Go Channel 和 go routine with pointer variables 所有 goroutines 都睡着了 - 死锁

Question

我整个晚上都在研究如何修复这个错误，但我没有成功。当我运行程序时出现以下错误:“所有 goroutines 都睡着了 - 死锁!”。我知道这是因为主程序在例程有可能执行其任务之前退出，我认为使用 sync.WaitGroup 会有所帮助但不是真的:/

我想设置一些例程并使用 channel 发送 url 以检查 http 状态代码。我想限制一个网站的并发调用数。我按照示例使用字符串而不是结构做同样的事情并且它起作用了。

任何帮助将不胜感激:)

package main

import (
    "fmt"
    "sync"
    "time"
)

const (
    numPollers = 2                // number of Poller goroutines to launch
)

var urls = []string{
    "http://www.google.com/",
    "http://golang.org/",
    "http://blog.golang.org/",
    "http://golangtutorials.blogspot.fr",
    "https://gobyexample.com/",
}

// Resource represents an HTTP URL to be polled by this program.
type Resource struct {
    url      string
}

func Poller(in <-chan *Resource, wg *sync.WaitGroup) {
    //defer wg.Done()
    for r := range in {
        fmt.Printf("Finished: %v - %v\n", r.url, time.Now())
    }
    wg.Done()
}

func main() {
    var wg sync.WaitGroup
    pending := make(chan *Resource)

    wg.Add(len(urls))

    go Poller(pending, &wg)

    go func() {
        for _, url := range urls {
            wg.Add(1)
            fmt.Println("SENT > Pending url " + url)
            pending <- &Resource{url: url}
        }
    }()

    wg.Wait()

    fmt.Printf("Finished all goroutines: %v\n", time.Now())
}

https://play.golang.org/p/B-HSiDo2Qg

Answer 1

首先，您对 wg.Add() 的调用过多。你为你正在运行的每个 goroutine 调用一次。参见 http://golang.org/pkg/sync/#WaitGroup .其次，您在完成写入后没有关闭 channel 。这是您的代码的修改版本:

package main

import (
    "fmt"
    "sync"
    "time"
)

const (
    numPollers = 2                // number of Poller goroutines to launch
)

var urls = []string{
    "http://www.google.com/",
    "http://golang.org/",
    "http://blog.golang.org/",
    "http://golangtutorials.blogspot.fr",
    "https://gobyexample.com/",
}

// Resource represents an HTTP URL to be polled by this program.
type Resource struct {
    url      string
}

func Poller(in <-chan *Resource, wg *sync.WaitGroup) {
    defer wg.Done()
    for r := range in {
        fmt.Printf("Finished: %v - %v\n", r.url, time.Now())
    }
}

func main() {
    var wg sync.WaitGroup
    pending := make(chan *Resource)

    wg.Add(2)

    go Poller(pending, &wg)

    go func() {
        defer close(pending)
        defer wg.Done()
        for _, url := range urls {
            fmt.Println("SENT > Pending url " + url)
            pending <- &Resource{url: url}
        }
    }()

    wg.Wait()

    fmt.Printf("Finished all goroutines: %v\n", time.Now())
}

和https://play.golang.org/p/ucUlZEZMZM