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Error checking for stale DOH object use - also with documentation.

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William S Fulton 2012-08-05 16:16:23 +00:00
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@ -42,6 +42,7 @@
<li><a name="i7" href="#7">7. Debugging SWIG</a>
<ul>
<li><a name="i7.1" href="#7.1">7.1 Debugging DOH Types The Hard Way</a>
<li><a name="i7.2" href="#7.2">7.2 Debugging DOH memory allocation problems</a>
</ul>
</ul>
@ -1179,6 +1180,34 @@ Either <br>
</ul>
<a name="7.2" href="#i7.2">
<h3>7.2 Debugging DOH memory allocation problems</h3>
</a>
<p>
The DOH objects are reference counted and use pools for memory allocation.
The implementation is in <tt>memory.c</tt>. When there are memory corruption problems,
various memory allocator tools are normally used to diagnose problems. These can be used
on SWIG and can be very useful. However, they won't necessarily find use of stale DOH objects,
that is, DOH objects
that are used after they have been deleted. This is because the DOH memory allocator
grabs a chunk of memory from the C memory allocator and manages the usage internally.
Stale DOH object usage can be checked for by defining <tt>DOH_DEBUG_MEMORY_POOLS</tt> in
<tt>memory.c</tt>. If an attempt to use an object is made after the reference count is
zero, an assertion is triggered instead of quietly re-using the stale object...
</p>
<blockquote>
<pre>
swig: DOH/memory.c:91: DohCheck: Assertion `!DOH_object_already_deleted' failed.
</pre>
</blockquote>
<p>
This can be memory intensive as previously used memory in the pool is not re-used so is
only recommended for diagnosing memory corruption problems.
</p>
<hr>
Copyright (C) 1999-2010 SWIG Development Team.