93 lines
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93 lines
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<title>Thread safety guarantees</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="intrusive.thread_safety"></a><a class="link" href="thread_safety.html" title="Thread safety guarantees">Thread safety guarantees</a>
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</h2></div></div></div>
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<p>
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Intrusive containers have thread safety guarantees similar to STL containers.
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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Several threads having read or write access to different instances is safe
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as long as inserted objects are different.
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</li>
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<li class="listitem">
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Concurrent read-only access to the same container is safe.
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</li>
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</ul></div>
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<p>
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Some Intrusive hooks (auto-unlink hooks, for example) modify containers without
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having a reference to them: this is considered a write access to the container.
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</p>
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<p>
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Other functions, like checking if an object is already inserted in a container
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using the <code class="computeroutput"><span class="identifier">is_linked</span><span class="special">()</span></code>
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member of safe hooks, constitute read access on the container without having
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a reference to it, so no other thread should have write access (direct or indirect)
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to that container.
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</p>
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<p>
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Since the same object can be inserted in several containers at the same time
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using different hooks, the thread safety of <span class="bold"><strong>Boost.Intrusive</strong></span>
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is related to the containers and also to the object whose lifetime is manually
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managed by the user.
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</p>
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<p>
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As we can see, the analysis of the thread-safety of a program using <span class="bold"><strong>Boost.Intrusive</strong></span> is harder than with non-intrusive containers.
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</p>
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<p>
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To analyze the thread safety, consider the following points:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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The auto-unlink hook's destructor and <code class="computeroutput"><span class="identifier">unlink</span><span class="special">()</span></code> functions modify the container indirectly.
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</li>
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<li class="listitem">
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The safe mode and auto-unlink hooks' <code class="computeroutput"><span class="identifier">is_linked</span><span class="special">()</span></code> functions are a read access to the container.
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</li>
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<li class="listitem">
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Inserting an object in containers that will be modified by different threads
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has no thread safety guarantee, although in most platforms it will be thread-safe
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without locking.
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</li>
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</ul></div>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2005 Olaf Krzikalla<br>Copyright © 2006-2015 Ion Gaztanaga<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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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</p>
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</div></td>
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</tr></table>
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<hr>
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<a accesskey="p" href="value_traits.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../intrusive.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="boost_intrusive_iterators.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
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