_top_of_stack"></a></span><a class="link" href="ff.html#context.ff.allocating_control_structures_on_top_of_stack">Allocating 344 control structures on top of stack</a> 345 </h4> 346<p> 347 Allocating control structures on top of the stack requires to allocated the 348 <span class="emphasis"><em>stack_context</em></span> and create the control structure with placement 349 new before <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> is created. 350 </p> 351<div class="note"><table border="0" summary="Note"> 352<tr> 353<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> 354<th align="left">Note</th> 355</tr> 356<tr><td align="left" valign="top"><p> 357 The user is responsible for destructing the control structure at the top 358 of the stack. 359 </p></td></tr> 360</table></div> 361<pre class="programlisting"><span class="keyword">namespace</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> 362<span class="comment">// stack-allocator used for (de-)allocating stack</span> 363<span class="identifier">fixedsize_stack</span> <span class="identifier">salloc</span><span class="special">(</span><span class="number">4048</span><span class="special">);</span> 364<span class="comment">// allocate stack space</span> 365<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> 366<span class="comment">// reserve space for control structure on top of the stack</span> 367<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"><</span><span class="keyword">char</span><span class="special">*>(</span><span class="identifier">sctx</span><span class="special">.</span><span class="identifier">sp</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> 368<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> 369<span class="comment">// placement new creates control structure on reserved space</span> 370<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> 371<span class="special">...</span> 372<span class="comment">// destructing the control structure</span> 373<span class="identifier">cs</span><span class="special">->~</span><span class="identifier">my_control_structure</span><span class="special">();</span> 374<span class="special">...</span> 375<span class="keyword">struct</span> <span class="identifier">my_control_structure</span> <span class="special">{</span> 376 <span class="comment">// captured fiber</span> 377 <span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="identifier">f</span><span class="special">;</span> 378 379 <span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">StackAllocator</span> <span class="special">></span> 380 <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> 381 <span class="comment">// create captured fiber</span> 382 <span class="identifier">f</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> 383 <span class="special">}</span> 384 <span class="special">...</span> 385<span class="special">};</span> 386</pre> 387<h4> 388<a name="context.ff.h7"></a> 389 <span class="phrase"><a name="context.ff.inverting_the_control_flow"></a></span><a class="link" href="ff.html#context.ff.inverting_the_control_flow">Inverting 390 the control flow</a> 391 </h4> 392<pre class="programlisting"><span class="keyword">namespace</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> 393<span class="comment">/* 394 * grammar: 395 * P ---> E '\0' 396 * E ---> T {('+'|'-') T} 397 * T ---> S {('*'|'/') S} 398 * S ---> digit | '(' E ')' 399 */</span> 400<span class="keyword">class</span> <span class="identifier">Parser</span><span class="special">{</span> 401 <span class="keyword">char</span> <span class="identifier">next</span><span class="special">;</span> 402 <span class="identifier">std</span><span class="special">::</span><span class="identifier">istream</span><span class="special">&</span> <span class="identifier">is</span><span class="special">;</span> 403 <span class="identifier">std</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">void</span><span class="special">(</span><span class="keyword">char</span><span class="special">)></span> <span class="identifier">cb</span><span class="special">;</span> 404 405 <span class="keyword">char</span> <span class="identifier">pull</span><span class="special">(){</span> 406 <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special"><</span><span class="keyword">char</span><span class="special">>::</span><span class="identifier">to_char_type</span><span class="special">(</span><span class="identifier">is</span><span class="special">.