goroutine_pool.go

package main

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

type Job struct {
	url string
}

type Worker struct {
	id int
}

func (w *Worker) Process(job interface{}) {
	j, ok := job.(Job)
	if ok {
		fmt.Printf("worker %d: processing %s\n", w.id, j.url)
		time.Sleep(2)
	}
}

type Dispatcher struct {
	numWorkers int
	jobChannel chan interface{}
	waitGroup  *sync.WaitGroup
}

func NewDispatcher(numWorkers int) *Dispatcher {
	return &Dispatcher{
		numWorkers,
		make(chan interface{}),
		&sync.WaitGroup{},
	}
}

func (d *Dispatcher) StartWorkers() {
	d.waitGroup.Add(d.numWorkers)
	for i := 0; i < d.numWorkers; i++ {
		worker := Worker{i}
		go func(worker Worker) {
			for job := range d.jobChannel {
				worker.Process(job)
			}
			d.waitGroup.Done()
		}(worker)
	}
}

func (d *Dispatcher) Submit(job interface{}) {
	// this will not be blocked!
	d.jobChannel <- job
}

func (d *Dispatcher) Close() {
	// close job channel
	close(d.jobChannel)
	// wait for all jobs to finish
	d.waitGroup.Wait()
}

func main() {
	dispatcher := NewDispatcher(5)
	dispatcher.StartWorkers()
	for i := 0; i < 30; i++ {
		dispatcher.Submit(
			Job{
				fmt.Sprintf("Job Number %d", i),
			},
		)
	}
	dispatcher.Close()

}