When talking about pointers, we generally assume it is something that can be represented by void* pointer which has a size of 8 bytes on the x86_64 architecture.

Hardware vendors like to add Unique Selling Points to their devices to convince you to buy them instead of someone else's. Of course, this typically leads to hardware vendors desperately copying each other's Unique Selling Points in a process eerily reminiscent of evolution's Red Queen Effect, all desperately trying to run faster than each other in order to stay in the same place. Putting effort into standardisation would risk them falling behind vendors who choose not to, so in the absence of some external force to compel them, vendor-specific solutions proliferate.

The behavior of dispatch_once is in the name. It does something once and only once.

It takes two parameters. The first is a predicate that tracks the "once". The second is a block to execute on the first call.