concurrent.go

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	fmt.Println(time.Now())

	n := 10

	ch := make(chan int, n)
	wg := &sync.WaitGroup{}
	wg.Add(cap(ch))

	for i := 0; i < n; i++ {
		go func(i int) {
			defer wg.Done()
			if execute(i) {
				fmt.Println("sending :", i)
				ch <- i
			}
		}(i)
	}
	go func(wg *sync.WaitGroup) {
		wg.Wait()
		close(ch)
	}(wg)

	for i := range ch {
		fmt.Println("received: ", i)
	}

	fmt.Println(time.Now())
}

func execute(i int) bool {
	time.Sleep(1 * time.Second)
	return i%2 == 0
}

output.txt

2020-01-29 11:08:32.194148 +0900 JST m=+0.000080461
sending : 2
received:  2
sending : 8
sending : 4
received:  8
received:  4
sending : 0
received:  0
sending : 6
received:  6
2020-01-29 11:08:33.194603 +0900 JST m=+1.000513577