Multi threaded core-data and logging - iphone

Question

Background info
I've almost completed my app. Everything was working perfectly. Then the client asked for logging in the app (i.e. various points that had to record what was done, what responses were, etc...).
The app allows the user to create "messages" which are saved into core-data. The messages are then uploaded to the server individually. The message are created on the main thread and uploaded in an NSOperation subclass on a background thread.
It is the same template for the NSOperation subclass that I have used before and works. I'm doing all the best practise stuff for multi-threaded core-data.
All this side of the app works fine.
I added the logging part of the app. I've created a singleton called MyLogManager and a CoreData entity called LogEntry. The entity is very simple, it only has a date and text.
Code
The function inside the MyLogManager is...
- (void)newLogWithText:(NSString*)text
{
NSLog(#"Logging: %#", text);
NSManagedObjectContext *context = [self context];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"LogEntry" inManagedObjectContext:context];
LogEntry *logEntry = [[LogEntry alloc] initWithEntity:entity insertIntoManagedObjectContext:context];
logEntry.text = text;
logEntry.date = [NSDate date];
[self saveContext:context];
}
which in turn runs...
- (NSManagedObjectContext*)context
{
AppDelegate *appDelegate = (ThapAppDelegate*)[[UIApplication sharedApplication] delegate];
NSManagedObjectContext *managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSConfinementConcurrencyType];
[managedObjectContext setPersistentStoreCoordinator:appDelegate.persistentStoreCoordinator];
return managedObjectContext;
}
and
- (void)saveContext:(NSManagedObjectContext*)context
{
MyAppDelegate *appDelegate = (MyAppDelegate*)[[UIApplication sharedApplication] delegate];
[[NSNotificationCenter defaultCenter] addObserver:appDelegate
selector:#selector(mergeChanges:)
name:NSManagedObjectContextDidSaveNotification
object:context];
NSError *error = nil;
if ([context hasChanges] && ![context save:&error]) {
NSLog(#"Unhandled error %#, %#", error, [error userInfo]);
abort();
}
[[NSNotificationCenter defaultCenter] removeObserver:appDelegate name:NSManagedObjectContextDidSaveNotification object:context];
}
The NSOperation main thread (well parts of it)...
- (void)main
{
//create context and retrieve NSManagedObject using the NSManagedObjectID passed in as a parameter to operation
self.message.lastSendAttempt = [NSDate date];
[self startUpload];
[self completeOperation]; //This doesn't get run because the startUpload method never returns
}
- (void)startUpload
{
[[MyLogManager sharedInstance] logSendingMessageWithURLParameters:[self.event URLParameters]]; //this is a convenience method. It just appends some extra info on the string and runs newLogWithText.
//Do some uploading stuff here...
//The operation stops before actually doing the upload when logging to CoreData.
}
The problem
My NSOperation subclass that uploads the messages (on a background thread) calls this newLogWithText function but it also updates the message it is uploading. The NSOperation uses the same methods to get and save the core-data context. (i.e. it updates the last sent date and also updates if the send was successful).
This is the first time I've tried to deal with simultaneous writes and saves to core-data.
I don't get any errors and the app carries on "working". But the operation never completes. I've tried to debug it with breakpoints but when I use breakpoints it works. Without breakpoints the operation never finishes and the upload never happens. And then it just sits there blocking the queue it is on and no other messages can be sent.
In my appDelegate (I know this isn't the ideal place for it but it's the default for a new project and I haven't changed it) the mergeChanges method is just...
- (void)mergeChanges:(NSNotification *)notification
{
[self.managedObjectContext performSelectorOnMainThread:#selector(mergeChangesFromContextDidSaveNotification:) withObject:notification waitUntilDone:NO];
}
I've tried throwing the 'newLogWithText' function off to another thread and even to the main thread with no luck.
I'm just about to try it now but change the "waitUntilDone" of the merge to YES. (Just noticed this). (This didn't work).
I'm 90% certain this is down to simultaneous writes to different contexts and the conflict resolution as it is the first time I've dealt with this. If I comment out the newLogWithText function then everything works as it should.
The only alternative at the moment is to scrap the LogEntry from core data and save the logs into an array inside NSUserDefaults but that doesn't feel right. Is there another way?
EDIT
I've changed it now so it users NSUserDefaults and it works without a problem. It just feels like a hacky solution.