Code from appliedgo.net/futures

futures.go

package main

import (
	"fmt"
	"time"
)

func main() {
	c := make(chan int)

	fmt.Println("\nA simple future")
	fmt.Println("---------------\n")

	go func(input int, result chan<- int) {
		fmt.Println("Calculating")
		time.Sleep(1 * time.Second)
		fmt.Println("done")
		result <- input * 2
	}(1, c)

	var value int
	fmt.Println("Waiting")
	value = <-c
	fmt.Println("got", value)


  fmt.Println("\nReading the future multiple times")
	fmt.Println("-----------------------------\n")

	c2 := make(chan int)

	go func(input int, res chan<- int) {
		fmt.Println("Calculating")
		time.Sleep(1 * time.Second)
		for {
			fmt.Println("Writing result")
			res <- input * 4
		}
	}(1, c2)

	fmt.Println("Waiting")
	fmt.Println("got", <-c2)
	fmt.Println("got", <-c2)


	fmt.Println("\nReading with a timeout")
	fmt.Println("-----------------------------\n")

	c3 := make(chan int)

	go func(input int, res chan<- int) {
		fmt.Println("Calculating")
		time.Sleep(2 * time.Second)
		for {
			fmt.Println("Writing result")
			res <- input * 8
		}
	}(1, c3)

	get := func(s int) (result int, timedout bool) {
		select {
		case result = <-c3:
			return result, false
		case <-time.After(time.Duration(s) * time.Second):
			return 0, true
		}
	}

	fmt.Println("Waiting")
	result, timedOut := get(1)
	if timedOut {
		// Handle the timeout.
		fmt.Println("Timed out")
		return
	}
	fmt.Println(result)
}