QThread Class Reference
[QtCore module]

Detailed Description

The QThread class provides platform-independent threads.

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(). By default, run() starts the event loop by calling exec() (see below). To create your own threads, subclass QThread and reimplement run(). For example:

 class MyThread : public QThread
 {
 public:
     void run();
 };

 void MyThread::run()
 {
     QTcpSocket socket;
     // connect QTcpSocket's signals somewhere meaningful
     ...
     socket.connectToHost(hostName, portNumber);
     exec();
 }

This will create a QTcpSocket in the thread and then execute the thread's event loop. Use the start() method to begin execution. Execution ends when you return from run(), just as an application does when it leaves main(). QThread will notifiy you via a signal when the thread is started(), finished(), and terminated(), or you can use isFinished() and isRunning() to query the state of the thread. Use wait() to block until the thread has finished execution.

Each thread gets its own stack from the operating system. The operating system also determines the default size of the stack. You can use setStackSize() to set a custom stack size.

Each QThread can have its own event loop. You can start the event loop by calling exec(); you can stop it by calling exit() or quit(). Having an event loop in a thread makes it possible to connect signals from other threads to slots in this thread, using a mechanism called queued connections. It also makes it possible to use classes that require the event loop, such as QTimer and QTcpSocket, in the thread. Note, however, that it is not possible to use any widget classes in the thread.

In extreme cases, you may want to forcibly terminate() an executing thread. However, doing so is dangerous and discouraged. Please read the documentation for terminate() and setTerminationEnabled() for detailed information.

The static functions currentThreadId() and currentThread() return identifiers for the currently executing thread. The former returns a platform specific ID for the thread; the latter returns a QThread pointer.

QThread also provides platform independent sleep functions in varying resolutions. Use sleep() for full second resolution, msleep() for millisecond resolution, and usleep() for microsecond resolution.

See also Thread Support in Qt, QThreadStorage, QMutex, QSemaphore, QWaitCondition, Mandelbrot Example, Semaphores Example, and Wait Conditions Example.

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