The issue is that dispatch needs to know what’s running and to allow for the threads to effectively work with the thread schedule to service dispatch in an appr

The issue is that dispatch needs to know what’s running and to allow for the threads to effectively work with the thread schedule to service dispatch in an appropriate way. On macOS, the implementation is done in kernel, although there is a front end user library that used to interact with it. This article, although a few years old, talks about the separation of the parts and goes to explain why it’s not a trivial port to other operating systems. https://gigaom.com/2009/09/14/apple-open-sources-grand-central-dispatch/ https://gigaom.com/2009/09/14/apple-open-sources-grand-centr...