Getting the goroutine freezing once recieving data from channel

Getting Help Code Review
1

I go have the below code that is working fine, and the goroutine is running 5 times as requested.

package main

import (
	"fmt"
	"log"
	"sync"
	pb "walistner/proto"

	"google.golang.org/grpc/metadata"
	"google.golang.org/grpc/peer"
	"google.golang.org/protobuf/types/known/emptypb"
)

// type server pb.StreamServiceServer
type server struct {
	pb.UnimplementedStreamServiceServer
}

func (s server) WaMessageStreame(_ *emptypb.Empty, srv pb.StreamService_WaMessageStreameServer) error {
	if p, ok := peer.FromContext(srv.Context()); ok {
		fmt.Println("Client ip is:", p.Addr.String())
	}
	md := metadata.New(map[string]string{"Content-Type": "text/event-stream", "Connection": "keep-alive"})
	srv.SetHeader(md)
	//use wait group to allow process to be concurrent
	var wg sync.WaitGroup

	for i := 0; i < 5; i++ {

		wg.Add(1)
		go func(count int64) {

			defer wg.Done()
     
			resp := myData

			if err := srv.Send(&resp); err != nil {
				log.Printf("send error %v", err)
			}
			log.Printf("finishing request number : %d", count)
		}(int64(i))
	}

	wg.Wait()
	return nil
}

I wanted to make slight change, so instead of running 5 times only, I want it to run upon recieving input data from channel, so I changed it to be:

	for { // removed the count

		wg.Add(1)
		go func() {

			defer wg.Done()
     
			resp := <- myData  // I changed mydata to be from channel

			if err := srv.Send(&resp); err != nil {
				log.Printf("send error %v", err)
			}
		}()

But with this change I got the app hang/freezed.

What mistake I made?

2

Looks like you are creating goroutines without limit.
Is what do you want?

3

Change post title to “Infinite loop runs forever”. The behavior has nothing to do with receiving data from a channel.

4

I was having 2 mistakes in my code:

  1. I’m listining for the same channel at 2 different places, so the data sometimes is consumed before it reached this channel.

  2. I’m listening to the channel inside the goroutine, while I should be listening to it before the goroutine, but inside the same for loop.

The correct code became:

	var wg sync.WaitGroup

	for {

		resp := <- myData

		wg.Add(1)

		go func() {
			defer wg.Done()

			if err := srv.Send(&resp); err != nil {
				log.Printf("send error %v", err)
			}

		}()
	}

	wg.Wait()
5

The WaitGroup is pointless because there is no exit from the infinite loop. wg.Wait() will never get called, so the wg.Add and wg.Done don’t make any sense.

1 Like
6

Thanks for your clarification, appreciated.