bpo-41503: Fix race between setTarget and flush in logging.handlers.MemoryHandler (GH-21765)

[iritkatriel]

…yHandler

The logging.handlers.MemoryHandler.setTarget() method does not acquire the lock, so it can change the target while flush is processing the buffer.

https://bugs.python.org/issue41503

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @vsajip for commit e3884b0 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[vsajip]

Does the test fail if you leave setTarget() unchanged?

[iritkatriel]

Yes, are you not seeing that?

======================================================================
ERROR: test_race_between_set_target_and_flush (test.test_logging.MemoryHandlerTest)

Traceback (most recent call last):
File "C:\Users\User\src\cpython\lib\test\test_logging.py", line 1201, in test_race_between_set_target_and_flush
self.mem_logger.warning("flushed")
File "C:\Users\User\src\cpython\lib\logging_init_.py", line 1390, in warning
self.log(WARNING, msg, args, **kwargs)
File "C:\Users\User\src\cpython\lib\logging_init.py", line 1514, in log
self.handle(record)
File "C:\Users\User\src\cpython\lib\logging_init.py", line 1524, in handle
self.callHandlers(record)
File "C:\Users\User\src\cpython\lib\logging_init_.py", line 1586, in callHandlers
hdlr.handle(record)
File "C:\Users\User\src\cpython\lib\logging_init_.py", line 894, in handle
self.emit(record)
File "C:\Users\User\src\cpython\lib\logging\handlers.py", line 1235, in emit
self.flush()
File "C:\Users\User\src\cpython\lib\logging\handlers.py", line 1311, in flush
self.target.handle(record)
AttributeError: 'NoneType' object has no attribute 'handle'

[vsajip]

Yes, are you not seeing that?

I didn't test it myself - just wanted to confirm that was the case. Thanks! I'll mark for automerge and approve as soon as the remaining buildbots are done.

[miss-islington]

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

[miss-islington]

Thanks @iritkatriel for the PR, and @vsajip for merging it 🌮🎉.. I'm working now to backport this PR to: 3.8.
🐍🍒⛏🤖

[bedevere-bot]

GH-21897 is a backport of this pull request to the 3.9 branch.

[bedevere-bot]

GH-21898 is a backport of this pull request to the 3.8 branch.