You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
149 lines
6.8 KiB
149 lines
6.8 KiB
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
|
|
<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="tqsemaphore-h.html">tqsemaphore.h</a>></tt>
|
|
<p><a href="tqsemaphore-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="tqmutex.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 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="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>. All Rights Reserved.<p><address><hr><div align=center>
|
|
<table width=100% cellspacing=0 border=0><tr>
|
|
<td>Copyright © 2007
|
|
<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
|
|
<td align=right><div align=right>TQt 3.3.8</div>
|
|
</table></div></address></body>
|
|
</html>
|