concurrent work with throttling

co-trottle.go

package main

import (
	"fmt"
	"log"
	"strconv"
	"strings"
	"sync"
	"time"
)

const things = 10

func main() {
	var wg sync.WaitGroup
	c := make(chan string, things)
	r := make(chan struct{}, 2)

	st := time.Now()
	for i := 0; i < things; i++ {
		wg.Add(1)
		log.Printf("waiting %v / %v in queue", i, len(r))
		r <- struct{}{}

		go func(x int) {
			defer wg.Done()
			defer func() {
				<-r
				log.Printf("done    %v / %v in queue", x, len(r))
			}()

			// do some work
			log.Printf("working %v / %v in queue", x, len(r))
			time.Sleep(1 * time.Second)

			c <- strconv.Itoa(x)
		}(i)
	}

	wg.Wait()
	close(c)
	close(r)

	d := time.Since(st)

	n := make([]string, 0, len(c))
	for j := range c {
		n = append(n, j)
	}

	fmt.Printf("\ntook %v / %s", d, strings.Join(n, ", "))
}