Go-routines with channels not running parallely

Question

package main
import "time"
func main() {
    stringCh := make(chan func() (string))
    go func() {
        stringCh <- func() (string) {
            return stringReturner()
        }
        close(stringCh)
    }()

    intCh := make(chan func() (int))
    go func() {
        intCh <- func() (int) {
            return intReturner()
        }
        close(intCh)
    }()

    str := (<-stringCh)()
    print("Printing str: ", str,"\n\n")
    num := (<-intCh)()
    print("Printing int: ", num,"\n\n")     
}

func intReturner()int{
    time.Sleep(5 * time.Second)
    print("Inside int returner\n\n");
    return 1;
}

func stringReturner()string{
    time.Sleep(5 * time.Second)
    print("Inside string returner\n\n");
    return "abcd";
}

Output:

Inside string returner

Printing str: abcd

WAIT OF 5 SECONDS

Inside int returner

Printing int: 1

https://play.golang.org/p/oE2ybs7Jo-W

Why is this coding taking 10 seconds to execute instead of 5? We are parallelizing the calls by spawning two go-routines right (1 for string returner and 1 for int returner), but why is the int returner executing after the string returner executes?

Answer 1

The channel is returning function with sleep, and such function got called in sequential manner. That is why it will take 10s in general.

https://play.golang.org/p/UpHD7Ttw03R

Answer 2

Thats because you are only writing to the channels parallelly. But the read from the channels are happening one-after-the-other. To fix this, you can read from both channels from separate go routines

var wg sync.WaitGroup
wg.Add(2)
go func() {
  defer wg.Done()
  str := (<-stringCh)()
  print("Printing str: ", str, "\n\n")
}()
go func() {
  defer wg.Done()
  num := (<-intCh)()
  print("Printing int: ", num, "\n\n")
}()
wg.Wait()

Answer 3

Based on the suggestions moving the sleep method into go routine to run both functions concurrently in 5s:

package main

import "time"

func main() {
    stringCh := make(chan func() string)
    go func() {
        time.Sleep(5 * time.Second)
        stringCh <- func() string {
            return stringReturner()
        }
        close(stringCh)
    }()

    intCh := make(chan func() int)
    go func() {
        time.Sleep(5 * time.Second)
        intCh <- func() int {
            return intReturner()
        }
        close(intCh)
    }()

    str := (<-stringCh)()
    print("Printing str: ", str, "\n\n")
    num := (<-intCh)()
    print("Printing int: ", num, "\n\n")
}

func intReturner() int {
    print("Inside int returner\n\n")
    return 1
}

func stringReturner() string {
    print("Inside string returner\n\n")
    return "abcd"
}

Output:

Inside string returner

Printing str: abcd

Inside int returner

Printing int: 1