[issue33623] Fix possible SIGSGV when asyncio.Future is created in __del__

[Peter Bašista]

Peter Bašista <pbasista at gmail.com> added the comment:

> Can this crash be reproduced without uvloop?
I am not aware of a way to reproduce this without uvloop.

> What is the backtrace of the assertion failure?
Without uvloop, the following exception is raised:

Exception ignored in: <bound method LoopWrapper.__del__ of <__main__.LoopWrapper object at 0x7fe14ec569b0>>
Traceback (most recent call last):
  File "uvloop_test.py", line 13, in __del__
  File "/usr/lib/python3.6/asyncio/base_events.py", line 276, in create_future
AttributeError: 'NoneType' object has no attribute 'Future'

With uvloop and with Python compiled with --with-pydebug configure option, the failed assertion is mentioned in the original uvloop bug report. In particular, this assertion fails:

python3.6-dbg: ../Objects/abstract.c:2300: _PyObject_FastCallDict: Assertion `func != NULL' failed. 

A full GDB backtrace is attached.

----------
nosy: +pbasista
Added file: https://bugs.python.org/file47619/uvloop-test.gdb-backtrace.txt

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