Crash: NSInternalInconsistencyException', reason: 'FIRESTORE INTERNAL ASSERTION FAILED: Enqueue methods cannot be called when we are already running on target executor

[mpalczew]

[REQUIRED] Step 1: Describe your environment

• Xcode version: 12.1
• Firebase SDK version: 7.0.0
• Installation method: Carthage
• Firebase Component: Auth, Core

[REQUIRED] Step 2: Describe the problem

Steps to reproduce:

Observing a crash when trying to delete a FirebaseApp object.

calling

app.delete {
}

where app is a FirebaseApp

Seeing this

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'FIRESTORE INTERNAL ASSERTION FAILED: Enqueue methods cannot be called when we are already running on target executor (this queue's executor: 'com.google.firebase.firestore.httpsinstacartfirebaseiocomv1', current executor: 'com.google.firebase.firestore.httpsinstacartfirebaseiocomv1') (expected !is_operation_in_progress_ || !executor_->IsCurrentExecutor())'

[var-const]

Thank you for filing the issue. From the error message, it sounds like you're using Firestore and somehow a callback run on the user callback queue ends up enqueuing another operation that is supposed to be run on the user callback queue. Are you running any code that involves Firestore in the app.delete callback? If that's the case, can you please check whether temporarily commenting that code out prevents the assertion? Another thing that might be helpful would be to enable logging and post the resulting log after reproducing the issue (please make sure to omit any sensitive data).

[mpalczew]

Here are the logs

	10:00:08.556	Instacart Beta	6.34.0 - [Firebase/Core][I-COR000006] Deleting app named httpsinstacartfirebaseiocomv1
	10:00:08.557	Instacart Beta	6.34.0 - [Firebase/Firestore][I-FST000001] RemoteStore 7f7f695bed50 shutting down
	10:00:08.557	Instacart Beta	6.34.0 - [Firebase/Firestore][I-FST000001] WatchStream (600000217d18) stop
	10:00:08.557	Instacart Beta	6.34.0 - [Firebase/Firestore][I-FST000001] WatchStream (600000217d18) Finishing gRPC stream
	10:00:08.557	Instacart Beta	6.34.0 - [Firebase/Firestore][I-FST000001] GrpcStream('600000cab3c0'): finishing without notifying observers
	10:00:08.557	Instacart Beta	6.34.0 - [Firebase/Firestore][I-FST000001] GrpcStream('600000cab3c0'): shutting down; completions: 1, is finished: false
	10:00:08.558	Instacart Beta	6.34.0 - [Firebase/Firestore][I-FST000001] GrpcStream('600000cab3c0'): finishing the underlying call
2	10:00:08.558	Instacart Beta	6.34.0 - [Firebase/Firestore][I-FST000001] GrpcStream('600000cab3c0'): fast finishing 1 completion(s)
	10:00:08.558	Instacart Beta	6.34.0 - [Firebase/Firestore][I-FST000001] GrpcStream('600000cab3c0'): destroying stream
	10:00:08.559	Instacart Beta	6.34.0 - [Firebase/Firestore][I-FST000001] WriteStream (7f7f5949be48) stop

[mpalczew]

I'm not running any code that involves firestore in the app.delete callback. Waiting for one second before calling delete does seem to work just fine. Trying to figure out if there are any firebase calls around this area. Though I don't see anything and nothing in the logs.

[mpalczew]

Also, Started seeing this after we upgraded from 6.14.0 to 6.33.0. We were not seeing this crash before.

[mpalczew]

This crash seems to happen only if I have active snapshot listeners for a document reference.
If I register all snapshot listeners and call remove on them before I delete the app, then this crash doesn't happen.

[var-const]

@mpalczew Thank you for providing additional information. There should be a stack trace associated with the exception, can you please post it?