Long live Qt 4.5!

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+/****************************************************************************
+**
+** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
+** Contact: Qt Software Information (qt-info@nokia.com)
+**
+** This file is part of the Qt3Support module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** No Commercial Usage
+** This file contains pre-release code and may not be distributed.
+** You may use this file in accordance with the terms and conditions
+** contained in the either Technology Preview License Agreement or the
+** Beta Release License Agreement.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain
+** additional rights. These rights are described in the Nokia Qt LGPL
+** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this
+** package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+** If you are unsure which license is appropriate for your use, please
+** contact the sales department at qt-sales@nokia.com.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "q3semaphore.h"
+
+#include "qmutex.h"
+#include "qwaitcondition.h"
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \class Q3Semaphore
+    \threadsafe
+    \brief The Q3Semaphore class provides a robust integer semaphore.
+
+    \compat
+
+    A Q3Semaphore can be used to serialize thread execution, in a
+    similar way to a QMutex. 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
+    restaurant. A semaphore is initialized to have a maximum count
+    equal to the number of chairs in the restaurant. 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. This amount
+    may be changed using operator++(), operator--(), operator+=() and
+    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 acquire accesses without
+    blocking.
+*/
+
+#ifdef max
+#undef max
+#endif
+
+class Q3SemaphorePrivate {
+public:
+    Q3SemaphorePrivate(int);
+
+    QMutex mutex;
+    QWaitCondition cond;
+
+    int value, max;
+};
+
+
+Q3SemaphorePrivate::Q3SemaphorePrivate(int m)
+    : value(0), max(m)
+{
+}
+
+
+/*!
+    Creates a new semaphore. The semaphore can be concurrently
+    accessed at most \a maxcount times.
+*/
+Q3Semaphore::Q3Semaphore(int maxcount)
+{
+    d = new Q3SemaphorePrivate(maxcount);
+}
+
+
+/*!
+    Destroys the semaphore.
+
+    \warning If you destroy a semaphore that has accesses in use the
+    resultant behavior is undefined.
+*/
+Q3Semaphore::~Q3Semaphore()
+{
+    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 Q3Semaphore::operator++(int)
+{
+    QMutexLocker 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 Q3Semaphore::operator--(int)
+{
+    QMutexLocker 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 Q3Semaphore::operator+=(int n)
+{
+    QMutexLocker locker(&d->mutex);
+
+    if (n < 0 || n > d->max) {
+        qWarning("Q3Semaphore::operator+=: parameter %d out of range", n);
+        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 Q3Semaphore::operator-=(int n)
+{
+    QMutexLocker locker(&d->mutex);
+
+    if (n < 0 || n > d->value) {
+        qWarning("Q3Semaphore::operator-=: parameter %d out of range", n);
+        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 Q3Semaphore::available() const
+{
+    QMutexLocker locker(&d->mutex);
+    return d->max - d->value;
+}
+
+
+/*!
+    Returns the total number of accesses to the semaphore.
+*/
+int Q3Semaphore::total() const
+{
+    QMutexLocker 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 Q3Semaphore::tryAccess(int n)
+{
+    QMutexLocker locker(&d->mutex);
+
+    if (d->value + n > d->max)
+        return false;
+
+    d->value += n;
+
+    return true;
+}
+
+QT_END_NAMESPACE