Simple worker pool in golang/ https://play.golang.org/p/6SRS2KScnuu

workerpool.go

// https://play.golang.org/p/6SRS2KScnuu

package main

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

const (
	numJobs = 30
	numWrks = 4
)

func main() {
	run()
}

func run() {
	var (
		// we should have just enough buffer so that work producer should not block
		in  = make(chan int, numWrks)
		out = make(chan int, numWrks)

		wg sync.WaitGroup
	)

	// create a pool of wrokers
	for i := 0; i < numWrks; i++ {
		wg.Add(1)
		go worker(i, in, out, &wg)
	}

	// produce some work in background
	go func() {
		for i := 0; i < numJobs; i++ {
			in <- i // this could block if we exhaust the buffer, hence this producer must process in background
		}

		close(in) // signal that we have finished producing work, so that all workers will return
	}()

	// wait for all workers to finish
	go func() {
		wg.Wait()

		// all workers returned, we can safely close the out chan
		close(out) // signal that we have finished producing output
	}()

	for i := range out {
		fmt.Printf("received %d\n", i)
	}

	fmt.Println("exiting...")
}

func worker(id int, in <-chan int, out chan<- int, wg *sync.WaitGroup) {
	for i := range in {
		out <- work(i)
		fmt.Printf("worker id %d processed %d\n", id, i)
	}

	fmt.Printf("worker id %d finished working\n", id)
	wg.Done() // signal that this worker has finished working
}

func work(i int) int {
	time.Sleep(time.Second)
	return i
}