diff options
Diffstat (limited to 'src/tools/qsemaphore.cpp')
| -rw-r--r-- | src/tools/qsemaphore.cpp | 255 |
1 files changed, 255 insertions, 0 deletions
diff --git a/src/tools/qsemaphore.cpp b/src/tools/qsemaphore.cpp new file mode 100644 index 000000000..608563ee5 --- /dev/null +++ b/src/tools/qsemaphore.cpp @@ -0,0 +1,255 @@ +/**************************************************************************** +** +** TQSemaphore class for Unix +** +** Created : 20010725 +** +** Copyright (C) 1992-2008 Trolltech ASA. All rights reserved. +** +** This file is part of the tools module of the TQt GUI Toolkit. +** +** This file may be used under the terms of the GNU General +** Public License versions 2.0 or 3.0 as published by the Free +** Software Foundation and appearing in the files LICENSE.GPL2 +** and LICENSE.GPL3 included in the packaging of this file. +** Alternatively you may (at your option) use any later version +** of the GNU General Public License if such license has been +** publicly approved by Trolltech ASA (or its successors, if any) +** and the KDE Free TQt Foundation. +** +** Please review the following information to ensure GNU General +** Public Licensing retquirements will be met: +** http://trolltech.com/products/qt/licenses/licensing/opensource/. +** If you are unsure which license is appropriate for your use, please +** review the following information: +** http://trolltech.com/products/qt/licenses/licensing/licensingoverview +** or contact the sales department at [email protected]. +** +** This file may be used under the terms of the Q Public License as +** defined by Trolltech ASA and appearing in the file LICENSE.TQPL +** included in the packaging of this file. Licensees holding valid TQt +** Commercial licenses may use this file in accordance with the TQt +** Commercial License Agreement provided with the Software. +** +** This file is provided "AS IS" with NO WARRANTY OF ANY KIND, +** INCLUDING THE WARRANTIES OF DESIGN, MERCHANTABILITY AND FITNESS FOR +** A PARTICULAR PURPOSE. Trolltech reserves all rights not granted +** herein. +** +**********************************************************************/ + +#if defined(QT_THREAD_SUPPORT) + +#include "qsemaphore.h" +#include "qmutex.h" +#include "qwaitcondition.h" + + +/*! + \class TQSemaphore qsemaphore.h + \threadsafe + \brief The TQSemaphore class provides a robust integer semaphore. + + \ingroup thread + \ingroup environment + + A TQSemaphore can be used to serialize thread execution, in a + similar way to a TQMutex. A semaphore differs from a mutex, in + that a semaphore can be accessed by more than one thread at a + time. + + For example, suppose we have an application that stores data in a + large tree structure. The application creates 10 threads + (commonly called a thread pool) to perform 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 two threads don't try to search + the same branch of the tree at the same time. + + A non-computing example of a semaphore would be dining at a + restuarant. A semaphore is 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). + + When a semaphore is created it is given a number which is the + maximum number of concurrent accesses it will permit. Accesses to + the sempahore are gained using operator++() or operator+=(), and + released with operator--() or operator-=(). The number of + accesses allowed is retrieved with available(), and the total + number with total(). Note that the incrementing functions will + block if there aren't enough available accesses. Use tryAccess() + if you want to actquire accesses without blocking. +*/ + + +class TQSemaphorePrivate { +public: + TQSemaphorePrivate(int); + + TQMutex mutex; + TQWaitCondition cond; + + int value, max; +}; + + +TQSemaphorePrivate::TQSemaphorePrivate(int m) + : mutex(FALSE), value(0), max(m) +{ +} + + +/*! + Creates a new semaphore. The semaphore can be concurrently + accessed at most \a maxcount times. +*/ +TQSemaphore::TQSemaphore(int maxcount) +{ + d = new TQSemaphorePrivate(maxcount); +} + + +/*! + Destroys the semaphore. + + \warning If you destroy a semaphore that has accesses in use the + resultant behavior is undefined. +*/ +TQSemaphore::~TQSemaphore() +{ + delete d; +} + + +/*! + Postfix ++ operator. + + Try to get access to the semaphore. If \l available() == 0, this + call will block until it can get access, i.e. until available() \> + 0. +*/ +int TQSemaphore::operator++(int) +{ + TQMutexLocker locker(&d->mutex); + while (d->value >= d->max) + d->cond.wait(locker.mutex()); + + ++d->value; + if (d->value > d->max) + d->value = d->max; + + return d->value; +} + + +/*! + Postfix -- operator. + + Release access of the semaphore. This wakes all threads waiting + for access to the semaphore. +*/ +int TQSemaphore::operator--(int) +{ + TQMutexLocker locker(&d->mutex); + + --d->value; + if (d->value < 0) + d->value = 0; + + d->cond.wakeAll(); + + return d->value; +} + + +/*! + Try to get access to the semaphore. If \l available() \< \a n, this + call will block until it can get all the accesses it wants, i.e. + until available() \>= \a n. +*/ +int TQSemaphore::operator+=(int n) +{ + TQMutexLocker locker(&d->mutex); + + if ( n < 0 || n > d->max ) { +#ifdef QT_CHECK_RANGE + qWarning( "TQSemaphore::operator+=: paramter %d out of range", n ); +#endif // QT_CHECK_RANGE + n = n < 0 ? 0 : d->max; + } + + while (d->value + n > d->max) + d->cond.wait(locker.mutex()); + + d->value += n; + + return d->value; +} + + +/*! + Release \a n accesses to the semaphore. +*/ +int TQSemaphore::operator-=(int n) +{ + TQMutexLocker locker(&d->mutex); + + if ( n < 0 || n > d->value ) { +#ifdef QT_CHECK_RANGE + qWarning( "TQSemaphore::operator-=: paramter %d out of range", n ); +#endif // QT_CHECK_RANGE + n = n < 0 ? 0 : d->value; + } + + d->value -= n; + d->cond.wakeAll(); + + return d->value; +} + + +/*! + Returns the number of accesses currently available to the + semaphore. +*/ +int TQSemaphore::available() const +{ + TQMutexLocker locker(&d->mutex); + return d->max - d->value; +} + + +/*! + Returns the total number of accesses to the semaphore. +*/ +int TQSemaphore::total() const +{ + TQMutexLocker locker(&d->mutex); + return d->max; +} + + +/*! + Try to get access to the semaphore. If \l available() \< \a n, this + function will return FALSE immediately. If \l available() \>= \a n, + this function will take \a n accesses and return TRUE. This + function does \e not block. +*/ +bool TQSemaphore::tryAccess(int n) +{ + TQMutexLocker locker(&d->mutex); + + if (d->value + n > d->max) + return FALSE; + + d->value += n; + + return TRUE; +} + +#endif // QT_THREAD_SUPPORT |