Can you explain what setting GOMAXPROCS means in Go language?

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

By default, GOMAXPROCS is set to the number of logical processors on the machine, which allows efficient utilization of multi-processor systems.

Setting GOMAXPROCS affects the program's parallelism — how many goroutines can run concurrently on different CPU cores.

Example of setting it in code:

import "runtime"

func main() {
    runtime.GOMAXPROCS(4) // limit to 4 threads
    // rest of the code
}

This is useful for resource control and performance optimization.