[Firebase] FirebaseCoreInternal.UnfairLock blocks main thread during app foregrounding → Watchdog 0x8BADF00D crash #15394
Description
Description
We are seeing watchdog termination (0x8BADF00D) crashes during app foregrounding. The main thread gets blocked inside FirebaseCoreInternal.UnfairLock, causing the app to hang for >5 seconds and get killed by the system.
-------------------------------------
Translated Report (Full Report Below)
-------------------------------------
Incident Identifier: 6471908E-F653-4EDD-95BF-ABCF81BD9FA6
Beta Identifier: 9BDFDC5B-8ADB-4E78-ABDC-F0987CD29E60
Hardware Model: iPhone16,1
Process: SomeHiddenApp [2320]
Path: /private/var/containers/Bundle/Application/C0313EF3-B2D9-41DE-BFE9-DB20CBB8639D/SomeHiddenApp.app/SomeHiddenApp
Identifier: my.hidden.app
Version: 1.62 (1.62.1400.1)
AppStoreTools: 17A323
AppVariant: 1:iPhone16,1:17.4
Beta: YES
Code Type: ARM-64 (Native)
Role: Background
Parent Process: launchd [1]
Coalition: my.hidden.app [1097]
Date/Time: 2025-10-08 10:27:39.7975 +0300
Launch Time: 2025-10-08 10:27:02.3197 +0300
OS Version: iPhone OS 17.6.1 (21G93)
Release Type: User
Baseband Version: 1.70.02
Report Version: 104
Exception Type: EXC_CRASH (SIGKILL)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Termination Reason: FRONTBOARD 2343432205
<RBSTerminateContext| domain:10 code:0x8BADF00D explanation:[app<my.hidden.app(1BEEAC49-B52E-4D36-B7E0-3F45427F7F4F)>:2320] failed to terminate gracefully after 5.0s
ProcessVisibility: Unknown
ProcessState: Running
WatchdogEvent: process-exit
WatchdogVisibility: Foreground
WatchdogCPUStatistics: (
"Elapsed total CPU time (seconds): 9.580 (user 6.990, system 2.590), 26% CPU",
"Elapsed application CPU time (seconds): 0.016, 0% CPU"
) reportType:CrashLog maxTerminationResistance:Interactive>
Triggered by Thread: 0
Thread 0 name: Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0 libsystem_kernel.dylib 0x1d56f14dc __ulock_wait2 + 8
1 libsystem_platform.dylib 0x1e94354d8 _os_unfair_lock_lock_slow + 188
2 SomeHiddenApp 0x1019bef4c $s20FirebaseCoreInternal10UnfairLockC04withE0yqd__qd__xzYuYTXElF + 48
3 SomeHiddenApp 0x102318360 RemoteSettings.sessionTimeout.getter + 56
4 SomeHiddenApp 0x102316328 SessionInitiator.appForegrounded() + 252
5 SomeHiddenApp 0x1023163a8 @objc SessionInitiator.appForegrounded() + 24
6 CoreFoundation 0x18ca6a78c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 148
7 CoreFoundation 0x18ca6a6a8 ___CFXRegistrationPost_block_invoke + 88
8 CoreFoundation 0x18ca6a5f0 _CFXRegistrationPost + 440
9 CoreFoundation 0x18ca68bb8 _CFXNotificationPost + 728
10 Foundation 0x18b8f6254 -[NSNotificationCenter postNotificationName:object:userInfo:] + 92
11 UIKitCore 0x18ef0ab58 -[UIApplication _stopDeactivatingForReason:] + 1240
12 UIKitCore 0x18f0a61d4 -[_UISceneLifecycleMultiplexer _performBlock:withApplicationOfDeactivationReasons:fromReasons:] + 280
13 UIKitCore 0x18ee35360 -[_UISceneLifecycleMultiplexer _evalTransitionToSettings:fromSettings:forceExit:withTransitionStore:] + 608
14 UIKitCore 0x18ee02594 -[_UISceneLifecycleMultiplexer uiScene:transitionedFromState:withTransitionContext:] + 248
15 UIKitCore 0x18ee01ebc __186-[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:]_block_invoke + 148
