[Core] Make instance manager conform to Swift 6 principles #13933
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paulb777 approved these changes Oct 19, 2024
FirebaseCore/Internal/Sources/HeartbeatLogging/HeartbeatStorage.swift Outdated Show resolved Hide resolved
andrewheard approved these changes Oct 21, 2024
FirebaseCore/Internal/Sources/HeartbeatLogging/HeartbeatStorage.swift Outdated Show resolved Hide resolved
paulb777 approved these changes Oct 23, 2024
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Problem:
Static property 'cachedInstances' is not concurrency-safe because it is nonisolated global shared mutable stateThe fix-it to add
nonisolated(unsafe)is for when it's okay toDisable concurrency-safety checks if accesses are protected by an external synchronization mechanism.The "external synchronization mechanism" is the added lock. I went with
NSLockofos_unfair_lockbecause the latter would need to be anotherstatic varand require an extranonisolated(unsafe)attribute. This would be technically okay, but it looked cleaner to use the NSLock. NSLock is slightly slower but I think it would have a negligible effect based on the use case here.Because core internal has < iOS 13 availability, structured concurrency cannot be used.
The added test crashes with the current implementation, and succeeds with this PR's changes.
#no-changelog