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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QMutex Class Reference</h1>
<p>The QMutex class provides access serialization between threads.
<a href="#details">More...</a>
<p><tt>#include <<a href="qmutex-h.html">qmutex.h</a>></tt>
<p><a href="qmutex-members.html">List of all member functions.</a>
<h2>Public Members</h2>
<ul>
<li><div class=fn><a href="#QMutex"><b>QMutex</b></a> ( bool recursive = FALSE )</div></li>
<li><div class=fn>virtual <a href="#~QMutex"><b>~QMutex</b></a> ()</div></li>
<li><div class=fn>void <a href="#lock"><b>lock</b></a> ()</div></li>
<li><div class=fn>void <a href="#unlock"><b>unlock</b></a> ()</div></li>
<li><div class=fn>bool <a href="#locked"><b>locked</b></a> ()</div></li>
<li><div class=fn>bool <a href="#tryLock"><b>tryLock</b></a> ()</div></li>
</ul>
<hr><a name="details"></a><h2>Detailed Description</h2>
The QMutex class provides access serialization between threads.
<p>
<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#qDebug">qDebug</a>("Hello");
<a href="qapplication.html#qDebug">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>
QMutex mutex;
void someMethod()
{
mutex.<a href="#lock">lock</a>();
<a href="qapplication.html#qDebug">qDebug</a>("Hello");
<a href="qapplication.html#qDebug">qDebug</a>("World");
mutex.<a href="#unlock">unlock</a>();
}
</pre>
<p> In Java terms this would be:
<p> <pre>
void someMethod()
{
synchronized {
<a href="qapplication.html#qDebug">qDebug</a>("Hello");
<a href="qapplication.html#qDebug">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.
<p> When you call <a href="#lock">lock</a>() in a thread, other threads that try to call
lock() in the same place will block until the thread that got the
lock calls <a href="#unlock">unlock</a>(). A non-blocking alternative to lock() is
<a href="#tryLock">tryLock</a>().
<p>See also <a href="environment.html">Environment Classes</a> and <a href="thread.html">Threading</a>.
<hr><h2>Member Function Documentation</h2>
<h3 class=fn><a name="QMutex"></a>QMutex::QMutex ( bool recursive = FALSE )
</h3>
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 (the default). 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="#unlock">unlock</a>() calls have
been made.
<h3 class=fn><a name="~QMutex"></a>QMutex::~QMutex ()<tt> [virtual]</tt>
</h3>
Destroys the mutex.
<h3 class=fn>void <a name="lock"></a>QMutex::lock ()
</h3>
Attempt to lock the mutex. If another thread has locked the mutex
then this call will <em>block</em> until that thread has unlocked it.
<p> <p>See also <a href="#unlock">unlock</a>() and <a href="#locked">locked</a>().
<h3 class=fn>bool <a name="locked"></a>QMutex::locked ()
</h3>
Returns TRUE if the mutex is locked by another thread; otherwise
returns FALSE.
<p> <b>Warning:</b> Due to differing implementations of recursive mutexes on various
platforms, calling this function from the same thread that previously locked
the mutex will return undefined results.
<p> <p>See also <a href="#lock">lock</a>() and <a href="#unlock">unlock</a>().
<h3 class=fn>bool <a name="tryLock"></a>QMutex::tryLock ()
</h3>
Attempt to lock the mutex. If the lock was obtained, this function
returns TRUE. If another thread has locked the mutex, this function
returns FALSE, instead of waiting for the mutex to become available,
i.e. it does not block.
<p> The mutex must be unlocked with <a href="#unlock">unlock</a>() before another thread can
successfully lock it.
<p> <p>See also <a href="#lock">lock</a>(), <a href="#unlock">unlock</a>() and <a href="#locked">locked</a>().
<h3 class=fn>void <a name="unlock"></a>QMutex::unlock ()
</h3>
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> <p>See also <a href="#lock">lock</a>() and <a href="#locked">locked</a>().
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