runtime/race: doesn't support the plugin package

[tiborvass]

What did you do?

// plugin/plugin.go

package main

import (
	"os"
	"time"
)

var counter int

func main() {
	os.Exit(Main())
}

func Main() int {
	go func() {
		counter++
	}()
	time.Sleep(500 * time.Millisecond)
	return counter
}

// plugin-runner.go

package main

import (
	"os"
	"plugin"
)

func main() {
	p, err := plugin.Open(os.Args[1])
	if err != nil {
		panic(err)
	}
	sym, err := p.Lookup("Main")
	if err != nil {
		panic(err)
	}
	f := sym.(func() int)
	_ = f()
}

$ go build -o plugin/plugin.so -race -buildmode=plugin plugin/plugin.go
$ go run -race plugin-runner.go plugin/plugin.so

What did you expect to see?

A DATA RACE output similar to this one:

$ go run -race plugin/plugin.go
==================
WARNING: DATA RACE
Read at 0x00000051da38 by main goroutine:
  main.Main()
      /go/src/github.com/tiborvass/goissues/plugin/race-nodetect/plugin/plugin.go:19 +0x5f
  main.main()
      /go/src/github.com/tiborvass/goissues/plugin/race-nodetect/plugin/plugin.go:11 +0x2f

Previous write at 0x00000051da38 by goroutine 6:
  main.Main.func1()
      /go/src/github.com/tiborvass/goissues/plugin/race-nodetect/plugin/plugin.go:16 +0x56

Goroutine 6 (finished) created at:
  main.Main()
      /go/src/github.com/tiborvass/goissues/plugin/race-nodetect/plugin/plugin.go:15 +0x42
  main.main()
      /go/src/github.com/tiborvass/goissues/plugin/race-nodetect/plugin/plugin.go:11 +0x2f
==================
exit status 1

What did you see instead?

No output. I reproduced it 100% on both linux and darwin.

System details

go version go1.10 linux/amd64
GOARCH="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/go"
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build269754766=/tmp/go-build -gno-record-gcc-switches"
GOROOT/bin/go version: go version go1.10 linux/amd64
GOROOT/bin/go tool compile -V: compile version go1.10
uname -sr: Linux 4.9.75-linuxkit-aufs
/lib/x86_64-linux-gnu/libc.so.6: GNU C Library (Debian GLIBC 2.24-11+deb9u1) stable release version 2.24, by Roland McGrath et al.

[mvdan]

/cc @dvyukov

[szuecs]

Sounds like an issue to our production application, which enables users to build their own Go plugins to enhance the application.

It would be nice if this would get a fix. Is this complicated or just not prioritized yet, because of plugin is not first class anyhow?

[ianlancetaylor]

It's not prioritized. It would help if somebody could figure out what the actual problem is. It may be obvious, it may not; I don't know.

[itsmontoya]

I've tested this by building the core app with --race, the plugin built with --race, and both built with --race and I've encountered no success. If anyone on the go team needs some examples. The vroomy team can provide some! :)

[adonespitogo]

In my case, a simple plugin that runs an http server with a simple handler func for root path / always produces data race when put under wrk stress test.

// plugin.go
func Init() {
  http.HandleFunc("/", func (w http.ResponseWriter,  _  *http.Request) {
    fmt.Fprint(w, "Hello World")
  })
  http.ListenAndServe(":3000", nil)
}

// load-plugin.go
func main () {
  p, err := plugin.Open("plugin.so")
  if err != nil {
    panic(err)
  }
  sym, err := p.Lookup("Init")
  if err != nil {
    panic(err)
  }
  init := sym.(func())
  init()
}

Error:

==================                                                                                      
WARNING: DATA RACE                                                                                      
Write at 0x00c000703380 by goroutine 513:                                                               
  bufio.(*Writer).Reset()                                                                               
      /Users/adonesp/.gvm/gos/go1.19.4/src/bufio/bufio.go:616 +0x100                                    
  net/http.newBufioWriterSize()                                                                         
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:844 +0x84                                 
  net/http.(*conn).readRequest()                                                                        
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:1061 +0x1388                              
  net/http.(*conn).serve()                                                                              
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:1916 +0x468                               
  net/http.(*Server).Serve.func3()                                                                      
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:3102 +0x4c                                
                                                                                                        
Previous read at 0x00c000703380 by goroutine 289:                                                       
  bufio.(*Writer).Write()                                                                               
      /Users/adonesp/.gvm/gos/go1.19.4/src/bufio/bufio.go:678 +0x24c                                    
  net/http.(*response).write()                                                                          
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:1640 +0x264                               
  net/http.(*response).Write()                                                                          
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:1598 +0x4c                                
  fmt.Fprint()                                                                                          
      /Users/adonesp/.gvm/gos/go1.19.4/src/fmt/print.go:243 +0x84                                       
  github.com/AdoPiSoft/base/web.SetupRoutes.func1()                                                     
      /Users/adonesp/Projects/adopisoft-v6/base/web/routes.go:30 +0x68  
  net/http.HandlerFunc.ServeHTTP()                                                                      
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:2109 +0x48                                
  net/http.(*ServeMux).ServeHTTP()                                                                      
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:2487 +0x9c                                
  net/http.serverHandler.ServeHTTP()                                                                    
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:2947 +0x4f4                               
  net/http.(*conn).serve()                                                                              
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:1991 +0x8d4                               
  net/http.(*Server).Serve.func3()                                                                      
      /Users/adonesp/.gvm/gos/go1.19.4/src/net/http/server.go:3102 +0x4c 

[ExtraE113]

Any update on when this might be fixed? I just lost like 4 hours to this problem.

[ianlancetaylor]

Honestly plugins are barely supported at all. If somebody sends in a fix we will review it, but it's unlikely that anybody on the core Go team is going to work on this any time soon. Sorry.

[ExtraE113]

Good to know, thanks. Any chance this could make it into the docs on plugins?

Edit: I've opened a PR #68792

[gopherbot]

Change https://go.dev/cl/604275 mentions this issue: plugin: include a warning about race detector compatability in docs