[libdispatch-dev] Does GCD has a "global view" of all running processes?

Hi, After reading several things on GCD on the net, it is not yet clear if GCD is mainly a "per process" library, or is supposed to have a "global view" of all processes, so that to allocate "not too much" threads in each process, and avoid having a number of threads that finally exceed the number of available cores on the machine. What is the situation? Thanks Stephane Letz