Thank you very much! :-)

@Buckwheat Thank you documents link. I will read it and trying to make change in my code. thank you @Buckwheat .

@SGaist I wish mean throw this message : QEventLoop: Cannot be used without QApplication

But this problem is no more. I have delete the project and create un other without dll...
It's not the best solution but it's gona work.

@QtExchange
Forgot to link those two, which are very important to understand before working with threads:
QObjects' thread affinity: http://doc.qt.io/qt-5/qobject.html#thread-affinity
Queued connections accros threads: http://doc.qt.io/qt-5/threads-qobject.html#signals-and-slots-across-threads

You can find the implementation in qtestsystem.h

It basically trigger event processing and sleeps a short time.

Can you show a picture of how your system should work ?

Hi and welcome to devnet,

That's because you are calling exec on _eventLoop twice. You should rather use a local QEventLoop or not allow the query to start if already in progress.

I never tried to start a thread with event loop in a program without main event loop (QApplication). My guess: it will work inside your thread, but you will not be able to communicate with the thread from main thread using signals/slots.

Ok guy thank you for that much replies :P! I solved the issue by myself anyway. In case sombebody has a similar problem here comes the solution:

What I did wrong was that I connected a time consuming function to the UpdateClient::tcpReady() slot. In this function I did some stuff which also lead to the emission of UpdateClient::tcpReady(). This broke the QEventQueue. So to what I had to chance was to skip the direct signal slot connection an do this in the UpdateClient::tcpReady():

QTimer::singleShot(0, this, SIGNAL(updateAvailable()));

No everything is working fine ;).

@ChrisW67

Thank you for you help.
Probably the thing is, QSerialPort has a problem to work in a new thread.

I can handle the other QObject in a new thread very well, and the exception only happens when the Object contains QSerialPort.
Also, in my last post, I actually never user QList, although Qt tells me something wrong with QList.

I have given up on working serialThread. QSerialPort does work good in the main thread.

@SGaist Hi. Thank you for your help. I'll give it a try, but I still don't get why my code doesn't work... If anyone could take a guess, I'd appreciate.