fixes stack overflow possibility with merge operators #2616
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fix subscribing immediately in merge operators can produce values immediately which can re-enter and cause stack overflows
geoffmacd
changed the title
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This looks like a good candidate for a dot release @freak4pc. What do you think? |
RxSwift/Observables/Merge.swift
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| @@ -170,7 +170,10 @@ private final class MergeLimitedSinkIter<SourceElement, SourceSequence: Observab | |||
| case .completed: | |||
| self.parent.group.remove(for: self.disposeKey) | |||
| if let next = self.parent.queue.dequeue() { | |||
| self.parent.subscribe(next, group: self.parent.group) | |||
| _ = CurrentThreadScheduler.instance.schedule(()) { _ in | |||
| self.parent.subscribe(next, group: self.parent.group) | |||
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I'm not sure how important this is, but scheduling the subscribe call will take the corresponding modification of self.parent.group out of the lock that is held while synchronized_on is executing.
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yea, I think you are right that there is an issue and I need to ensure the NSRecursiveLock is re-locking inside this block. I think for the current locking cycle from synchronized_on, there is no more mutation after this line to worry about. The lock will recursively lock on the next inner subscribe.
There is a separate issue here which is that the the disposable from _ = CurrentThreadScheduler.instance.schedule(()) needs to be added to the group otherwise this will not dispose if the CompositeDisposable is disposed. This is minor though since the parent.subscribe would have no impact.
Fixes #2615 See issue for details
when completing Merge operator iterations (concat(), concatMap() and
merge(maxConcurrent:), fixes subscribing immediately to the next in the queue, which can produce values immediately which can re-enter and cause stack overflows. ultimately usesCurrentThreadSchedulerand theisScheduleRequiredprop to know if it needs to schedule or not. This is similar toProducer.All tests pass