</span><span class="identifier">get</span><span class="special">());</span> 407 <span class="special">}</span> 408 409 <span class="keyword">void</span> <span class="identifier">scan</span><span class="special">(){</span> 410 <span class="keyword">do</span><span class="special">{</span> 411 <span class="identifier">next</span><span class="special">=</span><span class="identifier">pull</span><span class="special">();</span> 412 <span class="special">}</span> 413 <span class="keyword">while</span><span class="special">(</span><span class="identifier">isspace</span><span class="special">(</span><span class="identifier">next</span><span class="special">));</span> 414 <span class="special">}</span> 415 416<span class="keyword">public</span><span class="special">:</span> 417 <span class="identifier">Parser</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">istream</span><span class="special">&</span> <span class="identifier">is_</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">void</span><span class="special">(</span><span class="keyword">char</span><span class="special">)></span> <span class="identifier">cb_</span><span class="special">)</span> <span class="special">:</span> 418 <span class="identifier">next</span><span class="special">(),</span> <span class="identifier">is</span><span class="special">(</span><span class="identifier">is_</span><span class="special">),</span> <span class="identifier">cb</span><span class="special">(</span><span class="identifier">cb_</span><span class="special">)</span> 419 <span class="special">{}</span> 420 421 <span class="keyword">void</span> <span class="identifier">run</span><span class="special">()</span> <span class="special">{</span> 422 <span class="identifier">scan</span><span class="special">();</span> 423 <span class="identifier">E</span><span class="special">();</span> 424 <span class="special">}</span> 425 426<span class="keyword">private</span><span class="special">:</span> 427 <span class="keyword">void</span> <span class="identifier">E</span><span class="special">(){</span> 428 <span class="identifier">T</span><span class="special">();</span> 429 <span class="keyword">while</span> <span class="special">(</span><span class="identifier">next</span><span class="special">==</span><span class="char">'+'</span><span class="special">||</span><span class="identifier">next</span><span class="special">==</span><span class="char">'-'</span><span class="special">){</span> 430 <span class="identifier">cb</span><span class="special">(</span><span class="identifier">next</span><span class="special">);</span> 431 <span class="identifier">scan</span><span class="special">();</span> 432 <span class="identifier">T</span><span class="special">();</span> 433 <span class="special">}</span> 434 <span class="special">}</span> 435 436 <span class="keyword">void</span> <span class="identifier">T</span><span class="special">(){</span> 437 <span class="identifier">S</span><span class="special">();</span> 438 <span class="keyword">while</span> <span class="special">(</span><span class="identifier">next</span><span class="special">==</span><span class="char">'*'</span><span class="special">||</span><span class="identifier">next</span><span class="special">==</span><span class="char">'/'</span><span class="special">){</span> 439 <span class="identifier">cb</span><span class="special">(</span><span class="identifier">next</span><span class="special">);</span> 440 <span class="identifier">scan</span><span class="special">();</span> 441 <span class="identifier">S</span><span class="special">();</span> 442 <span class="special">}</span> 443 <span class="special">}</span> 444 445 <span class="keyword">void</span> <span class="identifier">S</span><span class="special">(){</span> 446 <span class="keyword">if</span> <span class="special">(</span><span class="identifier">isdigit</span><span class="special">(</span><span class="identifier">next</span><span class="special">)){</span> 447 <span class="identifier">cb</span><span class="special">(</span><span class="identifier">next</span><span class="special">);</span> 448 <span class="identifier">scan</span><span class="special">();</span> 449 <span class="special">}</span> 450 <span class="keyword">else</span> <span class="keyword">if</span><span class="special">(</span><span class="identifier">next</span><span class="special">==</span><span class="char">'('</span><span class="special">){</span> 451 <span class="identifier">cb</span><span class="special">(</span><span class="identifier">next</span><span class="special">);</span> 452 <span class="identifier">scan</span><span class="special">();</span> 453 <span class="identifier">E</span><span class="special">();</span> 454 <span class="keyword">if</span> <span class="special">(</span><span class="identifier">next</span><span class="special">==</span><span class="char">')'</span><span class="special">){</span> 455 <span class="identifier">cb</span><span class="special">(</span><span class="identifier">next</span><span class="special">);</span> 456 <span class="identifier">scan</span><span class="special">();</span> 457 <span class="special">}</span><span class="keyword">else</span><span class="special">{</span> 458 <span class="keyword">throw</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span><span class="special">(</span><span