buffered-channels.go

package main

import (
	"fmt"
	"math/rand"
	"sync/atomic"
	"time"
)

var (
	running int64
)

func work() {
	atomic.AddInt64(&running, 1)
	fmt.Printf("[")
	time.Sleep(time.Duration(rand.Intn(5)) * time.Second)
	fmt.Printf("]")
	atomic.AddInt64(&running, -1)
}

func worker(sema chan bool) {
	<-sema
	work()
	sema <- true
}

func main() {
	// A buffered channel
	sema := make(chan bool, 10)

	for i := 0; i < 1000; i++ {
		go worker(sema)
	}

	// Keep maximum 10 workers running at a time
	for i := 0; i < cap(sema); i++ {
		sema <- true
	}

	for {
		time.Sleep(2 * time.Second)
		fmt.Printf("<%d>", running)
	}

	time.Sleep(30 * time.Second)
}