Take the lock when closing a script log - #1284
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Every write to the log holds this lock, and the read in GetOutput holds it too, but closing did not. Closing could therefore interleave with a write in progress, and closing does more than release the handle: it completes any JSON array left open. Racing that against a half written entry can leave malformed JSON on disk, which the reader then fails on.
akirayamamoto
marked this pull request as ready for review
August 13, 2026 06:15
| json.Close(); | ||
| writer.Dispose(); | ||
| writeStream.Dispose(); | ||
| lock (sync) |
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It's interesting that this is the same lock object as the parent ScriptLog.
I don't know if disposing the json or writer objects cause changes to the underlying file. Maybe they do. If so, then yes, we would want disposing and reading (in ScriptLog) to wait for each other.
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Yes, they do. I checked with a small repro: closing the writer with an array still open finishes it off on disk, because AutoCompleteOnClose defaults to true. Disposing the StreamWriter also flushes whatever is buffered.
sburmanoctopus
approved these changes
Aug 13, 2026
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Background
ScriptLogguards access to one log file with a single lock. Reads take it and writes take it, but closing does not. Closing is not inert either, since it completes any JSON array still open, so in principle a close could overlap a write that is partway through.I came across this while looking at a nightly that failed reading a corrupt script log, build 23575913. That has happened once and I could not tie it to this, so it is more where I came across the gap than a reason to merge.
Results
Closing now takes the same lock as writes, so a close and a write cannot overlap.
Nothing else changes. A corrupt log still fails the caller as it does today, and writes that arrive after the log has closed are untouched.
How to review this PR
Small enough to read in full.
Two things I would welcome a second opinion on. There is no
disposedflag, so a double dispose calls through twice, which looked harmless when I tried it. AndDisposenow waits on a write, though it runs on a background task rather than a request thread.