fizzbuzz_4.go

package main

import (
	"fmt"
	"runtime"
	"sync"
)

func main() {

	// Best practice, declare the last routine first
	// the print (io) worker
	outputChan := make(chan string, 10)
	// goroutine with signal
	printDone := printWorker(outputChan)

	// start n fizzbuzzWorker
	// n = number of system cores
	coreCount := runtime.NumCPU()
	// bootstrap the waitgroup
	wg := &sync.WaitGroup{}
	wg.Add(coreCount)
	inputChan := make(chan int, 10)
	for i := 0; i < coreCount; i++ {
		go fizzbuzzWorker(inputChan, outputChan, wg)
	}

	for i := 1; i <= 100; i++ {
		inputChan <- i
	}
	// Always remember to close channel to avoid deadlock
	close(inputChan)

	// Block until all executed
	wg.Wait()
	// Close because no more new message to output channel
	close(outputChan)

	// Wait signal from printWorker
	<-printDone
}

func printWorker(in <-chan string) <-chan bool {
	signal := make(chan bool)
	go func() {
		// Iterate by range only works with buffered channel
		for msg := range in {
			fmt.Println(msg)
		}
		// Remember, close is a message too, remember to capture it
		close(signal)
	}()
	return signal
}

func fizzbuzzWorker(in <-chan int, out chan<- string, wg *sync.WaitGroup) {
	// This works across both buffered and unbuffered channel
	for {
		i, more := <-in
		// Check if this is the close signal
		if !more {
			break
		}

		msg := fmt.Sprintf("%03d - ", i)
		if i%3 == 0 {
			msg += "fizz"
		}

		if i%5 == 0 {
			msg += "buzz"
		}

		out <- msg
	}
	wg.Done()
}