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81 lines
1.8 KiB
C++
81 lines
1.8 KiB
C++
// Copyright (C) 2016 The Qt Company Ltd.
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// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
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#include "qplatformdefs.h"
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#include "qthreadonce.h"
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#include "qmutex.h"
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Q_GLOBAL_STATIC(QRecursiveMutex, onceInitializationMutex)
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enum QOnceExtra {
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MustRunCode = 0x01,
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MustUnlockMutex = 0x02
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};
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/*!
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\internal
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Initialize the Q_ONCE structure.
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Q_ONCE consists of two variables:
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- a static POD QOnceControl::ControlVariable (it's a QBasicAtomicInt)
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- an automatic QOnceControl that controls the former
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The POD is initialized to 0.
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When QOnceControl's constructor starts, it'll lock the global
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initialization mutex. It'll then check if it's the first to up
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the control variable and will take note.
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The QOnceControl's destructor will unlock the global
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initialization mutex.
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*/
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QOnceControl::QOnceControl(QBasicAtomicInt *control)
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{
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d = 0;
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gv = control;
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// check if code has already run once
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if (gv->loadAcquire() == 2) {
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// uncontended case: it has already initialized
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// no waiting
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return;
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}
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// acquire the path
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onceInitializationMutex()->lock();
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extra = MustUnlockMutex;
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if (gv->testAndSetAcquire(0, 1)) {
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// path acquired, we're the first
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extra |= MustRunCode;
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}
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}
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QOnceControl::~QOnceControl()
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{
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if (mustRunCode())
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// code wasn't run!
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gv->testAndSetRelease(1, 0);
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else
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gv->testAndSetRelease(1, 2);
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if (extra & MustUnlockMutex)
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onceInitializationMutex()->unlock();
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}
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/*!
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\internal
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Returns true if the initialization code must be run.
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Obviously, the initialization code must be run only once...
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*/
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bool QOnceControl::mustRunCode()
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{
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return extra & MustRunCode;
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}
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void QOnceControl::done()
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{
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extra &= ~MustRunCode;
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}
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