去通道不输出它传递的数据

Question

我是新手，我正在尝试频道并发现了这一点。func main() {    c := make(chan int)    fmt.Println("initialized channel")    go receiver(c)    go helper(c)    for x := range c {        fmt.Println(x)    }}func helper(c chan int) {    time.Sleep(time.Second * 3)    c <- 5    time.Sleep(time.Second * 3)    c <- 4    close(c)}func receiver(c chan int) {    for x := range c {        fmt.Println(x)    }}问题是即使我发送了两个号码，但控制台中只打印了一个号码。initialized channel5输出

Answer 1

行为无法预测。有时您的程序会工作，有时则不会。我已经解释了问题发生的代码（带有注释）。

package main

import (

    "fmt"

    "time"

)

func main() {

    c := make(chan int)

    fmt.Println("initialized channel")

    // This is a receiver receiving from c (spawned goroutine)

    go receiver(c)

    // This is a sender (spawned goroutine)

    go helper(c)

    // This is again a receiver receiving from c

    // NOTE: As reciever and helper are spawned in

    // separate goroutine, control eventually reaches

    // here.

    // Behaviour is unpredictable as sometimes the data

    // sent to the channel might be recieved here and

    // sometimes it might be recieved by the receiver function.

    for x := range c {

        fmt.Println(x)

    }

}

func helper(c chan int) {

    time.Sleep(time.Second * 3)

    c <- 5

    time.Sleep(time.Second * 3)

    c <- 4

    // When this close is triggered, the receiver in main

    // could get exited as the signal to stop ranging is sent

    // using signal. Right after that the main function ends

    // such that data recieved by the receiver couldn't get

    // printed (sometimes it would work as well) i.e., main

    // exited right before fmt.Println(x) in receiver function.

    close(c)

}

func receiver(c chan int) {

    for x := range c {

        fmt.Println(x)

    }

}

要修复它，你可以试试这个。还有更多可能的解决方案，但这已经足够了。我已经删除了time.Sleep电话，因为它们与我们无关并且为简洁起见。

package main

import (

    "fmt"

)

func main() {

    // Initialize the channel

    c := make(chan int)

    // Spawn a goroutine that sends data to the

    // channel. Also, it is expected from the sender

    // only to close the channel as it only knows

    // when then send stops. Send to a closed

    // channel would panic.

    go send(c)

    // As send is running asynchronously, control

    // reaches here i.e., the receiver. It ranges until

    // c is closed and is guaranteed to receive every

    // date sent to channel c and then exit.

    for x := range c {

        fmt.Println(x)

    }

}

// send data to c

func send(c chan int) {

    c <- 5

    c <- 4

    close(c)

}