Remove continuation resumption inside locks #2558
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Motivation: Whilst investigating deadlocking code elsewhere we discovered that resuming a continuation inside a lock can call deadlocks. The reason is that - `withTaskCancellationHandler` takes a sequence's underlying runtime lock then executes the cancellation handler. - The task cancellation handler then does work which requires taking the NIO-level lock - If a NIO method on a separate thread then takes the NIO-level lock and within it resumes a continuation e.g. in `yield` we will deadlock because the resumption attempts to obtain the underlying runtime lock. Modifications: Do not resume continuations within locks. Result: Fewer deadlock opportunities
FranzBusch
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Nice one fixing this - I started sporadically hitting this today and was just figuring out which locks were involved and dreading writing up the issue. |
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Motivation:
Whilst investigating deadlocking code elsewhere we discovered that resuming a continuation inside a lock can cause deadlocks.
The reason is that
withTaskCancellationHandlertakes a sequence's underlying runtime lock then executes the cancellation handler.yieldwe will deadlock because the resumption attempts to obtain the underlying runtime lock.Modifications:
Do not resume continuations within locks.
Result:
Fewer deadlock opportunities