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# QThread Class Reference

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

    #include <QThread>

Inherits QObject.

Note: All the functions in this class are thread-safe.

- List of all members, including inherited members
- Compatibility members

### Public Types

- enum Priority { IdlePriority, LowestPriority, LowPriority, NormalPriority, HighPriority, ..., InheritPriority }

### Writable Properties

- 1 writable property inherited from QObject

### Public Functions

- QThread ()
- virtual ~QThread ()
- void exit ( int retcode = 0 )
- bool isFinished () const
- bool isRunning () const
- void setStackSize ( uint stackSize )
- uint stackSize () const
- bool wait ( unsigned long time = ULONG_MAX )

- 24 public functions inherited from QObject

### Public Slots

- void quit ()
- void start ( Priority priority = InheritPriority )
- void terminate ()

- 1 public slot inherited from QObject

### Signals

- void finished ()
- void started ()
- void terminated ()

- 1 signal inherited from QObject

### Static Public Members

- QThread * currentQThread ()
- Qt::HANDLE currentThread ()

- 4 static public members inherited from QObject

### Protected Functions

- virtual void run () = 0

- 9 protected functions inherited from QObject

### Static Protected Members

- void msleep ( unsigned long msecs )
- void sleep ( unsigned long secs )
- void usleep ( unsigned long usecs )

## 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(). 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 and ..

## Member Type Documentation

### enum QThread::Priority

This enum type indicates how the operating system should schedule newly created threads.

`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 than 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 ()

Constructs a new thread. The thread does not 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. 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.

### QThread * QThread::currentQThread () `[static]`

Returns a pointer to the currently executing QThread. If the current thread was not started using the QThread API (e.g. the GUI thread), this function returns zero.

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

Returns the thread handle of the currently executing thread.

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 ( int retcode = 0 )

Tells the thread's event loop to exit with a return code.

After calling this function, the thread leaves the event loop and returns from the call to QEventLoop::exec(). The QEventLoop::exec() function returns retcode.

By convention, a retcode of 0 means success, any non-zero value indicates an error.

Note that unlike the C library function of the same name, this function does return to the caller -- it is event processing that stops.

This function does nothing if the thread does not have an event loop.

See also quit() and QEventLoop.

### void QThread::finished () `[signal]`

This signal is emitted when the thread has finished executing.

### bool QThread::isFinished () const

Returns true is the thread is finished; otherwise returns false.

### bool QThread::isRunning () const

Returns true if the thread is running; otherwise returns false.

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

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

### void QThread::quit () `[slot]`

Tells the thread's event loop to exit with return code 0 (success). Equivalent to calling QThread::exit(0).

This function does nothing if the thread does not have an event loop.

See also exit() and QEventLoop.

### 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().

### void QThread::setStackSize ( uint stackSize )

Set the maximum stack size for the thread to stackSize. 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.

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

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

### uint QThread::stackSize () const

Returns the maximum stack size for the thread (if set with setStackSize()); otherwise returns zero.

### void QThread::start ( Priority priority = InheritPriority ) `[slot]`

Begins execution of the thread by calling run(), which should be reimplemented in a QThread subclass to contain your code. The operating system will schedule the thread according to the priority argument.

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

See also Priority.

### void QThread::started () `[signal]`

This signal is emitted when the thread starts executing.

### void QThread::terminate () `[slot]`

This function terminates the execution of the thread. The thread may or may not be terminated immediately, depending on the operating systems scheduling policies. Use QThread::wait() after terminate() for synchronous termination.

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

Warning: This function is dangerous, and its use is discouraged. The thread can be terminate 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::terminated () `[signal]`

This signal is emitted when the thread is terminated.

### 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 )

A thread calling this function will block until either of these 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 (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.