Channels and Goroutines (Go)

goroutines.go

package main

import (
	"fmt"
	"time"
)

func worker(done chan int) {
	time.Sleep(time.Second)
	done <- 2000
}

func main() {
	// buffered channel === queue
	// channel ~ portal to send data

	// messages := make(chan string)// unbuffered, the "send" blocks until a "recv" happens (deadlock)

	// // go func() {
	// messages <- "ping"
	// // messages <- "pong"
	// // }()

	// msg := <-messages
	// // msg2 := <-messages
	// fmt.Println(msg)
	// // fmt.Println(msg2)

	messages := make(chan string, 10) // buffered, send is non blocking and stores stuff until recved

	messages <- "ping"
	messages <- "pong"

	fmt.Println(<-messages)
	fmt.Println(<-messages)

	done := make(chan int)
	go worker(done) // async function call

	fmt.Println(<-done) // await

	c1 := make(chan int, 1) // buffered, useful so that "send" isn't blocking (when no recver)
	c2 := make(chan int, 1)

	go func() {
		c1 <- 23
	}()
	go func() {
		c2 <- 34
	}()

	select { // blocks until one of the channels recv, first to resolve wins
	case msg1 := <-c1:
		fmt.Println(msg1)
	case msg2 := <-c2:
		fmt.Println(msg2)
	case <-time.After(time.Second):
		fmt.Println("time out")
		// use default for a non blocking recv (if no one resolves immmediately)
	}

	ch := make(chan string)

	select {
	case ch <- "hi": // no immediate recver, not buffered
		fmt.Println("sent message hi")
	default: // non blocking send
		fmt.Println("no message sent")
	}

	jobs := make(chan int)
	don := make(chan bool) // for awaiting

	go func() { // worker
		for {
			j, more := <-jobs // second return value is false if channel closes
			if more {
				fmt.Println("received job", j)
			} else {
				fmt.Println("received all jobs", j)
				don <- true
				return
			}
		}
	}()

	for j := 1; j <= 3; j++ {
		jobs <- j
		fmt.Println("sent job", j)
	}
	close(jobs) // close channel
	fmt.Println("sent all jobs")

	<-don // await worker

	queue := make(chan int, 5)
	queue <- 5 // sends are not blocking
	queue <- 4
	queue <- 3
	queue <- 2
	queue <- 1
	close(queue)
    
	for v := range queue {
		fmt.Println(v)
	}
}