@serhiy-storchaka If you don't mind, would you take a look at this refactor - see if you have any concerns?

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 FreeBSD 3.x has failed when building commit e9791ba.

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/1223/builds/222) and take a look at the build logs.
4. Check if the failure is related to this commit (e9791ba) 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/1223/builds/222

Failed tests:

• test.test_concurrent_futures.test_shutdown

Failed subtests:

• test_cancel_futures_wait_false - test.test_concurrent_futures.test_shutdown.ThreadPoolShutdownTest.test_cancel_futures_wait_false

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

==