GoLang: Concurrency example

concurrent.go

// Concurrent.go
// Simple example that demonstrates usage of Go routines.
package main

import (
  "fmt"
  "time"
  "math/rand" 
)

func main() {
	// zomg. no type declaration. 
	start := time.Now()
	
	decoupled_h()
	
	elapsed := time.Since(start)
	
	fmt.Println(elapsed)
}

// Demonstrates that although code is synchronous, execution is decoupled.
func decoupled_h() {
  	c := fanIn(foo("hello"), foo("world"))
  	for i := 0; i < 20; i++ {
  		fmt.Println(<-c)
  	}
}

// Demonstrates that the code can run in sync.
func sync_h() {
	h := foo("hello")
  	w := foo("world!")
  
  	for i := 0; i < 5; i++ {
    	fmt.Printf("f(Goroutine): %q\n", <-h)
    	fmt.Printf("f(Goroutine): %q\n", <-w)
  	}
}

// Function that prints a string and then sleeps.
func foo(msg string) <-chan string {
  c := make(chan string)
  go func() {
    for i := 0; ; i++ {
    	c <- fmt.Sprintf("%s %d", msg, i)
      	// sleep for pseudorandom time
      	time.Sleep(time.Duration(rand.Intn(1337)) * time.Millisecond)
      }
  }()
  return c
}

// Multiplexing: Takes two channels of input and returns one channel of output
func fanIn(input1, input2 <-chan string) <-chan string{
	c := make(chan string)
	go func() {
		for {
			select {
				// select the routine that is "ready" for execution
				case s:= <- input1: c <- s
				case s:= <- input2: c <- s
			}
		}
	}()
	return c
}