16 UIKitCore 0x18ee01868 +[BSAnimationSettings(UIKit) tryAnimatingWithSettings:fromCurrentState:actions:completion:] + 736
17 UIKitCore 0x18ee00ea8 _UISceneSettingsDiffActionPerformChangesWithTransitionContextAndCompletion + 224
18 UIKitCore 0x18eed4c80 -[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:] + 316
19 UIKitCore 0x18eed34b8 __64-[UIScene scene:didUpdateWithDiff:transitionContext:completion:]_block_invoke.226 + 612
20 UIKitCore 0x18eed2e10 -[UIScene _emitSceneSettingsUpdateResponseForCompletion:afterSceneUpdateWork:] + 216
21 UIKitCore 0x18ef9df48 -[UIScene scene:didUpdateWithDiff:transitionContext:completion:] + 244
22 UIKitCore 0x18ef9db28 -[UIApplicationSceneClientAgent scene:handleEvent:withCompletion:] + 336
23 FrontBoardServices 0x1a58166e4 -[FBSScene updater:didUpdateSettings:withDiff:transitionContext:completion:] + 660
24 FrontBoardServices 0x1a5826844 __94-[FBSWorkspaceScenesClient _queue_updateScene:withSettings:diff:transitionContext:completion:]_block_invoke_2 + 152
25 FrontBoardServices 0x1a58266cc -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:] + 168
26 FrontBoardServices 0x1a582b7fc __94-[FBSWorkspaceScenesClient _queue_updateScene:withSettings:diff:transitionContext:completion:]_block_invoke + 344
27 libdispatch.dylib 0x194942dd4 _dispatch_client_callout + 20
28 libdispatch.dylib 0x19494686c _dispatch_block_invoke_direct + 288
29 FrontBoardServices 0x1a5827d58 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 52
30 FrontBoardServices 0x1a5827cd8 -[FBSMainRunLoopSerialQueue _targetQueue_performNextIfPossible] + 240
31 FrontBoardServices 0x1a5827bb0 -[FBSMainRunLoopSerialQueue _performNextFromRunLoopSource] + 28
32 CoreFoundation 0x18ca6f834 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 28
33 CoreFoundation 0x18ca6f7c8 __CFRunLoopDoSource0 + 176
34 CoreFoundation 0x18ca6d2f8 __CFRunLoopDoSources0 + 340
35 CoreFoundation 0x18ca6c484 __CFRunLoopRun + 828
36 CoreFoundation 0x18ca6bcd8 CFRunLoopRunSpecific + 608
37 GraphicsServices 0x1d14b91a8 GSEventRunModal + 164
38 UIKitCore 0x18f0a5ae8 -[UIApplication _run] + 888
39 UIKitCore 0x18f159d98 UIApplicationMain + 340
40 SwiftUI 0x190c60294 0x19086c000 + 4145812
41 SwiftUI 0x190c0c860 0x19086c000 + 3803232
42 SwiftUI 0x190c1861c 0x19086c000 + 3851804
43 SomeHiddenApp 0x101403eb0 static SomeHiddenAppApp.$main() + 40
44 SomeHiddenApp 0x10140a780 main + 12
45 dyld 0x1b0243154 start + 2356
[crashreport.txt](https://github.com/user-attachments/files/22780775/crashreport.txt)
Reproducing the issue
No response
Firebase SDK Version
12.3.0
Xcode Version
26.0
Installation Method
Swift Package Manager
Firebase Product(s)
Remote Config
Targeted Platforms
iOS
Relevant Log Output
If using Swift Package Manager, the project's Package.resolved
Expand Package.resolved snippet
{
"originHash" : "057c7dbe71674adc8e41bfeb2396358a904056a75deaa79790bd44e21dfa2485",
"pins" : [
{
"identity" : "abseil-cpp-binary",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/abseil-cpp-binary.git",
"state" : {
"revision" : "194a6706acbd25e4ef639bcaddea16e8758a3e27",
"version" : "1.2024011602.0"
}
},
{
"identity" : "amplitude-ios",
"kind" : "remoteSourceControl",
