NSOperation and NSOperationQueue working thread vs main thread

Question

I have to carry out a series of download and database write operations in my app. I am using the NSOperation and NSOperationQueue for the same.

Answer 1

The summary from the docs is operations are always executed on a separate thread (post iOS 4 implies GCD underlying operation queues).

It's trivial to check that it is indeed running on a non-main thread:

NSLog(@"main thread? %@", [NSThread isMainThread] ? @"YES" : @"NO");

When running in a thread it's trivial to use GCD/libdispatch to run something on the main thread, whether core data, user interface or other code required to run on the main thread:

dispatch_async(dispatch_get_main_queue(), ^{
    // this is now running on the main thread
});