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.
- Recommended Reading
- The Threading Classes
- Multithreading Technologies in Qt
- Synchronizing Threads
- Reentrancy and Thread-Safety
- Threads and QObjects
- Thread-Support in Qt Modules
This document is intended for an audience that has knowledge of, and experience with, multithreaded applications. If you are new to threading see our Recommended Reading list:
- Threads Primer: A Guide to Multithreaded Programming
- Thread Time: The Multithreaded Programming Guide
- Pthreads Programming: A POSIX Standard for Better Multiprocessing
- Win32 Multithreaded Programming
The Threading Classes
These classes are relevant to threaded applications.
The QtConcurrent namespace provides high-level APIs that make it possible to write multi-threaded programs without using low-level threading primitives.
The QAtomicInt class provides platform-independent atomic operations on integers.
The QAtomicPointer class is a template class that provides platform-independent atomic operations on pointers.
The QFuture class represents the result of an asynchronous computation.
The QFutureSynchronizer class is a convenience class that simplifies QFuture synchronization.
The QFutureWatcher class allows monitoring a QFuture using signals and slots.
The QMutex class provides access serialization between threads.
The QMutexLocker class is a convenience class that simplifies locking and unlocking mutexes.
The QReadLocker class is a convenience class that simplifies locking and unlocking read-write locks for read access.
The QReadWriteLock class provides read-write locking.
The QWriteLocker class is a convenience class that simplifies locking and unlocking read-write locks for write access.
The QRunnable class is the base class for all runnable objects.
The QSemaphore class provides a general counting semaphore.
The QThread class provides a platform-independent way to manage threads.
The QThreadPool class manages a collection of QThreads.
The QThreadStorage class provides per-thread data storage.
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.