GO程序陷入循环

Question

// _Closing_ a channel indicates that no more values
// will be sent on it. This can be useful to communicate
// completion to the channel's receivers.

package main

import "fmt"

// In this example we'll use a `jobs` channel to
// communicate work to be done from the `main()` goroutine
// to a worker goroutine. When we have no more jobs for
// the worker we'll `close` the `jobs` channel.
func main() {
    jobs := make(chan int, 5)
    done := make(chan bool)

    // Here's the worker goroutine. It repeatedly receives
    // from `jobs` with `j, more := <-jobs`. In this
    // special 2-value form of receive, the `more` value
    // will be `false` if `jobs` has been `close`d and all
    // values in the channel have already been received.
    // We use this to notify on `done` when we've worked
    // all our jobs.

    for i := 1; i <= 3; i++ {
        go func() {
            for {
                j, more := <-jobs
                if more {
                    fmt.Println("received job", j)
                } else {
                    fmt.Println("received all jobs")
                    done <- true
                    return
                }
            }
        }()
    }

    // This sends 3 jobs to the worker over the `jobs`
    // channel, then closes it.
    j := 0
    for {
        j++
        jobs <- j
        fmt.Println("sent job", j)
    }
    close(jobs)
    fmt.Println("sent all jobs")

    // We await the worker using the
    // [synchronization](channel-synchronization) approach
    // we saw earlier.
    <-done
}

https://play.golang.org/p/x28R_g8ftS

What I'm trying to do is get all the responses from a paginated url endpoint. jobs is a channel storing the page number. I have a function in if more{} checking for empty reponse and I have

done <- true
return

I thought this would close the go routine. But, the page generator for{j++; jobs <- j} is causing it to get stuck in a loop. Any idea how this can be resolved?

Answer 1

This was I was looking for. I have a number generator in an infinite while loop. And the program exits on some condition, in this example, it is on the j value, but it can also be something else.

https://play.golang.org/p/Ud4etTjrmx

package main

import "fmt"



func jobs(job chan int) {
    i := 1
    for {
        job <- i
        i++
    }
}

func main() {
    jobsChan := make(chan int, 5)


    done := false
    j := 0

    go jobs(jobsChan)
    for !done {
        j = <-jobsChan
        if j < 20 {
            fmt.Printf("job %d
", j)
        } else {
            done = true
        }
    }
}