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/****************************************************************************
**
** 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 sales@trolltech.com.
**
** 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
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