Undo supposed fix for Issue #15798 until I understand why this is
causing test_multiprocessing_forkserver and test_multiprocessing_spawn
failures on head (3.4).
Undo supposed fix for Issue #15798 until I understand why this is
causing test_multiprocessing_forkserver and test_multiprocessing_spawn
failures on head (3.4).
Closes #19831: Stop tracemalloc later at Python shutdown to be able to use
tracemalloc in objects destructor

Replace atexit handler with an harcoded C function _PyTraceMalloc_Fini().
Issue #19842: Refactor BaseSelector to make it an actual usable ABC.