A worker pool for executing Redis commands using redigo

redis-worker.go

package main

import (
	"fmt"
	"github.com/gomodule/redigo/redis"
	"sync"
	"time"
)

var rconns *redis.Pool

func init() {
	// SET UP REDIS POOL
	rconns = &redis.Pool{
		MaxIdle:     3,
		MaxActive:   10,
		IdleTimeout: time.Second,

		Dial: func() (redis.Conn, error) {
			c, err := redis.Dial("tcp", "localhost:6379")
			if err != nil {
				return nil, err
			}
			return c, err
		},

		TestOnBorrow: func(c redis.Conn, t time.Time) error {
			_, err := c.Do("PING")
			return err
		},
	}
}

var WorkersUnavailable error = fmt.Errorf("Workers Unavailable")

type WorkPool struct {
	label    string
	queue    chan Work
	qtimeout time.Duration
	workers  []*Worker
	rpool    *redis.Pool
}

type Worker struct {
	rpool *redis.Pool
	queue chan Work
	quit  chan struct{}
}

type Work struct {
	cmd      Command
	response chan Response
}

type Command struct {
	cmd  string
	args []interface{}
}

type Response struct {
	v interface{}
	e error
}

// DoWork accepts a Redis command along with arguments and returns a Response
func (p *WorkPool) DoWork(cmd string, args ...interface{}) Response {
	r := make(chan Response, 1)
	if err := p.submit(Work{Command{cmd, args}, r}); err != nil {
		return Response{nil, err}
	}
	return <-r
}

func (p *WorkPool) submit(w Work) error {
	select {
	case p.queue <- w:
		return nil
	case <-time.After(p.qtimeout):
		return WorkersUnavailable
	}
}

// Shutdown terminates all workers in the pool
func (p *WorkPool) Shutdown() {
	for i, w := range p.workers {
		fmt.Println("Shutting down worker", i)
		w.quit <- struct{}{}
	}
}

// NewWorkPool initialises and launches a new worker pool\
// label is a string identifier for the pool
// maxBacklog is the avg. number of outstanding requests per worker allowed in queue
// workers is the number of redis worker routines available
// rpool is the Redis Connection pool shared between all workers.
//       Number of active connections in rpool should not be more than number of workers
func NewWorkPool(label string, maxBacklog, workers int, rpool *redis.Pool) *WorkPool {
	wq := make(chan Work, maxBacklog*workers)
	wlist := make([]*Worker, 0, workers)
	for i := 0; i < workers; i++ {
		quit := make(chan struct{}, 1)
		w := Worker{rpool, wq, quit}
		go w.Start()
		wlist = append(wlist, &w)
		//wlist[i] = &w
	}
	return &WorkPool{
		label:    label,
		queue:    wq,
		qtimeout: time.Millisecond * 20,
		workers:  wlist,
		rpool:    rpool}
}

func (w Worker) Start() {
	defer func() {
		if p := recover(); p != nil {
			w.Start() // Restart worker on panic
		}
	}()

	for {
		select {
		case <-w.quit:
			return
		case work := <-w.queue:
			w.process(work)
		}
	}
}

func (w Worker) process(work Work) {
	conn := w.rpool.Get()
	defer conn.Close()

	r, e := conn.Do(work.cmd.cmd, work.cmd.args...)
	work.response <- Response{r, e}
}

func main() {
	wp := NewWorkPool("demo", 2, 10, rconns)
	var wg sync.WaitGroup
	wg.Add(200)
	for i := 0; i < 100; i++ {
		go func(i int) {
			defer wg.Done()
			resp := wp.DoWork("SET", i, i)
			if resp.e != nil {
				fmt.Println("Error in SET", i, resp.e)
			}
		}(i)

		go func(i int) {
			defer wg.Done()
			resp := wp.DoWork("GET", i)
			val, err := redis.String(resp.v, resp.e)
			if err == nil {
				fmt.Println("GET", i, "=", val)
			} else {
				fmt.Println("GET", i, "error:", err)
			}
		}(i)
	}
	wg.Wait()
	wp.Shutdown()
}

/*
The MIT License

Copyright (c) 2018 Tahir Hashmi

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/