class="string">"parsing failed"</span><span class="special">);</span> 459 <span class="special">}</span> 460 <span class="special">}</span> 461 <span class="keyword">else</span><span class="special">{</span> 462 <span class="keyword">throw</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span><span class="special">(</span><span class="string">"parsing failed"</span><span class="special">);</span> 463 <span class="special">}</span> 464 <span class="special">}</span> 465<span class="special">};</span> 466 467<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> 468<span class="comment">// user-code pulls parsed data from parser</span> 469<span class="comment">// invert control flow</span> 470<span class="keyword">char</span> <span class="identifier">c</span><span class="special">;</span> 471<span class="keyword">bool</span> <span class="identifier">done</span><span class="special">=</span><span class="keyword">false</span><span class="special">;</span> 472<span class="comment">// execute parser in new fiber</span> 473<span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span> <span class="identifier">source</span><span class="special">{[&</span><span class="identifier">is</span><span class="special">,&</span><span class="identifier">c</span><span class="special">,&</span><span class="identifier">done</span><span class="special">](</span><span class="identifier">ctx</span><span class="special">::</span><span class="identifier">fiber</span><span class="special">&&</span> <span class="identifier">sink</span><span class="special">){</span> 474 <span class="comment">// create parser with callback function</span> 475 <span class="identifier">Parser</span> <span class="identifier">p</span><span class="special">(</span><span class="identifier">is</span><span class="special">,</span> 476 <span class="special">[&</span><span class="identifier">sink</span><span class="special">,&</span><span class="identifier">c</span><span class="special">](</span><span class="keyword">char</span> <span class="identifier">c_</span><span class="special">){</span> 477 <span class="comment">// resume main fiber</span> 478 <span class="identifier">c</span><span class="special">=</span><span class="identifier">c_</span><span class="special">;</span> 479 <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">sink</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 480 <span class="special">});</span> 481 <span class="comment">// start recursive parsing</span> 482 <span class="identifier">p</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span> 483 <span class="comment">// signal termination</span> 484 <span class="identifier">done</span><span class="special">=</span><span class="keyword">true</span><span class="special">;</span> 485 <span class="comment">// resume main fiber</span> 486 <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">sink</span><span class="special">);</span> 487<span class="special">}};</span> 488<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">source</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 489<span class="keyword">while</span><span class="special">(!</span><span class="identifier">done</span><span class="special">){</span> 490 <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> 491 <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">source</span><span class="special">).</span><span class="identifier">resume</span><span class="special">();</span> 492<span class="special">}</span> 493 494<span class="identifier">output</span><span class="special">:</span> 495 <span class="identifier">Parsed</span><span class="special">:</span> <span class="number">1</span> 496 <span class="identifier">Parsed</span><span class="special">:</span> <span class="special">+</span> 497 <span class="identifier">Parsed</span><span class="special">:</span> <span class="number">1</span> 498</pre> 499<p> 500 In this example a recursive descent parser uses a callback to emit a newly 501 passed symbol. Using <a class="link" href="ff.html#ff"><span class="emphasis"><em>fiber</em></span></a> the 502 control flow can be inverted, e.g. the user-code pulls parsed symbols from 503 the parser - instead to get pushed from the parser (via callback). 504 </p> 505<p> 506 The data (character) is transferred between the two fibers. 507 </p> 508</div> 509<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 510<td align="left"></td> 511<td align="right"><div class="copyright-footer">Copyright © 2014 Oliver Kowalke<p> 512 Distributed under the Boost Software License, Version 1.0. (See accompanying 513 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>) 514 </p> 515</div></td> 516</tr></table> 517<hr> 518<div class="spirit-nav"> 519<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="ff/implementations__fcontext_t__ucontext_t_and_winfiber.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 520</div> 521</body> 522</html> 523
