You want to learn how to create a block of code that can be executed by GCD.

There are two ways to submit tasks to dispatch queues:

Block objects are the best way of utilizing GCD and its enormous power. Some GCD functions have been extended to allow programmers to use C functions instead of block objects. However, the truth is that only a limited set of GCD functions allow programmers to use C functions, so please do read the recipe about block objects (Recipe 5.1) before proceeding any further.

C functions that have to be supplied to various GCD functions should be of type dispatch_function_t, which is defined as follows in the Apple libraries: