queues: Preserve items when waiting consumers are canceled - #3689
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queues: Preserve items when waiting consumers are canceled#3689Sanjays2402 wants to merge 1 commit into
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Queue.put_nowait resolves a waiting getter before its consumer task resumes. If that task is canceled in the gap, cancellation replaces the delivered result and the item disappears. Use a cancellation-aware getter future to return a delivered item to the queue when cancellation wins that race. Add regression coverage for the put-then-cancel ordering. Fixes tornadoweb#2826.
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Fixes #2826.
A queue item can be assigned to a waiting getter just before its consumer task is canceled; cancellation then replaces the getter's completed result and silently drops the item. Queue getters now return completed items to the queue when cancellation wins that race, without changing the unfinished-task count.
The regression test reproduces the put-then-cancel ordering: it fails with
QueueEmptybefore the fix and passes afterward. The queues test module passes all 43 tests.