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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>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 <<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 class=fn><a href="#QSemaphore"><b>QSemaphore</b></a> ( int maxcount )</li>
<li class=fn>virtual <a href="#~QSemaphore"><b>~QSemaphore</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 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. 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 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.
<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>QSemaphore::available () const
</h3>
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>
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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