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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>QMutexLocker Class Reference</h1>

<p>The QMutexLocker class simplifies locking and unlocking QMutexes.
<a href="#details">More...</a>
<p>All the functions in this class are <a href="threads.html#threadsafe">thread-safe</a> when Qt is built with thread support.</p>
<p><tt>#include &lt;<a href="qmutex-h.html">qmutex.h</a>&gt;</tt>
<p><a href="qmutexlocker-members.html">List of all member functions.</a>
<h2>Public Members</h2>
<ul>
<li class=fn><a href="#QMutexLocker"><b>QMutexLocker</b></a> ( QMutex&nbsp;*&nbsp;mutex )</li>
<li class=fn><a href="#~QMutexLocker"><b>~QMutexLocker</b></a> ()</li>
<li class=fn>QMutex * <a href="#mutex"><b>mutex</b></a> () const</li>
</ul>
<hr><a name="details"></a><h2>Detailed Description</h2>


The QMutexLocker class simplifies locking and unlocking QMutexes.
<p> 
<p> 

<p> The purpose of QMutexLocker is to simplify <a href="qmutex.html">QMutex</a> locking and
unlocking. Locking and unlocking a QMutex in complex functions and
statements or in exception handling code is error prone and
difficult to debug. QMutexLocker should be used in such situations
to ensure that the state of the mutex is well defined and always
locked and unlocked properly.
<p> QMutexLocker should be created within a function where a QMutex
needs to be locked. The mutex is locked when QMutexLocker is
created, and unlocked when QMutexLocker is destroyed.
<p> For example, this complex function locks a QMutex upon entering
the function and unlocks the mutex at all the exit points:
<p> <pre>
    int complexFunction( int flag )
    {
        mutex.lock();

        int return_value = 0;

        switch ( flag ) {
        case 0:
        case 1:
            {
                mutex.unlock();
                return moreComplexFunction( flag );
            }

        case 2:
            {
                int status = anotherFunction();
                if ( status &lt; 0 ) {
                    mutex.unlock();
                    return -2;
                }
                return_value = status + flag;
                break;
            }

        default:
            {
                if ( flag &gt; 10 ) {
                    mutex.unlock();
                    return -1;
                }
                break;
            }
        }

        mutex.unlock();
        return return_value;
    }
    </pre>
 
<p> This example function will get more complicated as it is
developed, which increases the likelihood that errors will occur.
<p> Using QMutexLocker greatly simplifies the code, and makes it more
readable:
<p> <pre>
    int complexFunction( int flag )
    {
        QMutexLocker locker( &amp;mutex );

        int return_value = 0;

        switch ( flag ) {
        case 0:
        case 1:
            {
                return moreComplexFunction( flag );
            }

        case 2:
            {
                int status = anotherFunction();
                if ( status &lt; 0 )
                    return -2;
                return_value = status + flag;
                break;
            }

        default:
            {
                if ( flag &gt; 10 )
                    return -1;
                break;
            }
        }

        return return_value;
    }
    </pre>
 
<p> Now, the mutex will always be unlocked when the QMutexLocker
object is destroyed (when the function returns since <tt>locker</tt> is
an auto variable). Note that the mutex will be unlocked after
the call to moreComplexFunction() in this example, avoiding
possible bugs caused by unlocking the mutex too early, as in
the first example.
<p> The same principle applies to code that throws and catches
exceptions. An exception that is not caught in the function that
has locked the mutex has no way of unlocking the mutex before the
exception is passed up the stack to the calling function.
<p> QMutexLocker also provides a <a href="#mutex">mutex</a>() member function that returns
the mutex on which the QMutexLocker is operating. This is useful
for code that needs access to the mutex, such as
<a href="qwaitcondition.html#wait">QWaitCondition::wait</a>(). For example:
<p> <pre>
    class SignalWaiter
    {
    private:
        QMutexLocker locker;

    public:
        SignalWaiter( <a href="qmutex.html">QMutex</a> *mutex )
            : locker( mutex )
        {
        }

        void waitForSignal()
        {
            ...
            ...
            ...

            while ( ! signalled )
                waitcondition.wait( locker.<a href="#mutex">mutex</a>() );

            ...
            ...
            ...
        }
    };
    </pre>
 
<p> <p>See also <a href="qmutex.html">QMutex</a>, <a href="qwaitcondition.html">QWaitCondition</a>, <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="QMutexLocker"></a>QMutexLocker::QMutexLocker ( <a href="qmutex.html">QMutex</a>&nbsp;*&nbsp;mutex )
</h3>

<p> Constructs a QMutexLocker and locks <em>mutex</em>. The mutex will be
unlocked when the QMutexLocker is destroyed. If <em>mutex</em> is zero,
QMutexLocker does nothing.
<p> <p>See also <a href="qmutex.html#lock">QMutex::lock</a>().

<h3 class=fn><a name="~QMutexLocker"></a>QMutexLocker::~QMutexLocker ()
</h3>

<p> Destroys the QMutexLocker and unlocks the mutex which was locked
in the constructor.
<p> <p>See also <a href="#QMutexLocker">QMutexLocker::QMutexLocker</a>() and <a href="qmutex.html#unlock">QMutex::unlock</a>().

<h3 class=fn><a href="qmutex.html">QMutex</a>&nbsp;* <a name="mutex"></a>QMutexLocker::mutex () const
</h3>

<p> Returns a pointer to the mutex which was locked in the
constructor.
<p> <p>See also <a href="#QMutexLocker">QMutexLocker::QMutexLocker</a>().

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