x/exp/shiny: gldriver(x11) race condition showWindow/onConfigure

[barnex]

What did you do?

$ cd $GOPATH/src/golang.org/x/exp/shiny/example/basicgl
$ go build -race main.go
$ ./main

What did you see?

==================
WARNING: DATA RACE
Write at 0x00c4200fa0c8 by goroutine 6:
  golang.org/x/exp/shiny/driver/gldriver.showWindow()
      /home/arne/src/golang.org/x/exp/shiny/driver/gldriver/x11.go:73 +0x1f3
  golang.org/x/exp/shiny/driver/gldriver.(*screenImpl).NewWindow()
      /home/arne/src/golang.org/x/exp/shiny/driver/gldriver/screen.go:145 +0x33d
  golang.org/x/exp/shiny/widget.RunWindow()
      /home/arne/src/golang.org/x/exp/shiny/widget/widget.go:77 +0xb1
  main.main.func1()
      /home/arne/src/golang.org/x/exp/shiny/example/basicgl/main.go:51 +0x4cd
  golang.org/x/exp/shiny/driver/gldriver.main.func1()
      /home/arne/src/golang.org/x/exp/shiny/driver/gldriver/x11.go:127 +0x5b

Previous read at 0x00c4200fa0c8 by main goroutine:
  golang.org/x/exp/shiny/driver/gldriver.onConfigure()
      /home/arne/src/golang.org/x/exp/shiny/driver/gldriver/x11.go:279 +0x1ac
  golang.org/x/exp/shiny/driver/gldriver._cgoexpwrap_0cf67038b08c_onConfigure()
      golang.org/x/exp/shiny/driver/gldriver/_obj/_cgo_gotypes.go:221 +0x68
  runtime.call32()
      /home/arne/bin/go/src/runtime/asm_amd64.s:479 +0x4b
  golang.org/x/exp/shiny/driver/gldriver.main()
      /home/arne/src/golang.org/x/exp/shiny/driver/gldriver/x11.go:162 +0x5d6
  golang.org/x/exp/shiny/driver/gldriver.Main()
      /home/arne/src/golang.org/x/exp/shiny/driver/gldriver/gldriver.go:26 +0x3c
  main.main()
      /home/arne/src/golang.org/x/exp/shiny/example/basicgl/main.go:54 +0x3a

Goroutine 6 (running) created at:
  golang.org/x/exp/shiny/driver/gldriver.main()
      /home/arne/src/golang.org/x/exp/shiny/driver/gldriver/x11.go:129 +0x2ae
  golang.org/x/exp/shiny/driver/gldriver.Main()
      /home/arne/src/golang.org/x/exp/shiny/driver/gldriver/gldriver.go:26 +0x3c
  main.main()
      /home/arne/src/golang.org/x/exp/shiny/example/basicgl/main.go:54 +0x3a
==================

Sometimes onConfigure even segfaults:

$ ./main
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x498 pc=0x49799c]

goroutine 21 [running]:
panic(0x56e6c0, 0xc42000c140)
	/home/arne/bin/go/src/runtime/panic.go:500 +0x1ae
golang.org/x/exp/shiny/driver/gldriver.onConfigure.func1(0xc420110000, 0x58900000358)
	/home/arne/src/golang.org/x/exp/shiny/driver/gldriver/x11.go:274 +0x6c
created by golang.org/x/exp/shiny/driver/gldriver.onConfigure
	/home/arne/src/golang.org/x/exp/shiny/driver/gldriver/x11.go:276 +0x14d

This behaviour is flaky and hard to reproduce. I use the i3 window manager, which re-sizes windows as soon as they are created. This may tickle the race.

Playing with w.glctxMu guarding w.glctx I could avoid the race, but I introduced deadlocks later on instead.

What version of Go are you using (go version)?

go version go1.7.1 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/arne"
GORACE=""
GOROOT="/home/arne/bin/go"
GOTOOLDIR="/home/arne/bin/go/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build838115997=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"

[barnex]

Thanks @nigeltao for the prompt fix: https://go-review.googlesource.com/#/c/34873/