Have you ever faced crashes while sending nested actions synchronously?

[maximkrouk]

I use https://github.com/trading-point/reactiveswift-composable-architecture with UIKit and I had to wrap a lot of viewStore.send calls into DispatchQueue.main.async call, because viewStore.send caused crashes in @MutableProperty var state (== @Published) in reducer due to the deadlock in the private UnfairLock. I guess it's just a ReactiveSwift's implementation that causes these problems, but I'm not sure, so I decided to make a DisscussionThread/Poll on that topic.

For now I'm waiting for OpenCombine to add Publishers.Merge to make a port of TCA asap, but I'd like to improve my hopes on stability by this thread 😅

[mluisbrown]

I was discussing this with a colleague of mine (@p4checo) the other day and he experimented doing the same thing using Combine and it apparently does not crash. So somehow Combine allows changing the value of a CurrentValueSubject without locking 🤯

I looked at the implementation of CurrentValueSubject in OpenCombine and it also uses an UnfairLock just like ReactiveSwift, so I'm not quite sure how Combine manages this without locks.

[mluisbrown]

Actually I did some experiments with OpenCombine, and it doesn't have the problem, despite using locks. In it's CurrentValueSubject it release the lock before publishing values to its subscribers. The lock is only around the modification of the value itself. I guess that is how Combine does it too.

I'm going to see if I can do something similar in RAS-TCA, by using something custom instead of MutableProperty for the state.

[maximkrouk]

Actually that makes sense, glad u figured it 😍

[mluisbrown]

FYI: I have a WIP PR of RAS-TCA where I'm replicating this behaviour of CurrentValueSubject, in that the sending of updates to observers is outside the scope of the lock.

I haven't tried it yet to see if it solves the problem. If you have time @maximkrouk it would be great if you could try it in your project, as you seem to be having this issue a lot.