Goroutine rate limiter

rate_limiter.go

package main

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

// limiter is a counting semaphore for limiting concurrency in action function.
var limiter = make(chan struct{}, 4)

func action(i int) {
	limiter <- struct{}{}
	defer func() { <-limiter }()

	fmt.Println("Perform action:", i)
	time.Sleep(4 * time.Second)
}

// ===================================

func main() {
	var n sync.WaitGroup
	for i := 0; i < 12; i++ {
		n.Add(1)
		go func(i int) {
			defer n.Done()
			action(i)
		}(i)
	}
	n.Wait()
}