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<title>Thread safety guarantees</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<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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<p>
Intrusive containers have thread safety guarantees similar to STL containers.
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
Several threads having read or write access to different instances is safe
as long as inserted objects are different.
</li>
<li class="listitem">
Concurrent read-only access to the same container is safe.
</li>
</ul></div>
<p>
Some Intrusive hooks (auto-unlink hooks, for example) modify containers without
having a reference to them: this is considered a write access to the container.
</p>
<p>
Other functions, like checking if an object is already inserted in a container
using the <code class="computeroutput"><span class="identifier">is_linked</span><span class="special">()</span></code>
member of safe hooks, constitute read access on the container without having
a reference to it, so no other thread should have write access (direct or indirect)
to that container.
</p>
<p>
Since the same object can be inserted in several containers at the same time
using different hooks, the thread safety of <span class="bold"><strong>Boost.Intrusive</strong></span>
is related to the containers and also to the object whose lifetime is manually
managed by the user.
</p>
<p>
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.
</p>
<p>
To analyze the thread safety, consider the following points:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
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.
</li>
<li class="listitem">
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.
</li>
<li class="listitem">
Inserting an object in containers that will be modified by different threads
has no thread safety guarantee, although in most platforms it will be thread-safe
without locking.
</li>
</ul></div>
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<td align="right"><div class="copyright-footer">Copyright © 2005 Olaf Krzikalla<br>Copyright © 2006-2012 Ion Gaztanaga<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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