As a consequence, no event will be dispatched to it. Hence, myObject is also living in the GUI thread.Īn object created before a QCoreApplication object has no thread affinity. At this point, thread is living in the GUI thread. In this snippet, myObject is constructed in the Thread constructor, which is created in turn in MainWindow. Here’s an example: class Thread : public QThread This is referred to as the thread affinity of an object. This includes all objects created in that thread or moved to that thread. It will block and wait until QThread::exit() is called.Ī crucial thing to note is that a thread event loop delivers events for all QObject classes that are living in that thread. The started()signal will be processed by the Thread event loop only upon the exec() call. You can also override QThread and call exec(), as follows: class Thread : public QThread If not overridden, run() calls the QThread::exec() function, which starts the thread’s event loop. Qt is an event-driven framework, where a main event loop (or the GUI loop) processes events (user input, graphical, and so on) to refresh the UI.Įach QThread comes with its own event loop that can process events outside the main loop. This brings us to a fundamental aspect of QThread: it works seamlessly with the signal/slot mechanism. When run() is completed, thread will emit the finished() signal. Only at this point, the new thread of execution will be created. The start() function calling will automatically call the run() function of thread and emit the started() signal. Here is how you can create and start a QThread: QThread thread You can subclass QThread to override the run() function, which will be executed in the QThread class. A QThread instance manages one thread of execution within the program.
The QThread is the central class for of the Qt threading system. We assume that you already know threading basics and the associated issues (deadlocks, threads synchronization, resource sharing, and so on) and we will focus on how Qt implements it. Qt provides a sophisticated threading system.
Understanding the QThread framework in depth.More specifically, we will cover the following: (For more resources related to this topic, see here.)
#Qt update gui from different thread how to#
In this article by Guillaume Lazar and Robin Penea, authors of the book Mastering Qt 5, we will study how to use Qt and the available tools provided by the Qt folks. Qt has its own cross-platform implementation of threading.
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