ALAssetsLibrary error - "Too many contexts. No space in contextList." - ios

Question

I've received a couple of crash reports from users. I don't even know where to begin on this one. I am showing images from the asset library in a table view starting with a list of groups. I load the groups with the following code (on the main thread):
- (ALAssetsLibrary *)library {
if (!_library) {
_library = [[ALAssetsLibrary alloc] init];
}
return _library;
}
- (void)determineGroups {
ALAssetsLibrary *lib = [self library];
[lib enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos | ALAssetsGroupPhotoStream | ALAssetsGroupFaces | ALAssetsGroupLibrary | ALAssetsGroupAlbum | ALAssetsGroupEvent usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
if (group) {
if (!_groups) {
_groups = [[NSMutableArray alloc] init];
}
if ([group numberOfAssets]) {
[group setAssetsFilter:[ALAssetsFilter allPhotos]];
if ([[group valueForProperty:ALAssetsGroupPropertyType] isEqual:#(ALAssetsGroupSavedPhotos)]) {
[_groups insertObject:group atIndex:0];
} else {
[_groups addObject:group];
}
}
} else {
dispatch_async(dispatch_get_main_queue(), ^{
[self.tableView reloadData];
});
}
} failureBlock:^(NSError *error) {
// denied
dispatch_async(dispatch_get_main_queue(), ^{
self.tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
[self.tableView reloadData];
});
}];
}
When populating the table view I want to show the number of photos in each group. I do this by calling the "numberOfAssets" method on the group.
This all works just fine most of the time but crashes on rare occasions. Here is one of the stack traces with the relevant info (thread 5 crashed while the main thread was busy getting the number of assets in the group):
Crashed Thread: 5
Application Specific Information:
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Too many contexts. No space in contextList.'
Thread 0:
0 CoreFoundation 0x313a1c42 _CFStringGetLength2 + 26
1 CoreFoundation 0x313aba41 -[__NSDictionaryM objectForKey:] + 133
2 CoreData 0x312b5d2f -[NSSQLOrderIntermediate generateSQLStringInContext:] + 1283
3 CoreData 0x312018f7 -[NSSQLFetchIntermediate generateSQLStringInContext:] + 515
4 CoreData 0x311fe625 -[NSSQLGenerator newSQLStatementForFetchRequest:ignoreInheritance:countOnly:nestingLevel:] + 425
5 CoreData 0x311fe3ad -[NSSQLAdapter _newSelectStatementWithFetchRequest:ignoreInheritance:] + 509
6 CoreData 0x311fdfc5 -[NSSQLCore newRowsForFetchPlan:] + 117
7 CoreData 0x311fd73f -[NSSQLCore objectsForFetchRequest:inContext:] + 683
8 CoreData 0x311fd205 -[NSSQLCore executeRequest:withContext:error:] + 469
9 CoreData 0x311fc61d -[NSPersistentStoreCoordinator executeRequest:withContext:error:] + 1645
10 CoreData 0x311faf17 -[NSManagedObjectContext executeFetchRequest:error:] + 647
11 PhotoLibraryServices 0x366cd4e5 -[PLManagedObjectContext executeFetchRequest:error:] + 49
12 CoreData 0x3121ad07 _faultBatchAtIndex + 623
13 CoreData 0x3121aa53 -[_PFBatchFaultingArray getObjects:range:] + 143
14 CoreData 0x3121a9c1 -[_PFBatchFaultingArray getObjects:] + 41
15 Foundation 0x31cfbbe1 _filterObjectsUsingPredicate + 325
16 Foundation 0x31d01b8d -[NSArray(NSPredicateSupport) filteredArrayUsingPredicate:] + 273
17 PhotoLibraryServices 0x366d86ad +[PLFilteredAlbum filteredIndexesInAlbum:predicate:] + 265
18 PhotoLibraryServices 0x366d8bd1 -[PLFilteredAlbum filteredIndexes] + 117
