/****************************************************************************

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** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).

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** Contact: Nokia Corporation (qt-info@nokia.com)

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** This file is part of the test suite of the Qt Toolkit.

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** No Commercial Usage

** This file contains pre-release code and may not be distributed.

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** contained in the Technology Preview License Agreement accompanying

** this package.

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****************************************************************************/

#ifndef QTHREADONCE_H

#define QTHREADONCE_H

#include <QtCore/qglobal.h>

#include <QtCore/qatomic.h>

QT_BEGIN_HEADER

QT_MODULE(Core)

#ifndef QT_NO_THREAD

class QOnceControl

{

public:

    QOnceControl(QBasicAtomicInt *);

    ~QOnceControl();

    bool mustRunCode();

    void done();

private:

    QBasicAtomicInt *gv;

    union {

        qint32 extra;

        void *d;

    };

};

#define Q_ONCE_GV_NAME2(prefix, line)   prefix ## line

#define Q_ONCE_GV_NAME(prefix, line)    Q_ONCE_GV_NAME2(prefix, line)

#define Q_ONCE_GV                       Q_ONCE_GV_NAME(_q_once_, __LINE__)

#define Q_ONCE \

    static QBasicAtomicInt Q_ONCE_GV = Q_BASIC_ATOMIC_INITIALIZER(0);   \

    if (0){} else                                                       \

        for (QOnceControl _control_(&Q_ONCE_GV); _control_.mustRunCode(); _control_.done())

template<typename T>

class QSingleton

{

    // this is a POD-like class

    struct Destructor

    {

        T *&pointer;

        Destructor(T *&ptr) : pointer(ptr) {}

        ~Destructor() { delete pointer; }

    };

public:

    T *_q_value;

    QBasicAtomicInt _q_guard;

    inline T *value()

    {

        for (QOnceControl control(&_q_guard); control.mustRunCode(); control.done()) {

            _q_value = new T();

            static Destructor cleanup(_q_value);

        }

        return _q_value;

    }

    inline T& operator*() { return *value(); }

    inline T* operator->() { return value(); }

    inline operator T*() { return value(); }

};

#endif // QT_NO_THREAD

QT_END_HEADER

#endif