Golang goroutine channel sync and timeout example

main.go

package main

import (
	"fmt"
	"time"
)

func greet(st string, done chan bool) {
	fmt.Println(st)
	done <- true
}

func slowGreet(st string, done chan bool) {
	time.Sleep(2 * time.Second)
	fmt.Println(st)
	done <- true
}

func main() {

	const doneCount = 4

	done := make(chan bool, doneCount)
	go greet("Hello", done)
	go greet("How are you?", done)

	go slowGreet("How...Are...You...?", done)
	go greet("Bye", done)

	// len of done is 0 here, as no goroutine has finished yet
	fmt.Println("len of done is", len(done))

	// wait for all goroutines to finish
  	// we need to wait, else code will exit before output
  	// coroutines are daemons
	for i := 1; i <= cap(done); i++ {
		select {
		case <-done:
			// in case you want to fail if you have hung
			// try changing doneCount to 5 to see this in action
		case <-time.After(4 * time.Second):
			fmt.Println("Timed out waiting for goroutines to complete")
			return
		}
	}

}