Go ignores GOMAXPROCS

Issue

I’m trying to run a goroutine (go version go1.4.1 darwin/amd64) simultaneously with endless loop in main thread and I can’t make it works. If I understood correctly go should schedule a goroutine to other threads if I specify GOMAXPROCS but it won’t. Even if I write explicitly LockOSThread() in main I still can see no output. How to make go to run goroutine in separate os thread?

package main

import(
    "fmt"
    "time"
    "runtime"
)

func main() {
    runtime.GOMAXPROCS(runtime.NumCPU() * 8)

    go func() {
        for {
            time.Sleep(1 * time.Second)
            fmt.Println("From routine")
        }
    }()

    for {}
}

Solution

The problem is that the new goroutine is not yet created (so it cannot be scheluded) when you enter for{}. The scheduler can only work then a goroutine is blocked or calls another function, so in a closed loop the scheduler cannot schedule.

Add a time.Sleep(time.Millisecond) before the for{} and it will work.

However, I don’t know if you are doing this just for fun, but if you want to wait forever (or until the other gorounties are dead-locked or die) while the goroutines work, it is much better to use select{} that will block without wasting CPU cycles.

Answered By – siritinga

Answer Checked By – Katrina (GoLangFix Volunteer)

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