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#include "qplatformdefs.h"

#include "qthreadonce.h"

#ifndef QT_NO_THREAD

#include "qmutex.h"

Q_GLOBAL_STATIC_WITH_ARGS(QMutex, onceInitializationMutex, (QMutex::Recursive))

enum QOnceExtra {

    MustRunCode = 0x01,

    MustUnlockMutex = 0x02

};

/*!

    \internal

    Initialize the Q_ONCE structure.

    Q_ONCE consists of two variables:

     - a static POD QOnceControl::ControlVariable (it's a QBasicAtomicInt)

     - an automatic QOnceControl that controls the former

    The POD is initialized to 0.

    When QOnceControl's constructor starts, it'll lock the global

    initialization mutex. It'll then check if it's the first to up

    the control variable and will take note.

    The QOnceControl's destructor will unlock the global

    initialization mutex.

*/

QOnceControl::QOnceControl(QBasicAtomicInt *control)

{

    d = 0;

    gv = control;

    // check if code has already run once

    if (*gv == 2) {

        // uncontended case: it has already initialized

        // no waiting

        return;

    }

    // acquire the path

    onceInitializationMutex()->lock();

    extra = MustUnlockMutex;

    if (gv->testAndSetAcquire(0, 1)) {

        // path acquired, we're the first

        extra |= MustRunCode;

    }

}

QOnceControl::~QOnceControl()

{

    if (mustRunCode())

        // code wasn't run!

        gv->testAndSetRelease(1, 0);

    else

        gv->testAndSetRelease(1, 2);

    if (extra & MustUnlockMutex)

        onceInitializationMutex()->unlock();

}

/*!

    \internal

    Returns true if the initialization code must be run.

    Obviously, the initialization code must be run only once...

*/

bool QOnceControl::mustRunCode()

{

    return extra & MustRunCode;

}

void QOnceControl::done()

{

    extra &= ~MustRunCode;

}

#endif // QT_NO_THREAD