Add mutex protection on ConversationHandler

[SnowyCoder]

Advances #1029 adding thread safety on the mutable variables of the class (conversations and timeout_jobs).
The original issue also asked to internalize all the other properties but it would incur breaking changes and a lot of refactoring, I'll leave this task to someone more proficient with the codebase.

[Poolitzer]

Hey man, this looks good to me, but there should be definitly someone else to look over this cough cough @Eldinnie? cough cough. Can you remove the #Todo line though and either put it in this conversation or in the related issue? Then codacy should be fine with it.

[jh0ker]

If you address the TODO, I think this is good

[SnowyCoder]

I've addressed the todo, should I squash the commits?
Sorry for the trouble, I wanted to help you a bit but It's my first time doing a PR in a big repo 😅.

[Poolitzer]

No need to, we will before merging into master. Just go ahead and make as many commits as you want :)

[jh0ker]

@SnowyCoder Now you have the chance to get the true big repo experience™️ 😉
It would be great to have a test for that last change you made regarding the removal of the timeout job. Basically a test that demonstrates that the timeout job will be removed and not executed, even if you have a child handler that starts before the timeout would run out and ends after.

Refer to https://github.com/python-telegram-bot/python-telegram-bot/blob/master/tests/test_conversationhandler.py line 414 and following for inspiration.

[SnowyCoder]

I've been studying the test code and I noticed something strange: the assignment at line 494 (that has moved to 552 in the master branch) is duplicated, it seems like a merge error or a typo.

[jh0ker]

@SnowyCoder Interesting find ^^
Edit: e75615c introduced it, not quite sure what was going on here...

[jh0ker]

Thanks a lot for your contribution @SnowyCoder!

[SnowyCoder]

Thank you for the support!