QThread Class Reference

The QThread class provides platform-independent threads More...

#include <qthread.h>

Inherits Qt.

List of all member functions.

Public Members

• QThread () 
• virtual ~QThread () 
• bool wait ( unsigned long time = ULONG_MAX ) 
• void start () 
• bool finished () const
• bool running () const

Static Public Members

• HANDLE currentThread () 
• void postEvent ( QObject *, QEvent * ) 
• void exit () 

Protected Members

• virtual void run () 

Static Protected Members

• void sleep ( unsigned long ) 
• void msleep ( unsigned long ) 
• void usleep ( unsigned long ) 

Detailed Description

A QThread represents a separate thread of control within the program; it shares all data with 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(), however, QThreads begin executing in run(), which you inherit to provide your code. For instance:

  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 the paragraph on Thread Support in Qt

Member Function Documentation

QThread::QThread ()

Constructs a new thread. The thread does not actually begin executing until start() is called.

QThread::~QThread () [virtual]

QThread destructor. Note that deleting a QThread object will not stop the execution of the thread it represents, and that deleting a QThread object while the thread is running is unsafe.

HANDLE QThread::currentThread () [static]

This returns the thread handle of the currently executing thread. The handle returned by this function is used for internal reasons and should not be used in any application code. On Windows, the returned value is a pseudo handle for the current thread, and it can not be used for numerical comparison.

void QThread::exit () [static]

Ends execution of the calling thread and wakes up any threads waiting for its termination.

bool QThread::finished () const

Returns TRUE is the thread is finished.

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

System independent sleep. This causes the current thread to sleep for msecs milliseconds.

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

Provides a way of posting an event from a thread which is not the event thread to an object. The event is put into a queue, then the event thread is woken which then sends the event to the object. It is important to note that the event handler for the event, when called, will be called from the event thread and not from the thread calling QThread::postEvent().

Same as with QApplication::postEvent(), event must be allocated on the heap, as it is deleted when the event has been posted.

void QThread::run () [virtual protected]

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

bool QThread::running () const

Returns TRUE if the thread is running.

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

System independent sleep. This causes the current thread to sleep for secs seconds.

void QThread::start ()

This begins actual execution of the thread by calling run(), which should be reimplemented in a QThread subclass to contain your code. If you try to start a thread that is already running, this call will wait until the thread has finished, and then restart the thread.

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

System independent sleep. This causes the current thread to sleep for usecs microseconds.

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

This allows similar functionality to POSIX pthread_join. A thread calling this will block until one of 2 conditions is met:

• 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 (default argument), 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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