<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/src/tools/qsemaphore.cpp:45 --> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <title>TQSemaphore Class</title> <style type="text/css"><!-- fn { margin-left: 1cm; text-indent: -1cm; } a:link { color: #004faf; text-decoration: none } a:visited { color: #672967; text-decoration: none } body { background: #ffffff; color: black; } --></style> </head> <body> <table border="0" cellpadding="0" cellspacing="0" width="100%"> <tr bgcolor="#E5E5E5"> <td valign=center> <a href="index.html"> <font color="#004faf">Home</font></a> | <a href="classes.html"> <font color="#004faf">All Classes</font></a> | <a href="mainclasses.html"> <font color="#004faf">Main Classes</font></a> | <a href="annotated.html"> <font color="#004faf">Annotated</font></a> | <a href="groups.html"> <font color="#004faf">Grouped Classes</font></a> | <a href="functions.html"> <font color="#004faf">Functions</font></a> </td> <td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>TQSemaphore Class Reference</h1> <p>The TQSemaphore class provides a robust integer semaphore. <a href="#details">More...</a> <p>All the functions in this class are <a href="threads.html#threadsafe">thread-safe</a> when TQt is built with thread support.</p> <p><tt>#include <<a href="qsemaphore-h.html">ntqsemaphore.h</a>></tt> <p><a href="qsemaphore-members.html">List of all member functions.</a> <h2>Public Members</h2> <ul> <li class=fn><a href="#TQSemaphore"><b>TQSemaphore</b></a> ( int maxcount )</li> <li class=fn>virtual <a href="#~TQSemaphore"><b>~TQSemaphore</b></a> ()</li> <li class=fn>int <a href="#available"><b>available</b></a> () const</li> <li class=fn>int <a href="#total"><b>total</b></a> () const</li> <li class=fn>int <a href="#operator++"><b>operator++</b></a> ( int )</li> <li class=fn>int <a href="#operator--"><b>operator--</b></a> ( int )</li> <li class=fn>int <a href="#operator+-eq"><b>operator+=</b></a> ( int n )</li> <li class=fn>int <a href="#operator--eq"><b>operator-=</b></a> ( int n )</li> <li class=fn>bool <a href="#tryAccess"><b>tryAccess</b></a> ( int n )</li> </ul> <hr><a name="details"></a><h2>Detailed Description</h2> The TQSemaphore class provides a robust integer semaphore. <p> <p> A TQSemaphore can be used to serialize thread execution, in a similar way to a <a href="ntqmutex.html">TQMutex</a>. A semaphore differs from a mutex, in that a semaphore can be accessed by more than one thread at a time. <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> A non-computing example of a semaphore would be dining at a restuarant. A semaphore is initialized to have a maximum count equal to the number of chairs in the restuarant. 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> When a semaphore is created it is given a number which is the maximum number of concurrent accesses it will permit. Accesses to the sempahore are gained using <a href="#operator++">operator++</a>() or <a href="#operator+-eq">operator+=</a>(), and released with <a href="#operator--">operator--</a>() or <a href="#operator--eq">operator-=</a>(). The number of accesses allowed is retrieved with <a href="#available">available</a>(), and the total number with <a href="#total">total</a>(). Note that the incrementing functions will block if there aren't enough available accesses. Use <a href="#tryAccess">tryAccess</a>() if you want to actquire accesses without blocking. <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="TQSemaphore"></a>TQSemaphore::TQSemaphore ( int maxcount ) </h3> Creates a new semaphore. The semaphore can be concurrently accessed at most <em>maxcount</em> times. <h3 class=fn><a name="~TQSemaphore"></a>TQSemaphore::~TQSemaphore ()<tt> [virtual]</tt> </h3> Destroys the semaphore. <p> <b>Warning:</b> If you destroy a semaphore that has accesses in use the resultant behavior is undefined. <h3 class=fn>int <a name="available"></a>TQSemaphore::available () const </h3> Returns the number of accesses currently available to the semaphore. <h3 class=fn>int <a name="operator++"></a>TQSemaphore::operator++ ( int ) </h3> Postfix ++ operator. <p> Try to get access to the semaphore. If <a href="#available">available</a>() == 0, this call will block until it can get access, i.e. until <a href="#available">available</a>() > 0. <h3 class=fn>int <a name="operator+-eq"></a>TQSemaphore::operator+= ( int n ) </h3> Try to get access to the semaphore. If <a href="#available">available</a>() < <em>n</em>, this call will block until it can get all the accesses it wants, i.e. until <a href="#available">available</a>() >= <em>n</em>. <h3 class=fn>int <a name="operator--"></a>TQSemaphore::operator-- ( int ) </h3> Postfix -- operator. <p> Release access of the semaphore. This wakes all threads waiting for access to the semaphore. <h3 class=fn>int <a name="operator--eq"></a>TQSemaphore::operator-= ( int n ) </h3> Release <em>n</em> accesses to the semaphore. <h3 class=fn>int <a name="total"></a>TQSemaphore::total () const </h3> Returns the total number of accesses to the semaphore. <h3 class=fn>bool <a name="tryAccess"></a>TQSemaphore::tryAccess ( int n ) </h3> Try to get access to the semaphore. If <a href="#available">available</a>() < <em>n</em>, this function will return FALSE immediately. If <a href="#available">available</a>() >= <em>n</em>, this function will take <em>n</em> accesses and return TRUE. This function does <em>not</em> block. <!-- eof --> <hr><p> This file is part of the <a href="index.html">TQt toolkit</a>. Copyright © 1995-2007 <a href="http://www.trolltech.com/">Trolltech</a>. 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