QThread

NAME

SYNOPSIS

#include <qthread.h>

Inherits Qt.

Public Members

Static Public Members

Protected Members

Static Protected Members

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 Type Documentation

QThread::Priority

QThread::IdlePriority - scheduled only when no other threads are running.

QThread::LowestPriority - scheduled less often than LowPriority.

QThread::LowPriority - scheduled less often than NormalPriority.

QThread::NormalPriority - the default priority of the operating system.

QThread::HighPriority - scheduled more often than NormalPriority.

QThread::HighestPriority - scheduled more often then HighPriority.

QThread::TimeCriticalPriority - scheduled as often as possible.

QThread::InheritPriority - use the same priority as the creating thread. This is the default.

MEMBER FUNCTION DOCUMENTATION

QThread::QThread ( unsigned int stackSize = 0 )

If stackSize is greater than zero, the maximum stack size is set to stackSize bytes, otherwise the maximum stack size is automatically determined by the operating system.

Warning: Most operating systems place minimum and maximum limits on thread stack sizes. The thread will fail to start if the stack size is outside these limits.  

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]

Use QApplication::postEvent() instead.  

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

See also wait().  

bool QThread::running () const

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

void QThread::start ( Priority priority = InheritPriority )

If you try to start a thread that is already running, this function will wait until the the thread has finished and then restart the thread.

See also Priority.  

void QThread::terminate ()

When the thread is terminated, all threads waiting for the the thread to finish will be woken up.

Warning: This function is dangerous, and its use is discouraged. The thread can be terminated at any point in its code path. Threads can be terminated while modifying data. There is no chance for the thread to cleanup after itself, unlock any held mutexes, etc. In short, use this function only if absolutely necessary.  

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.

This provides similar functionality to the POSIX pthread_join() function.

SEE ALSO

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