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<h1 class="title">Q3Semaphore Class Reference</h1>
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<!-- $$$Q3Semaphore-brief -->
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<p>The Q3Semaphore class provides a robust integer semaphore. <a href="#details">More...</a></p>
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<!-- @@@Q3Semaphore -->
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<pre class="cpp"> <span class="preprocessor">#include <Q3Semaphore></span></pre><p><b>This class is part of the Qt 3 support library.</b> It is provided to keep old source code working. We strongly advise against using it in new code. See <a href="porting4.html">Porting to Qt 4</a> for more information.</p>
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<p><b>Note:</b> All functions in this class are <a href="threads-reentrancy.html#thread-safe">thread-safe</a>.</p>
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<h2>Public Functions</h2>
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<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="q3semaphore.html#Q3Semaphore">Q3Semaphore</a></b> ( int <i>maxcount</i> )</td></tr>
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<tr><td class="memItemLeft rightAlign topAlign"> virtual </td><td class="memItemRight bottomAlign"><b><a href="q3semaphore.html#dtor.Q3Semaphore">~Q3Semaphore</a></b> ()</td></tr>
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<tr><td class="memItemLeft rightAlign topAlign"> int </td><td class="memItemRight bottomAlign"><b><a href="q3semaphore.html#available">available</a></b> () const</td></tr>
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<tr><td class="memItemLeft rightAlign topAlign"> int </td><td class="memItemRight bottomAlign"><b><a href="q3semaphore.html#total">total</a></b> () const</td></tr>
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<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="q3semaphore.html#tryAccess">tryAccess</a></b> ( int <i>n</i> )</td></tr>
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<tr><td class="memItemLeft rightAlign topAlign"> int </td><td class="memItemRight bottomAlign"><b><a href="q3semaphore.html#operator-2b-2b">operator++</a></b> ( int )</td></tr>
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<tr><td class="memItemLeft rightAlign topAlign"> int </td><td class="memItemRight bottomAlign"><b><a href="q3semaphore.html#operator-2b-eq">operator+=</a></b> ( int <i>n</i> )</td></tr>
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<tr><td class="memItemLeft rightAlign topAlign"> int </td><td class="memItemRight bottomAlign"><b><a href="q3semaphore.html#operator--">operator--</a></b> ( int )</td></tr>
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<tr><td class="memItemLeft rightAlign topAlign"> int </td><td class="memItemRight bottomAlign"><b><a href="q3semaphore.html#operator--eq">operator-=</a></b> ( int <i>n</i> )</td></tr>
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<a name="details"></a>
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<!-- $$$Q3Semaphore-description -->
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<div class="descr">
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<h2>Detailed Description</h2>
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<p>The Q3Semaphore class provides a robust integer semaphore.</p>
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<p>A Q3Semaphore can be used to serialize thread execution, in a similar way to a <a href="qmutex.html">QMutex</a>. A semaphore differs from a mutex, in that a semaphore can be accessed by more than one thread at a time.</p>
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<p>For example, suppose we have an application that stores data in a large tree structure. The application creates 10 threads (commonly called a thread pool) to perform searches on the tree. When the application searches the tree for some piece of data, it uses one thread per base node to do the searching. A semaphore could be used to make sure that two threads don't try to search the same branch of the tree at the same time.</p>
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<p>A non-computing example of a semaphore would be dining at a restaurant. A semaphore is initialized to have a maximum count equal to the number of chairs in the restaurant. As people arrive, they want a seat. As seats are filled, the semaphore is accessed, once per person. As people leave, the access is released, allowing more people to enter. If a party of 10 people want to be seated, but there are only 9 seats, those 10 people will wait, but a party of 4 people would be seated (taking the available seats to 5, making the party of 10 people wait longer).</p>
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<p>When a semaphore is created it is given a number which is the maximum number of concurrent accesses it will permit. This amount may be changed using operator++(), operator--(), operator+=() and operator-=(). The number of accesses allowed is retrieved with <a href="q3semaphore.html#available">available</a>(), and the total number with <a href="q3semaphore.html#total">total</a>(). Note that the incrementing functions will block if there aren't enough available accesses. Use <a href="q3semaphore.html#tryAccess">tryAccess</a>() if you want to acquire accesses without blocking.</p>
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</div>
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<!-- @@@Q3Semaphore -->
