bpo-35046: do only one system call per line (logging.StreamHandler) #10042
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When sys.stderr (or whatever other stream) is unbuffered, the current behavior results in two system calls and allows log records from different processes to concatenate on the same line in the output stream (followed by multiple newlines). This issue is new in Python 3.7, as stdout and stderr became "truly unbuffered" (cf. bpo-30404).
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Due to the recent GitHub outage and the resulting fallout, I didn't realise you'd created this PR, and so I went ahead and created my own (#10043). The only difference is that I added a comment referencing the issue, so that people could refer to it to see the detail of the reason (multiple syscalls leading to coalescing, and so forth). Would you add that comment? Then I can merge this and close my PR. Thanks! |
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Thanks @hashbrowncipher for the PR, and @vsajip for merging it 🌮🎉.. I'm working now to backport this PR to: 3.7. |
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Oct 23, 2018
…ythonGH-10042) (cherry picked from commit b7d6205) Co-authored-by: Josh Snyder <hashbrowncipher@users.noreply.github.com>
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GH-10050 is a backport of this pull request to the 3.7 branch. |
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Hi! The buildbot AMD64 FreeBSD CURRENT Shared 3.7 has failed when building commit d730719. You can take a look here: |
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When sys.stderr (or whatever other stream) is unbuffered, this results in two system calls and allows log records from different processes to concatenate on the same line in the output stream (followed by multiple newlines). This issue is new in Python 3.7, as stdout and stderr became "truly unbuffered" (cf. #30404).
https://bugs.python.org/issue35046