Firebase-ios-sdk: Deadlock in +[FPRRemoteConfigFlags sharedInstance]

Created on 18 Aug 2020 · 6Comments · Source: firebase/firebase-ios-sdk

[REQUIRED] Step 1: Describe your environment

Xcode version: 11.5
Firebase SDK version: 6.30.0
Firebase Component: Performance
Component version: 6.30.0?
Installation method: Carthage

[REQUIRED] Step 2: Describe the problem

I've been experiencing some intermittent crashes when running my app's tests. The crash dump points to:

Crashed Thread:        11  Dispatch queue: com.apple.dt.xctest.xctwaiter

Exception Type:        EXC_CRASH (SIGABRT)
Exception Codes:       0x0000000000000000, 0x0000000000000000
Exception Note:        EXC_CORPSE_NOTIFY

Application Specific Information:
abort() called

...

    Thread 11 Crashed:: Dispatch queue: com.apple.dt.xctest.xctwaiter
    0   libsystem_kernel.dylib              0x00007fff51af733a __pthread_kill + 10
    1   libsystem_pthread.dylib             0x00007fff51ba1e60 pthread_kill + 430
    2   libsystem_c.dylib                   0x00007fff51a868f6 __abort + 139
    3   libsystem_c.dylib                   0x00007fff51a8686b abort + 135
    4   com.apple.dt.XCTest                 0x000000011a3c9360 +[XCTWaiter handleStalledWaiter:] + 224

Whenever this happens, I see two other threads stuck in a wait state inside +[FPRRemoteConfigFlags sharedInstance] (or somewhere deeper in the stack), such as:

Thread 0:: Dispatch queue: com.apple.main-thread
0   libsystem_kernel.dylib              0x00007fff51af255e __ulock_wait + 10
1   libdispatch.dylib                   0x00007fff5197a0cc _dlock_wait + 44
2   libdispatch.dylib                   0x00007fff5197a04b _dispatch_once_wait + 80
3   redacted                            0x0000000111ab5201 +[FPRRemoteConfigFlags sharedInstance] + 45
4   redacted                            0x0000000111aa49e0 -[FPRConfigurations setupRemoteConfigFlags] + 140
5   redacted                            0x0000000111aa491b -[FPRConfigurations update] + 71
6   com.apple.CoreFoundation            0x00007fff23d68d0c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 12
7   com.apple.CoreFoundation            0x00007fff23d68185 _CFXRegistrationPost1 + 421
8   com.apple.CoreFoundation            0x00007fff23d67ef1 ___CFXNotificationPost_block_invoke + 193
9   com.apple.CoreFoundation            0x00007fff23e652d3 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1795
10  com.apple.CoreFoundation            0x00007fff23d67846 _CFXNotificationPost + 950
11  com.apple.Foundation                0x00007fff2590de2b -[NSNotificationCenter postNotificationName:object:userInfo:] + 59
...

Thread 6:: Dispatch queue: com.google.perf.FPREventsQueue
0   libsystem_kernel.dylib              0x00007fff51af3882 __psynch_cvwait + 10
1   libsystem_pthread.dylib             0x00007fff51ba2425 _pthread_cond_wait + 698
2   com.apple.Foundation                0x00007fff25913646 -[NSOperation waitUntilFinished] + 706
3   com.apple.Foundation                0x00007fff2590d65d -[__NSObserver _doit:] + 232
4   com.apple.CoreFoundation            0x00007fff23d68d0c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 12
5   com.apple.CoreFoundation            0x00007fff23d68185 _CFXRegistrationPost1 + 421
6   com.apple.CoreFoundation            0x00007fff23d67ef1 ___CFXNotificationPost_block_invoke + 193
7   com.apple.CoreFoundation            0x00007fff23e652d3 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1795
8   com.apple.CoreFoundation            0x00007fff23d67846 _CFXNotificationPost + 950
9   com.apple.Foundation                0x00007fff2590de2b -[NSNotificationCenter postNotificationName:object:userInfo:] + 59
10  redacted                            0x0000000111af511c -[RCNUserDefaultsManager resetInstanceUserDefaults] + 210
11  redacted                            0x0000000111af05ee -[RCNConfigSettings initWithDatabaseManager:namespace:firebaseAppName:googleAppID:] + 682
12  redacted                            0x0000000111ae3282 -[FIRRemoteConfig initWithAppName:FIROptions:namespace:DBManager:configContent:analytics:] + 331
13  redacted                            0x0000000111ae677c -[FIRRemoteConfigComponent remoteConfigForNamespace:] + 771
14  redacted                            0x0000000111ae3006 +[FIRRemoteConfig remoteConfigWithFIRNamespace:app:] + 133
15  redacted                            0x0000000111ab5250 __38+[FPRRemoteConfigFlags sharedInstance]_block_invoke + 76
16  libdispatch.dylib                   0x00007fff519798cb _dispatch_client_callout + 8
17  libdispatch.dylib                   0x00007fff5197ab02 _dispatch_once_callout + 20
18  redacted                            0x0000000111ab5201 +[FPRRemoteConfigFlags sharedInstance] + 45
19  redacted                            0x0000000111aa49e0 -[FPRConfigurations setupRemoteConfigFlags] + 140
20  redacted                            0x0000000111aa491b -[FPRConfigurations update] + 71
21  redacted                            0x0000000111aa2e7b __42-[FPRClient startWithConfiguration:error:]_block_invoke + 140
...

Steps to reproduce:

This happens intermittently when running tests in Jenkins CI builds. CI nodes are running Mac OS X 10.15.5 (19F101). I haven't seen it on my local machine, nor when running the app normally.

The failing test targets use the main app as a host so we can take UI snapshots. Unit tests without the host app appear unaffected. It seems to happen much more frequently since I updated from Fabric Crashlytics to Firebase Crashlytics; maybe that's affecting the timing somehow?

I'd appreciate any help/workarounds or a bug fix. Thanks!

performance needs-attention

Source

mike-kerley

All 6 comments

Hello @mike-kerley, thank you for reporting this issue and providing us with the snippets and environment details!

While we work on investigating and narrowing down a root cause, it would be helpful to know what iOS version you're seeing this issue occur within. If you're able to provide this information, please do so -- otherwise we'll continue investigating without it.

Thanks again