我正在用 Go 编写 minecraft 服务器，当服务器受到 2000 多个连接的压力时，我遇到了这个崩溃:

fatal error: concurrent map read and map write/root/work/src/github.com/user/imoobler/limbo.go:78 +0x351 created by main.main /root/work/src/github.com/user/imoobler/limbo.go:33 +0x368

我的代码:

package main

import (
    "log"
    "net"
    "bufio"
    "time"
    "math/rand"
    "fmt"
)

var (
    connCounter = 0
)

func main() {
    InitConfig()
    InitPackets()

    port := int(config["port"].(float64))
    ln, err := net.Listen("tcp", fmt.Sprintf(":%d", port))
    if err != nil {
        log.Fatal(err)
    }
    log.Println("Server launched on port", port)
    go KeepAlive()
    for {
        conn, err := ln.Accept()
        if err != nil {
            log.Print(err)
        } else {
            connCounter+=1
            go HandleConnection(conn, connCounter)
        }
    }
}

func KeepAlive() {
    r := rand.New(rand.NewSource(15768735131534))
    keepalive := &PacketPlayKeepAlive{
        id: 0,
    }
    for {
        for _, player := range players {
            if player.state == PLAY {
                id := int(r.Uint32())
                keepalive.id = id
                player.keepalive = id
                player.WritePacket(keepalive)
            }
        }
        time.Sleep(20000000000)
    }
}

func HandleConnection(conn net.Conn, id int) {
    log.Printf("%s connected.", conn.RemoteAddr().String())

    player := &Player {
        id: id,
        conn: conn,
        state: HANDSHAKING,
        protocol: V1_10,
        io: &ConnReadWrite{
            rdr: bufio.NewReader(conn),
            wtr: bufio.NewWriter(conn),
        },
        inaddr: InAddr{
            "",
            0,
        },
        name: "",
        uuid: "d979912c-bb24-4f23-a6ac-c32985a1e5d3",
        keepalive: 0,
    }

    for {
        packet, err := player.ReadPacket()
        if err != nil {
            break
        }

        CallEvent("packetReceived", packet)
    }

    player.unregister()
    conn.Close()
    log.Printf("%s disconnected.", conn.RemoteAddr().String())
}

目前服务器只是“悬而未决”。

最佳答案

一般来说(无法访问发生错误的代码)您有几种选择。这是其中两个:

同步.RWMutex

使用 sync.RWMutex{} 控制对 map 的访问。如果您有单次读取和写入，而不是在 map 上循环，请使用此选项。参见 RWMutex

这里是一个示例，通过 someMapMutex 对 someMap 进行了访问控制:

var (
    someMap      = map[string]string{}
    someMapMutex = sync.RWMutex{}
)

go func() {
    someMapMutex.Lock()
    someMap["key"] = "value"
    someMapMutex.Unlock()
}()

someMapMutex.RLock()
v, ok := someMap["key"]
someMapMutex.RUnlock()
if !ok {
    fmt.Println("key missing")
    return
}
fmt.Println(v)

syncmap.Map

使用 syncmap.Map{} 而不是普通的 map。该 map 已经在处理种族问题，但根据您的使用情况可能会更慢。 syncmap.Map{} 的主要优势在于 for 循环。参见 syncmap

var (
    someMap = syncmap.Map{}
)

go func() {
    someMap.Store("key", "value")
}()

v, ok := someMap.Load("key")
if !ok {
    fmt.Println("key missing")
    return
}
fmt.Println(v)

// with syncmap, looping over all keys is simple without locking the whole map for the entire loop
someMap.Range(func(key, value interface{}) bool {
    // cast value to correct format
    val, ok := value.(string)
    if !ok {
        // this will break iteration
        return false
    }
    // do something with key/value
    fmt.Println(key, val)

    // this will continue iterating
    return true
})

一般建议

您应该使用 -race 选项测试您的服务器，然后消除它抛出的所有竞争条件。这样您就可以更轻松地在此类错误发生之前将其消除。

go run -race server.go

参见 golang race detector

关于dictionary - Golang fatal error : concurrent map read and map write，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45585589/