concurrency - 所有 go routines 都睡着了 - 死锁

Question

我正在使用 Go 构建工作系统的框架，但我收到“ fatal error :所有 goroutines 都在 sleep - 死锁!”。

我使用两个 channel 进行协调，一个用于创建工作，第二个用于发送结果。创建作业后，我关闭输入 channel 。

我的问题是如何关闭输出 channel 以便程序可以正确退出。代码是:

package main

import (
    "bufio"
    "flag"
    "fmt"
    "log"
    "math/rand"
    "os"
    "time"
)

type Work struct {
    id int
    ts time.Duration
}

const (
    NumWorkers = 5000
    NumJobs    = 100000
)

func worker(in <-chan *Work, out chan<- *Work) {
    for w := range in {
        st := time.Now()
        time.Sleep(time.Duration(rand.Int63n(int64(200 * time.Millisecond))))
        w.ts = time.Since(st)
        out <- w
    }
}

func main() {
    wait := flag.Bool("w", false, "wait for <enter> before starting")
    flag.Parse()

    if *wait {
        fmt.Printf("I'm <%d>, press <enter> to continue", os.Getpid())
        reader := bufio.NewReader(os.Stdin)
        reader.ReadString('\n')
    }

    Run()
}

func Run() {
    in, out := make(chan *Work, 100), make(chan *Work, 100)
    for i := 0; i < NumWorkers; i++ {
        go worker(in, out)
    }
    go createJobs(in)
    receiveResults(out)
}

func createJobs(queue chan<- *Work) {
    for i := 0; i < NumJobs; i++ {
        work := &Work{i, 0}
        queue <- work
    }
    close(queue)
}

func receiveResults(completed <-chan *Work) {
    for w := range completed {
        log.Printf("job %d completed in %s", w.id, w.ts)
    }
}

感谢任何帮助:)

Answer 1

我错过了关于您知道原始答案中死锁原因的部分。

• 您提到了 WaitGroup，它基本上只是一个信号量
• 您可以使用另一个“控制” channel ，让工作人员在完成后发送信号

-

func worker(ctrl chan<- bool, in <-chan *Work, out chan<- *Work) {
    for w := range in {
        st := time.Now()
        time.Sleep(time.Duration(rand.Int63n(int64(200 * time.Millisecond))))
        w.ts = time.Since(st)
        out <- w
    }
    ctrl <- true
}

func control(ctrl <-chan bool, numWorkers int, out chan<- *Work) {
    for i=0; i<numWorkers; i++ {
        <-ctrl
    }
    close(out)
}

原答案:

你在完成时做一个range:

for w := range completed {
    log.Printf("job %d completed in %s", w.id, w.ts)
}

但是那个 channel 永远不会关闭