![]() ![]() |
The QSemaphore class provides a robust integer semaphore. More...
#include <qthread.h>
Inherits Qt.
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).
Creates a new semaphore. The semaphore can be concurrently accessed at most maxcount times.
[virtual]
Destroys the semaphore.
This function returns the number of accesses currently available to the semaphore.
Postfix ++ operator.
Try to get access to the semaphore. If available() is >= total(), this call will block until it can get access.
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.
Postfix -- operator.
Release access of the semaphore. This wakes all threads waiting for access to the semaphore.
Release \n accesses to the semaphore.
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 © 1995-2000 Trolltech, all rights reserved.
Copyright İ 2000 Trolltech | Trademarks | Qt version 2.2.0-beta2
|