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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="context.overview"></a><a class="link" href="overview.html" title="Overview">Overview</a> |
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| <p> |
| <span class="bold"><strong>Boost.Context</strong></span> is a foundational library that |
| provides a sort of cooperative multitasking on a single thread. By providing |
| an abstraction of the current execution state in the current thread, including |
| the stack (with local variables) and stack pointer, all registers and CPU flags, |
| and the instruction pointer, a <span class="emphasis"><em>fcontext_t</em></span> instance represents |
| a specific point in the application's execution path. This is useful for building |
| higher-level abstractions, like <span class="emphasis"><em>coroutines</em></span>, <span class="emphasis"><em>cooperative |
| threads (userland threads)</em></span> or an equivalent to <a href="http://msdn.microsoft.com/en-us/library/9k7k7cf0%28v=vs.80%29.aspx" target="_top">C# |
| keyword <span class="emphasis"><em>yield</em></span></a> in C++. |
| </p> |
| <p> |
| A <span class="emphasis"><em>fcontext_t</em></span> provides the means to suspend the current |
| execution path and to transfer execution control, thereby permitting another |
| <span class="emphasis"><em>fcontext_t</em></span> to run on the current thread. This state full |
| transfer mechanism enables a <span class="emphasis"><em>fcontext_t</em></span> to suspend execution |
| from within nested functions and, later, to resume from where it was suspended. |
| While the execution path represented by a <span class="emphasis"><em>fcontext_t</em></span> only |
| runs on a single thread, it can be migrated to another thread at any given |
| time. |
| </p> |
| <p> |
| A context switch between threads requires system calls (involving the OS kernel), |
| which can cost more than thousand CPU cycles on x86 CPUs. By contrast, transferring |
| control among them requires only few CPU cycles because it does not involve |
| system calls as it is done within a single thread. |
| </p> |
| <p> |
| In order to use the classes and functions described here, you can either include |
| the specific headers specified by the descriptions of each class or function, |
| or include the master library header: |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">context</span><span class="special">/</span><span class="identifier">all</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| </pre> |
| <p> |
| which includes all the other headers in turn. |
| </p> |
| <p> |
| All functions and classes are contained in the namespace <span class="emphasis"><em>boost::context</em></span>. |
| </p> |
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| <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>) |
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