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<h1 align=center>QMutex Class Reference</h1><br clear="all">
<p>
The QMutex class provides access serialization between threads.
<a href="#details">More...</a>
<p>
<code>#include <<a href="qthread-h.html">qthread.h</a>></code>
<p>
Inherits <a href="qt.html">Qt</a>.
<p><a href="qmutex-members.html">List of all member functions.</a>
<h2>Public Members</h2>
<ul>
<li><div class="fn"><a href="#29e2e7"><b>QMutex</b></a>(boolrecursive=FALSE)</div>
<li><div class="fn">virtual<a href="#9ef650"><b>~QMutex</b></a>()</div>
<li><div class="fn">void<a href="#4e6e5d"><b>lock</b></a>()</div>
<li><div class="fn">void<a href="#da15c3"><b>unlock</b></a>()</div>
<li><div class="fn">bool<a href="#b61471"><b>locked</b></a>()</div>
</ul>
<hr><h2><a name="details"></a>Detailed Description</h2>
The QMutex class provides access serialization between threads.
<p>
The purpose of a QMutex is to protect an object, data structure
or section of code so that only one thread can access it at a time
(In Java terms, this is similar to the synchronized keyword).
For example, say there is a method which prints a message to the
user on two lines:
<p><pre> void someMethod()
{
<a href="qapplication.html#72e78c">qDebug</a>("Hello");
<a href="qapplication.html#72e78c">qDebug</a>("World");
}
</pre>
<p>If this method is called simultaneously from two threads then
the following sequence could result:
<p><pre> Hello
Hello
World
World
</pre>
<p>If we add a mutex:
<p><pre> <a href="qmutex.html">QMutex</a> mutex;
void someMethod()
{
mutex.<a href="#4e6e5d">lock</a>();
<a href="qapplication.html#72e78c">qDebug</a>("Hello");
<a href="qapplication.html#72e78c">qDebug</a>("World");
mutex.<a href="#da15c3">unlock</a>();
}
</pre>
<p>In Java terms this would be:
<p><pre> void someMethod()
{
synchronized {
<a href="qapplication.html#72e78c">qDebug</a>("Hello");
<a href="qapplication.html#72e78c">qDebug</a>("World");
}
}
</pre>
<p>Then only one thread can execute someMethod at a time and the order
of messages is always correct. This is a trivial example, of course,
but applies to any other case where things need to happen in a particular
sequence.
<hr><h2>Member Function Documentation</h2>
<h3 class="fn"><a name="29e2e7"></a>QMutex::QMutex(boolrecursive=FALSE)</h3>
<p>Constructs a new mutex. The mutex is created in an unlocked state. A
recursive mutex is created if <em>recursive</em> is TRUE; a normal mutex is
created if <em>recursive</em> is FALSE (default argument). With a recursive
mutex, a thread can lock the same mutex multiple times and it will
not be unlocked until a corresponding number of <a href="#da15c3">unlock</a>() calls have
been made.
<h3 class="fn"><a name="9ef650"></a>QMutex::~QMutex() <code>[virtual]</code></h3>
<p>Destroys the mutex.
<h3 class="fn">void<a name="4e6e5d"></a>QMutex::lock()</h3>
<p>Attempt to lock the mutex. If another thread has locked the mutex
then this call will block until that thread has unlocked it.
<p>See also <a href="#da15c3">unlock</a>().
<h3 class="fn">bool<a name="b61471"></a>QMutex::locked()</h3>
<p>Returns TRUE if the mutex is locked by another thread and FALSE if not.
<p><em>NOTE:</em> Due to differing implementations of recursive mutexes on various
platforms, calling this function from the same thread that previous locked
the mutex will return undefined results.
<h3 class="fn">void<a name="da15c3"></a>QMutex::unlock()</h3>
<p>Unlocks the mutex. Attempting to unlock a mutex in a different thread
to the one that locked it results in an error. Unlocking a mutex that
is not locked results in undefined behaviour (varies between
different Operating Systems' thread implementations).
<p>See also <a href="#4e6e5d">lock</a>().
<hr><p>
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