QSemaphore(3qt)QSemaphore(3qt)NAMEQSemaphore - 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 DOCUMENTATIONQSemaphore::QSemaphore ( int maxcount )
Creates a new semaphore. The semaphore can be concurrently
accessed at most maxcount times.
QSemaphore::~QSemaphore () [virtual]
Destroys the semaphore.
Trolltech AS 13 June 2001 1
QSemaphore(3qt)QSemaphore(3qt)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).
Trolltech AS 13 June 2001 2
