Core Data and threads / Grand Central Dispatch

Here’s a good example for you to try. Feel free to come back if you have any questions:

self.mainThreadContext... // This is a reference to your main thread context
NSPersistentStoreCoordinator *mainThreadContextStoreCoordinator = [self.mainThreadContext persistentStoreCoordinator];
dispatch_queue_t request_queue = dispatch_queue_create("com.yourapp.DescriptionOfMethod", NULL);
dispatch_async(request_queue, ^{

    // Create a new managed object context
    // Set its persistent store coordinator
    NSManagedObjectContext *newMoc = [[NSManagedObjectContext alloc] init];
    [newMoc setPersistentStoreCoordinator:mainThreadContextStoreCoordinator]];

    // Register for context save changes notification
    NSNotificationCenter *notify = [NSNotificationCenter defaultCenter];
    [notify addObserver:self 
               selector:@selector(mergeChanges:) 
                   name:NSManagedObjectContextDidSaveNotification 
                 object:newMoc];

    // Do the work
    // Your method here
    // Call save on context (this will send a save notification and call the method below)
    BOOL success = [newMoc save:&error];
    if (!success)
        // Deal with error
    [newMoc release];
});
dispatch_release(request_queue);

And in response to the context save notification:

- (void)mergeChanges:(NSNotification*)notification 
{
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.mainThreadContext mergeChangesFromContextDidSaveNotification:notification waitUntilDone:YES];
    });
}

And don’t forget to remove the observer from the notification center once you are done with the background thread context.

[[NSNotificationCenter defaultCenter] removeObserver:self];