fix: judge concurrency safety#329
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gsonntag wants to merge 4 commits into
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MichaelZhao21
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May 22, 2026
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| state.Clock.Mutex.Lock() | ||
| running := state.Clock.State.Running | ||
| state.Clock.Mutex.Unlock() |
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I don't think it's necessary to lock the clock mutex here. Because the running state is a boolean, it shouldn't need to be locked for reading.
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| // IMPORTANT: do NOT call ctx.JSON inside the callback. Mongo's | ||
| // session.WithTransaction retries the callback on | ||
| // TransientTransactionError (which includes WriteConflict). If we | ||
| // wrote the response on a doomed first attempt, a successful retry | ||
| // would still leave the client looking at the 500. |
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I feel like we don't need to explain all of this here; perhaps just including the explanation in the PR/commit is good enough and just adding a note to not call ctx.JSON in the callback. The same comment goes for the top of the callback for /judge/next.
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Description
Fixes concurrency bugs in judge assignment and scoring.
This updates
/judge/nextto re-read the judge inside the transaction before assigning a new project, so concurrent requests cannot assign multiple projects from a stale middleware snapshot. It also preserves the existing behavior of returning an already-assigned current project even when judging is paused or deliberation mode is enabled.This updates
/judge/finishto re-read the judge inside the transaction before scoring, so concurrent finish requests cannot duplicate the same project inseen_projectsor double-increment project seen counts.It also preserves Mongo transaction retry behavior by wrapping transaction errors with
%winUpdateAfterSeen, so transient transaction labels survive error wrapping.Fixes
N/A
Type of Change
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Is this a breaking change?