Crashed: AppSync.DeltaSyncOperationQueue

[Behnoud]

Describe the bug
Hi, We are getting this error:
Crashed: AppSync.DeltaSyncOperationQueue.pRRtklDI6pAPl6kdkwRkdQ8e5oVDugecgADAAy3QM1w= (QOS: UNSPECIFIED)

To Reproduce
Steps to reproduce the behavior:

1. lock the screen
2. unlock after some time
3. app would crash
   Note: it is not producible every time but number of crashes is increasing

Environment(please complete the following information):

• AWSAppSync (3.0.0):
  • AWSCore (~> 2.12.0)
  • ReachabilitySwift (~> 5.0.0)
  • SQLite.swift (~> 0.12.2)
  • Starscream (~> 3.0.2)
• AWSCore (2.12.2)
• Dependency Manager: Cocoapods
• Swift Version : 5

Device Information (please complete the following information):

• Device: [iPhone 6, iPhone 6s, iPhone 5s, iPhone 6s+, iPhone 7]
• iOS Version: [12, 13]

Stack trace :
Crashed: AppSync.DeltaSyncOperationQueue.pRRtklDI6pAPl6kdkwRkdQ8e5oVDugecgADAAy3QM1w= (QOS: UNSPECIFIED)
0 AWSAppSync 0x10158f010 AppSyncSubscriptionWithSync.scheduleNextSync(from:lastSyncWasSuccessful:) + 458 (AppSyncSubscriptionWithSync.swift:458)
1 AWSAppSync 0x10158ec80 $defer #1 <A, B, C>() in AppSyncSubscriptionWithSync.performSync() + 420 (:420)
2 AWSAppSync 0x10158ab74 AppSyncSubscriptionWithSync.performSync() + 418 (AppSyncSubscriptionWithSync.swift:418)
3 AWSAppSync 0x10158fa10 closure #1 in AppSyncSubscriptionWithSync.applicationWillEnterForeground() + 560 (AppSyncSubscriptionWithSync.swift:560)
4 AWSAppSync 0x10161f648 thunk for @escaping @callee_guaranteed () -> () + 4355651144 (:4355651144)
5 Foundation 0x19d653b6c NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK + 16
6 Foundation 0x19d55bcc8 -[NSBlockOperation main] + 72
7 Foundation 0x19d55b19c -[__NSOperationInternal _start:] + 740
8 Foundation 0x19d655a40 __NSOQSchedule_f + 272
9 libdispatch.dylib 0x19c5ff6c8 _dispatch_call_block_and_release + 24
10 libdispatch.dylib 0x19c600484 _dispatch_client_callout + 16
11 libdispatch.dylib 0x19c5a3874 _dispatch_continuation_pop$VARIANT$mp + 412
12 libdispatch.dylib 0x19c5a2f3c _dispatch_async_redirect_invoke + 600
13 libdispatch.dylib 0x19c5afa60 _dispatch_root_queue_drain + 376
14 libdispatch.dylib 0x19c5b0308 _dispatch_worker_thread2 + 128
15 libsystem_pthread.dylib 0x19c7e2190 _pthread_wqthread + 472
16 libsystem_pthread.dylib 0x19c7e4d00 start_wqthread + 4

[palpatim]

@Behnoud Thanks for the report. The log indicates the crash is occurring in code that is using a force-unwrapped reference to appSyncClient to find an appropriate delay for scheduling the next sync attempt.

We'll look at this and see a) why the client might be nil at the time we're trying to dereference it, and b) what an appropriate mitigation is for this.

[palpatim]

This is merged into master and will be pushed on the next release.

[palpatim]

This was release on https://github.com/awslabs/aws-mobile-appsync-sdk-ios/releases/tag/3.0.2