Where is libdispatch AKA Grand Central Dispatch imported?

Question

I am reading Apple's documentation on Concurrency, more specifically on NSOperationQueue vs a Dispatch Queue.

They say this:

"An operation queue is the Cocoa equivalent of a concurrent dispatch queue ..."

Which made me wonder, if NSOperationQueue is available through the Cocoa framework, how is GCD available?

When I call dispatch_after..., why is it that I don't need to #import <Cocoa/Cocoa.h>?

How does the compiler recognize GCD selectors?

Answer 1

You need to include dispatch/dispatch.h header file for using GCD APIs.

dispatch manual:

$ man dispatch
dispatch(3)              BSD Library Functions Manual              dispatch(3)

NAME
     dispatch -- the dispatch framework

SYNOPSIS
     #include <dispatch/dispatch.h>

Cocoa headers also import the header file (For example, NSOperation.h), so in most cases you don't need to import the header file explicitly.