golang 多协程执行通过channel收集结果

package main
import (
    "fmt"
    "sync"
    "time"
)
func job(index int) int {
    time.Sleep(time.Millisecond * 500)
    //fmt.Println(index)
    return index
}
func main() {
    start := time.Now()
    num := 5
    res := make(chan int)
    wg := sync.WaitGroup{}
    for i := 0; i < num; i++ {
        wg.Add(1)
        go func(i int) {
            defer wg.Done()
            res <- job(i)
        }(i)
    }
    //等待所有goroutine执行完之后再关闭通道 defer方式关闭
    go func() {
        defer close(res)
        wg.Wait()
    }()
    for v := range res {
        fmt.Println("v:", v)
    }
    end := time.Since(start)
    fmt.Println(" 耗时 ： ", end.String())
}