channels.go

package main

import "fmt"
import "time"
import "syscall"
import "os"
import "os/signal"

type fn func(os.Signal)
func catchSigterm(fun fn) {
	c := make(chan os.Signal, 1)
	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
	go func() {
	    s := <- c  // we get signal
	    fun(s)
	}()
}

func main() {

	sigterm := false
	catchSigterm(func (sig os.Signal) {
		fmt.Println("\nCaught sigterm...\n")
		sigterm = true
	});

	c := make(chan string)
	words := []string{"hello", "world", "here", "are", "a", "bunch", "of", "words"}

	i := 0
	pending := 0
	
	for j:=0;j<4;j++ {
		go sleepThenSay(words[0], i, c)
		pending += 1
	}
	for {
		w := <- c
		fmt.Println(w)
		fmt.Printf("[%d] Waiting...\n", pending)
		w = <- c
		pending -= 1
		fmt.Println(w)
		i += 1
		if (i >= len(words)) {
			i = 0
		}
		if sigterm {
			if pending == 0 {
				fmt.Printf("Done waiting...!")
				os.Exit(0)
			}
			fmt.Printf("\nSkipping next call, waiting for %d threads to finish...", pending)
		} else {
			pending += 1
			go sleepThenSay(words[i], i, c)
		}
	}

}

func sleepThenSay(str string, seconds int, c chan string) {
	c <- fmt.Sprintf("sleeping for %d seconds before saying, '%s'...\n", seconds, str)
	time.Sleep(time.Duration(seconds) * time.Second)
	c <- fmt.Sprintf("%s\n", str)
}