Python multiprocessing regression on Windows after updating to Python 3.9.2 #13785
Description
Just to mark this down for future Google searches..
After we updated Emscripten SDK to Python 3.9.2, its multiprocessing library has gained a new regression, failing deterministically on one of the my two Windows systems on error message
Exception in thread Thread-1:
Traceback (most recent call last):
File "threading.py", line 954, in _bootstrap_inner
File "threading.py", line 892, in run
File "multiprocessing\pool.py", line 519, in _handle_workers
File "multiprocessing\pool.py", line 499, in _wait_for_updates
File "multiprocessing\connection.py", line 884, in wait
File "multiprocessing\connection.py", line 816, in _exhaustive_wait
ValueError: need at most 63 handles, got a sequence of length 66
On the other Windows system, this issue does not seem to ever occur. The affected system is a 64-thread Threadripper 2990WX, and the numbers are quite close to 64, so I wonder if that has a meaning here. The unaffected system is a 16-thread system.
Can be reproduced with embuilder build ALL command.
It looks like the upcoming PR #13493 fixes the issue.