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<chapter>
<title>Graphical modules</title>
<sect1>
<title>GDI Module</title>
<sect2>
<title>X Windows System interface</title>
<para>
The X libraries used to implement X clients (such as Wine)
do not work properly if multiple threads access the same
display concurrently. It is possible to compile the X
libraries to perform their own synchronization (initiated
by calling <function>XInitThreads()</function>). However,
Wine does not use this approach. Instead Wine performs its
own synchronization using the
<function>wine_tsx11_lock()</function> / <function>wine_tsx11_unlock()</function>
functions. This locking protects library access
with a critical section, and also arranges things so that
X libraries compiled without <option>-D_REENTRANT</option>
(eg. with global <varname>errno</varname> variable) will
work with Wine.
</para>
<para>
In the past, all calls to X used to go through a wrapper called
<function>TSX...()</function> (for "Thread Safe X ...").
While it is still being used in the code, it's inefficient
as the lock is potentially aquired and released unnecessarily.
New code should explicitly aquire the lock.
</para>
</sect2>
</sect1>
</chapter>
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