在一定时间内从goroutine接收值

Question

I have a goroutine which can generate an infinite number of values (each more suitable than the last), but it takes progressively longer to find each values. I'm trying to find a way to add a time limit, say 10 seconds, after which my function does something with the best value received so far.

This is my current "solution", using a channel and timer:

// the goroutine which runs infinitely
// (or at least a very long time for high values of depth)
func runSearch(depth int, ch chan int) {
    for i := 1; i <= depth; i++ {
        fmt.Printf("Searching to depth %v
", i)
        ch <- search(i)
    }
}

// consumes progressively better values until the channel is closed
func awaitBestResult(ch chan int) {
    var result int
    for result := range ch {
        best = result
    }

    // do something with best result here
}

// run both consumer and producer
func main() {
    timer := time.NewTimer(time.Millisecond * 2000)

    ch := make(chan int)

    go runSearch(1000, ch)
    go awaitBestResult(ch)

    <-timer.C
    close(ch)
}

This mostly works - the best result is processed after the timer ends and the channel is closed. However, I then get a panic (panic: send on closed channel) from the runSearch goroutine, since the channel has been closed by the main function.

How can I stop the first goroutine running after the timer has completed? Any help is very appreciated.

Answer 1

You need to ensure that the goroutine knows when it is done processing, so that it doesn't attempt to write to a closed channel, and panic.

This sounds like a perfect case for the context package:

func runSearch(ctx context.Context, depth int, ch chan int) {
    for i := 1; i <= depth; i++ {
        select {
        case <- ctx.Done()
            // Context cancelled, return
            return
        default:
        }
        fmt.Printf("Searching to depth %v
", i)
        ch <- search(i)
    }
}

Then in main():

// run both consumer and producer
func main() {
    ctx := context.WithTimeout(context.Background, 2 * time.Second)

    ch := make(chan int)

    go runSearch(ctx, 1000, ch)
    go awaitBestResult(ch)

    close(ch)
}