Crash After App Delete: Fatal Exception: NSRangeException

[min]

[REQUIRED] Step 1: Describe your environment

• Xcode version: 11.3.1
• Firebase SDK version: 6.14.0
• Firebase Component: Core, Database
• Component version: 6.14.0
• Installation method: Carthage

[REQUIRED] Step 2: Describe the problem

Steps to reproduce:

We're observing a crash that's slowly increasing when executing this code block:

database.purgeOutstandingWrites()
app.delete()

Stack Trace

Fatal Exception: NSRangeException
*** -[__NSArrayM objectAtIndexedSubscript:]: index 9223372036854775807 beyond bounds for empty array

Fatal Exception: NSRangeException
0   CoreFoundation                      0x00007fff23c7127e __exceptionPreprocess + 350
1   libobjc.A.dylib                     0x00007fff513fbb20 objc_exception_throw + 48
2   CoreFoundation                      0x00007fff23d03ab1 _CFThrowFormattedException + 194
3   CoreFoundation                      0x00007fff23b8572e -[__NSArrayM objectAtIndexedSubscript:] + 142
4   Foo                                 0x0000000103c22a0c -[FWriteTree removeWriteId:] + 171
5   Foo                                 0x0000000103c0b2bd -[FSyncTree ackUserWriteWithWriteId:revert:persist:clock:] + 166
6   Foo                                 0x0000000103bf9a1d -[FRepo ackWrite:rerunTransactionsAtPath:status:] + 212
7   Foo                                 0x0000000103bf876b __39-[FRepo update:withNodes:withCallback:]_block_invoke + 114
8   Foo                                 0x0000000103bf1361 -[FPersistentConnection ackPuts] + 343
9   Foo                                 0x0000000103bf0de5 -[FPersistentConnection purgeOutstandingWrites] + 54
10  Foo                                 0x0000000103bf9144 -[FRepo purgeOutstandingWrites] + 287
11  Foo                                 0x0000000103bd37be __37-[FIRDatabase purgeOutstandingWrites]_block_invoke + 52
12  libdispatch.dylib                   0x000000010d90fdd4 _dispatch_call_block_and_release + 12
13  libdispatch.dylib                   0x000000010d910d48 _dispatch_client_callout + 8
14  libdispatch.dylib                   0x000000010d9175ef _dispatch_lane_serial_drain + 788
15  libdispatch.dylib                   0x000000010d91817f _dispatch_lane_invoke + 422
16  libdispatch.dylib                   0x000000010d923a4e _dispatch_workloop_worker_thread + 719
17  libsystem_pthread.dylib             0x00007fff524636fc _pthread_wqthread + 290
18  libsystem_pthread.dylib             0x00007fff52462827 start_wqthread + 15

[ryanwilson]

Looks like the purgeOutstandingWrites call does some async work on [FIRDatabaseQuery sharedQueue] and we should wait that out when an app is deleted.

This should likely be done in the following:

firebase-ios-sdk/Firebase/Database/Api/FIRDatabaseComponent.m

Lines 85 to 100 in 9bfbb9e

	- (void)appWillBeDeleted:(FIRApp *)app {
	NSString *appName = app.name;
	if (appName == nil) {
	return;
	}
	FIRDatabaseDictionary *instances = [self instances];
	@synchronized(instances) {
	// Clean up the deleted instance in an effort to remove any resources
	// still in use. Note: Any leftover instances of this exact database
	// will be invalid.
	for (FIRDatabase *database in [instances allValues]) {
	[FRepoManager disposeRepos:database.config];
	}
	[instances removeAllObjects];
	}
	}

@min: are you doing anything after app.delete()? It does have a completion handler you can provide that's called when all cleanup is done for each SDK.

Also it's always helpful to hear what the use case for app.delete() is so we can better understand what developers are doing with it.

Thanks!

[min]

@ryanwilson we’re basically calling delete to clear out the session when a user logs out. wondering if the purge is even necessary.

[ryanwilson]

It's likely not for the moment to unblock you, but something we should still try to fix :)

[min]

@ryanwilson thanks!

[paulb777]

@ryanwilson Should the label be changed to database?

[ryanwilson]

Great call - not sure why Googelbot thought it was auth...