Limit the number of concurrently running goroutines

bounded_goroutines.go

package main

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

func main() {
	rand.Seed(time.Now().Unix())
	var wg = sync.WaitGroup{}
	maxGoroutines := 4
	guard := make(chan struct{}, maxGoroutines)

	for i := 0; i < 15; i++ {
		guard <- struct{}{}
		wg.Add(1)
		go func(n int) {
			worker(n)
			<-guard
			wg.Done()
		}(i)
	}

	wg.Wait()
	fmt.Println("done")
}

func worker(i int) {
	s := time.Duration(int64(rand.Intn(3) + 2) * int64(time.Second))
	fmt.Printf("doing work on %d, sleep %v\n", i, s)
	time.Sleep(s)
	fmt.Println("done sleeping", i)
}