fib-calculator-fan-in-fan-out

func fibonacci(n int) int {
	if n <= 1 {
		return n
	}
	return fibonacci(n-1) + fibonacci(n-2)
}

func main() {
	// fibCalculator will calculate fibonacci number for a stream of numbers 
	fibCalculator := func(done <-chan interface{}, numbers <-chan int) <-chan interface{} {
		fibStream := make(chan interface{})
		go func() {
			defer close(fibStream)
			for i := range numbers {
				f := fibonacci(i)
				select {
				case fibStream <- f:
				case <-done:
					return
				}
			}
		}()
		return fibStream
	}

	fanIn := func(
		done <-chan interface{},
		channels ...<-chan interface{},
	) <-chan interface{} {
		var wg sync.WaitGroup
		multiplexedStream := make(chan interface{})
		multiplex := func(c <-chan interface{}) {
			defer wg.Done()
			for i := range c {
				select {
				case <-done:
					return
				case multiplexedStream <- i:
				}
			}
		}
		// Select from all the channels
		wg.Add(len(channels))
		for _, c := range channels {
			go multiplex(c)
		}
		// Wait for all the reads to complete
		go func() {
			wg.Wait()
			close(multiplexedStream)
		}()
		return multiplexedStream
	}
	
	done := make(chan interface{})
	randomNumbersStream := make(chan int)

	go func(
		done <-chan interface{},
		numbers chan int) {
		for {
			r := rand.Intn(50)
			select {
			case numbers <- r:
			case <-done:
				return
			}
		}
	}(done, randomNumbersStream)
		
	calculators := make([]<-chan interface{}, runtime.NumCPU())
	for i := 0; i < runtime.NumCPU(); i++ {
		calculators[i] = fibCalculator(done, randomNumbersStream)
	}

	go func() {
		fmt.Println("let's see how many fabonacci can the Fan-in Fan-out calculate in 10 seconds")
		time.Sleep(10 * time.Second)
		close(done)
		close(randomNumbersStream)
	}()

	start := time.Now()
	i := 0
	for fab := range fanIn(done, calculators...) {
		fmt.Println(fmt.Sprintf("calculated the following fab: %d at iteration %d", fab, i))
		i++
	}
	fmt.Printf("calculation took: %v", time.Since(start))
	
	// When running it on my 8 cpu cores: it calculated 40 numbers in 19 seconds
	// When I run one calculator it calculated 2 numbers in 40 seconds
}