谁能解释一下 <-done 将在 close [close] 后运行的执行

Question

我无法理解这个程序for select，所以我需要帮助来解释这个程序的顺序，    done := make(chan interface{})    go func() {        time.Sleep(5 * time.Second)        close(done)    }()    workcount := 0loop:    for {        select {        case <-done:            break loop        default:        }        workcount++        fmt.Println(workcount)        time.Sleep(1 * time.Second)    }    fmt.Printf("Achieved %v cycles of work before signalled to stop \n", workcount)

Answer 1

// Our communication channel is created

    done := make(chan interface{})

    // run this function as goroutine

    go func() {

        // wait/sleep 5 seconds

        time.Sleep(5 * time.Second)

        // close our communication channel

        close(done)

    }()

    // initialize workcount with 0

    workcount := 0

loop:

    // loop

    for {

        // read channel data

        select {

        // if channel is closed break this loop, break = stop!

        case <-done:

            break loop

        // default do nothing

        default:

        }

        // if our channel doesn't send anything, just add +1 to workcount

        workcount++

        // print workcount

        fmt.Println(workcount)

        // wait 1 second before we run this loop again

        time.Sleep(1 * time.Second)

    }

    // so workcount is 5, cuz our goroutine will send term signal after 5 seconds

    fmt.Printf("Achieved %v cycles of work before signalled to stop \n", workcount)

解决这个问题的一个更干净的方法是

package main

import (

    "fmt"

    "time"

)

func main() {

    // sends after 5 seconds to this channel https://golang.org/pkg/time/#After

    timeout := time.After(5 * time.Second)

    // sends each second to this channel https://golang.org/pkg/time/#Tick

    tick := time.Tick(1 * time.Second)

    // our workcount var

    workcount := 0

    // for infinite

    for {

        // waits for data on each channel

        select {

        // fired if time.After wrote in timeout

        case <-timeout:

            fmt.Printf("Achieved %v cycles of work before signalled to stop \n", workcount)

            return

        // fired if time.Tick wrote in tick

        case <-tick:

            workcount++

            fmt.Println(workcount)

        }

    }

}

您在主函数中运行代码，因此我们需要返回。我们将使用 return 修复此代码

package main

import (

    "fmt"

    "time"

)

func main() {

    // Our communication channel is created

    done := make(chan interface{})

    // run this function as goroutine

    go func() {

        // wait/sleep 5 seconds

        time.Sleep(5 * time.Second)

        // close our communication channel

        close(done)

    }()

    // initialize workcount with 0

    workcount := 0

    // loop

    for {

        // read channel data

        select {

        // if channel is closed break this loop, break = stop!

        case <-done:

            fmt.Printf("Achieved %v cycles of work before signalled to stop \n", workcount)

            return

        // default do nothing

        default:

        }

        // if our channel doesn't send anything, just add +1 to workcount

        workcount++

        // print workcount

        fmt.Println(workcount)

        // wait 1 second before we run this loop again

        time.Sleep(1 * time.Second)

    }

}