How Can I Accurately Determine the Number of Processors Used by a Running Go Program?

Verifying Number of Processors for a Running Go Program

In Golang, the runtime.GOMAXPROCS function allows you to set the maximum number of processor cores available to the program. However, it may not always reflect the actual number of processors utilized. This article explains how to verify the number of processors actively used by a Go program.

The code snippet provided, taken from the discussion about runtime.Gosched, demonstrates a simple Go program with a single goroutine and varying values for runtime.GOMAXPROCS.

package main

import (
    "fmt"
    "runtime"
    "sync"
)

var wg sync.WaitGroup

func doTasks() {
    fmt.Println(" Doing task ")
    for ji := 1; ji < 100000000; ji++ {
        for io := 1; io < 10; io++ {
            //Some computations
        }
    }
    runtime.Gosched()

    wg.Done()
}

func main() {
    wg.Add(1)
    runtime.GOMAXPROCS(1) // or 2 or 4
    go doTasks()
    doTasks()
    wg.Wait()
}

To verify the number of processors the program is utilizing, the suggested method is to use the runtime.NumCPU function. This function returns the total number of available logical CPUs on the system, even for machines with hyperthreading.

The formula to determine the maximum parallelism is as follows:

func MaxParallelism() int {
    maxProcs := runtime.GOMAXPROCS(0)
    numCPU := runtime.NumCPU()
    if maxProcs < numCPU {
        return maxProcs
    }
    return numCPU
}

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