Coredata crash while fetching

问题:

I am getting some weird coredata error in the production app and I was able to get hold of the Crash Report.

Its Crashing with the following message at times

*** error for object 0x17e400000: Freeing unallocated pointer

*** error for object 0x17fd03730: pointer being reallocated was not allocated

And here is the stack trace

Crashed: SQLQueue 0x13ff15250 for datastore.sqlite SIGABRT ABORT 0x0000000183986014  0 libsystem_kernel.dylib    __pthread_kill + 8 1   libsystem_pthread.dylib  pthread_kill + 112 2   libsystem_c.dylib   abort + 140 3   libsystem_malloc.dylib  _nano_vet_and_size_of_live + 330 4   libsystem_malloc.dylib  nano_free + 220 5   libsqlite3.dylib    sqlite3_finalize + 244 6   CoreData    -[NSSQLiteConnection _finalizeStatement] + 100 7   CoreData    -[NSSQLiteConnection releaseSQLStatement] + 52 8   CoreData    newFetchedRowsForFetchPlan_MT + 2420 9   CoreData    _executeFetchRequest + 72 10  CoreData    -[NSSQLFetchRequestContext executeRequestUsingConnection:] + 60 11  CoreData    __52-[NSSQLDefaultConnectionManager handleStoreRequest:]_block_invoke + 260 12  libdispatch.dylib   _dispatch_client_callout + 16 13  libdispatch.dylib   _dispatch_barrier_sync_f_invoke + 84 14  CoreData    -[NSSQLDefaultConnectionManager handleStoreRequest:] + 208 15  CoreData    -[NSSQLCoreDispatchManager routeStoreRequest:] + 288 16  CoreData    -[NSSQLCore dispatchRequest:withRetries:] + 200 17  CoreData    -[NSSQLCore processFetchRequest:inContext:] + 108 18  CoreData    -[NSSQLCore executeRequest:withContext:error:] + 504 19  CoreData    __65-[NSPersistentStoreCoordinator executeRequest:withContext:error:]_block_invoke + 4512 20  CoreData    -[NSPersistentStoreCoordinator _routeHeavyweightBlock:] + 276 21  CoreData    -[NSPersistentStoreCoordinator executeRequest:withContext:error:] + 408 22  CoreData    -[NSManagedObjectContext executeFetchRequest:error:] + 572 23  CoreData    -[NSManagedObjectContext(_NestedContextSupport) _parentObjectsForFetchRequest:inContext:error:] + 456 24  CoreData    __82-[NSManagedObjectContext(_NestedContextSupport) executeRequest:withContext:error:]_block_invoke + 584 25  CoreData    internalBlockToNSManagedObjectContextPerform + 92 26  libdispatch.dylib   _dispatch_client_callout + 16 27  libdispatch.dylib   _dispatch_barrier_sync_f_invoke + 84 28  CoreData    _perform + 232 29  CoreData    -[NSManagedObjectContext(_NestedContextSupport) executeRequest:withContext:error:] + 188 30 CoreData -[NSManagedObjectContext executeFetchRequest:error:] + 572 31  *MY_APP*    NSManagedObject+MagicalRecord.m line 50__67+[NSManagedObject(MagicalRecord) MR_executeFetchRequest:inContext:]_block_invoke 

It did happen on the main thread and I am puzzled on how to debug this. Looks like a memory issue though. Also while using instruments its showing some leaks in the app when it comes across NSPrivateQueueConcurrencyType .

Looking for some insights on nailing it down.

App is using MagicalRecord Extensively and here is the code block in the App Which leads to above crash. Its just a normal fetch from Main Thread. Most interestingly it crash randomly, ie it doesn't always crash but at times it crashes while doing a Fetch.

NSPredicate *filterPredicate = [NSPredicate predicateWithFormat:@"code == %@ and pid == %@", aCode,pid]; Permission *aPermission = [Permission MR_findFirstWithPredicate:filterPredicate]; 

回答1:

Accessing (Write or Read) a Managed Object on any thread other than the Managed Object Context Queue causes undefined behaviour & leads to random weird crashes.
It looks like your Managed Object Context was created with NSPrivateQueueConcurrencyType & your performing fetch on the Main Queue. This is the source of the weird crash.
You can either initialize MOC with NSMainQueueConcurrencyType or nest all your fetchRequests inside [MOC performBlock:{...}]

回答2:

Core-date managedObjectContext and managedObjects are not thread-safe - neither for writing or for reading. If you ever violate this rule core-date can crash at any time - not necessarily where/when the violation occurred. So even if you are on the main thread and accessing a context designed for the main thread it can still crash if you did something wrong somewhere else in your app.

文章来源: Coredata crash while fetching