What is DataBuffer? And how do you render the data in the GUI thread?

@After
For the reason why Qt::BlockingQueuedConnection does not work for you and gives you the error message, from the manual page @SGaist references:

Same as Qt::QueuedConnection, except that the signalling thread blocks until the slot returns. This connection must not be used if the receiver lives in the signalling thread, or else the application will deadlock.

It's for use across different threads for emitter/receiver, only.

@Lorence
When a signal is emitted that is connected to a slot through a queued connection, the actual invocation is deferred - an event is put into the event queue that belongs to the thread the receiver object lives in for later processing. This is why when you have a multithreaded application the slot is executed in the thread where the receiver lives in, and not in the thread where the actual signal was emitted.

Here in the documentation is a more complete discussion.

@Leonardo said:

nections, the parameters must be of types that are known to Qt's meta-object system, because Qt needs to copy the arguments to store them in an event behind the scenes.
...
Call qRegisterMetaType() to register the data type before you establish the connectio

Wow, that really helps!

Thank you so much!

I will try it right now