[pyqt] Slot crashed in secondary thread without error and works in GUI thread

jsulm

@Thombou Do you access any GUI elements form your non-GUI thread?

Thombou

Hi,
That's what I thought first but i don't think so looking at my code.
The only non self variable I am using are locals to the function. I imported the apt library outside that thread but could that be the reason?

SGaist

Hi,

To get more information about the crash you can use pdb or ipdb and start you script from there.

Thombou

Hi,
Same behavior when using ipdb, no error message.

I found out tha tif I import he thorlabs_apt library from within the slots it works.
How can it be? Is that something that often happen and shall I keep my code this way?
This does not sound very "clean"...

SGaist

Can't you step in your code until the crash happens ?

Thombou

@SGaist Yes I can. I see that the crashing line is self.shutter = apt.Motor(thorlabs_stages_available[i][1])

But when executing this line it crashes and does not drop any error message...

Thombou

Could it be because I instantiate an object of a class that has been defined in the main thread? How to do it in that case?

jsulm

@Thombou said in [pyqt] Slot crashed in secondary thread without error and works in GUI thread:

I instantiate an object of a class that has been defined in the main thread?

What does that mean? If you create the instance in the correct thread then all is fine. A class is not "defined" in a thread.

jeremy_k

@jsulm said in [pyqt] Slot crashed in secondary thread without error and works in GUI thread:

@Thombou said in [pyqt] Slot crashed in secondary thread without error and works in GUI thread:

I instantiate an object of a class that has been defined in the main thread?

What does that mean? If you create the instance in the correct thread then all is fine. A class is not "defined" in a thread.

Technically, a class definition does happen within a particular thread in python or likely any other interpreted language. It's possible that the definition creates or captures a QObject reference, making the class unusable from other threads.

The same general hazard is possible in C++ with lambda objects with captures, use of global QObjects, and likely additional scenarios.

I don't have any reason to suspect the OP is doing this. If I'm wrong, stop doing this!

jeremy_k

@Thombou You might learn more by attaching a C++/native code debugger to the running process. After the process stops, allow it to continue and trigger the crash. Or set breakpoints in Qt or any other native code that might be of interest.