QSemaphore(3qt)

NAME
QSemaphore - Robust integer semaphore

#include <qthread.h>

Inherits Qt.

  Public Members
QSemaphore ( int )
virtual ~QSemaphore ()
int available () const
int total () const
int operator++ ( int )
int operator-- ( int )
int operator+= ( int )
int operator-= ( int )

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.

SEE ALSO
http://doc.trolltech.com/qsemaphore.html http://www.trolltech.com/faq/tech.html

COPYRIGHT
Copyright 1992-2001 Trolltech AS, http://www.trolltech.com. See the license file included in the distribution for a complete license statement.

AUTHOR
Generated automatically from the source code.

BUGS
If you find a bug in Qt, please report it as described in http://doc.trolltech.com/bughowto.html. Good bug reports make our job much simpler. Thank you.

In case of content or formattting problems with this manual page, please report them to qt-bugs@trolltech.com. Please include the name of the manual page (qsemaphore.3qt) and the Qt version (2.3.1).