qmutex_p.h

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// Copyright (C) 2016 The Qt Company Ltd.
// Copyright (C) 2016 Intel Corporation.
// Copyright (C) 2012 Olivier Goffart <ogoffart@woboq.com>
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#ifndef QMUTEX_P_H
#define QMUTEX_P_H
 
//
//  W A R N I N G
//  -------------
//
// This file is not part of the Qt API. It exists for the convenience of
// qmutex.cpp and qmutex_unix.cpp. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
 
#include <QtCore/private/qglobal_p.h>
#include <QtCore/qnamespace.h>
#include <QtCore/qmutex.h>
#include <QtCore/qatomic.h>
#include <QtCore/qdeadlinetimer.h>
 
#include "qplatformdefs.h" // _POSIX_VERSION
 
#if defined(Q_OS_DARWIN)
# include <mach/semaphore.h>
#elif defined(Q_OS_UNIX)
#  include <semaphore.h>
#endif
 
struct timespec;
 
QT_BEGIN_NAMESPACE
 
// We manipulate the pointer to this class in inline, atomic code,
// so syncqt mustn't mark them as private, so ELFVERSION:ignore-next
class QMutexPrivate
{
public:
    ~QMutexPrivate();
    QMutexPrivate();
 
    bool wait(QDeadlineTimer timeout = QDeadlineTimer::Forever);
    void wakeUp() noexcept;
 
    // Control the lifetime of the privates
    QAtomicInt refCount;
    int id;
 
    bool ref()
    {
        Q_ASSERT(refCount.loadRelaxed() >= 0);
        int c;
        do {
            c = refCount.loadRelaxed();
            if (c == 0)
                return false;
        } while (!refCount.testAndSetRelaxed(c, c + 1));
        Q_ASSERT(refCount.loadRelaxed() >= 0);
        return true;
    }
    void deref()
    {
        Q_ASSERT(refCount.loadRelaxed() >= 0);
        if (!refCount.deref())
            release();
        Q_ASSERT(refCount.loadRelaxed() >= 0);
    }
    void release();
    static QMutexPrivate *allocate();
 
    QAtomicInt waiters; // Number of threads waiting on this mutex. (may be offset by -BigNumber)
    QAtomicInt possiblyUnlocked; /* Boolean indicating that a timed wait timed out.
                                    When it is true, a reference is held.
                                    It is there to avoid a race that happens if unlock happens right
                                    when the mutex is unlocked.
                                  */
    enum { BigNumber = 0x100000 }; //Must be bigger than the possible number of waiters (number of threads)
    void derefWaiters(int value) noexcept;
 
    //platform specific stuff
#if defined(Q_OS_DARWIN)
    semaphore_t mach_semaphore;
#elif defined(Q_OS_UNIX)
    sem_t semaphore;
#endif
};
 
QT_END_NAMESPACE
 
#endif // QMUTEX_P_H