Golang Simple Worker Pool Example

workerpool1.go

// Copyright 2020 Abhijit Bose. All rights reserved.
// Use of this source code is governed by a Apache 2.0 license

package main

import (
	"log"
	"sync"
	"time"
)

const limit = 4 // Maximum 4 Go routines at a time

// Used for some randomness in sleep patterns
var sleepList = [limit]time.Duration{
	20 * time.Millisecond,
	40 * time.Millisecond,
	10 * time.Millisecond,
	80 * time.Millisecond,
}

// Type of Work that would be provided
type work func()

// Group of workers
type group struct {
	jobs    chan work
	allDone chan bool
}

func createGroup(n int) group {
	g := group{
		jobs:    make(chan work),
		allDone: make(chan bool),
	}

	var wg sync.WaitGroup

	// Start Workers
	for i := 0; i < n; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for {
				select {
				case f, ok := <-g.jobs:
					if !ok {
						log.Println("Channel Close Exit from", id)
						return
					}
					log.Println("Start", id)
					f()
					log.Println("Finished", id)
				}
			}
		}(i)
	}

	// All done Signalling Routine
	go func() {
		wg.Wait()
		log.Println("All workers Exitted")
		g.allDone <- true
	}()

	return g
}

func (g group) Add(w work) {
	g.jobs <- w
}

func (g group) Close() {
	close(g.jobs)
	<-g.allDone
}

func main() {
	g := createGroup(limit)
	defer g.Close()

	for i := 0; i < (limit * 4); i++ {
		v := i % limit
		g.Add(func() {
			dur := sleepList[v]
			log.Println("Sleeping for", dur)
			time.Sleep(dur)
		})
	}
}