Thread Support in Qt

A detailed discussion of thread handling in Qt.

Qt provides thread support in the form of platform-independent threading classes, a thread-safe way of posting events, and signal-slot connections across threads. This makes it easy to develop portable multithreaded Qt applications and take advantage of multiprocessor machines. Multithreaded programming is also a useful paradigm for performing time-consuming operations without freezing the user interface of an application.

Earlier versions of Qt offered an option to build the library without thread support. Since Qt 4.0, threads are always enabled.

Topics:

These articles assume that the reader has basic knowledge about multithreaded applications.

• The Threading Classes

• Multithreading Technologies in Qt

• Synchronizing Threads

• Reentrancy and Thread-Safety

• Threads and QObjects

• Thread-Support in Qt Modules

The Threading Classes

These classes are relevant to threaded applications.

QtConcurrent.QTaskBuilder	The QTaskBuilder class is used for adjusting task parameters.
Concurrent Filter and Filter-Reduce	Selecting values from a sequence and combining them, all in parallel.
qtconcurrent.html	The QtConcurrent namespace provides high-level APIs that make it possible to write multi-threaded programs without using low-level threading primitives.
Concurrent Map and Map-Reduce	Transforming values from a sequence and combining them, all in parallel.
Concurrent Run	A simple way to run a task in a separate thread.
Concurrent Task	A configurable way to run a task in a separate thread.
QAtomicInteger	The QAtomicInteger class provides platform-independent atomic operations on integers.
QAtomicPointer	The QAtomicPointer class is a template class that provides platform-independent atomic operations on pointers.
PySide6.QtCore.QFuture	The QFuture class represents the result of an asynchronous computation.
QtFuture.WhenAnyResult	QtFuture::WhenAnyResult is used to represent the result of QtFuture::whenAny().
QFutureSynchronizer	The QFutureSynchronizer class is a convenience class that simplifies QFuture synchronization.
PySide6.QtCore.QFutureWatcher	The QFutureWatcher class allows monitoring a QFuture using signals and slots.
PySide6.QtCore.QMutex	The QMutex class provides access serialization between threads.
PySide6.QtCore.QRecursiveMutex	The QRecursiveMutex class provides access serialization between threads.
QMutexLocker	The QMutexLocker class is a convenience class that simplifies locking and unlocking mutexes.
QPromise	The QPromise class provides a way to store computation results to be accessed by QFuture.
PySide6.QtCore.QReadWriteLock	The QReadWriteLock class provides read-write locking.
PySide6.QtCore.QReadLocker	The QReadLocker class is a convenience class that simplifies locking and unlocking read-write locks for read access.
PySide6.QtCore.QWriteLocker	The QWriteLocker class is a convenience class that simplifies locking and unlocking read-write locks for write access.
PySide6.QtCore.QRunnable	The QRunnable class is the base class for all runnable objects.
PySide6.QtCore.QSemaphore	The QSemaphore class provides a general counting semaphore.
PySide6.QtCore.QSemaphoreReleaser	The QSemaphoreReleaser class provides exception-safe deferral of a QSemaphore::release() call.
PySide6.QtCore.QThread	The QThread class provides a platform-independent way to manage threads.
PySide6.QtCore.QThreadPool	The QThreadPool class manages a collection of QThreads.
QThreadStorage	The QThreadStorage class provides per-thread data storage.
PySide6.QtCore.QWaitCondition	The QWaitCondition class provides a condition variable for synchronizing threads.

Note

Qt’s threading classes are implemented with native threading APIs; e.g., Win32 and pthreads. Therefore, they can be used with threads of the same native API.