Virtual functions



Static functions

Detailed Description

The PySide.QtCore.QThread class provides a platform-independent way to manage threads.

A PySide.QtCore.QThread object manages one thread of control within the program. QThreads begin executing in PySide.QtCore.QThread.run() . By default, PySide.QtCore.QThread.run() starts the event loop by calling exec() and runs a Qt event loop inside the thread.

You can use worker objects by moving them to the thread using QObject.moveToThread() .

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The code inside the Worker’s slot would then execute in a separate thread. However, you are free to connect the Worker’s slots to any signal, from any object, in any thread. It is safe to connect signals and slots across different threads, thanks to a mechanism called queued connections .

Another way to make code run in a separate thread, is to subclass PySide.QtCore.QThread and reimplement PySide.QtCore.QThread.run() . For example:

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In that example, the thread will exit after the run function has returned. There will not be any event loop running in the thread unless you call exec() .

It is important to remember that a PySide.QtCore.QThread object usually lives in the thread where it was created, not in the thread that it manages. This oft-overlooked detail means that a PySide.QtCore.QThread ‘s slots will be executed in the context of its home thread, not in the context of the thread it is managing. For this reason, implementing new slots in a PySide.QtCore.QThread subclass is error-prone and discouraged.


If you interact with an object, using any technique other than queued signal/slot connections (e.g. direct function calls), then the usual multithreading precautions need to be taken.


It is not possible to change the thread affinity of GUI objects; they must remain in the main thread.

Managing threads

PySide.QtCore.QThread will notifiy you via a signal when the thread is PySide.QtCore.QThread.started() , PySide.QtCore.QThread.finished() , and PySide.QtCore.QThread.terminated() , or you can use PySide.QtCore.QThread.isFinished() and PySide.QtCore.QThread.isRunning() to query the state of the thread.

You can stop the thread by calling PySide.QtCore.QThread.exit() or PySide.QtCore.QThread.quit() . In extreme cases, you may want to forcibly PySide.QtCore.QThread.terminate() an executing thread. However, doing so is dangerous and discouraged. Please read the documentation for PySide.QtCore.QThread.terminate() and PySide.QtCore.QThread.setTerminationEnabled() for detailed information.

From Qt 4.8 onwards, it is possible to deallocate objects that live in a thread that has just ended, by connecting the PySide.QtCore.QThread.finished() signal to QObject.deleteLater() .

Use PySide.QtCore.QThread.wait() to block the calling thread, until the other thread has finished execution (or until a specified time has passed).

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

To choose the name that your thread will be given (as identified by the command ps -L on Linux, for example), you can call PySide.QtCore.QObject.setObjectName() before starting the thread. If you don’t call PySide.QtCore.QObject.setObjectName() , the name given to your thread will be the class name of the runtime type of your thread object (for example, "RenderThread" in the case of the Mandelbrot Example , as that is the name of the PySide.QtCore.QThread subclass). Note that this is currently not available with release builds on Windows.

PySide.QtCore.QThread also provides static, platform independent sleep functions: PySide.QtCore.QThread.sleep() , PySide.QtCore.QThread.msleep() , and PySide.QtCore.QThread.usleep() allow full second, millisecond, and microsecond resolution respectively.


PySide.QtCore.QThread.wait() and the PySide.QtCore.QThread.sleep() functions should be unnecessary in general, since Qt is an event-driven framework. Instead of PySide.QtCore.QThread.wait() , consider listening for the PySide.QtCore.QThread.finished() signal. Instead of the PySide.QtCore.QThread.sleep() functions, consider using PySide.QtCore.QTimer .

See also

Thread Support in Qt QThreadStorage PySide.QtCore.QMutex PySide.QtCore.QSemaphore PySide.QtCore.QWaitCondition Mandelbrot Example Semaphores Example Wait Conditions Example

class PySide.QtCore.QThread([parent=None])

Constructs a new PySide.QtCore.QThread to manage a new thread. The parent takes ownership of the PySide.QtCore.QThread . The thread does not begin executing until PySide.QtCore.QThread.start() is called.


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

Constant Description
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.
static PySide.QtCore.QThread.cleanup()
static PySide.QtCore.QThread.currentThread()
Return type:PySide.QtCore.QThread

Returns a pointer to a PySide.QtCore.QThread which manages the currently executing thread.

static PySide.QtCore.QThread.currentThreadId()
Return type:PySide.QtCore.Qt::HANDLE

Returns the thread handle of the currently executing thread.


