One of Go’s signature features is goroutines, which are lightweight threads that are managed by the Go runtime. The Go runtime implements goroutines using a M:N work stealing scheduler to multiplex goroutines on to operating system threads. The scheduler has special terminology for three important entities; a G is a goroutine, an M is an OS thread (a ‘machine’), and a P is a ‘processor’, which at its core is a limited resource that must be claimed by an M in order to run Go code. Having a limited supply of Ps is how Go limits how many things it will do at once, so as to not overload the overall system; generally there is one P per actual CPU that the OS reports (the number of Ps is GOMAXPROCS).

source: HN