Associate thread-local data/context with a faulthandler traceback

Feature or enhancement

I’d like to be able to associate a thread-local string with the faulthandler module.

Pitch

The faulthandler module is invaluable for tracking down segfaults in native code, however it is really lacking the ability to add some kind of useful breadcumb to aide debugging. Imagine you are running a large-scale distributed job over tens of millions of images and a single one causes opencv to segfault reliably. This can be very difficult to track down.

It would be very useful to be able to add a string (limited by size) via the faulthandler module that is outputted along with the traceback. For example:

for image in millions_of_images():
    faulthandler.context(f'{image.id=}')
    segfaulty_function(image)

# Or maybe:
for image in millions_of_images():
    with faulthandler.context(f'{image.id=}'):
        segfaulty_function(image)

The traceback might be something like:

Fatal Python error: Segmentation fault

Current thread 0x00007fb899f39700 (most recent call first):
  .... (traceback)
Segmentation fault
Context: image_id=foo

You could of course add logging to this function to print out the image ID before you run it through segfaulty_function, but if you're running this at high volume on a huge number of machines, this becomes a bit of an overhead, and it doesn't handle multiple threads running the function well.

Previous discussion

This is lifted from the following thread on Python-ideas: https://mail.python.org/archives/list/python-ideas@python.org/message/BG36W24KEEX4YJA7CZ3PGW4ISZGVXMH6/

Commencez par le module faulthandler et examinez la discussion Python-ideas liée pour comprendre le contexte local au thread proposé et ses contraintes. Comparez les exemples de fonction et de gestionnaire de contexte avec la sortie de traceback demandée ; pour considérer le travail comme terminé, il faudrait disposer d’une API et d’un comportement convenus pour associer et émettre le contexte.