parent: 14564:3350c94fe6b7 tip

test$ go run -race run.go

WARNING: DATA RACE
Read by goroutine 4:
  io/ioutil.nextSuffix()
      /usr/local/google/home/dvyukov/go_prefetch/src/pkg/io/ioutil/tempfile.go:25 +0x2d
  io/ioutil.TempDir()
      /usr/local/google/home/dvyukov/go_prefetch/src/pkg/io/ioutil/tempfile.go:77 +0xad
  main.(*test).makeTempDir()
      /usr/local/google/home/dvyukov/go_prefetch/test/run.go:496 +0x41
  main.(*test).run()
      /usr/local/google/home/dvyukov/go_prefetch/test/run.go:323 +0x74a
  main.func·001()
      /usr/local/google/home/dvyukov/go_prefetch/test/run.go:233 +0x3a

Previous write by goroutine 3:
  io/ioutil.nextSuffix()
      /usr/local/google/home/dvyukov/go_prefetch/src/pkg/io/ioutil/tempfile.go:30 +0x64
  io/ioutil.TempDir()
      /usr/local/google/home/dvyukov/go_prefetch/src/pkg/io/ioutil/tempfile.go:77 +0xad
  main.(*test).makeTempDir()
      /usr/local/google/home/dvyukov/go_prefetch/test/run.go:496 +0x41
  main.(*test).run()
      /usr/local/google/home/dvyukov/go_prefetch/test/run.go:323 +0x74a
  main.func·001()
      /usr/local/google/home/dvyukov/go_prefetch/test/run.go:233 +0x3a

Goroutine 4 (running) created at:
  main.runTests()
      /usr/local/google/home/dvyukov/go_prefetch/test/run.go:235 +0xc6

Goroutine 3 (running) created at:
  main.runTests()
      /usr/local/google/home/dvyukov/go_prefetch/test/run.go:235 +0xc6

This can break badly under gccgo:

var rand uint32
func nextSuffix() string {
        r := rand
        if r == 0 {
                r = reseed()
        }
        r = r*1664525 + 1013904223 // constants from Numerical Recipes
        rand = r
        return strconv.Itoa(int(1e9 + r%1e9))[1:]
}