[issue36780] Interpreter exit blocks waiting for futures of shut-down ThreadPoolExecutors

[Hrvoje Nikšić]

Hrvoje Nikšić <hniksic at gmail.com> added the comment:

> The only way I could see this to work as intended without making any changes to threading would be to optionally use daemon threads and avoid joining the threads in `executor.shutdown()` if `wait_at_exit` is set to False in the constructor for the executor.

Agreed, and that is precisely what I suggested in my previous comment. The attached PR already deals with the executor-specific part of the wait, but it would be straightforward to have it also affect the executor to create daemon threads, and the flag moved to the constructor.

> IMO, it also would require some fairly extensive testing to make sure it works as intended, which the patch currently lacks.

It is quite easy to check that a hanging thread (emulated by a simple sleep) is not joined by the executor with the appropriate flag set.

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<https://bugs.python.org/issue36780>
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