go - 比赛模拟 fatal error : all goroutines are asleep - deadlock

Question

我正在使用 Golang 构建护理模拟，但遇到了死锁问题。
Goroutines 用于代表每个赛车手。
这个想法是，一旦赛车手达到目标，就会使用一个 channel 来传达哪个赛车手获胜。
谁能发现我的错误？

package main

import (
    "fmt"
    "math/rand"
    "strconv"
    "sync"
    "time"
)

var wg sync.WaitGroup
var counter Counter
var tracks Tracks
var winner chan int

func newCounter(size int) Counter {
    return Counter{racers: make([]int, size+1)} // not using the zero'th index
}

func newTracks(size int) Tracks {
    return Tracks{racers: make([]string, size+1)}
}

func incrementCounter(n int) {
    counter.racers[n]++
}

func equalCounter() bool {
    rv := true
    for i, _ := range counter.racers {
        if counter.racers[0] != counter.racers[i] {
            rv = false
            break
        }
    }
    return rv
}

func smallerCounter(racerNumber int) bool {
    var rv bool
    for v := range counter.racers {
        if counter.racers[racerNumber] < v {
            rv = true
        } else {
            rv = false
        }
    }

    return rv
}

func checkCounter(racerNumber int) bool {
    var rv bool
    if equalCounter() || smallerCounter(racerNumber) {
        rv = true
    } else {
        rv = false
    }

    return rv
}

func racer(racerNum int) {
    steps := rand.Intn(5) + 1
    distance := 0
    goal := 100
    if checkCounter(racerNum) {
        for j := distance; distance < goal; j++ {
            for i := 0; i < steps; i++ {
                tracks.racers[racerNum] += "x"
            }
            distance += steps
            duration := rand.Int31n(200)
            time.Sleep(time.Duration(duration) * time.Millisecond)
            fmt.Println(tracks.racers[racerNum] + "[" + strconv.Itoa(racerNum) + "]")
        }

        incrementCounter(racerNum)
    }

    if distance >= goal {
        winner <- racerNum
        close(winner)
    }

    wg.Done()
}

func main() {
    racers := 5
    counter = newCounter(racers)
    tracks = newTracks(racers)

    for i := 1; i <= racers; i++ {
        wg.Add(1)
        go racer(i)
    }

    wg.Wait()

    fmt.Print("Winner is:")
    fmt.Print(<-winner)
}


type Counter struct {
    racers []int
}

type Tracks struct {
    racers []string
}

代码也在此处运行:

https://play.golang.org/p/Skr5Es3ItFQ

Answer 1

死锁是因为:

结果 channel 是无缓冲的，因此多次写入将阻塞，因此 wg.Done()从不运行

在所有 5 wg.Done() 之前，没有任何内容从结果 channel 中读取跑(鸡/蛋问题)

快速修复，使结果 channel 缓冲和所有总写入的大小:

winner = make(chan int, racers)

https://play.golang.org/p/sbHfOr9YS_z

channel 也将在 channel 队列中获得所有亚军结果。

如果您只关心获胜者，则有更有效的方法来满足这种情况，例如创建 referee go-routine 观察第一次写入(获胜者)到结果 channel ，然后取消比赛 context (每个赛车手都会注意上下文取消，一旦宣布一个获胜者，他们就会放弃他们的任务)