Long stack trace ending with a SIGBUS in libSwiftCore getCache()

Using Swift
,
1

I have a (ReactiveSwift) timer running indefinitely that fires every x minutes. After ~6 days and having accumulated about 500 stack frames, the iOS application crashes with the following few stack frames:

0   libswiftCore.dylib                   0x0000000191876178 getCache(swift::TargetTypeContextDescriptor<swift::InProcess> const&) + 8
1   LLLLLLLL                             0x0000000100d62208 __swift_instantiateGenericMetadata (<compiler-generated>:0)
2   LLLLLLLL                             0x0000000100d9f338 ReactiveSwift.Signal.(Core in _6DF632AE8A9288C3EAD8EFDF3D3AF99E).send(ReactiveSwift.Signal<A, B>.Event) -> () (<compiler-generated>:0)
3   LLLLLLLL                             0x0000000100d9e364 ReactiveSwift.Signal.Observer.send(ReactiveSwift.Signal<A, B>.Event) -> () (Signal.Observer.swift:111)
4   LLLLLLLL                             0x0000000100d7ca80 generic partial specialization <Signature = @escaping @convention(thin) @convention(method) <A, B><A1 where B: Swift.Error, A1 == ReactiveSwift.Lock> (@in_guaranteed ReactiveSwift.Signal<A, B>.Event, @guaranteed ReactiveSwift.Signal<A, B>.(Core in _6DF632AE8A9288C3EAD8EFDF3D3AF99E)<ReactiveSwift.Lock>) -> ()> of ReactiveSwift.Signal.(Core in _6DF632AE8A9288C3EAD8EFDF3D3AF99E).send(ReactiveSwift.Signal<A, B>.Event) -> () (Signal.swift:124)

The stack frames from 5 to 511 are repetitions of the following:

5   LLLLLLLL                            0x0000000100d9e364 ReactiveSwift.Signal.Observer.send(ReactiveSwift.Signal<A, B>.Event) -> () (Signal.Observer.swift:111)
6   LLLLLLLL                            0x0000000100d760b8 closure #3 (ReactiveSwift.Signal<A.Value, B>.Event) -> () in closure #1 (ReactiveSwift.Signal<A.Value, B>, ReactiveSwift.Disposable) -> () in closure #1 (ReactiveSwift.Signal<A, B>.Event) -> () in (extension in ReactiveSwift):ReactiveSwift.Signal< where A: ReactiveSwift.SignalProducerConvertible, B == A.Error>.(observeSwitchToLatest in _6345D8752C3E65AA1118F4C784F9873D)(ReactiveSwift.Signal<A.Value, B>.Observer, ReactiveSwift.SerialDisposable) -> ReactiveSwift.Disposable? (Flatten.swift:677)

Note that the app has been running for 6 days until the crash occurs.

Crash details are as follows:

Exception Type:  SIGBUS
Exception Codes: BUS_ADRERR at 0x16f4a3f90
Crashed Thread:  0

Could this be a Swift runtime bug that causes the cache to get corrupted?

2

Try changing x minutes to, say, 0.0 second1 to see if it'll crash quickly.

3

Thank you. It seems to be an infinite recursion. Can't reproduce it so far, and not all users report it. I have identified suspicious code and will rewrite it to break any potential circular dependencies between the signals.

4

One of the easiest things to check: assuming the structure is used from the main thread and unprotected, make sure it is not called accidentally from another thread:

dispatchPrecondition(condition: .onQueue(.main))
... access the structure