go: basic implementation of semaphore

Channels are ideal data structure for sync between goroutines:

	package main

	import (
	"fmt"
	"time"
	)

	type Sem struct {
	c chan struct{}
	name string
	locker string
	}

	func Semaphore(name string) Sem {
	return Sem{
	make(chan struct{}, 1),
	name,
	"",
	}
	}

	func (s *Sem) Lock(l string) {
	s.c <- struct{}{}
	s.locker = l
	fmt.Printf("lock %s locked by %s\n", s.name, l)
	}

	func (s *Sem) Unlock() {
	<-s.c
	fmt.Printf("lock %s unlocked by %s\n", s.name, s.locker)
	}

	func main() {
	sum := 0
	a := Semaphore("A")

	go func() {
	a.Lock("1")
	defer a.Unlock()

	fmt.Println("1. go")
	sum += 1
	}()

	go func() {
	a.Lock("2")
	defer a.Unlock()

	fmt.Println("2. go")
	sum += 1
	}()

	time.Sleep(2 * time.Second)

	fmt.Println(sum)
	}

by GitHub