resize consumer

resize_consumer.go

package main

import (
	"fmt"
	"os"
	"os/signal"

	"github.com/fsnotify/fsnotify"
	"github.com/spf13/viper"
	"github.com/streadway/amqp"
)

func loadConf() {
	viper.SetConfigName("config") // name of config file (without extension)
	viper.SetConfigType("yaml")   // REQUIRED if the config file does not have the extension in the name
	viper.AddConfigPath(".")      // optionally look for config in the working directory
	err := viper.ReadInConfig()   // Find and read the config file
	if err != nil {               // Handle errors reading the config file
		panic(fmt.Errorf("Fatal error config file: %s \n", err))
	}
	amqp_url = viper.GetString("amqp_url")
	consumer_count = viper.GetInt("consumer_count")
	queue_name = viper.GetString("queue_name")
}

type ConsumerRoutine struct {
	Id       int
	Status   string
	Exit     chan bool
	Channel  *amqp.Channel
	Delivery <-chan amqp.Delivery
	Done     chan bool
}

var amql_conn *amqp.Connection
var amqp_url string
var consumer []*ConsumerRoutine

const max_count = 100

var consumer_count int
var queue_name string

func initConsumerTask() {
	consumer = make([]*ConsumerRoutine, max_count)
}

func initAMQPConn() (err error) {
	amql_conn, err = amqp.Dial(amqp_url)
	if err != nil {
		panic(err)
	}
	return err
}

func watchConsumerCount() {
	viper.WatchConfig()
	viper.OnConfigChange(func(e fsnotify.Event) {
		fmt.Println("Config file changed:", e.Name)
		n := viper.GetInt("consumer_count")
		if n != consumer_count {
			fmt.Println("resize consumer count to => ", n)
			go ResizeConsumerCount(n)
		}
	})
}

func init() {
	loadConf()
	initAMQPConn()
	initConsumerTask()
	go watchConsumerCount()
}

func startNewConsumer(m *ConsumerRoutine) {
	m.Status = "started"
	m.Exit = make(chan bool)
	m.Done = make(chan bool)
	m.Channel, _ = amql_conn.Channel()
	m.Channel.QueueDeclare(queue_name, true, false, false, false, nil)
	m.Delivery, _ = m.Channel.Consume(queue_name, "", false, false, false, false, nil)
	fmt.Println("Consumer : ", m.Id, "started", "Exit pointer val = ", &m.Exit)
	for {
		select {
		case <-m.Exit:
			fmt.Println("have to exit now")
			m.Channel.Close()
			m.Channel = nil
			m.Done <- true
			m.Status = "ended"
			fmt.Println("Consumer ", m.Id, " ended")
			return
		case msg := <-m.Delivery:
			// fmt.Println("Consumer ", m.Id, " recived message = ", string(msg.Body))
			msg.Reject(true)
		}
	}

}

func ResizeConsumerCount(n int) {
	// scale up
	if n >= consumer_count {
		val := consumer_count
		consumer_count = n
		for i := val; i < n; i++ {
			consumer[i] = &ConsumerRoutine{
				Id:     i,
				Status: "stated",
				Exit:   make(chan bool),
				Done:   make(chan bool),
			}
			go startNewConsumer(consumer[i])
		}
		return
	}
	// scale down
	val := consumer_count
	consumer_count = n
	for i := n; i < val; i++ {
		fmt.Println("shuting down consumer : ", i)
		go func(m *ConsumerRoutine) {
			fmt.Println("Exit Chan Pointer = ", &m.Exit)
			m.Exit <- true
		}(consumer[i])
		<-consumer[i].Done
	}

}

func main() {
	for i := 0; i < consumer_count; i++ {
		consumer[i] = &ConsumerRoutine{
			Id: i,
		}
		go startNewConsumer(consumer[i])
	}
	stop := make(chan os.Signal, 1)
	signal.Notify(stop)
	for {
		v := <-stop
		fmt.Println("SIGNAL : ", v.String())
		if v.String() == "hangup" {
			ResizeConsumerCount(0)
			os.Exit(0)
		}
	}
}