channel之阻塞七

思考：看结果结果？会不定时出现两个结果
package main

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

func main() {
var wg sync.WaitGroup
var ch chan int // 未初始化，值为 nil
ch = make(chan int)
for i := 0; i < 3; i++ {
wg.Add(1)
go func(i int, group *sync.WaitGroup) {
defer group.Done()
ch <- i
}(i, &wg)
}

go func() {
    fmt.Println("start select")
    for {
        select {
        case v,ok := <-ch:
            if !ok {
                fmt.Println("select return")
                return
            }
            fmt.Println(v, "select ing")
        }
    }
    fmt.Println("select end")
}()

time.Sleep(1*time.Second)
ch <- 4
wg.Wait()
close(ch)
fmt.Println("all finish")
//var ch chan int // 未初始化，值为 nil
//ch = make(chan int)
//for i := 0; i < 3; i++ {
//  go func(i int) {
//      ch <- i
//  }(i)
//}
//for v := range ch {
//  fmt.Println(v)
//}
//close(ch)
//time.Sleep(2 * time.Second)

}

结果1：
D:\work\go\src\wm\test>go run channel6.go
start select
0 select ing
1 select ing
2 select ing
all finish

结果2：
D:\work\go\src\wm\test>go run channel6.go
start select
1 select ing
0 select ing
2 select ing
4 select ing
select return
all finish

原因：
是因为主main已经执行结束，goroutine还没执行完。