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<div class="func">
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<h2>Member Function Documentation</h2>
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<!-- $$$Q3Semaphore[overload1]$$$Q3Semaphoreint -->
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<h3 class="fn"><a name="Q3Semaphore"></a>Q3Semaphore::<span class="name">Q3Semaphore</span> ( <span class="type">int</span> <i>maxcount</i> )</h3>
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<p>Creates a new semaphore. The semaphore can be concurrently accessed at most <i>maxcount</i> times.</p>
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<!-- @@@Q3Semaphore -->
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<!-- $$$~Q3Semaphore[overload1]$$$~Q3Semaphore -->
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<h3 class="fn"><a name="dtor.Q3Semaphore"></a>Q3Semaphore::<span class="name">~Q3Semaphore</span> ()<tt> [virtual]</tt></h3>
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<p>Destroys the semaphore.</p>
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<p><b>Warning:</b> If you destroy a semaphore that has accesses in use the resultant behavior is undefined.</p>
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<!-- @@@~Q3Semaphore -->
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<!-- $$$available[overload1]$$$available -->
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<h3 class="fn"><a name="available"></a><span class="type">int</span> Q3Semaphore::<span class="name">available</span> () const</h3>
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<p>Returns the number of accesses currently available to the semaphore.</p>
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<!-- @@@available -->
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<!-- $$$total[overload1]$$$total -->
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<h3 class="fn"><a name="total"></a><span class="type">int</span> Q3Semaphore::<span class="name">total</span> () const</h3>
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<p>Returns the total number of accesses to the semaphore.</p>
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<!-- @@@total -->
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<!-- $$$tryAccess[overload1]$$$tryAccessint -->
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<h3 class="fn"><a name="tryAccess"></a><span class="type">bool</span> Q3Semaphore::<span class="name">tryAccess</span> ( <span class="type">int</span> <i>n</i> )</h3>
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<p>Try to get access to the semaphore. If <a href="q3semaphore.html#available">available</a>() < <i>n</i>, this function will return false immediately. If <a href="q3semaphore.html#available">available</a>() >= <i>n</i>, this function will take <i>n</i> accesses and return true. This function does <i>not</i> block.</p>
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<!-- @@@tryAccess -->
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<!-- $$$operator++[overload1]$$$operator++int -->
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<h3 class="fn"><a name="operator-2b-2b"></a><span class="type">int</span> Q3Semaphore::<span class="name">operator++</span> ( <span class="type">int</span> )</h3>
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<p>Postfix ++ operator.</p>
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<p>Try to get access to the semaphore. If <a href="q3semaphore.html#available">available</a>() == 0, this call will block until it can get access, i.e. until <a href="q3semaphore.html#available">available</a>() > 0.</p>
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<!-- @@@operator++ -->
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<!-- $$$operator+=[overload1]$$$operator+=int -->
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<h3 class="fn"><a name="operator-2b-eq"></a><span class="type">int</span> Q3Semaphore::<span class="name">operator+=</span> ( <span class="type">int</span> <i>n</i> )</h3>
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<p>Try to get access to the semaphore. If <a href="q3semaphore.html#available">available</a>() < <i>n</i>, this call will block until it can get all the accesses it wants, i.e. until <a href="q3semaphore.html#available">available</a>() >= <i>n</i>.</p>
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<!-- @@@operator+= -->
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<!-- $$$operator--[overload1]$$$operator--int -->
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<h3 class="fn"><a name="operator--"></a><span class="type">int</span> Q3Semaphore::<span class="name">operator--</span> ( <span class="type">int</span> )</h3>
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<p>Postfix -- operator.</p>
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<p>Release access of the semaphore. This wakes all threads waiting for access to the semaphore.</p>
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<!-- @@@operator-- -->
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<!-- $$$operator-=[overload1]$$$operator-=int -->
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<h3 class="fn"><a name="operator--eq"></a><span class="type">int</span> Q3Semaphore::<span class="name">operator-=</span> ( <span class="type">int</span> <i>n</i> )</h3>
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<p>Release <i>n</i> accesses to the semaphore.</p>
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<!-- @@@operator-= -->
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