[Interest] Is it OK to emit from different thread?

[maitai]

Agreed. It took me a long time and pain to realize that deriving from 
QThread is a bad idea. Just using connect options, or 
QTimer::singleShot(0, etc) to queue it on the wanted thread, is a much 
better implementation.

I was really misled by the documentation.

Le 30-11-2018 20:15, Jérôme Godbout a écrit :
> The fact that QObject belong to Thread A and a method is used into
> Thread B should raise a flag, each QObject belong to a QThread and
> they should be used by that QThread only. You should move the Object
> to the other thread or use a signals / slots to communicate between
> thread.
> 
> You will have many problems the way you describe it, the fact that the
> thread B is launching the signal of Object that belong on Thread A,
> the automatic connection will check the ownership of the object
> emiting the signal to queue or not the signal and this will be wrong
> since the related thread is not the current thread.
> 
> Note: inheriting QThread is wrong practice and should probably never
> be done. Since the Qthread belong to the thread creator and not the
> created thread you will have the wrong current thread for the current
> QObject that inherit QThread.
> 
> You can see this article that explain the problem by inheriting the
> QThread:
> http://blog.debao.me/2013/08/how-to-use-qthread-in-the-right-way-part-1/
> 
> The Qthread doc and example should really be updated if they still
> show inheritance of QThread, many green developer fall into the pit
> every time and I can understand if the doc still do this.
> 
> -----Original Message-----
> From: Interest <interest-bounces at lists.qt-project.org> On Behalf Of
> Alexander Dyagilev
> Sent: November 30, 2018 1:53 PM
> To: interest at qt-project.org
> Subject: [Interest] Is it OK to emit from different thread?
> 
> Hello,
> 
> Let's suppose some QObject derived class belongs to thread A. It has
> some method, which emits some signal.
> 
> This method may be called from another thread B. Thus, signal will be
> issued for this object from the thread it does not belong to.
> 
> Is it OK?
> 
> source code (just in case):
> 
> class MyObject {
> Q_OBJECT
> signals:
> void mySignal();
> public:
> void test();
> }
> 
> void MyObject::test()
> {
>       emit mySignal();
> }
> 
> // thread A:
> ...
> auto obj = new MyObject();
> ...
> 
> // thread B:
> ...
> obj->test();
> ...
> 
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