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256 lines
6.8 KiB
256 lines
6.8 KiB
/****************************************************************************
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**
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** TQSemaphore class for Unix
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**
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** Created : 20010725
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**
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** Copyright (C) 1992-2008 Trolltech ASA. All rights reserved.
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**
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** This file is part of the tools module of the TQt GUI Toolkit.
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**
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** This file may be used under the terms of the GNU General
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** Public License versions 2.0 or 3.0 as published by the Free
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** Software Foundation and appearing in the files LICENSE.GPL2
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** and LICENSE.GPL3 included in the packaging of this file.
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** Alternatively you may (at your option) use any later version
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** of the GNU General Public License if such license has been
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** publicly approved by Trolltech ASA (or its successors, if any)
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** and the KDE Free TQt Foundation.
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**
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** Please review the following information to ensure GNU General
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** Public Licensing requirements will be met:
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** http://trolltech.com/products/qt/licenses/licensing/opensource/.
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** If you are unsure which license is appropriate for your use, please
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** review the following information:
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** http://trolltech.com/products/qt/licenses/licensing/licensingoverview
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** or contact the sales department at sales@trolltech.com.
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**
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** This file may be used under the terms of the Q Public License as
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** defined by Trolltech ASA and appearing in the file LICENSE.TQPL
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** included in the packaging of this file. Licensees holding valid TQt
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** Commercial licenses may use this file in accordance with the TQt
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** Commercial License Agreement provided with the Software.
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**
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** This file is provided "AS IS" with NO WARRANTY OF ANY KIND,
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** INCLUDING THE WARRANTIES OF DESIGN, MERCHANTABILITY AND FITNESS FOR
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** A PARTICULAR PURPOSE. Trolltech reserves all rights not granted
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** herein.
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**
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**********************************************************************/
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#if defined(TQT_THREAD_SUPPORT)
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#include "ntqsemaphore.h"
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#include "ntqmutex.h"
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#include "ntqwaitcondition.h"
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/*!
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\class TQSemaphore ntqsemaphore.h
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\threadsafe
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\brief The TQSemaphore class provides a robust integer semaphore.
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\ingroup thread
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\ingroup environment
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A TQSemaphore can be used to serialize thread execution, in a
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similar way to a TQMutex. A semaphore differs from a mutex, in
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that a semaphore can be accessed by more than one thread at a
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time.
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For example, suppose we have an application that stores data in a
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large tree structure. The application creates 10 threads
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(commonly called a thread pool) to perform searches on the tree.
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When the application searches the tree for some piece of data, it
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uses one thread per base node to do the searching. A semaphore
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could be used to make sure that two threads don't try to search
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the same branch of the tree at the same time.
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A non-computing example of a semaphore would be dining at a
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restuarant. A semaphore is initialized to have a maximum count
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equal to the number of chairs in the restuarant. As people
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arrive, they want a seat. As seats are filled, the semaphore is
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accessed, once per person. As people leave, the access is
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released, allowing more people to enter. If a party of 10 people
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want to be seated, but there are only 9 seats, those 10 people
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will wait, but a party of 4 people would be seated (taking the
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available seats to 5, making the party of 10 people wait longer).
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When a semaphore is created it is given a number which is the
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maximum number of concurrent accesses it will permit. Accesses to
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the sempahore are gained using operator++() or operator+=(), and
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released with operator--() or operator-=(). The number of
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accesses allowed is retrieved with available(), and the total
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number with total(). Note that the incrementing functions will
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block if there aren't enough available accesses. Use tryAccess()
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if you want to acquire accesses without blocking.
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*/
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class TQSemaphorePrivate {
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public:
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TQSemaphorePrivate(int);
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TQMutex mutex;
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TQWaitCondition cond;
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int value, max;
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};
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TQSemaphorePrivate::TQSemaphorePrivate(int m)
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: mutex(FALSE), value(0), max(m)
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{
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}
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/*!
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Creates a new semaphore. The semaphore can be concurrently
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accessed at most \a maxcount times.
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*/
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TQSemaphore::TQSemaphore(int maxcount)
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{
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d = new TQSemaphorePrivate(maxcount);
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}
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/*!
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Destroys the semaphore.
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\warning If you destroy a semaphore that has accesses in use the
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resultant behavior is undefined.
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*/
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TQSemaphore::~TQSemaphore()
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{
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delete d;
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}
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/*!
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Postfix ++ operator.
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Try to get access to the semaphore. If \l available() == 0, this
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call will block until it can get access, i.e. until available() \>
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0.
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*/
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int TQSemaphore::operator++(int)
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{
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TQMutexLocker locker(&d->mutex);
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while (d->value >= d->max)
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d->cond.wait(locker.mutex());
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++d->value;
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if (d->value > d->max)
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d->value = d->max;
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return d->value;
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}
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/*!
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Postfix -- operator.
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Release access of the semaphore. This wakes all threads waiting
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for access to the semaphore.
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*/
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int TQSemaphore::operator--(int)
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{
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TQMutexLocker locker(&d->mutex);
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--d->value;
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if (d->value < 0)
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d->value = 0;
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d->cond.wakeAll();
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return d->value;
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}
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/*!
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Try to get access to the semaphore. If \l available() \< \a n, this
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call will block until it can get all the accesses it wants, i.e.
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until available() \>= \a n.
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*/
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int TQSemaphore::operator+=(int n)
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{
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TQMutexLocker locker(&d->mutex);
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if ( n < 0 || n > d->max ) {
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#ifdef QT_CHECK_RANGE
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tqWarning( "TQSemaphore::operator+=: paramter %d out of range", n );
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#endif // QT_CHECK_RANGE
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n = n < 0 ? 0 : d->max;
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}
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while (d->value + n > d->max)
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d->cond.wait(locker.mutex());
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d->value += n;
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return d->value;
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}
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/*!
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Release \a n accesses to the semaphore.
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*/
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int TQSemaphore::operator-=(int n)
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{
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TQMutexLocker locker(&d->mutex);
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if ( n < 0 || n > d->value ) {
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#ifdef QT_CHECK_RANGE
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tqWarning( "TQSemaphore::operator-=: paramter %d out of range", n );
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#endif // QT_CHECK_RANGE
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n = n < 0 ? 0 : d->value;
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}
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d->value -= n;
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d->cond.wakeAll();
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return d->value;
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}
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/*!
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Returns the number of accesses currently available to the
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semaphore.
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*/
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int TQSemaphore::available() const
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{
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TQMutexLocker locker(&d->mutex);
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return d->max - d->value;
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}
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/*!
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Returns the total number of accesses to the semaphore.
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*/
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int TQSemaphore::total() const
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{
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TQMutexLocker locker(&d->mutex);
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return d->max;
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}
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/*!
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Try to get access to the semaphore. If \l available() \< \a n, this
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function will return FALSE immediately. If \l available() \>= \a n,
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this function will take \a n accesses and return TRUE. This
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function does \e not block.
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*/
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bool TQSemaphore::tryAccess(int n)
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{
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TQMutexLocker locker(&d->mutex);
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if (d->value + n > d->max)
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return FALSE;
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d->value += n;
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return TRUE;
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}
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#endif // TQT_THREAD_SUPPORT
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