go - 工作池上的 channel 死锁

Question

我正在通过创建一个包含 1000 个工作人员的工作池来玩弄 channel 。目前我收到以下错误:

fatal error: all goroutines are asleep - deadlock!

这是我的代码:

package main

import "fmt"
import "time"


func worker(id int, jobs <-chan int, results chan<- int) {
    for j := range jobs {
        fmt.Println("worker", id, "started  job", j)
        time.Sleep(time.Second)
        fmt.Println("worker", id, "finished job", j)
        results <- j * 2
    }
}

func main() {
    jobs := make(chan int, 100)
    results := make(chan int, 100)

    for w := 1; w <= 1000; w++ {
        go worker(w, jobs, results)
    }

    for j := 1; j < 1000000; j++ {
        jobs <- j
    }
    close(jobs)
    fmt.Println("==========CLOSED==============")

    for i:=0;i<len(results);i++ {
        <-results
    }
}

为什么会这样？我还是个新手，我希望能理解这一点。

Answer 1

虽然 Thomas 的回答基本上是正确的，但我发布了我的版本，IMO 更好的 Go，也适用于无缓冲 channel :

func main() {
    jobs := make(chan int)
    results := make(chan int)

    var wg sync.WaitGroup

    // you could init the WaitGroup's count here with one call but this is error
    // prone - if you change the loop's size you could forget to change the
    // WG's count. So call wg.Add in loop
    //wg.Add(1000)
    for w := 1; w <= 1000; w++ {
        wg.Add(1)
        go func() {
            defer wg.Done()
            worker(w, jobs, results)
        }()
    }

    go func() {
        for j := 1; j < 2000; j++ {
            jobs <- j
        }
        close(jobs)
        fmt.Println("==========CLOSED==============")
    }()

    // in this gorutine we wait until all "producer" routines are done
    // then close the results channel so that the consumer loop stops
    go func() {
        wg.Wait()
        close(results)
    }()

    for i := range results {
        fmt.Print(i, " ")
    }
    fmt.Println("==========DONE==============")
}