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

#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()

    static bool executedOnce = false;

    if (executedOnce) {

        QSKIP("tst_QThreadOnce can only run once");

        return;

    executedOnce = true;

    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()

    static bool executedOnce = false;

    if (executedOnce) {

        QSKIP("tst_QThreadOnce can only run once");

        return;

    executedOnce = true;

#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()

    static bool executedOnce = false;

    if (executedOnce) {

        QSKIP("tst_QThreadOnce can only run once");

        return;

    executedOnce = true;

    int variable = 0;

    Q_ONCE {

        Q_ONCE {

            ++variable;

    QCOMPARE(variable, 1);

static void reentrant(int control, int &counter)

    static bool executedOnce = false;

    if (executedOnce) {

        QSKIP("tst_QThreadOnce can only run once");

        return;

    executedOnce = true;

    Q_ONCE {

        if (counter)

            reentrant(--control, counter);

        ++counter;

    static QSingleton<SingletonObject> s;

    s->val.ref();

void tst_QThreadOnce::reentering()

    static bool executedOnce = false;

    if (executedOnce) {

        QSKIP("tst_QThreadOnce can only run once");

        return;

    executedOnce = true;

    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()

    static bool executedOnce = false;

    if (executedOnce) {

        QSKIP("tst_QThreadOnce can only run once");

        return;

    executedOnce = true;

    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"