1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Other APIs</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="../rationale.html" title="Rationale"> 9<link rel="prev" href="../rationale.html" title="Rationale"> 10<link rel="next" href="x86_and_floating_point_env.html" title="x86 and floating-point env"> 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="../rationale.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../rationale.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="x86_and_floating_point_env.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="context.rationale.other_apis_"></a><a class="link" href="other_apis_.html" title="Other APIs">Other APIs </a> 28</h3></div></div></div> 29<h5> 30<a name="context.rationale.other_apis_.h0"></a> 31 <span class="phrase"><a name="context.rationale.other_apis_.setjmp___longjmp__"></a></span><a class="link" href="other_apis_.html#context.rationale.other_apis_.setjmp___longjmp__">setjmp()/longjmp()</a> 32 </h5> 33<p> 34 C99 defines <code class="computeroutput"><span class="identifier">setjmp</span><span class="special">()</span></code>/<code class="computeroutput"><span class="identifier">longjmp</span><span class="special">()</span></code> 35 to provide non-local jumps but it does not require that <span class="emphasis"><em>longjmp()</em></span> 36 preserves the current stack frame. Therefore, jumping into a function which 37 was exited via a call to <span class="emphasis"><em>longjmp()</em></span> is undefined <a href="#ftn.context.rationale.other_apis_.f0" class="footnote" name="context.rationale.other_apis_.f0"><sup class="footnote">[2]</sup></a>. 38 </p> 39<a name="ucontext"></a><h5> 40<a name="context.rationale.other_apis_.h1"></a> 41 <span class="phrase"><a name="context.rationale.other_apis_.ucontext_t"></a></span><a class="link" href="other_apis_.html#context.rationale.other_apis_.ucontext_t">ucontext_t</a> 42 </h5> 43<p> 44 Since POSIX.1-2004 <code class="computeroutput"><span class="identifier">ucontext_t</span></code> 45 is deprecated and was removed in POSIX.1-2008! The function signature of 46 <code class="computeroutput"><span class="identifier">makecontext</span><span class="special">()</span></code> 47 is: 48 </p> 49<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">makecontext</span><span class="special">(</span><span class="identifier">ucontext_t</span> <span class="special">*</span><span class="identifier">ucp</span><span class="special">,</span> <span class="keyword">void</span> <span class="special">(*</span><span class="identifier">func</span><span class="special">)(),</span> <span class="keyword">int</span> <span class="identifier">argc</span><span class="special">,</span> <span class="special">...);</span> 50</pre> 51<p> 52 The third argument of <code class="computeroutput"><span class="identifier">makecontext</span><span class="special">()</span></code> specifies the number of integer arguments 53 that follow which will require function pointer cast if <code class="computeroutput"><span class="identifier">func</span></code> 54 will accept those arguments which is undefined in C99 <a href="#ftn.context.rationale.other_apis_.f1" class="footnote" name="context.rationale.other_apis_.f1"><sup class="footnote">[3]</sup></a>. 55 </p> 56<p> 57 The arguments in the var-arg list are required to be integers, passing pointers 58 in var-arg list is not guaranteed to work, especially it will fail for architectures 59 where pointers are larger than integers. 60 </p> 61<p> 62 <code class="computeroutput"><span class="identifier">ucontext_t</span></code> preserves signal 63 mask between context switches which involves system calls consuming a lot 64 of CPU cycles (ucontext_t is slower; a context switch takes <a class="link" href="../performance.html#performance"><span class="emphasis"><em>two 65 magnitutes of order more CPU cycles</em></span></a> more than <span class="emphasis"><em>fcontext_t</em></span>). 66 </p> 67<h5> 68<a name="context.rationale.other_apis_.h2"></a> 69 <span class="phrase"><a name="context.rationale.other_apis_.windows_fibers"></a></span><a class="link" href="other_apis_.html#context.rationale.other_apis_.windows_fibers">Windows 70 fibers</a> 71 </h5> 72<p> 73 A drawback of Windows Fiber API is that <code class="computeroutput"><span class="identifier">CreateFiber</span><span class="special">()</span></code> does not accept a pointer to user allocated 74 stack space preventing the reuse of stacks for other context instances. Because 75 the Windows Fiber API requires to call <code class="computeroutput"><span class="identifier">ConvertThreadToFiber</span><span class="special">()</span></code> if <code class="computeroutput"><span class="identifier">SwitchFiber</span><span class="special">()</span></code> is called for a thread which has not been 76 converted to a fiber. For the same reason <code class="computeroutput"><span class="identifier">ConvertFiberToThread</span><span class="special">()</span></code> must be called after return from <code class="computeroutput"><span class="identifier">SwitchFiber</span><span class="special">()</span></code> 77 if the thread was forced to be converted to a fiber before (which is inefficient). 78 </p> 79<pre class="programlisting"><span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span> <span class="identifier">is_a_fiber</span><span class="special">()</span> <span class="special">)</span> 80<span class="special">{</span> 81 <span class="identifier">ConvertThreadToFiber</span><span class="special">(</span> <span class="number">0</span><span class="special">);</span> 82 <span class="identifier">SwitchToFiber</span><span class="special">(</span> <span class="identifier">ctx</span><span class="special">);</span> 83 <span class="identifier">ConvertFiberToThread</span><span class="special">();</span> 84<span class="special">}</span> 85</pre> 86<p> 87 If the condition <code class="computeroutput"><span class="identifier">_WIN32_WINNT</span> <span class="special">>=</span> <span class="identifier">_WIN32_WINNT_VISTA</span></code> 88 is met function <code class="computeroutput"><span class="identifier">IsThreadAFiber</span><span class="special">()</span></code> is provided in order to detect if the current 89 thread was already converted. Unfortunately Windows XP + SP 2/3 defines 90 <code class="computeroutput"><span class="identifier">_WIN32_WINNT</span> <span class="special">>=</span> 91 <span class="identifier">_WIN32_WINNT_VISTA</span></code> without providing 92 <code class="computeroutput"><span class="identifier">IsThreadAFiber</span><span class="special">()</span></code>. 93 </p> 94<div class="footnotes"> 95<br><hr style="width:100; text-align:left;margin-left: 0"> 96<div id="ftn.context.rationale.other_apis_.f0" class="footnote"><p><a href="#context.rationale.other_apis_.f0" class="para"><sup class="para">[2] </sup></a> 97 ISO/IEC 9899:1999, 2005, 7.13.2.1:2 98 </p></div> 99<div id="ftn.context.rationale.other_apis_.f1" class="footnote"><p><a href="#context.rationale.other_apis_.f1" class="para"><sup class="para">[3] </sup></a> 100 ISO/IEC 9899:1999, 2005, J.2 101 </p></div> 102</div> 103</div> 104<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 105<td align="left"></td> 106<td align="right"><div class="copyright-footer">Copyright © 2014 Oliver Kowalke<p> 107 Distributed under the Boost Software License, Version 1.0. (See accompanying 108 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>) 109 </p> 110</div></td> 111</tr></table> 112<hr> 113<div class="spirit-nav"> 114<a accesskey="p" href="../rationale.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../rationale.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="x86_and_floating_point_env.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 115</div> 116</body> 117</html> 118
