Golang Fatal Error: Concurrent Map Read and Map Write
I'm Writing Minecraft Server in Go, When Server Is Being Stressed by 2000+ Connections I Get This Crash: Fatal Error: Concurrent Map Read and Map...
I'm writing minecraft server in Go, when server is being stressed by 2000+ connections I get this crash:
fatal error: concurrent map read and map write/root/work/src/ +0x351 created by main.main /root/work/src/ +0x368
My code:
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())
}
For now server is only "limbo".
1 Answer
Generally speaking (without having access to the code where the error occurs) you have a few options. Here are two of them:
sync.RWMutex
Control access to the map with sync.RWMutex{}. Use this option if you have single reads and writes, not loops over the map. See RWMutex
Here a sample with access control to someMap via someMapMutex:
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
Use a syncmap.Map{} instead of a normal map. This map is already taking care of race issues but may be slower depending on your usage. syncmap.Map{}s main advantage lies with for loops. See 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
})
General Advice
You should test your server with -race option and then eliminate all the race conditions it throws. That way you can easier eliminate such errors before they occur.
go run -race server.go
David Miller brings 15 years of experience in global economics, personal finance strategy, and market dynamics. He specializes in turning complex economic trends into actionable insights for everyday readers.
