Add advice how to freeze fewer modules

[gvanrossum]

(And fix a bug that only occurs when you follow the advice.)

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot s390x SLES 3.x has failed when building commit 1417712.

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/540/builds/4459) and take a look at the build logs.
4. Check if the failure is related to this commit (1417712) 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/540/builds/4459

Failed tests:

• test_asyncio

Failed subtests:

• test_subprocess_consistent_callbacks - test.test_asyncio.test_subprocess.SubprocessPidfdWatcherTests.test_subprocess_consistent_callbacks
• test_fork_signal_handling - test.test_asyncio.test_unix_events.TestFork.test_fork_signal_handling
• test_subprocess_consistent_callbacks - test.test_asyncio.test_subprocess.SubprocessThreadedWatcherTests.test_subprocess_consistent_callbacks

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

== Tests result: FAILURE then FAILURE ==

414 tests OK.

10 slowest tests:

• test_concurrent_futures: 2 min 46 sec
• test_tools: 2 min 25 sec
• test_multiprocessing_spawn: 1 min 51 sec
• test_asyncio: 1 min 47 sec
• test_math: 1 min 26 sec
• test_multiprocessing_forkserver: 1 min 21 sec
• test_multiprocessing_fork: 1 min 10 sec
• test_signal: 1 min 9 sec
• test_capi: 54.6 sec
• test_tokenize: 49.9 sec

1 test failed:
test_asyncio

18 tests skipped:
test_check_c_globals test_devpoll test_ioctl test_kqueue
test_launcher test_msilib test_nis test_peg_generator
test_perf_profiler test_startfile test_tix test_tkinter test_ttk
test_winconsoleio test_winreg test_winsound test_wmi
test_zipfile64

1 re-run test:
test_asyncio

Total duration: 6 min 53 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/unittest/async_case.py", line 90, in _callTestMethod
    if self._callMaybeAsync(method) is not None:
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/unittest/async_case.py", line 117, in _callMaybeAsync
    return self._asyncioTestContext.run(func, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/support/hashlib_helper.py", line 49, in wrapper
    return func_or_class(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/test_unix_events.py", line 1938, in test_fork_signal_handling
    self.assertTrue(child_handled.is_set())
AssertionError: False is not true


Traceback (most recent call last):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/test_subprocess.py", line 771, in test_subprocess_consistent_callbacks
    self.loop.run_until_complete(main())
  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/asyncio/base_events.py", line 664, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/test_subprocess.py", line 763, in main
    self.assertEqual(events, [
AssertionError: Lists differ: [('pi[29 chars]t'), 'pipe_connection_lost', ('pipe_data_recei[57 chars]ted'] != [('pi[29 chars]t'), ('pipe_data_received', 2, b'stderr'), 'pi[57 chars]ted']


Traceback (most recent call last):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/test_subprocess.py", line 771, in test_subprocess_consistent_callbacks
    self.loop.run_until_complete(main())
  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/asyncio/base_events.py", line 664, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/test_subprocess.py", line 763, in main
    self.assertEqual(events, [
AssertionError: Lists differ: [('pi[69 chars]), 'process_exited', 'pipe_connection_lost', '[17 chars]ost'] != [('pi[69 chars]), 'pipe_connection_lost', 'pipe_connection_lo[17 chars]ted']

[gvanrossum]

@kumaraditya303 Can you look at the asyncio failure? It's in test_subprocess_consistent_callbacks where it looks like the events are happening in a different order. It's clearly not due to this PR, but maybe it's a legitimate order of events and the test needs to be fixed?

[gvanrossum]

(Oh I just realized that Kumar said he would be busy. I don't think it's important, that buildbot's history looks super flaky. :-( )