qt 6.5.1 original

tests/auto/corelib/thread/qthreadonce/CMakeLists.txt

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+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+#####################################################################
+## tst_qthreadonce Test:
+#####################################################################
+
+qt_internal_add_test(tst_qthreadonce
+    SOURCES
+        qthreadonce.cpp
+        tst_qthreadonce.cpp
+    LIBRARIES
+        Qt::TestPrivate
+)

tests/auto/corelib/thread/qthreadonce/qthreadonce.cpp

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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;
+}

tests/auto/corelib/thread/qthreadonce/qthreadonce.h

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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
+
+
+#ifndef QTHREADONCE_H
+#define QTHREADONCE_H
+
+#include <QtCore/qglobal.h>
+#include <QtCore/qatomic.h>
+
+
+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

tests/auto/corelib/thread/qthreadonce/tst_qthreadonce.cpp

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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 <QTest>
+#include <QSemaphore>
+
+#include <qcoreapplication.h>
+#include <qmutex.h>
+#include <qthread.h>
+#include <qwaitcondition.h>
+#include "qthreadonce.h"
+
+#include <QtTest/private/qemulationdetector_p.h>
+
+class tst_QThreadOnce : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void initTestCase();
+    void sameThread();
+    void sameThread_data();
+    void multipleThreads();
+
+    void nesting();
+    void reentering();
+#ifndef QT_NO_EXCEPTIONS
+    void exception();
+#endif
+};
+
+void tst_QThreadOnce::initTestCase()
+{
+    if (QTestPrivate::isRunningArmOnX86())
+        QSKIP("Flaky on QEMU, QTBUG-94737");
+}
+
+class SingletonObject: public QObject
+{
+    Q_OBJECT
+public:
+    static int runCount;
+    SingletonObject() { val.storeRelaxed(42); ++runCount; }
+    ~SingletonObject() { }
+
+    QBasicAtomicInt val;
+};
+
+class IncrementThread: public QThread
+{
+public:
+    static QBasicAtomicInt runCount;
+    static QSingleton<SingletonObject> singleton;
+    QSemaphore &sem1, &sem2;
+    int &var;
+
+    IncrementThread(QSemaphore *psem1, QSemaphore *psem2, int *pvar, QObject *parent)
+        : QThread(parent), sem1(*psem1), sem2(*psem2), var(*pvar)
+        { start(); }
+
+    ~IncrementThread() { wait(); }
+
+protected:
+    void run() override
+        {
+            sem2.release();
+            sem1.acquire();             // synchronize
+
+            Q_ONCE {
+                ++var;
+            }
+            runCount.ref();
+            singleton->val.ref();
+        }
+};
+int SingletonObject::runCount = 0;
+QBasicAtomicInt IncrementThread::runCount = Q_BASIC_ATOMIC_INITIALIZER(0);
+QSingleton<SingletonObject> IncrementThread::singleton;
+
+void tst_QThreadOnce::sameThread_data()
+{
+    SingletonObject::runCount = 0;
+    QTest::addColumn<int>("expectedValue");
+
+    QTest::newRow("first") << 42;
+    QTest::newRow("second") << 43;
+}
+
+void tst_QThreadOnce::sameThread()
+{
+    static int controlVariable = 0;
+    Q_ONCE {
+        QCOMPARE(controlVariable, 0);
+        ++controlVariable;
+    }
+    QCOMPARE(controlVariable, 1);
+
+    static QSingleton<SingletonObject> s;
+    QTEST(int(s->val.loadRelaxed()), "expectedValue");
+    s->val.ref();
+
+    QCOMPARE(SingletonObject::runCount, 1);
+}
+
+void tst_QThreadOnce::multipleThreads()
+{
+#if defined(Q_OS_VXWORKS)
+    const int NumberOfThreads = 20;
+#else
+    const int NumberOfThreads = 100;
+#endif
+    int controlVariable = 0;
+    QSemaphore sem1, sem2(NumberOfThreads);
+
+    QObject *parent = new QObject;
+    for (int i = 0; i < NumberOfThreads; ++i)
+        new IncrementThread(&sem1, &sem2, &controlVariable, parent);
+
+    QCOMPARE(controlVariable, 0); // nothing must have set them yet
+    SingletonObject::runCount = 0;
+    IncrementThread::runCount.storeRelaxed(0);
+
+    // wait for all of them to be ready
+    sem2.acquire(NumberOfThreads);
+    // unleash the threads
+    sem1.release(NumberOfThreads);
+
+    // wait for all of them to terminate:
+    delete parent;
+
+    QCOMPARE(controlVariable, 1);
+    QCOMPARE(int(IncrementThread::runCount.loadRelaxed()), NumberOfThreads);
+    QCOMPARE(SingletonObject::runCount, 1);
+}
+
+void tst_QThreadOnce::nesting()
+{
+    int variable = 0;
+    Q_ONCE {
+        Q_ONCE {
+            ++variable;
+        }
+    }
+
+    QCOMPARE(variable, 1);
+}
+
+static void reentrant(int control, int &counter)
+{
+    Q_ONCE {
+        if (counter)
+            reentrant(--control, counter);
+        ++counter;
+    }
+    static QSingleton<SingletonObject> s;
+    s->val.ref();
+}
+
+void tst_QThreadOnce::reentering()
+{
+    const int WantedRecursions = 5;
+    int count = 0;
+    SingletonObject::runCount = 0;
+    reentrant(WantedRecursions, count);
+
+    // reentrancy is undefined behavior:
+    QVERIFY(count == 1 || count == WantedRecursions);
+    QCOMPARE(SingletonObject::runCount, 1);
+}
+
+#if !defined(QT_NO_EXCEPTIONS)
+static void exception_helper(int &val)
+{
+    Q_ONCE {
+        if (val++ == 0) throw 0;
+    }
+}
+#endif
+
+#ifndef QT_NO_EXCEPTIONS
+void tst_QThreadOnce::exception()
+{
+    int count = 0;
+
+    try {
+        exception_helper(count);
+    } catch (...) {
+        // nothing
+    }
+    QCOMPARE(count, 1);
+
+    try {
+        exception_helper(count);
+    } catch (...) {
+        QVERIFY2(false, "Exception shouldn't have been thrown...");
+    }
+    QCOMPARE(count, 2);
+}
+#endif
+
+QTEST_MAIN(tst_QThreadOnce)
+#include "tst_qthreadonce.moc"