bpo-43498: Fix dictionary iteration error in _ExecutorManagerThread

[kulikjak]

This prevents RuntimeError: dictionary changed size during iteration which we recently encountered several times during make install.

https://bugs.python.org/issue43498

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[kulikjak]

Still very much relevant.

[sweeneyde]

Is it possible to find a test case that reliably (or usually) fails before this, and reliably passes after?

[kulikjak]

Is it possible to find a test case that reliably (or usually) fails before this, and reliably passes after?

I mentioned one way to force this in the issue, but you have to modify library files for that. I will look into reliably reproducing this with user code.

[mgorny]

Thanks for the patch. We're hitting this too, apparently, so I'll just backport it to Gentoo.

[miss-islington]

Thanks @kulikjak for the PR, and @asvetlov for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9, 3.10.
🐍🍒⛏🤖

[asvetlov]

Thanks!

[bedevere-bot]

GH-29836 is a backport of this pull request to the 3.10 branch.

[bedevere-bot]

GH-29837 is a backport of this pull request to the 3.9 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot x86 Gentoo Installed with X 3.9 has failed when building commit 3b9d886.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/527/builds/326) and take a look at the build logs.
4. Check if the failure is related to this commit (3b9d886) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/527/builds/326

Summary of the results of the build (if available):

Click to see traceback logs

fatal: unable to access 'https://github.com/python/cpython.git/': Failed to connect to github.com port 443 after 131194 ms: Connection timed out

chmod: cannot access 'target/': No such file or directory

make: *** No rule to make target 'distclean'.  Stop.