Crash in FlagsUnchangedObserver

[NikolajMosbaek]

A portion of the sessions crash in FlagsUnchangedObserver. I am unable to recreate the crash but it has happened on iOS 12, 13 & 14 for LaunchDarkly 5.1.0. The stack trace is as follows:

0 libdispatch.dylib     dispatch_group_leave$VARIANT$mp.cold.1
1 libdispatch.dylib     dispatch_group_leave$VARIANT$mp
2 LaunchDarkly          closure #2 () -> () in LaunchDarkly.LDClient.(go in _14C52C04C80D938C2FE76924F7908AD1)(online: Swift.Bool, reasonOnlineUnavailable: Swift.String, completion: () -> ()?) -> () LDClient.swift:143
3 LaunchDarkly          partial apply forwarder for closure #1 () -> () in closure #1 (LaunchDarkly.FlagsUnchangedObserver) -> () in closure #1 () -> () in LaunchDarkly.FlagChangeNotifier.notifyObservers(user: LaunchDarkly.LDUser, oldFlags: [Swift.String : LaunchDarkly.FeatureFlag]) -> () FlagChangeNotifier.swift:94
4 LaunchDarkly          reabstraction thunk helper from @escaping @callee_guaranteed () -> () to @escaping @callee_unowned @convention(block) () -> () <compiler-generated>:0
5 libdispatch.dylib     _dispatch_call_block_and_release

[torchhound]

Hi @NikolajMosbaek thanks for reporting this issue.

Filed internally as 91704.

[torchhound]

Hi @NikolajMosbaek would you please provide some additional context? Anything you can share (that isn't private or proprietary) about your SDK version, client configuration, or what code or part of your app's lifecycle is executing when the error happens. If additional context is private or proprietary information please reach out to our support staff to share it.

[NikolajMosbaek]

Hi @torchhound. I'm runnung version 5.1.0 on iOS. Since there's no reference to my app in the stack trace and the app has been running for various amounts of time it's hard for me to guess where in the app's lifecycle the crash occurs. I don't know which part of my LaunchDarkly setup that's relevant to be shared.
Before running version 5.1.0 I was running the same setup on version 4.7.0 without any problems.

[NikolajMosbaek]

@torchhound Please let me know if there's anything in particular you need from me to get to the bottom of this. This issue is my most often occurring crash at the moment.

[torchhound]

@NikolajMosbaek Are you rapidly calling identify? Or perhaps calling identify quickly after SDK initialization or before/after your app going into the foreground/background?

[NikolajMosbaek]

@torchhound I cannot see any scenario in my code where identify would be rapidly called. I do, however, call it in the completion closure of LDClient.start. Do you believe that could be the issue? I will refactor my code so that is no longer the case and monitor whether it affect the crash.

[NikolajMosbaek]

It seems that did the trick, so I'll close this issue. Thanks to @torchhound!

[torchhound]

Thanks for bringing this to our attention @NikolajMosbaek! Glad you found a fix. We will try and patch this.