StackTrace shows xxxxx is causing the crash. But “specialized closure #1” means what?

Question

Please explain the below crash..

#3. NSManagedObjectContext 0x1701c9ab0: xxxxxxxxxx 0 libsystem_kernel.dylib 0x1848898e8 __ulock_wait + 8 1 libdispatch.dylib 0x18475977c _dispatch_ulock_wait + 48 2 libdispatch.dylib 0x1847598a4 _dispatch_thread_event_wait_slow + 36 3 libdispatch.dylib 0x1847574f0 _dispatch_barrier_sync_f_slow + 236 4 CoreData 0x187c0703c _perform + 232 5 CoreData 0x187c178b8 -[NSManagedObjectContext(_NestedContextSupport) executeRequest:withContext:error:] + 176 6 CoreData 0x187b675e0 -[NSManagedObjectContext executeFetchRequest:error:] + 580 7 MyApp 0x1002f596c specialized static RecentItemsController.cleanupItems(inContext:ofType:limitingTo:sortingByAttribute:withPredicate:) (xxxxx.swift:182) 8 MyApp 0x1002f6574 specialized closure #1 in static xxx.xxx(inStore:completion:) (xxx.swift:163) 9 MyApp 0x1002f5118 partial apply for closure #1 in static xxx.xxx(inStore:completion:) (xxx.swift) 10 CoreData 0x187c0c214 developerSubmittedBlockToNSManagedObjectContextPerform + 152 11 libdispatch.dylib 0x1847469a0 _dispatch_client_callout + 16 12 libdispatch.dylib 0x184754ad4 _dispatch_queue_serial_drain + 928 13 libdispatch.dylib 0x18474a2cc _dispatch_queue_invoke + 884 14 libdispatch.dylib 0x184754fa8 _dispatch_queue_override_invoke + 344 15 libdispatch.dylib 0x184756a50 _dispatch_root_queue_drain + 540 16 libdispatch.dylib 0x1847567d0 _dispatch_worker_thread3 + 124 17 libsystem_pthread.dylib 0x18494f100 _pthread_wqthread + 1096 18 libsystem_pthread.dylib 0x18494ecac start_wqthread + 4

If you look toward the end of those lines you'll see RecentItemsController.swift:182. That's where the crash happened, in that file at line 182. That's the code you need to look at. — Tom Harrington
It says that the code on line 163 called the code on line 182. Line 163 may be involved but line 182 is where the crash happened. — Tom Harrington
How to interpret that line number 163 called line number 182 & not the vice versa? — user804417
Because that's how stack trace ordering works. Also if you look at those two lines you can probably tell which one calls the other. — Tom Harrington

Tushar Tushar · Accepted Answer · 2017-10-14T06:02:06

Looking at the stack trace and the code inside cleanupItems func, I believe the problem is in the force unwrapping code:

let itemsToDelete = try context.fetch(request) as! [R]

The first thing to write a crash preventive code is below

if let itemsToDelete = try context.fetch(request) as? [R] {
   itemsToDelete.forEach(context.delete(_:))
   log("Deleted \(itemsToDelete.count) \(type) item(s)")

}

Let me know if that works.

StackTrace shows xxxxx is causing the crash. But “specialized closure #1” means what?

1 Answers