fin.go

package main

import (
	"fmt"
	"sync"
)

func work(num int, ch chan int) {
	// Do Somthing
	ch <- num
}

// Version 1 must know morker num for check
func workWrap(work_num int, ch chan int) {
	for i := 0; i < work_num; i++ {
		go work(i, ch)
	}
}

func checkWork(work_num int, ch chan int) {
	for i := 0; i < work_num; i++ {
		fmt.Println(<-ch)
	}
}

// Version 2 no worker num for check
func workWrap2(work_num int, ch chan int, fin chan int) {
	var wg sync.WaitGroup
	for i := 0; i < work_num; i++ {
		wg.Add(1)
		go func(i int) {
			work(i, ch)
			wg.Done()
		}(i)
	}
	wg.Wait()
	fin <- 1
}

func checkWork2(ch chan int, fin chan int) {
	for {
		select {
		case v := <-ch:
			fmt.Println(v)
		case <-fin:
			return
		}
	}
}

// Version 3 no fin channel for check
func workWrap3(work_num int, ch chan int) {
	var wg sync.WaitGroup
	for i := 0; i < work_num; i++ {
		wg.Add(1)
		go func(i int) {
			work(i, ch)
			wg.Done()
		}(i)
	}
	wg.Wait()
	close(ch)
}

func checkWork3(ch chan int) {
	for v := range ch {
		fmt.Println(v)
	}
}

func main() {
	ch := make(chan int)
	const WorkerNum = 10

	// Version 1 must know morker num for check
	go workWrap(WorkerNum, ch)
	checkWork(WorkerNum, ch)

	// Version 2 no worker num for check
	fin := make(chan int)
	go workWrap2(WorkerNum, ch, fin)
	checkWork2(ch, fin)

	// Version 3 no fin channel for check
	go workWrap3(WorkerNum, ch)
	checkWork3(ch)
}

version2のほうではsync.WaitGroupを使ってる
すべてのworker-goroutineの同期を取らないとfinが送れないから

version3だとcloseで終了してる
同じような書き方だけど記述量が少なくて、finチャンネルも書かなくてすむ