Live crash on Mac OS

[chrisbenseler]

When trying to use the live feature, the video does not open and the app crashes. On a MacOS (10.14.5)

The log outputs:

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '+[NSUndoManager(NSInternal) _endTopLevelGroupings] is only safe to invoke on the main thread.'

Any idea?

[tamerthamoqa]

Hi chrisbenseler,

It is a weird issue since I did not face this with Ubuntu 18.04 and Windows 10, it seems cv2.VideoCapture() follows the same logic as cv2.imshow() like in the github issue here:
opencv/opencv-python#134

It seems these calls must be from the main thread only and flask (or waitress in this case) creates a thread per each request which causes this issue, I suppose disallowing threaded mode would fix the issue.

Changing the serve() command to include the parameter 'threads=0' or 'threads=1' (not sure which) might solve the issue:
https://docs.pylonsproject.org/projects/waitress/en/stable/arguments.html

Or replacing the waitress.serve() with the flask app.run() method with parameter 'threaded=False' might work.

I will try to install a MacOS virtual machine soon and try to help but I can't promise anything as I am currently having a bit of a workload.