On macOS and iOS, when you want to talk to another process, you use libxpc. I believe that libxpc will automatically send a "dispatch token" (? don't remember exact name, you can see it on lists of mach syscalls) which boosts the priority of the process you're calling (I believe it also generates an OS transaction so the process isn't killed for memory reasons). I believe this priority will fan out as you described. Pierre Habouzit implemented this stuff I believe, you can see a lot of it in libdispatch.