Parallel processing in golang

Question

Given the following code:

package main

import (
    "fmt"
    "math/rand"
    "time"
)

func main() {
    for i := 0; i < 3; i++ {
        go f(i)
    }

    // prevent main from exiting immediately
    var input string
    fmt.Scanln(&input)
}

func f(n int) {
    for i := 0; i < 10; i++ {
        dowork(n, i)
        amt := time.Duration(rand.Intn(250))
        time.Sleep(time.Millisecond * amt)
    }
}

func dowork(goroutine, loopindex int) {
    // simulate work
    time.Sleep(time.Second * time.Duration(5))
    fmt.Printf("gr[%d]: i=%d\n", goroutine, loopindex)
}

Can i assume that the 'dowork' function will be executed in parallel?

Is this a correct way of achieving parallelism or is it better to use channels and separate 'dowork' workers for each goroutine?

Answer 1

Regarding GOMAXPROCS, you can find this in Go 1.5's release docs:

By default, Go programs run with GOMAXPROCS set to the number of cores available; in prior releases it defaulted to 1.

Regarding preventing the main function from exiting immediately, you could leverage WaitGroup's Wait function.

I wrote this utility function to help parallelize a group of functions:

import "sync"

// Parallelize parallelizes the function calls
func Parallelize(functions ...func()) {
    var waitGroup sync.WaitGroup
    waitGroup.Add(len(functions))

    defer waitGroup.Wait()

    for _, function := range functions {
        go func(copy func()) {
            defer waitGroup.Done()
            copy()
        }(function)
    }
}

So in your case, we could do this

func1 := func() {
    f(0)
}

func2 = func() {
    f(1)
}

func3 = func() {
    f(2)
}

Parallelize(func1, func2, func3)

If you wanted to use the Parallelize function, you can find it here https://github.com/shomali11/util