[issue43944] Processes in Python 3.9 exiting with code 1 when It's created inside a ThreadPoolExecutor

[Jack DeVries]

Jack DeVries <jdevries3133 at gmail.com> added the comment:

I've identified the first bad commit with git-bisect:

commit b61b818d916942aad1f8f3e33181801c4a1ed14b
Author: Kyle Stanley <aeros167 at gmail.com>
Date:   Fri Mar 27 15:31:22 2020 -0400

    bpo-39812: Remove daemon threads in concurrent.futures (GH-19149)

    Remove daemon threads from :mod:`concurrent.futures` by adding
    an internal `threading._register_atexit()`, which calls registered functions
    prior to joining all non-daemon threads. This allows for compatibility
    with subinterpreters, which don't support daemon threads.

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<https://bugs.python.org/issue43944>
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