[3.7] Revert "bpo-34172: multiprocessing.Pool leaks resources after being deleted (GH-8450) (GH-9676)"

[vstinner]

This reverts commit 97f998a.

https://bugs.python.org/issue34172

[vstinner]

@ned-deily, @pablogsal: I propose to revert the change since it caused a regression:
https://bugs.python.org/issue34172#msg330955

@pablogsal is working on a fix https://bugs.python.org/issue35378 but I'm not fully happy with it. Even if it's a good change, I dislike pushing late fix just before a release. I would prefer to have more time to experiment the overall change and make sure that it's the best option.

https://bugs.python.org/issue34172 is likely a very old bug, as old as multiprocessing. So yeah, it should be fixed, but not by changing the behavior in a stable branch.

[pablogsal]

Even if it's a good change, I dislike pushing late fix just before a release. I would prefer to have more time to experiment with the overall change and make sure that it's the best option.

I fully agree with this. Is better not to change the behaviour in maintenance branches especially when the change introduces a regression. Letś iterate over this in master.

[vstinner]

@pablogsal: For the NEWS entry, I had to add a new "REVERT: xxx" entry, since the previous one is already part of 3.7.1rc2. Is it ok?

[pablogsal]

@vstinner Looks good to me.

[bedevere-bot]

@vstinner: Please replace # with GH- in the commit message next time. Thanks!