goroutines-correct.go

package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/signal"
	"sync"
	"syscall"
	"time"

	"github.com/labstack/echo"
	"github.com/labstack/echo/middleware"
)

var wGGlobal sync.WaitGroup
var pollQChannel = make(chan int, 3)
var pollYChannel = make(chan int, 3)

func A() {
	fmt.Println("A")
}

func D() {
	fmt.Println("C")
}

func B() {
	defer func() {
		fmt.Println(<-pollQChannel)
	}()
	fmt.Println("B")
	A()
}

func C() {
	fmt.Println("C")
	defer func() {
		fmt.Println(<-pollYChannel)
	}()
	D()
}

func PollQ(ctx context.Context, gouroutinesWG *sync.WaitGroup) {
	defer gouroutinesWG.Done()
	for {
		select {
		case pollQChannel <- 1:
			time.Sleep(10 * time.Second)
			fmt.Println("Send for processing")
			go B()

		case <-ctx.Done():
			return // exit this function so we don't consume anything more
		}
	}

}

func PollY(ctx context.Context, gouroutinesWG *sync.WaitGroup) {
	defer gouroutinesWG.Done()

	for {
		select {
		case pollYChannel <- 1:
			time.Sleep(10 * time.Second)
			fmt.Println("Send for processing")
			go C()

		case <-ctx.Done():
			return // exit this function so we don't consume anything more
		}
	}

}

func main() {
	//var wG sync.WaitGroup

	e := echo.New()

	// Middleware
	e.Use(middleware.Logger())
	e.Use(middleware.Recover())

	// Routes
	e.GET("/", hello)

	ctx, cancelFunc := context.WithCancel(context.Background())

	wGGlobal.Add(2)
	go PollQ(ctx, &wGGlobal)
	go PollY(ctx, &wGGlobal)

	go e.Start(":1323")

	gracefullShutdown(e, &wGGlobal, cancelFunc)
}

func hello(c echo.Context) error {
	return c.String(http.StatusOK, "Hello, World!")
}

func gracefullShutdown(e *echo.Echo, gouroutinesWG *sync.WaitGroup, cancelFunc context.CancelFunc) {
	channel := make(chan os.Signal, 1)
	signal.Notify(channel, os.Interrupt, syscall.SIGTERM, syscall.SIGINT)
	<-channel
	log.Println("Service SHUTDOWN")
	shutdownCtx, cancel := context.WithTimeout(context.Background(), time.Second*time.Duration(120))
	defer cancel()
	log.Println("Waiting for go routines to shut down")
	cancelFunc()
	gouroutinesWG.Wait()
	log.Println("Go routines cleared succesfully to shut down")
	e.Shutdown(shutdownCtx)
}