19 PhotoLibraryServices 0x366d8d75 -[PLFilteredAlbum countOfFilteredAssets] + 21
20 AssetsLibrary 0x30ce25d5 __31-[ALAssetsGroup numberOfAssets]_block_invoke_0 + 41
21 CoreData 0x31257fd1 developerSubmittedBlockToNSManagedObjectContextPerform + 89
22 libdispatch.dylib 0x3971d4b7 _dispatch_client_callout + 23
23 libdispatch.dylib 0x397219f7 _dispatch_barrier_sync_f_invoke + 31
24 CoreData 0x31258153 -[NSManagedObjectContext performBlockAndWait:] + 175
25 AssetsLibrary 0x30ce414f -[ALAssetsLibrary _performBlockAndWait:] + 135
26 AssetsLibrary 0x30ce8f59 -[ALAssetsGroupPrivate _performBlockAndWait:] + 177
27 AssetsLibrary 0x30ce254b -[ALAssetsGroup numberOfAssets] + 259
Thread 5 Crashed:
0 libsystem_kernel.dylib 0x39804350 __pthread_kill + 8
1 libsystem_c.dylib 0x397b7973 abort + 95
2 MyApp 0x0074685f ___lldb_unnamed_function30167$$MyApp + 27
3 CoreFoundation 0x3145b57f __handleUncaughtException + 615
4 libobjc.A.dylib 0x39306a65 _objc_terminate() + 129
5 libc++abi.dylib 0x38d5307b safe_handler_caller(void (*)()) + 79
6 libc++abi.dylib 0x38d53114 std::terminate() + 20
7 libc++abi.dylib 0x38d54513 __cxa_throw + 123
8 libobjc.A.dylib 0x393069bf objc_exception_throw + 95
9 CoreFoundation 0x3145b15d +[NSException raise:format:] + 1
10 Foundation 0x31d30b13 -[NSAssertionHandler handleFailureInFunction:file:lineNumber:description:] + 87
11 PhotoLibraryServices 0x366d0afb __addContextToList_block_invoke_0 + 179
12 libdispatch.dylib 0x3971e11f _dispatch_call_block_and_release + 11
13 libdispatch.dylib 0x39721ecf _dispatch_queue_drain$VARIANT$mp + 143
14 libdispatch.dylib 0x39721dc1 _dispatch_queue_invoke$VARIANT$mp + 41
15 libdispatch.dylib 0x3972291d _dispatch_root_queue_drain + 185
16 libdispatch.dylib 0x39722ac1 _dispatch_worker_thread2 + 85
17 libsystem_c.dylib 0x39752a11 _pthread_wqthread + 361
The crash was from an iPad running iOS 6.1.3. The app was built with a Base SDK of iOS 7 GM. The app uses ARC.
Is there something i should be doing different in my code to get the groups?

Answer 1

Definitely it is iOS issue and is reproduced when enumerateGroupsWithTypes:... method contains ALAssetsGroupLibrary inside types enumeration.
You must use either ALAssetsGroupALL (that does not include ALAssetsGroupLibrary)
or you may enumerate types with OR but don't include ALAssetsGroupLibrary to enumeration.
I don't know what to do if you really need ALAssetGroupLibrary in types enumeration.
My code is very similar to yours; if you want to reproduce this issue try to call determineGroups method many times (my issue reproduces when I do this 11 times exactly) but library object must be recreated each time you call this method (f.e. You may remove library at the end of determineGroups method.
Or you may call determineGroups method each time for new receiver.). Also to reproduce this issue don't call determineGroups method inside single run loop
it would be better if you create button and tap on this button would create new receiver and calls determineGroups for it. Now try to tap on this button many times.
Hope my answer will help you.

Answer 2

I fix this by creating a sigleton object when using the ALAssetsLibrary.
+ (instancetype)defaultAssetsLibrary
{
#synchronized(self) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
defaultAssetsLibrary = [[self alloc] init];
});
}
return defaultAssetsLibrary;
}