Fixed a race condition in Signal terminal event handling.
#267
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Sources/Signal.swift
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| s.state = .alive(AliveState(observers: observers, | ||
| retaining: observers.isEmpty ? nil : self)) | ||
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| withExtendedLifetime(snapshot.retaining) { |
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What is retaining here? This line reads a little weirdly to me, I wonder if we can improve the name.
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As mentioned in AliveState:
A self-retaining reference [of the signal]. It is set when there are one or more active observers.
Sources/Signal.swift
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| withExtendedLifetime(snapshot.retaining) { | ||
| s.state = .alive(AliveState(observers: observers, | ||
| retaining: observers.isEmpty ? nil : self)) |
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Thoughts on extracting this to a local newState so we can remove the awkward formatting over two lines?
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An explicit guard is added to ensure the old signal state snapshot does not deinitialize before `updateLock` is released. Otherwise, it might result in a deadlock in cases where a `Signal` legitimately receives terminal events recursively as a result of the deinitialization of the snapshot.
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@sharplet Addressed both in code and in the commit. The implementation has been updated too. |
| // deadlock in cases where a `Signal` legitimately receives terminal | ||
| // events recursively as a result of the deinitialization of the | ||
| // snapshot. | ||
| withExtendedLifetime(snapshot) { |
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This is not strictly necessary, since snapshot is guaranteed to live till the end of the scope. But it serves a documentation purpose, and would be optimised away by the compiler IIRC.
| let action1 = Action<(), ViewModel, NoError> { SignalProducer(value: ViewModel()) } | ||
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| action1.values | ||
| .flatMap(.latest) { viewModel in viewModel.action2.values.map { _ in viewModel } } |
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The deadlock happens as the observer disposable releases the closure { _ in viewModel } here without releasing the mapped signal's updateLock first. The deinitialization triggers the propagation of terminal event of the Action, which eventually hits the mapped signal.
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