使用 select 时转到 channel 丢失偶数

Question

我正在使用此函数获取从 0 到 100 的数字。

func addone(c chan int) {
    for i:= 0; i <= 100; i++{
        c <- i
    }
    close(c)
}

然后我尝试输出它:

func printone(c chan int) {
    for {
        select {
            case <-c:
                fmt.Println(<-c)
                time.Sleep(time.Millisecond * 50)
            default:
                fmt.Println("dropped")
        }
    }
}

主要功能:

func main() {
    ch := make(chan int)
    go addone(ch)
    printone(ch)    
}

go channel 在使用select 时缺少偶数，例如输出:

掉落1个3个5个7911131517192123252729313335373941434547495153555759616365676971737577798183858789919395979900

2、4、6、8 等在哪里？

为什么在关闭 channel 后它向 c channel 发送零？我认为它会等待新数据进入并获得“默认”案例？

Answer 1

这是因为您正在从 channel 中读取两次。

首先尝试将 channel 数据分配给一个变量。

这是一个例子:https://play.golang.org/p/ZdSOPe1Gj13

package main

import "time"
import "fmt"

func main() {

    // For our example we'll select across two channels.
    c1 := make(chan string)
    c2 := make(chan string)

    // Each channel will receive a value after some amount
    // of time, to simulate e.g. blocking RPC operations
    // executing in concurrent goroutines.
    go func() {
        time.Sleep(1 * time.Second)
        c1 <- "one"
    }()
    go func() {
        time.Sleep(2 * time.Second)
        c2 <- "two"
    }()

    // We'll use `select` to await both of these values
    // simultaneously, printing each one as it arrives.
    for i := 0; i < 2; i++ {
        select {
        case msg1 := <-c1:
            fmt.Println("received", msg1)
        case msg2 := <-c2:
            fmt.Println("received", msg2)
        }
    }
}