qsemaphore.3qt

Trolltech公司发布的基于C++图形开发环境

'\" t
.TH QSemaphore 3qt "24 January 2005" "Trolltech AS" \" -*- nroff -*-
.\" Copyright 1992-2001 Trolltech AS.  All rights reserved.  See the
.\" license file included in the distribution for a complete license
.\" statement.
.\"
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.nh
.SH NAME
QSemaphore \- Robust integer semaphore
.br
.PP
\fC#include <qthread.h>\fR
.PP
Inherits Qt.
.PP
.SS "Public Members"
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.BI "\fBQSemaphore\fR ( int ) "
.br
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.BI "virtual \fB~QSemaphore\fR () "
.br
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.BI "int \fBavailable\fR () const"
.br
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.BI "int \fBtotal\fR () const"
.br
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.BI "int \fBoperator++\fR ( int ) "
.br
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.BI "int \fBoperator--\fR ( int ) "
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.BI "int \fBoperator+=\fR ( int ) "
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.BI "int \fBoperator-=\fR ( int ) "
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.SH DESCRIPTION
The QSemaphore class provides a robust integer semaphore.
.PP
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.
.PP
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.
.PP
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).
.SH MEMBER FUNCTION DOCUMENTATION
.SH "QSemaphore::QSemaphore ( int maxcount )"
Creates a new semaphore. The semaphore can be concurrently accessed at most \fImaxcount\fR times.
.SH "QSemaphore::~QSemaphore () \fC[virtual]\fR"
Destroys the semaphore.
.SH "int QSemaphore::available () const"
This function returns the number of accesses currently available to the semaphore.
.SH "int QSemaphore::operator++ ( int )"
Postfix ++ operator.
.PP
Try to get access to the semaphore. If available() is >= total(), this call will block until it can get access.
.SH "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 \fIn\fR accesses at once.
.SH "int QSemaphore::operator-- ( int )"
Postfix -- operator.
.PP
Release access of the semaphore. This wakes all threads waiting for access to the semaphore.
.SH "int QSemaphore::operator-= ( int n )"
Release \fIn\fR accesses to the semaphore.
.SH "int QSemaphore::total () const"
This function returns the total number of accesses to the semaphore.
.SH "SEE ALSO"
.BR http://doc.trolltech.com/qsemaphore.html
.BR http://www.trolltech.com/faq/tech.html
.SH COPYRIGHT
Copyright 1992-2001 Trolltech AS, http://www.trolltech.com.  See the
license file included in the distribution for a complete license
statement.
.SH AUTHOR
Generated automatically from the source code.
.SH BUGS
If you find a bug in Qt, please report it as described in
.BR http://doc.trolltech.com/bughowto.html .
Good bug reports make our job much simpler. Thank you.
.P
In case of content or formattting problems with this manual page, please
report them to
.BR [e-mail] .
Please include the name of the manual page (qsemaphore.3qt) and the Qt
version (2.3.10).