src_corelib_thread_qmutex.cpp

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
#include <QMutex>
#include <QMutexLocker>
#include <QWaitCondition>
 
//! [0]
int number = 6;
 
void method1()
{
    number *= 5;
    number /= 4;
}
 
void method2()
{
    number *= 3;
    number /= 2;
}
//! [0]
 
void examples()
{
    //! [1]
    // method1()
    number *= 5;        // number is now 30
    number /= 4;        // number is now 7
 
    // method2()
    number *= 3;        // number is now 21
    number /= 2;        // number is now 10
    //! [1]
 
 
    //! [2]
    // Thread 1 calls method1()
    number *= 5;        // number is now 30
 
    // Thread 2 calls method2().
    //
    // Most likely Thread 1 has been put to sleep by the operating
    // system to allow Thread 2 to run.
    number *= 3;        // number is now 90
    number /= 2;        // number is now 45
 
    // Thread 1 finishes executing.
    number /= 4;        // number is now 11, instead of 10
    //! [2]
}
 
namespace duplicate_examples
{
    //! [3]
    QMutex mutex;
    int number = 6;
 
    void method1()
    {
        mutex.lock();
        number *= 5;
        number /= 4;
        mutex.unlock();
    }
 
    void method2()
    {
        mutex.lock();
        number *= 3;
        number /= 2;
        mutex.unlock();
    }
    //! [3]
 
    int moreComplexFunction(int flag) { return 0; }
 
    int anotherFunction() { return 0; }
 
    //! [4]
    int complexFunction(int flag)
    {
        mutex.lock();
 
        int retVal = 0;
 
        switch (flag) {
        case 0:
        case 1:
            retVal = moreComplexFunction(flag);
            break;
        case 2:
            {
                int status = anotherFunction();
                if (status < 0) {
                    mutex.unlock();
                    return -2;
                }
                retVal = status + flag;
            }
            break;
        default:
            if (flag > 10) {
                mutex.unlock();
                return -1;
            }
            break;
        }
 
        mutex.unlock();
        return retVal;
    }
    //! [4]
}
 
QMutex mutex;
 
int moreComplexFunction(int flag) { return 0; }
 
int anotherFunction() { return 0; }
 
//! [5]
int complexFunction(int flag)
{
    QMutexLocker locker(&mutex);
 
    int retVal = 0;
 
    switch (flag) {
    case 0:
    case 1:
        return moreComplexFunction(flag);
    case 2:
        {
            int status = anotherFunction();
            if (status < 0)
                return -2;
            retVal = status + flag;
        }
        break;
    default:
        if (flag > 10)
            return -1;
        break;
    }
 
    return retVal;
}
//! [5]
 
bool signalled = false;
QWaitCondition waitCondition;
 
//! [6]
class SignalWaiter
{
private:
    QMutexLocker<QMutex> locker;
 
public:
    SignalWaiter(QMutex *mutex)
        : locker(mutex)
    {
    }
 
    void waitForSignal()
    {
        //...
        while (!signalled)
            waitCondition.wait(locker.mutex());
        //...
    }
};
//! [6]