"location" : "https://github.com/amplitude/Amplitude-iOS",
"state" : {
"revision" : "bfdec453a31fd35942a619ef472fcf2f09e2313a",
"version" : "8.19.2"
}
},
{
"identity" : "analytics-connector-ios",
"kind" : "remoteSourceControl",
"location" : "https://github.com/amplitude/analytics-connector-ios.git",
"state" : {
"revision" : "e2ca17ac735bcbc48b13062484541702ef45153d",
"version" : "1.0.3"
}
},
{
"identity" : "app-check",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/app-check.git",
"state" : {
"revision" : "61b85103a1aeed8218f17c794687781505fbbef5",
"version" : "11.2.0"
}
},
{
"identity" : "appauth-ios",
"kind" : "remoteSourceControl",
"location" : "https://github.com/openid/AppAuth-iOS.git",
"state" : {
"revision" : "2781038865a80e2c425a1da12cc1327bcd56501f",
"version" : "1.7.6"
}
},
{
"identity" : "appsflyerframework-dynamic",
"kind" : "remoteSourceControl",
"location" : "https://github.com/AppsFlyerSDK/AppsFlyerFramework-Dynamic",
"state" : {
"revision" : "8523443286ba788ca6ec11ec99e7df49e62e9042",
"version" : "6.14.2"
}
},
{
"identity" : "devicekit",
"kind" : "remoteSourceControl",
"location" : "https://github.com/devicekit/DeviceKit.git",
"state" : {
"revision" : "97acf830fd0e0b719126e9450a51c95a91f66858",
"version" : "5.2.3"
}
},
{
"identity" : "firebase-ios-sdk",
"kind" : "remoteSourceControl",
"location" : "https://github.com/firebase/firebase-ios-sdk.git",
"state" : {
"revision" : "8328630971a8fdd8072b36bb22bef732eb15e1f0",
"version" : "11.4.0"
}
},
{
"identity" : "googleappmeasurement",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/GoogleAppMeasurement.git",
"state" : {
"revision" : "4f234bcbdae841d7015258fbbf8e7743a39b8200",
"version" : "11.4.0"
}
},
{
"identity" : "googledatatransport",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/GoogleDataTransport.git",
"state" : {
"revision" : "617af071af9aa1d6a091d59a202910ac482128f9",
"version" : "10.1.0"
}
},
{
"identity" : "googlesignin-ios",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/GoogleSignIn-iOS.git",
"state" : {
"revision" : "65fb3f1aa6ffbfdc79c4e22178a55cd91561f5e9",
"version" : "8.0.0"
}
},
{
"identity" : "googleutilities",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/GoogleUtilities.git",
"state" : {
"revision" : "53156c7ec267db846e6b64c9f4c4e31ba4cf75eb",
"version" : "8.0.2"
}
},
{
"identity" : "grpc-binary",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/grpc-binary.git",
"state" : {
"revision" : "f56d8fc3162de9a498377c7b6cea43431f4f5083",
"version" : "1.65.1"
}
},
{
"identity" : "gtm-session-fetcher",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/gtm-session-fetcher.git",
"state" : {
"revision" : "0382ca27f22fb3494cf657d8dc356dc282cd1193",
"version" : "3.4.1"
}
},
{
"identity" : "gtmappauth",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/GTMAppAuth.git",
"state" : {
"revision" : "5d7d66f647400952b1758b230e019b07c0b4b22a",
"version" : "4.1.1"
}
},
{
"identity" : "interop-ios-for-google-sdks",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/interop-ios-for-google-sdks.git",
"state" : {
"revision" : "2d12673670417654f08f5f90fdd62926dc3a2648",
"version" : "100.0.0"
}
},
{
"identity" : "keychain-swift",
"kind" : "remoteSourceControl",
