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.


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:

The Threading Classes

These classes are relevant to threaded applications.

Asynchronous Run

The <QtConcurrentRun> header provides a way to run a function in a separate thread.

Concurrent Filter and Filter-Reduce

The <QtConcurrentFilter> header provides concurrent Filter and Filter-Reduce.

Concurrent Map and Map-Reduce

The <QtConcurrentMap> header provides concurrent Map and MapReduce.


Platform-independent atomic operations on integers


Template class that provides platform-independent atomic operations on pointers


Represents the result of an asynchronous computation


Convenience class that simplifies QFuture synchronization


Allows monitoring a QFuture using signals and slots


Access serialization between threads


Convenience class that simplifies locking and unlocking mutexes


Convenience class that simplifies locking and unlocking read-write locks for read access


Read-write locking


The base class for all runnable objects


General counting semaphore


Platform-independent way to manage threads


Manages a collection of QThreads


Per-thread data storage


Condition variable for synchronizing threads


Convenience class that simplifies locking and unlocking read-write locks for write access


High-level APIs that make it possible to write multi-threaded programs without using low-level threading primitives

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.

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