QThread Class Reference

Detailed Description

A QThread represents a separate thread of control within the program; it shares data with all the other threads within the process but executes independently in the way that a separate program does on a multitasking operating system. Instead of starting in main(), QThreads begin executing in run(). You inherit run() to include your code. For example:

    class MyThread : public QThread {

    public:

        virtual void run();

    };

    void MyThread::run()
    {
        for( int count = 0; count < 20; count++ ) {
            sleep( 1 );
            qDebug( "Ping!" );
        }
    }

    int main()
    {
        MyThread a;
        MyThread b;
        a.start();
        b.start();
        a.wait();
        b.wait();
    }
    

This will start two threads, each of which writes Ping! 20 times to the screen and exits. The wait() calls at the end of main() are necessary because exiting main() ends the program, unceremoniously killing all other threads. Each MyThread stops executing when it reaches the end of MyThread::run(), just as an application does when it leaves main().

See also Thread Support in Qt, Environment Classes and Threading.

Member Function Documentation

QThread::QThread ()

QThread::~QThread () [virtual]

Note that deleting a QThread object will not stop the execution of the thread it represents. Deleting a running QThread (i.e. finished() returns FALSE) will probably result in a program crash. You can wait() on a thread to make sure that it has finished.

Qt::HANDLE QThread::currentThread () [static]

Warning: The handle returned by this function is used for internal purposes and should not be used in any application code. On Windows, the returned value is a pseudo handle for the current thread, and it cannot be used for numerical comparison.

void QThread::exit () [static]

bool QThread::finished () const

void QThread::msleep ( unsigned long msecs ) [static protected]

void QThread::postEvent ( QObject * receiver, QEvent * event ) [static]

This is achieved as follows:

• The event is put into a queue;
• the event thread is woken up;
• the event thread sends the event to the receiver object.

Since QThread::postEvent() posts events into the event queue of QApplication, you must create a QApplication object before calling QThread::postEvent().

The event must be allocated on the heap since the post event queue will take ownership of the event and delete it once it has been posted.

See also QApplication::postEvent().

void QThread::run () [pure virtual protected]

This method is pure virtual, and must be implemented in derived classes in order to do useful work. Returning from this method will end the execution of the thread.

See also wait().

bool QThread::running () const

void QThread::sleep ( unsigned long secs ) [static protected]

void QThread::start ()

void QThread::usleep ( unsigned long usecs ) [static protected]

bool QThread::wait ( unsigned long time = ULONG_MAX )

• The thread associated with this QThread object has finished execution (i.e. when it returns from run()). This function will return TRUE if the thread has finished. It also returns TRUE if the thread has not been started yet.
• time milliseconds has elapsed. If time is ULONG_MAX (the default), then the wait will never timeout (the thread must return from run()). This function will return FALSE if the wait timed out.

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