How does GOMAXPROCS work and what is the purpose of P (processor) in the GMP model?

In Go, the environment variable or the runtime parameter runtime.GOMAXPROCS sets the maximum number of operating system threads (OS threads) that can execute Go routines simultaneously.

In the GMP model:

• G — goroutine (lightweight thread of execution)
• M — OS thread (machine thread)
• P — processor (virtual processor)

P is a resource required to execute G on M. The number of P limits the number of Go routines that can run simultaneously. G cannot run without P, and M can only execute G if it has P.

GOMAXPROCS sets the number of P, i.e., how many Go routines can run in parallel at the OS level. Increasing GOMAXPROCS allows better utilization of multi-core processors, but too high a value can lead to excessive competition for resources.