SIGSEGV : Sporadic crash issue - ios

Question

Here is my first attempt to solve crash issue in iOS app. Sharing some crash logs here.
Exception Type: SIGSEGV
Exception Codes: SEGV_ACCERR at 0x97ad6beb8
Crashed Thread: 11
Application Specific Information:
objc_msgSend() selector name: length
and here is my 11th thread.
Thread 11 Crashed:
0 libobjc.A.dylib 0x0000000180558150 objc_msgSend + 16
1 Foundation 0x00000001824f3f60 -[NSString compare:] + 28
2 Foundation 0x00000001824d88e0 _NSCompareObject + 60
3 CoreFoundation 0x0000000181a99bd0 __CFSimpleMergeSort + 88
4 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
5 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
6 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
7 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
8 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
9 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
10 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
11 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
12 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
13 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
14 CoreFoundation 0x0000000181a99c60 __CFSimpleMergeSort + 232
15 CoreFoundation 0x00000001819c585c CFSortIndexes + 460
16 CoreFoundation 0x00000001819c6f9c CFMergeSortArray + 372
17 Foundation 0x00000001824d80e8 _sortedObjectsUsingDescriptors + 568
18 Foundation 0x00000001825c64e0 -[NSSet(NSKeyValueSorting) sortedArrayUsingDescriptors:] + 536
19 Eikon 0x0000000100198b98 __51-[EIKNewsHeadlineStoreManager saveHeadlines:block:]_block_invoke (EIKNewsHeadlineStoreManager.m:67)
20 CoreData 0x0000000183e5e214 developerSubmittedBlockToNSManagedObjectContextPerform + 148
21 libdispatch.dylib 0x000000018099a9a0 _dispatch_client_callout + 12
22 libdispatch.dylib 0x00000001809a8ad4 _dispatch_queue_serial_drain + 924
23 libdispatch.dylib 0x000000018099e2cc _dispatch_queue_invoke + 880
24 libdispatch.dylib 0x00000001809a8fa8 _dispatch_queue_override_invoke + 340
25 libdispatch.dylib 0x00000001809aaa50 _dispatch_root_queue_drain + 536
26 libdispatch.dylib 0x00000001809aa7d0 _dispatch_worker_thread3 + 120
27 libsystem_pthread.dylib 0x0000000180ba31d0 _pthread_wqthread + 1092
28 libsystem_pthread.dylib 0x0000000180ba2d7c start_wqthread + 0
What i am trying to do is get some news headlines from server every 5 or 10 secs, sort them in some order using NSSortDescriptors and then store them in my CoreData. And that is what exactly saveHeadlines:block method is doing inside my class.
What exactly objc_msgSend() selector name: length
mean here? Any help is appreciated.
Note: Its a sporadic issue. When i test in simulator or my devices its not crashing. But some users of our app are reporting this crash.
Edited question: inside saveHeadlines:block method
__weak typeof(self) weakSelf = self;
[self.privateMOC performBlock:^{
NSMutableArray *newsTopics = [[EIKNewsTopicStoreManager managedObjectsInManagedObjectContext:self.privateMOC] mutableCopy];
[newsTopics addObjectsFromArray:[EIKNewsTopicStoreManager topicsManagedObjectForNewsFeedInContext:self.privateMOC]];
weakSelf.storedHeadlines = [NSMutableSet set];
for (NSManagedObject *storedTopic in newsTopics) {
[weakSelf.storedHeadlines addObjectsFromArray:[[storedTopic valueForKey:EIKFeedTopicRelationshipItems] allObjects]];
}
NSArray *sortDescriptors = #[[NSSortDescriptor sortDescriptorWithKey:EIKNewsHeadlineAttributeHeadlineId ascending:YES]];
NSArray *orderedItems = [items sortedArrayUsingDescriptors:sortDescriptors];
NSArray *orderedHeadlines = [weakSelf.storedHeadlines sortedArrayUsingDescriptors:sortDescriptors];
And the crash is happening on the last line. i.e
NSArray *orderedHeadlines = [weakSelf.storedHeadlines sortedArrayUsingDescriptors:sortDescriptors];
Not able to figure out why.!
My NSManagedObjectContext is initialised like this[i.e privateMOC as shown in above code]
NSManagedObjectContext *confinementContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];

Answer 1

Not much info here, but it looks to me that NSManagedObjectContext isn't valid on the thread you are performing your operation.
Please make sure that you perform all operations on the context's private queue. You can do this for example by using performBlock: or performBlockAndWait:.
Also you can't reuse instances of NSManagedObject on different threads than the one you fetched them on.
Hope that helps.