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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="boost_asio.overview.core.threads"></a><a class="link" href="threads.html" title="Threads and Boost.Asio">Threads and Boost.Asio</a> |
| </h4></div></div></div> |
| <a name="boost_asio.overview.core.threads.thread_safety"></a><h6> |
| <a name="id761937"></a> |
| <a class="link" href="threads.html#boost_asio.overview.core.threads.thread_safety">Thread Safety</a> |
| </h6> |
| <p> |
| In general, it is safe to make concurrent use of distinct objects, but |
| unsafe to make concurrent use of a single object. However, types such as |
| <code class="computeroutput"><span class="identifier">io_service</span></code> provide a stronger |
| guarantee that it is safe to use a single object concurrently. |
| </p> |
| <a name="boost_asio.overview.core.threads.thread_pools"></a><h6> |
| <a name="id761970"></a> |
| <a class="link" href="threads.html#boost_asio.overview.core.threads.thread_pools">Thread Pools</a> |
| </h6> |
| <p> |
| Multiple threads may call <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code> to set up a pool of threads from which |
| completion handlers may be invoked. This approach may also be used with |
| <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">post</span><span class="special">()</span></code> |
| to use a means to perform any computational tasks across a thread pool. |
| </p> |
| <p> |
| Note that all threads that have joined an <code class="computeroutput"><span class="identifier">io_service</span></code>'s |
| pool are considered equivalent, and the <code class="computeroutput"><span class="identifier">io_service</span></code> |
| may distribute work across them in an arbitrary fashion. |
| </p> |
| <a name="boost_asio.overview.core.threads.internal_threads"></a><h6> |
| <a name="id762058"></a> |
| <a class="link" href="threads.html#boost_asio.overview.core.threads.internal_threads">Internal |
| Threads</a> |
| </h6> |
| <p> |
| The implementation of this library for a particular platform may make use |
| of one or more internal threads to emulate asynchronicity. As far as possible, |
| these threads must be invisible to the library user. In particular, the |
| threads: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| must not call the user's code directly; and |
| </li> |
| <li class="listitem"> |
| must block all signals. |
| </li> |
| </ul></div> |
| <p> |
| This approach is complemented by the following guarantee: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> |
| Asynchronous completion handlers will only be called from threads that |
| are currently calling <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>. |
| </li></ul></div> |
| <p> |
| Consequently, it is the library user's responsibility to create and manage |
| all threads to which the notifications will be delivered. |
| </p> |
| <p> |
| The reasons for this approach include: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| By only calling <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code> from a single thread, the user's |
| code can avoid the development complexity associated with synchronisation. |
| For example, a library user can implement scalable servers that are |
| single-threaded (from the user's point of view). |
| </li> |
| <li class="listitem"> |
| A library user may need to perform initialisation in a thread shortly |
| after the thread starts and before any other application code is executed. |
| For example, users of Microsoft's COM must call <code class="computeroutput"><span class="identifier">CoInitializeEx</span></code> |
| before any other COM operations can be called from that thread. |
| </li> |
| <li class="listitem"> |
| The library interface is decoupled from interfaces for thread creation |
| and management, and permits implementations on platforms where threads |
| are not available. |
| </li> |
| </ul></div> |
| <a name="boost_asio.overview.core.threads.see_also"></a><h6> |
| <a name="id762214"></a> |
| <a class="link" href="threads.html#boost_asio.overview.core.threads.see_also">See Also</a> |
| </h6> |
| <p> |
| <a class="link" href="../../reference/io_service.html" title="io_service">io_service</a>. |
| </p> |
| </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 © 2003 - 2010 Christopher M. Kohlhoff<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> |
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