Data race when closing listener

[alarmfox]

Hello, I'm using this library and i get data race when i run the following program with the command:

go run -race main.go

func main() {
	exitCh := make(chan os.Signal, 1)
	signal.Notify(exitCh, os.Interrupt, syscall.SIGTERM)
	defer close(exitCh)

	wg := sync.WaitGroup{}
	// start listening
	listener := gosnmp.NewTrapListener()
	wg.Add(1)
	go func() {
		defer wg.Done()

		listener.Listen("0.0.0.0:2162")
	}()

	<-exitCh
	listener.Close()
	wg.Wait()
}

This is the output:

==================
WARNING: DATA RACE
Read at 0x00c000186018 by main goroutine:
  github.com/gosnmp/gosnmp.(*TrapListener).Close()
      /home/giuseppe/go/pkg/mod/github.com/gosnmp/[email protected]/trap.go:164 +0x5a
  main.main()
      /home/giuseppe/dev/gosnmp-test/main.go:28 +0x370

Previous write at 0x00c000186018 by goroutine 9:
  github.com/gosnmp/gosnmp.(*TrapListener).listenUDP()
      /home/giuseppe/go/pkg/mod/github.com/gosnmp/[email protected]/trap.go:181 +0xdc
  github.com/gosnmp/gosnmp.(*TrapListener).Listen()
      /home/giuseppe/go/pkg/mod/github.com/gosnmp/[email protected]/trap.go:348 +0x4f4
  main.main.func1()
      /home/giuseppe/dev/gosnmp-test/main.go:24 +0x9e

Goroutine 9 (running) created at:
  main.main()
      /home/giuseppe/dev/gosnmp-test/main.go:21 +0x35a
==================
==================
WARNING: DATA RACE
Read at 0x00c0000a2018 by main goroutine:
  net.(*conn).ok()
      /usr/local/go/src/net/net.go:174 +0x89
  net.(*conn).LocalAddr()
      /usr/local/go/src/net/net.go:218 +0x93
  github.com/gosnmp/gosnmp.(*TrapListener).Close()
      /home/giuseppe/go/pkg/mod/github.com/gosnmp/[email protected]/trap.go:167 +0x6b
  main.main()
      /home/giuseppe/dev/gosnmp-test/main.go:28 +0x370

Previous write at 0x00c0000a2018 by goroutine 9:
  net.newUDPConn()
      /usr/local/go/src/net/udpsock.go:198 +0x114
  net.(*sysListener).listenUDP()
      /usr/local/go/src/net/udpsock_posix.go:113 +0x145
  net.ListenUDP()
      /usr/local/go/src/net/udpsock.go:243 +0x199
  github.com/gosnmp/gosnmp.(*TrapListener).listenUDP()
      /home/giuseppe/go/pkg/mod/github.com/gosnmp/[email protected]/trap.go:181 +0xab
  github.com/gosnmp/gosnmp.(*TrapListener).Listen()
      /home/giuseppe/go/pkg/mod/github.com/gosnmp/[email protected]/trap.go:348 +0x4f4
  main.main.func1()
      /home/giuseppe/dev/gosnmp-test/main.go:24 +0x9e

Goroutine 9 (running) created at:
  main.main()
      /home/giuseppe/dev/gosnmp-test/main.go:21 +0x35a
==================
==================
WARNING: DATA RACE
Read at 0x00c0000d4060 by main goroutine:
  net.(*conn).LocalAddr()
      /usr/local/go/src/net/net.go:221 +0xbc
  github.com/gosnmp/gosnmp.(*TrapListener).Close()
      /home/giuseppe/go/pkg/mod/github.com/gosnmp/[email protected]/trap.go:167 +0x6b
  main.main()
      /home/giuseppe/dev/gosnmp-test/main.go:28 +0x370

Previous write at 0x00c0000d4060 by goroutine 9:
  net.newFD()
      /usr/local/go/src/net/fd_unix.go:28 +0x104
  net.socket()
      /usr/local/go/src/net/sock_posix.go:28 +0xc9
  net.internetSocket()
      /usr/local/go/src/net/ipsock_posix.go:142 +0x12f
  net.(*sysListener).listenUDP()
      /usr/local/go/src/net/udpsock_posix.go:109 +0xf1
  net.ListenUDP()
      /usr/local/go/src/net/udpsock.go:243 +0x199
  github.com/gosnmp/gosnmp.(*TrapListener).listenUDP()
      /home/giuseppe/go/pkg/mod/github.com/gosnmp/[email protected]/trap.go:181 +0xab
  github.com/gosnmp/gosnmp.(*TrapListener).Listen()
      /home/giuseppe/go/pkg/mod/github.com/gosnmp/[email protected]/trap.go:348 +0x4f4
  main.main.func1()
      /home/giuseppe/dev/gosnmp-test/main.go:24 +0x9e

Goroutine 9 (running) created at:
  main.main()
      /home/giuseppe/dev/gosnmp-test/main.go:21 +0x35a
==================
Found 3 data race(s)
exit status 66

Anyone had the same issue? Am i doing something wrong?

[sedyh]

It looks like the internal listener doesn't release the connection during the entire lifetime. Looks like a bug.
Right now, you can set the finish field manually, which will lead to a normal closing of the connection.

func closeTrapListener(f *g.TrapListener) {
	pointerVal := reflect.ValueOf(f)
	val := reflect.Indirect(pointerVal)
	member := val.FieldByName("finish")
	if !member.IsValid() {
		return
	}
	ptrToY := unsafe.Pointer(member.UnsafeAddr())
	realPtrToY := (*int32)(ptrToY)
	atomic.StoreInt32(realPtrToY, 1)
}

Full example:

package main

import (
	"fmt"
	"log"
	"reflect"
	"sync/atomic"
	"time"
	"unsafe"

	"github.com/gosnmp/gosnmp"
)

func main() {
	listener := gosnmp.NewTrapListener()
	go func() {
		fmt.Println("started")
		if err := listener.Listen("0.0.0.0:2162"); err != nil {
			log.Fatal(err)
		}
	}()
	<-time.After(1 * time.Second)

	fmt.Println("closed")
	closeTrapListener(listener)
	<-time.After(1 * time.Second)
}

func closeTrapListener(f *g.TrapListener) {
	pointerVal := reflect.ValueOf(f)
	val := reflect.Indirect(pointerVal)
	member := val.FieldByName("finish")
	if !member.IsValid() {
		return
	}
	ptrToY := unsafe.Pointer(member.UnsafeAddr())
	realPtrToY := (*int32)(ptrToY)
	atomic.StoreInt32(realPtrToY, 1)
}

go run -race .
started
closed

[alarmfox]

Thank you for the response, i was writing a more diligent way to handle connection with context.Context support and i got this problem.