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StopAtEOF is racy #67

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tgummerer opened this issue Apr 3, 2024 · 0 comments · May be fixed by #70
Open

StopAtEOF is racy #67

tgummerer opened this issue Apr 3, 2024 · 0 comments · May be fixed by #70
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bug Something isn't working

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@tgummerer
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If you sent an issue/PR to hpcloud, you can have a look at
this meta issue tracking issues
and PRs of the dormant upstream. However, as the code bases diverge the
issue may have been solved already.

Describe the bug
The StopAtEOF function can sometimes stop tailing the file before we actually encounter an EOF. In particular, when using the polling function for checking for file changes, we might select this tail.Dying channel here first before the poller gets another chance to notify us of new changes, which I believe makes us then return here, even though we should probably be waiting for another poll cycle.

Expected behaviour
The library checks again for new changes in the file after StopAtEOF is reached.

To Reproduce
This is a bit awkward to reproduce, since it's based on racyness. However tailing a file that's being written to in short intervals, and calling StopAtEOF might not return all data before exiting.

Additional context
I'd be happy to contribute a PR for this, but probably won't have the time to do so before next week.
@tgummerer tgummerer added the bug Something isn't working label Apr 3, 2024
@tgummerer tgummerer mentioned this issue Apr 3, 2024
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github-merge-queue bot pushed a commit to pulumi/pulumi that referenced this issue Apr 3, 2024
@tgummerer
avoid racyness from the polling library (#15856)
98fc51e 
The library we're using unfortunately has a race condition that's
especially worse when using polling to check for new changes of the
file. Avoid this racyness by sleeping for a bit for now, but really this
should be fixed upstream ideally.

I opened a upstream issue for this in
nxadm/tail#67. I think we should merge this in
the meantime, as it makes this work, even though it's very hacky.

I tested this in #15853, where I
could no longer reproduce the failure we've seen before.

Fixes #15659
Fixes #15235
@tgummerer tgummerer linked a pull request Apr 8, 2024 that will close this issue
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fix a race when StopAtEOF is called tgummerer/tail
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@tgummerer