Why is time.sleep required to run certain goroutines?

Question

In the GO tutorial, we have this slide: Goroutines

package main

import (
    \"fmt\"
    \"time\"
)

func say(s string) {
    for i := 0; i < 5; i++ {
           


        

Answer 1

If you remove time.Sleep from the say function the main will execute say("hello") and terminate without executing the goroutine. If you add a time.Sleep (or otherwise a select {}) before the main end it will give time to the goroutine to run and that thread will be picked from the scheduler.

Example:

package main

import (
    "fmt"
    "time"
)

func say(s string) {
    for i := 0; i < 5; i++ {
        // time.Sleep(100 * time.Millisecond)
        fmt.Println(s)
    }
}

func main() {
    go say("world")
    say("hello")

    time.Sleep(1*time.Second)
    // Vs: 
    // select {} // blocks indefinitely, requires manual interrupt
          // In CSP-speak the empty select is like STOP.
          // for{} would cause the cpu to max and the process's STATE will be `running`
          // select{} will not cause the cpu to max and the process state will be `sleeping`
}

The output will usually be 5 hello followed by 5 world but it could also manage to print one of the world before the last hello

TRY IT --> (http://) goo.gl/K2v7H0