"location" : "https://github.com/evgenyneu/keychain-swift.git",
"state" : {
"revision" : "75677d8be3c50898c8ffd0d107f88aa2740301fc",
"version" : "22.0.0"
}
},
{
"identity" : "leveldb",
"kind" : "remoteSourceControl",
"location" : "https://github.com/firebase/leveldb.git",
"state" : {
"revision" : "a0bc79961d7be727d258d33d5a6b2f1023270ba1",
"version" : "1.22.5"
}
},
{
"identity" : "lottie-ios",
"kind" : "remoteSourceControl",
"location" : "https://github.com/airbnb/lottie-ios",
"state" : {
"revision" : "769b88d83a42ca8d5572b020c96f47e3690b3796",
"version" : "4.4.3"
}
},
{
"identity" : "mathjaxswift",
"kind" : "remoteSourceControl",
"location" : "https://github.com/colinc86/MathJaxSwift",
"state" : {
"revision" : "01797ab2738a8852d70fb81479bcf76768716220",
"version" : "3.3.0"
}
},
{
"identity" : "nanopb",
"kind" : "remoteSourceControl",
"location" : "https://github.com/firebase/nanopb.git",
"state" : {
"revision" : "b7e1104502eca3a213b46303391ca4d3bc8ddec1",
"version" : "2.30910.0"
}
},
{
"identity" : "networkimage",
"kind" : "remoteSourceControl",
"location" : "https://github.com/gonzalezreal/NetworkImage",
"state" : {
"revision" : "2849f5323265386e200484b0d0f896e73c3411b9",
"version" : "6.0.1"
}
},
{
"identity" : "promises",
"kind" : "remoteSourceControl",
"location" : "https://github.com/google/promises.git",
"state" : {
"revision" : "540318ecedd63d883069ae7f1ed811a2df00b6ac",
"version" : "2.4.0"
}
},
{
"identity" : "qonversion-ios-sdk",
"kind" : "remoteSourceControl",
"location" : "https://github.com/qonversion/qonversion-ios-sdk",
"state" : {
"revision" : "1f1a8129c52c7c288b2bbb95c4b2a191174e56e7",
"version" : "5.8.4"
}
},
{
"identity" : "swift-collections",
"kind" : "remoteSourceControl",
"location" : "https://github.com/apple/swift-collections",
"state" : {
"revision" : "ee97538f5b81ae89698fd95938896dec5217b148",
"version" : "1.1.1"
}
},
{
"identity" : "swift-markdown-ui",
"kind" : "remoteSourceControl",
"location" : "https://github.com/gonzalezreal/swift-markdown-ui",
"state" : {
"revision" : "9a8119b37e09a770367eeb26e05267c75d854053",
"version" : "2.3.1"
}
},
{
"identity" : "swift-package-manager-google-user-messaging-platform",
"kind" : "remoteSourceControl",
"location" : "https://github.com/googleads/swift-package-manager-google-user-messaging-platform.git",
"state" : {
"revision" : "cfe8b2ae16b9bc81f4cdf1d1a12a01a452489c32",
"version" : "2.3.0"
}
},
{
"identity" : "swift-protobuf",
"kind" : "remoteSourceControl",
"location" : "https://github.com/apple/swift-protobuf.git",
"state" : {
"revision" : "9f0c76544701845ad98716f3f6a774a892152bcb",
"version" : "1.26.0"
}
},
{
"identity" : "swiftui-introspect",
"kind" : "remoteSourceControl",
"location" : "https://github.com/siteline/SwiftUI-Introspect",
"state" : {
"revision" : "807f73ce09a9b9723f12385e592b4e0aaebd3336",
"version" : "1.3.0"
}
},
{
"identity" : "swiftuix",
"kind" : "remoteSourceControl",
"location" : "https://github.com/SwiftUIX/SwiftUIX",
"state" : {
"revision" : "cdc902f828e8c457f601e744cc7607148dcdb91a",
"version" : "0.2.2"
}
}
],
"version" : 3
}
If using CocoaPods, the project's Podfile.lock
Expand Podfile.lock snippet
Replace this line with the contents of your Podfile.lock!