gistfile1.m

- (void)_updateResults:(void (^)(void))block caller:(dispatch_queue_t)callerqueue
{
    __unsafe_unretained NUData* wself = self;
    
    dispatch_sync(_serial_results_queue, ^{
        
        NSManagedObjectContext* ctx = updateContext;
        __block NSArray* results = nil;
        
        [ctx performBlockAndWait:^{
            __autoreleasing NSError* fetchError = nil;
            NSFetchRequest* request = [[NSFetchRequest alloc] initWithEntityName:@"Event"];
            results = [ctx executeFetchRequest:request error:&fetchError];
        }];
        
        dispatch_group_t group = dispatch_group_create();
        dispatch_queue_t background = dispatch_queue_create("com.ft.results.update.concurrent", DISPATCH_QUEUE_CONCURRENT);
        
        for (SKEvent* event in results)
        {
            dispatch_group_async(group, background, ^{
                [wself __updateResults:^{} forEvent:event caller:callerqueue];
            });
        }
        
        dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
        dispatch_release(group);
        dispatch_release(background);
        
        void(^block_c)(void) = ^(void) {
            NSLog(@"completed update results");
            if (block) block();
        };
        
        // Notify Observers
        dispatch_async(dispatch_get_main_queue(), ^{
            [[NSNotificationCenter defaultCenter] postNotificationName:kSKNotifResultsDownloaded object:nil];
        });
        
        // Execute completion block
        dispatch_async(callerqueue, block_c);
        
    });
}