Assertion failure in MYBackgroundMonitor beginBackgroundTaskNamed

[combinatorial]

I am seeing a fairly common crash through monitoring our live build (#6 most common crash). It is not something I can reproduce at the moment. But here are the details I have...

This is the raw crash stack...

Fatal Exception: NSInternalInconsistencyException
0  CoreFoundation                 0x180e8adb0 __exceptionPreprocess
1  libobjc.A.dylib                0x1804eff80 objc_exception_throw
2  CoreFoundation                 0x180e8ac80 +[NSException raise:format:]
3  Foundation                     0x1818101c0 -[NSAssertionHandler handleFailureInFunction:file:lineNumber:description:]
4  Concepts                       0x100644528 _AssertFailed
5  Concepts                       0x100605b7c MYSliceReadVarUInt
6  Concepts                       0x100646f50 MYMapError
7  Concepts                       0x100646d50 MYMapError
8  CoreFoundation                 0x180e2cdfc __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__
9  CoreFoundation                 0x180e2c61c _CFXRegistrationPost
10 CoreFoundation                 0x180e2c39c ___CFXNotificationPost_block_invoke
11 CoreFoundation                 0x180e95414 -[_CFXNotificationRegistrar find:object:observer:enumerator:]
12 CoreFoundation                 0x180d6a6c8 _CFXNotificationPost
13 Foundation                     0x18177280c -[NSNotificationCenter postNotificationName:object:userInfo:]
14 UIKit                          0x18628f214 __47-[UIApplication _applicationDidEnterBackground]_block_invoke
15 UIKit                          0x18635f6d4 +[UIViewController _performWithoutDeferringTransitions:]
16 UIKit                          0x18628f080 -[UIApplication _applicationDidEnterBackground]
17 UIKit                          0x18628f604 -[UIApplication _handleApplicationDeactivationWithScene:shouldForceExit:transitionContext:completion:]
18 UIKit                          0x18629fa80 -[UIApplication _handleApplicationLifecycleEventWithScene:transitionContext:completion:]
19 UIKit                          0x18628970c __70-[UIApplication scene:didUpdateWithDiff:transitionContext:completion:]_block_invoke
20 UIKit                          0x186289394 -[UIApplication scene:didUpdateWithDiff:transitionContext:completion:]
21 FrontBoardServices             0x18282b7ac __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__
22 FrontBoardServices             0x18282b618 -[FBSSerialQueue _performNext]
23 FrontBoardServices             0x18282b9c8 -[FBSSerialQueue _performNextFromRunLoopSource]
24 CoreFoundation                 0x180e4109c __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
25 CoreFoundation                 0x180e40b30 __CFRunLoopDoSources0
26 CoreFoundation                 0x180e3e830 __CFRunLoopRun
27 CoreFoundation                 0x180d68c50 CFRunLoopRunSpecific
28 GraphicsServices               0x182650088 GSEventRunModal
29 UIKit                          0x18604a088 UIApplicationMain
30 Concepts                       0x1000e3060 main (main.m:19)
31 libdispatch.dylib              0x1809068b8 (Missing)

Crashlytics reports the exception as:

"Fatal Exception: NSInternalInconsistencyException Assertion failed: Background task already running"

Digging through the couchbase lite code this would point to this line of code being where the assertion is failing...

https://github.com/snej/MYUtilities/blob/99e03aeaafd09fd7a3c7717ee4efd33007faee02/MYBackgroundMonitor.m#L66

which is called while the app is being backgrounded...

couchbase-lite-ios/Source/CBLRestReplicator+Backgrounding.m

Line 54 in 0705423

- (void) appBackgrounding {

which would be consistent with the UIApplication _applicationDidEnterBackground portion of the stack above.

It does seem that there are two places that appBackgrounding can be called...

couchbase-lite-ios/Source/CBLRestReplicator+Backgrounding.m

Line 32 in 0705423

_bgMonitor.onAppBackgrounding = ^{ [weakSelf appBackgrounding]; };

couchbase-lite-ios/Source/API/CBLDatabase.m

Line 73 in d7b1eac

selector: @selector(appBackgrounding:)

---

• Version: 1.2.1
• Client OS: iOS 9.3.2
• Server: sync_gateway 1.2.1

[snej]

There aren't any debug symbols for CBL so the stack frames show bogus names like MYSliceReadVarUInt.

This should have been fixed in 1.2.1; see #1006.

[combinatorial]

I am definitely using 1.2.1
I agree symbols are bogus which is why the exception information is important in tracking this down. Fatal Exception: NSInternalInconsistencyException Assertion failed: Background task already running

[snej]

Ah, there was also #1152 which is likely what you're hitting — that's fixed in 1.3. (So is the lack of debug symbols, so if you try with the 1.3 dev preview and it still crashes, we'll at least know where...)

[combinatorial]

I can confirm this is fixed with those changes.