[ovokinder]

You're missing the most important point of the entire Throttler goal: gracefully returning fast, with success or failure. Nowhere is it stated that the goal is to enqueue tasks for execution.

If you had read 'til the end you would have found multiple statements that OSAtomic* is merely an alternative. Not a silver bullet. Not the fastest.

From the conclusion:

"It's very important to understand that every example in this article could have legitimately been solved with different concurrency primitives — like semaphores and locks — without any noticeable impact to a human playing around with your app."

Also, "(...) is always going to be best executed, quickest, using GCD." is kind of a blanket statement. I'd be careful around the use of "always".