Number of threads created by GCD?

Question

Is there any good documention on how many threads are created by GCD? At WWDC, they told us it\'s modeled around CPU cores. However, if I call this example:

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Answer 1

The documentation avoids mentioning the number of threads created. Mostly because the optimal number of threads depends heavily on the context.

One issue with Grand Cendral Dispatch is that it will spawn a new thread if a running task blocks. That is, you should avoid blocking when using GCD as having more threads than cores is suboptimal.

In your case, GCD detects that the task is inactive, and spawns a new thread for the next task.

Why 66 is the limit is beyond me.