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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>QSemaphore Class Reference</h1>
<p>The QSemaphore class provides a robust integer semaphore.
<a href="#details">More...</a>
<p><tt>#include <<a href="qsemaphore-h.html">qsemaphore.h</a>></tt>
<p><a href="qsemaphore-members.html">List of all member functions.</a>
<h2>Public Members</h2>
<ul>
<li><div class=fn><a href="#QSemaphore"><b>QSemaphore</b></a> ( int maxcount )</div></li>
<li><div class=fn>virtual <a href="#~QSemaphore"><b>~QSemaphore</b></a> ()</div></li>
<li><div class=fn>int <a href="#available"><b>available</b></a> () const</div></li>
<li><div class=fn>int <a href="#total"><b>total</b></a> () const</div></li>
<li><div class=fn>int <a href="#operator++"><b>operator++</b></a> ( int )</div></li>
<li><div class=fn>int <a href="#operator--"><b>operator--</b></a> ( int )</div></li>
<li><div class=fn>int <a href="#operator+-eq"><b>operator+=</b></a> ( int n )</div></li>
<li><div class=fn>int <a href="#operator--eq"><b>operator-=</b></a> ( int n )</div></li>
<li><div class=fn>bool <a href="#tryAccess"><b>tryAccess</b></a> ( int n )</div></li>
</ul>
<hr><a name="details"></a><h2>Detailed Description</h2>
The QSemaphore class provides a robust integer semaphore.
<p>
<p> A QSemaphore 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> 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. This amount
may be changed using <a href="#operator++">operator++</a>(), <a href="#operator--">operator--</a>(), <a href="#operator+-eq">operator+=</a>() and
<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 acquire 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="QSemaphore"></a>QSemaphore::QSemaphore ( int maxcount )
</h3>
Creates a new semaphore. The semaphore can be concurrently accessed at
most <em>maxcount</em> times.
<h3 class=fn><a name="~QSemaphore"></a>QSemaphore::~QSemaphore ()<tt> [virtual]</tt>
</h3>
Destroys the semaphore.
<h3 class=fn>int <a name="available"></a>QSemaphore::available () const
</h3>
This function returns the number of accesses currently available to
the semaphore.
<h3 class=fn>int <a name="operator++"></a>QSemaphore::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>QSemaphore::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>QSemaphore::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>QSemaphore::operator-= ( int n )
</h3>
Release <em>n</em> accesses to the semaphore.
<h3 class=fn>int <a name="total"></a>QSemaphore::total () const
</h3>
This function returns the total number of accesses to the semaphore.
<h3 class=fn>bool <a name="tryAccess"></a>QSemaphore::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.
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