Go: Goroutines and channels

channels.go

package main

import (
	"fmt"
	"strconv"
	"sync"
	"sync/atomic"
)

// No deadlock on all sleeping, etc.
// Careful use of WaitGroups and closing of channel

func producersConsumers() {
	receivedTotal := 0
	receivedTotalAtomic := atomic.Int32{}

	var recvWg sync.WaitGroup
	var sendWg sync.WaitGroup

	ch := make(chan string, 5)

	recvSimple := func(s string) {
		defer recvWg.Done()
		for {
			msg, open := <-ch
			if !open {
				break
			}
			receivedTotal++
			receivedTotalAtomic.Add(1)
			fmt.Printf("Receiver %s received %s\n", s, msg)
		}
	}
	go recvSimple("One")
	go recvSimple("Two")
	recvWg.Add(2)

	recvRange := func(s string) {
		defer recvWg.Done()
		for msg := range ch {
			fmt.Printf("Receiver %s received %s\n", s, msg)
		}
	}
	go recvRange("Three")
	go recvRange("Four")
	recvWg.Add(2)

	send := func(name string) {
		defer sendWg.Done()
		for i := 0; i < 1000; i++ {
			s := name + " " + strconv.Itoa(i)
			//fmt.Printf("Sending %s\n", s)
			ch <- s
		}
		fmt.Printf("Sender %s exiting\n", name)
	}
	go send("Uno")
	go send("Due")
	go send("Tre")
	sendWg.Add(3)
	sendWg.Wait()
	close(ch)

	recvWg.Wait()
	fmt.Printf("Processed %d (not necessarily %d!) messages\n", receivedTotalAtomic.Load(), receivedTotal)
}

func pingPong() {
	cnt := 0
	ch := make(chan string)
	var wg sync.WaitGroup

	f := func(me string) {
		defer wg.Done()
		for {
			msg, hasMore := <-ch
			if !hasMore {
				fmt.Println(me, ": Good game")
				break
			}
			fmt.Println(msg)
			cnt += 1
			ch <- me

		}
	}

	go f("Pong")
	go f("Ping")

	wg.Add(2)
	ch <- "Start!"

	for cnt < 10 {
		// Wait (we're sleeping above)
	}
	s := <-ch
	fmt.Println("Ok, this was the last ", s)
	close(ch)
	wg.Wait()
}

func main() {
	producersConsumers()
	fmt.Println("*****************************************")
	pingPong()

}