122 lines
3.5 KiB
C++
122 lines
3.5 KiB
C++
/****************************************************************************
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**
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** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
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** Contact: http://www.qt-project.org/legal
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**
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** This file is part of the QtCore module of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:LGPL$
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** Commercial License Usage
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** Licensees holding valid commercial Qt licenses may use this file in
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** accordance with the commercial license agreement provided with the
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** Software or, alternatively, in accordance with the terms contained in
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** a written agreement between you and Digia. For licensing terms and
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** conditions see http://qt.digia.com/licensing. For further information
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** use the contact form at http://qt.digia.com/contact-us.
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**
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** GNU Lesser General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU Lesser
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** General Public License version 2.1 as published by the Free Software
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** Foundation and appearing in the file LICENSE.LGPL included in the
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** packaging of this file. Please review the following information to
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** ensure the GNU Lesser General Public License version 2.1 requirements
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** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
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**
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** In addition, as a special exception, Digia gives you certain additional
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** rights. These rights are described in the Digia Qt LGPL Exception
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** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
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**
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** GNU General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU
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** General Public License version 3.0 as published by the Free Software
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** Foundation and appearing in the file LICENSE.GPL included in the
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** packaging of this file. Please review the following information to
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** ensure the GNU General Public License version 3.0 requirements will be
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** met: http://www.gnu.org/copyleft/gpl.html.
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**
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**
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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#ifndef QORDEREDMUTEXLOCKER_P_H
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#define QORDEREDMUTEXLOCKER_P_H
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//
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// W A R N I N G
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// -------------
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//
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// This file is not part of the Qt API. It exists purely as an
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// implementation detail. This header file may change from version to
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// version without notice, or even be removed.
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//
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// We mean it.
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//
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#include <QtCore/qmutex.h>
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QT_BEGIN_NAMESPACE
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/*
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Locks 2 mutexes in a defined order, avoiding a recursive lock if
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we're trying to lock the same mutex twice.
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*/
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class QOrderedMutexLocker
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{
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public:
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QOrderedMutexLocker(QMutex *m1, QMutex *m2)
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: mtx1((m1 == m2) ? m1 : (m1 < m2 ? m1 : m2)),
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mtx2((m1 == m2) ? 0 : (m1 < m2 ? m2 : m1)),
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locked(false)
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{
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relock();
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}
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~QOrderedMutexLocker()
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{
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unlock();
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}
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void relock()
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{
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if (!locked) {
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if (mtx1) mtx1->lock();
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if (mtx2) mtx2->lock();
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locked = true;
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}
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}
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void unlock()
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{
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if (locked) {
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if (mtx1) mtx1->unlock();
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if (mtx2) mtx2->unlock();
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locked = false;
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}
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}
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static bool relock(QMutex *mtx1, QMutex *mtx2)
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{
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// mtx1 is already locked, mtx2 not... do we need to unlock and relock?
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if (mtx1 == mtx2)
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return false;
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if (mtx1 < mtx2) {
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mtx2->lock();
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return true;
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}
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if (!mtx2->tryLock()) {
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mtx1->unlock();
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mtx2->lock();
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mtx1->lock();
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}
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return true;
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}
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private:
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QMutex *mtx1, *mtx2;
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bool locked;
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};
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QT_END_NAMESPACE
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#endif
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