Core Data managed object context thread synchronisation
- by Ben Reeves
I'm have an issue where i'm updating a many-to-many relationship in a background thread, which works fine in that threa, but when I send the object back to the main thread the changes do not show. If I close the app and reopen the data is saved fine and the changes show on the main thread. Also using [context lock] instead of a different managed object context works fine.
I have tried NSManagedObjectContext:
- (BOOL)save:(NSError **)error;
- (void)refreshObject:(NSManagedObject *)object mergeChanges:(BOOL)flag;
at different stages throughout the process but it doesn't seem to help.
My core data code uses the following getter to ensure any operations are thread safe:
- (NSManagedObjectContext *) managedObjectContext
{
NSThread * thisThread = [NSThread currentThread];
if (thisThread == [NSThread mainThread])
{
//Main thread just return default context
return managedObjectContext;
}
else
{
//Thread safe trickery
NSManagedObjectContext * threadManagedObjectContext = [[thisThread threadDictionary] objectForKey:CONTEXT_KEY];
if (threadManagedObjectContext == nil)
{
threadManagedObjectContext = [[[NSManagedObjectContext alloc] init] autorelease];
[threadManagedObjectContext setPersistentStoreCoordinator: [self persistentStoreCoordinator]];
[[thisThread threadDictionary] setObject:threadManagedObjectContext forKey:CONTEXT_KEY];
}
return threadManagedObjectContext;
}
}
and when I pass object between threads i'm using
-(NSManagedObject*)makeSafe:(NSManagedObject*)object
{
if ([object managedObjectContext] != [self managedObjectContext])
{
NSError * error = nil;
object = [[self managedObjectContext] existingObjectWithID:[object objectID] error:&error];
if (error)
{
NSLog(@"Error makeSafe: %@", error);
}
}
return object;
}
Any help appreciated
