Goroutines

ping-output.md

In ping.go the printer runs in a goroutine and the main thread is blocked by fmt.Scanln. As expected it prints ping, then pong.

In ping2.go the printer itself is blocking the main thread. When run it returns ping twice before returning a pong.

$ go run ping.go
ping
pong
ping
pong
^C

$ go run ping2.go
ping
ping
pong
ping
pong

ping.go

package main

import(
	"fmt"
	"time"
)

func pinger(c chan<- string) {
	for i := 0; ; i++ {
		c <- "ping"
	}
}

func ponger(c chan<- string) {
	for i := 0; ; i++ {
		c <- "pong"
	}
}

func printer(c <-chan string) {
	for {
		msg := <- c
		fmt.Println(msg)
		time.Sleep(time.Second * 1)
	}
}

func main() {
	var c chan string = make(chan string)

	go pinger(c)
	go ponger(c)
	// Printer is run in a goroutine
	go printer(c)
	var input string
	fmt.Scanln(&input)
}

ping2.go

package main

import(
	"fmt"
	"time"
)

func pinger(c chan<- string) {
	for i := 0; ; i++ {
		c <- "ping"
	}
}

func ponger(c chan<- string) {
	for i := 0; ; i++ {
		c <- "pong"
	}
}

func printer(c <-chan string) {
	for {
		msg := <- c
		fmt.Println(msg)
		time.Sleep(time.Second * 1)
	}
}

func main() {
	var c chan string = make(chan string)

	go pinger(c)
	go ponger(c)
	// Printer blocks the main thread
	printer(c)
}