Question

My code as follow:

int main(int argc, char* argv[])
{
    MyThread myThread1;
    MyThread myThread2;
    myThread1.start();
    myThread2.start();

    qDebug("Hello World");

    myThread1.wait();
    qDebug("myThread1 is finished...");
    myThread2.wait();
    qDebug("myThread2 is finished...");

    return 0;
}

>

class MyThread : public QThread
{
    Q_OBJECT
public:
    explicit MyThread(QObject *parent = 0);
    void run();
};

>

void MyThread::run()
{
    QMutex mutex();
    int x = 10000;
    mutex.lock();

    while(x != 0) {
        sleep(1);
        qDebug("%d, x = %d ", thread()->currentThreadId(), x);
        x--;
    }

    mutex.unlock();
}

But the result is :

Hello World
5516, x = 10000 
6060, x = 10000 
5516, x = 9999 
6060, x = 9999 
5516, x = 9998 
6060, x = 9998 
5516, x = 9997 
6060, x = 9997
...
...

I want to the result is :

xxxx: 10000 
xxxx:  9999 
xxxx:  9998 
xxxx:  9997 
... 
... 
xxxx:     1

yyyy: 10000 
yyyy:  9999 
... 
...  
yyyy:     1

why? where is my fault ? And how to use QMutex.. Thank you …

Answer 1

You are creating the mutex within the scope of the run call. If you wanted the mutex to halt/delay exectution of the thread2 you would need to declare so that your objects don’t create their own mutex each time.

// .h
class MyThread {
   ...
private:
 static QMutex mutex;
}


// .cpp
QMutex MyThread::mutex; 



// .cpp
void MyThread::run()
{
  QMutexLocker lock(&mutex)

  // do stuff then return 
  // and the mutex will be unlocked when 
  // you leave this scope
}