EXC_BAD_INSTRUCTION from com.apple.xpc.activity.com.apple.cloudkit.scheduler.com.apple.coredata.cloudkit.activity.export

Question

I have an app that runs fine on iOS, but when running with catalyst, it gives me this crash intermittently if I swipe to another virtual Desktop on macOS, and then back, for about 10 times. It mostly happens on a UICollectionViewController

This is the backtrace:

(lldb) bt
* thread #5, queue = 'com.apple.xpc.activity.com.apple.cloudkit.scheduler.com.apple.coredata.cloudkit.activity.export', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
  * frame #0: 0x00007fff68c373ae libxpc.dylib`___xpc_activity_dispatch_block_invoke.107.cold.3 + 19
    frame #1: 0x00007fff68c1ecdb libxpc.dylib`___xpc_activity_dispatch_block_invoke.107 + 746
    frame #2: 0x00000001010377b3 libdispatch.dylib`_dispatch_call_block_and_release + 12
    frame #3: 0x000000010103878f libdispatch.dylib`_dispatch_client_callout + 8
    frame #4: 0x000000010103fd31 libdispatch.dylib`_dispatch_lane_serial_drain + 777
    frame #5: 0x0000000101040ae8 libdispatch.dylib`_dispatch_lane_invoke + 438
    frame #6: 0x000000010104df2e libdispatch.dylib`_dispatch_workloop_worker_thread + 681
    frame #7: 0x00000001010c4053 libsystem_pthread.dylib`_pthread_wqthread + 290
    frame #8: 0x00000001010c3eb3 libsystem_pthread.dylib`start_wqthread + 15
(lldb) 

I have tried reviewing the codes, adding print statements, adding breakpoints, commenting out certain parts etc, trying to figure out which part of my code causes this, but failed so far.

I am using NSPersistentCloudKitContainer from iOS 13. Does the stack trace points to a bug inside there?

Answer 1

I've wasted so much time trying to understand the source of the problem and hope that this answer helps many others.

This problems seems to persist now since a long time and has not been fixed, nor understood. But the big hint I've read in the comments: This crash happens only when the app is run from within Xcode.

Another important hint: You can can run your build product directly from Finder without crashing. Even if it is a "Debug" build.

Based on this, I've come to the conclusion that the problem is related to the Debug execution environment and I found the solution: Disable "Debug XPC services used by this application"
There must be some bug in the debugging code used by this option.

You can find this option in your targets scheme.

1. Click on your target in the window bar
2. Select "Edit Scheme..."
3. Make sure "Run" is selected and remove the checkmark for "Debug XPC services used by this application"

I hope this helps everybody!