Concurrency example in Go

a-main.go

// Manual Semaphore
package main

import (
	"fmt"
	"time"
)

func main() {
	startTime := time.Now().Unix()
  	isFinished := false
  	// Remember arguments are passed by value ?
	// Let's pass it by reference here
	go sleepTime(&isFinished) 

	for(!isFinished){
    		fmt.Println(time.Now().Unix())
	}

	endTime := time.Now().Unix() 
	duration := endTime - startTime
  	fmt.Println("Done in", duration, "seconds, from ", startTime, "until", endTime)
}

func sleepTime(isFinished *bool) {
	time.Sleep(2 * time.Second)
  	*isFinished = true
}

b-main.go

// Using sync package
package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	var wg sync.WaitGroup
	wg.Add(1)

	startTime := time.Now().Unix()

	go sleepTime(&wg)

	wg.Wait()
	endTime := time.Now().Unix()
	duration := endTime - startTime
	fmt.Println("Done in", duration, "seconds, from ", startTime, "until", endTime)

}

func sleepTime(wg *sync.WaitGroup) {
	time.Sleep(2 * time.Second)
	wg.Done()
}