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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the QtCore 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 Technology Preview License Agreement accompanying
** this package.
**
** 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 1.1, included in the file LGPL_EXCEPTION.txt in this
** package.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
**
**
**
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
#ifndef QORDEREDMUTEXLOCKER_P_H
#define QORDEREDMUTEXLOCKER_P_H
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
QT_BEGIN_NAMESPACE
class QMutex;
/*
Locks 2 mutexes in a defined order, avoiding a recursive lock if
we're trying to lock the same mutex twice.
*/
class QOrderedMutexLocker
{
public:
QOrderedMutexLocker(QMutex *m1, QMutex *m2)
: mtx1((m1 == m2) ? m1 : (m1 < m2 ? m1 : m2)),
mtx2((m1 == m2) ? 0 : (m1 < m2 ? m2 : m1)),
locked(false)
{
relock();
}
~QOrderedMutexLocker()
{
unlock();
}
void relock()
{
if (!locked) {
if (mtx1) mtx1->lock();
if (mtx2) mtx2->lock();
locked = true;
}
}
void unlock()
{
if (locked) {
if (mtx1) mtx1->unlock();
if (mtx2) mtx2->unlock();
locked = false;
}
}
static bool relock(QMutex *mtx1, QMutex *mtx2)
{
// mtx1 is already locked, mtx2 not... do we need to unlock and relock?
if (mtx1 == mtx2)
return false;
if (mtx1 < mtx2) {
mtx2->lock();
return true;
}
mtx1->unlock();
mtx2->lock();
mtx1->lock();
return true;
}
private:
QMutex *mtx1, *mtx2;
bool locked;
};
QT_END_NAMESPACE
#endif
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