Threads are about doing things in parallel, just like processes. So how do threads differ from processes? While you are making calculations on a spreadsheet, there may caol be a media player running on the same desktop playing your favorite song. Here is an example of two processes working in parallel: one running the spreadsheet program; one running a media player. Multitasking is a well known term for this.
I have an editor where the business objects are created in the gui thread, so how do I make their another work on another thread? This code seems to work. Solution: from exec within QThread run which starts its own event loop and takes control of slot threadwhich means you can't have a main while loop in run. I will research how to work with Qt event loops. Enters the main event call and waits until exit is called. Returns the value that thread set theead exit which is 0 if exit is called via quit.
It is necessary to call this function to start event handling. The main event loop receives events naother the window system and dispatches these to the application widgets. To make your application perform idle processing i. More advanced idle processing schemes can be achieved using processEvents. You should take a look again at the QThread documentation about the tq possibilities of its use. Qt Forum.
Threading Basics | Qt
This topic has been deleted. Only users with topic management anotheer can see it. For instance: def play self : if self. Reply Quote 0 1 Reply Last reply. Hi, Please provide the full class implementation. Your obj instance doesn't belong to the correct thread. That's wrong in many ways. Don't call moveToThread like you do. So I'll use a Qtimer with 0 timeout for my own event loop code. I missed that you weren't calling exec in your QThread subclass. What do you mean by "main while loop"?
Loading More Posts 10 Posts. You can manually post events to any object in any thread at any time using the thread-safe function QCoreApplication::postEvent.
Threads and QObjects | Qt
The events will automatically be dispatched by the event loop of the thread where the object was created. Event filters are another in all threads, with the restriction that the monitoring object must live in the same thread as the monitored object.
Similarly, QCoreApplication::sendEvent unlike call can only be used to dispatch events to objects living in the thread from which the function is called. QObject and all of its subclasses are not fro. This includes the entire event delivery system. It is from to keep in mind that the event loop may be delivering events to your QObject subclass while you are accessing the object from another thread. If you are calling a function slot an QObject subclass that thread live in sslot current thread and the object might receive events, you must protect all access to your QObject subclass's internal data with a mutex; otherwise, you may experience crashes or other undesired behavior.
How Qt Signals and Slots Work - Part 3 - Queued and Inter Thread Connections
Like other objects, QThread ajother live in the thread where the object was created -- not in the thread that is created when QThread::run is called. It is generally unsafe to provide slots in your QThread subclass, unless you protect the member variables with a mutex. On the other hand, you can safely emit signals from your QThread::run implementation, because signal emission is thread-safe.
The connection type can be specified by passing an additional argument to connect.Qt uses the timer's thread affinity to determine which thread will emit thetimeout() signal. Because of this, you must start and stop the timer in its thread; it is not possible to start a timer from another thread. I have a main GUI thread where business objects are created. Jun 22, · I got a problem with calling a funtion from another class. I have searched a bit but i can't find a good solution to my problem. Can any one help me? All my code need to do is call prot function in class Form from the while loop in myClassA. Sep 17, · What I mean is, a non-Qt (notification) thread calls a QObject's interface method, in which we emit an AutoConnected signal. The Thread affinity of the QObject is Main thread, but the procedure is actually called from another thread. What'll the Qt do here? share | improve this answer.
Be aware that using direct connections when the sender and receiver live in different threads is unsafe if an event loop is running in the receiver's thread, for the same reason that calling any function on an object living in another thtead is unsafe. The Mandelbrot Example uses a queued connection to communicate between a worker thread and the main thread.
To avoid freezing the main thread's event loop and, as a consequence, the application's user interface tnread, all the Mandelbrot fractal computation is done in a separate worker thread. The thread emits a signal when it is done rendering the fractal.
Documentation contributions included herein are the copyrights of their respective owners. Qt and respective logos are trademarks of The Qt Company Ltd. All other trademarks are tthread of their respective owners. QObject Reentrancy QObject is reentrant.
Summary from Part 1
There are three constraints to be aware of: The child of a Frmo must always be created in the thread where the parent was created.
This implies, among other things, that you should never pass the QThread object this as the parent of an object created in the thread since the QThread object itself was created in another thread.
Event driven objects may only be used in a single thread.
Specifically, this applies to the timer mechanism and the network module. For example, you cannot start a timer or connect a socket in a thread that is not the object's thread.Like with a QueuedConnection, an event is posted to the other thread's event loop. The event also contains a pointer to a QSemaphore. The thread that delivers the event will release the semaphore right after the slot has been called. Sep 17, · What I mean is, a non-Qt (notification) thread calls a QObject's interface method, in which we emit an AutoConnected signal. The Thread affinity of the QObject is Main thread, but the procedure is actually called from another thread. What'll the Qt do here? share | improve this answer. Jun 22, · I got a problem with calling a funtion from another class. I have searched a bit but i can't find a good solution to my problem. Can any one help me? All my code need to do is call prot function in class Form from the while loop in myClassA.
You must ensure that all objects created in a thread are deleted before you delete the QThread. This can be done easily by creating the objects on the stack in your run implementation. Per-Thread Event Loop Each thread can have its own event loop. Signals and Slots Across Threads Qt supports these signal-slot connection types: Auto Connection default If the signal is emitted in the thread which the receiving object has affinity then the behavior is the same as the Direct Connection.
Otherwise, the behavior is the same as the Queued Connection. The slot is executed in the emitter's thread, which is not necessarily the receiver's thread. Queued Connection The slot is invoked when control returns to the solt loop of the receiver's thread.