Thread Support 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.

Concurrent Filter and Filter-Reduce
Concurrent Map and Map-Reduce
Concurrent Run
Concurrent Task
QAtomicInteger	Platform-independent atomic operations on integers
QAtomicPointer	Template class that provides platform-independent atomic operations on pointers
QFuture	Represents the result of an asynchronous computation
QFutureSynchronizer	Convenience class that simplifies QFuture synchronization
QFutureWatcher	Allows monitoring a QFuture using signals and slots
QMutex	Access serialization between threads
QMutexLocker	Convenience class that simplifies locking and unlocking mutexes
QPromise	Way to store computation results to be accessed by QFuture
QReadLocker	Convenience class that simplifies locking and unlocking read-write locks for read access
QReadWriteLock	Read-write locking
QRecursiveMutex	Access serialization between threads
QRunnable	The base class for all runnable objects
QSemaphore	General counting semaphore
QSemaphoreReleaser	Exception-safe deferral of a QSemaphore::release() call
QThread	Platform-independent way to manage threads
QThreadPool	Manages a collection of QThreads
QThreadStorage	Per-thread data storage
QWaitCondition	Condition variable for synchronizing threads
QWriteLocker	Convenience class that simplifies locking and unlocking read-write locks for write access
QtConcurrent	High-level APIs that make it possible to write multi-threaded programs without using low-level threading primitives
QtConcurrent::QTaskBuilder	Used for adjusting task parameters

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.