semaphore.go

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)
}