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

From NSOperationQueue

In iOS 4 and later, operation queues use Grand Central Dispatch to execute operations. Prior to iOS 4, they create separate threads for non-concurrent operations and launch concurrent operations from the current thread.

So,

[NSOperationQueue mainQueue] // added operations execute on main thread
[NSOperationQueue new] // post-iOS4, guaranteed to be not the main thread

In your case, you might want to create your own "database thread" by subclassing NSThread and send messages to it with performSelector:onThread:.