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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
#include "qplatformdefs.h"
#include "qthreadonce.h"
#include "qmutex.h"
Q_GLOBAL_STATIC(QRecursiveMutex, onceInitializationMutex)
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->loadAcquire() == 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;
}
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