Incomplete: Wake waiting tower-batch clones on close #1764
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When other tower-batch tasks drop, wake any tasks that are waiting for a semaphore permit. Otherwise, tower-batch can hang. We currently pin tower in our workspace to: d4d1c67 hedge: use auto-resizing histograms (tower-rs/tower#484) Copy tower/src/semaphore.rs from that commit, to pick up tower-rs/tower#480.
teor2345
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dconnolly
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Feb 17, 2021
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teor2345
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This fix was incomplete, for details see: |
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Motivation
tower-rs/tower#480 fixes tower's semaphore, to avoid a hang when clones are waiting on another dropped clone. The fix wakes waiting clones when another clone is dropped.
We should apply the same fix to
tower-batch, which has a copy of tower's semaphore impl.Solution
semaphore.rsfrom our pinned version oftowertotower-batchSyncbound on the semaphore's futureReview
We don't know if this hang is happening in practice, so this isn't urgent.
Related Issues
Closes #1671.
Follow Up Work
When we upgrade to tokio 1.0, we can use
tokio_util::PollSemaphore, rather than copying this code fromtower.