QSemaphore Class Reference
The QSemaphore class provides a robust integer semaphore.
More...
#include <qthread.h>
Inherits Qt.
List of all member functions.
Public Members
Detailed Description
The QSemaphore class provides a robust integer semaphore.
QSemaphore can be used to serialize thread execution, similar to a
QMutex. A semaphore differs from a mutex, in that a semaphore can be
accessed by more than one thread at a time.
An example would be an application that stores data in a large tree
structure. The application creates 10 threads (commonly called a
thread pool) to do 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 2 threads
don't try to search the same branch of the tree.
A real world example of a semaphore would be dining at a restuarant.
A semaphore 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).
Member Function Documentation
QSemaphore::QSemaphore ( int maxcount )
Creates a new semaphore. The semaphore can be concurrently accessed at
most maxcount times.
QSemaphore::~QSemaphore () [virtual]
Destroys the semaphore.
int QSemaphore::available () const
This function returns the number of accesses currently available to
the semaphore.
int QSemaphore::operator++ ( int )
Postfix ++ operator.
Try to get access to the semaphore. If available() is >= total(),
this call will block until it can get access.
int QSemaphore::operator+= ( int n )
Try to get access to the semaphore. If available() is >= total(),
the calling thread blocks until it can get access. The calling will
only get access from the semaphore if it can get all n accesses
at once.
int QSemaphore::operator-- ( int )
Postfix -- operator.
Release access of the semaphore. This wakes all threads waiting for
access to the semaphore.
int QSemaphore::operator-= ( int n )
Release n accesses to the semaphore.
int QSemaphore::total () const
This function returns the total number of accesses to the semaphore.
Search the documentation, FAQ, qt-interest archive and more (uses
www.trolltech.com):
This file is part of the Qt toolkit,
copyright © 1995-2005
Trolltech, all rights reserved.
