🐛 fix deadlocks in depends by using a separate CapacityLimiter for teardown#15388
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olliemath wants to merge 1 commit into
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🐛 fix deadlocks in depends by using a separate CapacityLimiter for teardown#15388olliemath wants to merge 1 commit into
olliemath wants to merge 1 commit into
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…ardown If there is a limited pool of resources, like database connections, we need separate pools of threads for acquiring and releasing those resources, otherwise there will always be deadlocks.
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what
This is #12066 but with a single global "teardown" CapacityLimiter instead of unlimited one-off capacity limiters (and hence threads).
why
If there is a limited pool of resources, like database connections, we need separate pools of threads for acquiring and releasing those resources, otherwise there will always be deadlocks. However the PR doesn't seem to have moved for a while due to the use of one-off / unlimited CapacityLimiters.
anything else
We use a fixed, but arbitrary, limit of 5. It seems that a limit of 1 is too low as operations will serialise. Testing locally with a concurrency of 1000 I didn't notice any difference beyond a limit of ~3. Any number under 40 could be deemed "wrong" if the user has expensive teardown operations.
We can still trigger similar deadlocks by releasing resources in the "finally" section of a middleware. However this is not recommended in the documentation (although it's not explicitly prohibited), so I think it's OK.