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| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="context.rationale.other_apis_"></a><a class="link" href="other_apis_.html" title="Other APIs">Other APIs </a> |
| </h3></div></div></div> |
| <h5> |
| <a name="context.rationale.other_apis_.h0"></a> |
| <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> |
| </h5> |
| <p> |
| 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> |
| to provide non-local jumps but it does not require that <span class="emphasis"><em>longjmp()</em></span> |
| preserves the current stack frame. Therefore, jumping into a function which |
| 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>. |
| </p> |
| <h5> |
| <a name="context.rationale.other_apis_.h1"></a> |
| <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> |
| </h5> |
| <p> |
| Since POSIX.1-2003 <code class="computeroutput"><span class="identifier">ucontext_t</span></code> |
| is deprecated and was removed in POSIX.1-2008! The function signature of |
| <code class="computeroutput"><span class="identifier">makecontext</span><span class="special">()</span></code> |
| is: |
| </p> |
| <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> |
| </pre> |
| <p> |
| The third argument of <code class="computeroutput"><span class="identifier">makecontext</span><span class="special">()</span></code> specifies the number of integer arguments |
| that follow which will require function pointer cast if <code class="computeroutput"><span class="identifier">func</span></code> |
| 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>. |
| </p> |
| <p> |
| The arguments in the var-arg list are required to be integers, passing pointers |
| in var-arg list is not guaranteed to work, especially it will fail for architectures |
| where pointers are larger than integers. |
| </p> |
| <p> |
| <code class="computeroutput"><span class="identifier">ucontext_t</span></code> preserves signal |
| mask between context switches which involves system calls consuming a lot |
| of CPU cycles (ucontext_t is slower by perfomance_link[factor 13x] relative |
| to <code class="computeroutput"><span class="identifier">fcontext_t</span></code>). |
| </p> |
| <h5> |
| <a name="context.rationale.other_apis_.h2"></a> |
| <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 |
| fibers</a> |
| </h5> |
| <p> |
| 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 |
| stack space preventing the reuse of stacks for other context instances. Because |
| 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 |
| 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> |
| if the thread was forced to be converted to a fiber before (which is inefficient). |
| </p> |
| <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> |
| <span class="special">{</span> |
| <span class="identifier">ConvertThreadToFiber</span><span class="special">(</span> <span class="number">0</span><span class="special">);</span> |
| <span class="identifier">SwitchToFiber</span><span class="special">(</span> <span class="identifier">ctx</span><span class="special">);</span> |
| <span class="identifier">ConvertFiberToThread</span><span class="special">();</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| If the condition <code class="computeroutput"><span class="identifier">_WIN32_WINNT</span> <span class="special">>=</span> <span class="identifier">_WIN32_WINNT_VISTA</span></code> |
| 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 |
| thread was already converted. Unfortunately Windows XP + SP 2/3 defines |
| <code class="computeroutput"><span class="identifier">_WIN32_WINNT</span> <span class="special">>=</span> |
| <span class="identifier">_WIN32_WINNT_VISTA</span></code> without providing |
| <code class="computeroutput"><span class="identifier">IsThreadAFiber</span><span class="special">()</span></code>. |
| </p> |
| <div class="footnotes"> |
| <br><hr style="width:100; text-align:left;margin-left: 0"> |
| <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> |
| ISO/IEC 9899:1999, 2005, 7.13.2.1:2 |
| </p></div> |
| <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> |
| ISO/IEC 9899:1999, 2005, J.2 |
| </p></div> |
| </div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2014 Oliver Kowalke<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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>) |
| </p> |
| </div></td> |
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