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. It can’t be used for numerical comparison. i.e., this function returns the DWORD (Windows-Thread ID) returned by the Win32 function getCurrentThreadId(), not the HANDLE (Windows-Thread HANDLE) returned by the Win32 function getCurrentThread().

Return type:PySide.QtCore.int

Enters the event loop and waits until PySide.QtCore.QThread.exit() is called, returning the value that was passed to PySide.QtCore.QThread.exit() . The value returned is 0 if PySide.QtCore.QThread.exit() is called via PySide.QtCore.QThread.quit() .

It is necessary to call this function to start event handling.


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 returnCode .

By convention, a returnCode 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.

No QEventLoops will be started anymore in this thread until QThread.exec() has been called again. If the eventloop in QThread.exec() is not running then the next call to QThread.exec() will also return immediately.

static PySide.QtCore.QThread.idealThreadCount()
Return type:PySide.QtCore.int

Returns the ideal number of threads that can be run on the system. This is done querying the number of processor cores, both real and logical, in the system. This function returns -1 if the number of processor cores could not be detected.

static PySide.QtCore.QThread.initialize()
Return type:PySide.QtCore.bool

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

Return type:PySide.QtCore.bool

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

static PySide.QtCore.QThread.msleep(arg__1)
Parameters:arg__1 – long

Forces the current thread to sleep for msecs milliseconds.

Return type:PySide.QtCore.QThread.Priority

Returns the priority for a running thread. If the thread is not running, this function returns InheritPriority .


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.


The starting point for the thread. After calling PySide.QtCore.QThread.start() , the newly created thread calls this function. The default implementation simply calls exec() .

You can reimplement this function to facilitate advanced thread management. Returning from this method will end the execution of the thread.


This function sets the priority for a running thread. If the thread is not running, this function does nothing and returns immediately. Use PySide.QtCore.QThread.start() to start a thread with a specific priority.

The priority argument can be any value in the QThread::Priority enum except for InheritPriorty .

The effect of the priority parameter is dependent on the operating system’s scheduling policy. In particular, the priority will be ignored on systems that do not support thread priorities (such as on Linux, see http://linux.die.net/man/2/sched_setscheduler for more details).


Sets 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.


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.

static PySide.QtCore.QThread.setTerminationEnabled([enabled=true])

Enables or disables termination of the current thread based on the enabled parameter. The thread must have been started by PySide.QtCore.QThread .

When enabled is false, termination is disabled. Future calls to QThread.terminate() will return immediately without effect. Instead, the termination is deferred until termination is enabled.

When enabled is true, termination is enabled. Future calls to QThread.terminate() will terminate the thread normally. If termination has been deferred (i.e. QThread.terminate() was called with termination disabled), this function will terminate the calling thread immediately . Note that this function will not return in this case.

static PySide.QtCore.QThread.sleep(arg__1)
Parameters:arg__1 – long

Forces the current thread to sleep for secs seconds.

Return type:PySide.QtCore.uint

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


Begins execution of the thread by calling PySide.QtCore.QThread.run() . The operating system will schedule the thread according to the priority parameter. If the thread is already running, this function does nothing.

The effect of the priority parameter is dependent on the operating system’s scheduling policy. In particular, the priority will be ignored on systems that do not support thread priorities (such as on Linux, see http://linux.die.net/man/2/sched_setscheduler for more details).


Terminates the execution of the thread. The thread may or may not be terminated immediately, depending on the operating system’s scheduling policies. Listen for the PySide.QtCore.QThread.terminated() signal, or use QThread.wait() after PySide.QtCore.QThread.terminate() , to be sure.

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


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 clean up after itself, unlock any held mutexes, etc. In short, use this function only if absolutely necessary.

Termination can be explicitly enabled or disabled by calling QThread.setTerminationEnabled() . Calling this function while termination is disabled results in the termination being deferred, until termination is re-enabled. See the documentation of QThread.setTerminationEnabled() for more information.

static PySide.QtCore.QThread.usleep(arg__1)
Parameters:arg__1 – long

Forces the current thread to sleep for usecs microseconds.

Parameters:time – long
Return type:PySide.QtCore.bool

Blocks the thread until either of these conditions is met:

  • The thread associated with this PySide.QtCore.QThread object has finished execution (i.e. when it returns from PySide.QtCore.QThread.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 PySide.QtCore.QThread.run() ). This function will return false if the wait timed out.

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

static PySide.QtCore.QThread.yieldCurrentThread()

Yields execution of the current thread to another runnable thread, if any. Note that the operating system decides to which thread to switch.