var wg sync.WaitGroup
	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			var buf [1]byte
			r.ReadAt(buf[:], int64(i))
		}(i)
	}
	wg.Wait()
}

func TestEmptyReaderConcurrent(t *testing.T) {
	// Test for the race detector, to verify a Read that doesn't yield any bytes
	// is okay to use from multiple goroutines. This was our historic behavior.

			log.Printf(" url %s has #%s", url, id)
		}
		fragExists[urlFrag{url, id}] = true
	}
	return nil
}

func main() {
	flag.Parse()

	go crawlLoop()
	crawl(*root, "")

	wg.Wait()
	close(urlq)
	for uf, needers := range neededFrags {
		if !fragExists[uf] {
			problems = append(problems, fmt.Sprintf("Missing fragment for %+v from %v", uf, needers))
		}
	}

				time.Sleep(time.Millisecond)
				continue
			}

			t.Error(err)
			return
		}
		cmds = append(cmds, cmd)
	}

	failures := 0
	for _, cmd := range cmds {
		err := cmd.Wait()
		if err == nil {
			continue
		}

		t.Errorf("syscall.Exec failed: %v\n%s", err, cmd.Stdout)
		failures++
	}

	if failures > 0 {
		t.Logf("Failed %v of %v attempts.", failures, len(cmds))

	for _, context := range contexts {
		context := context
		wg.Add(1)
		go func() {
			defer wg.Done()
			_ = NewWalker(context, filepath.Join(testenv.GOROOT(nil), "src"))
		}()
	}
	wg.Wait()
})

func TestIssue21181(t *testing.T) {
	if testing.Short() {
		t.Skip("skipping with -short")
	}
	if *flagCheck {
		// slow, not worth repeating in -check
		t.Skip("skipping with -check set")

linkage to the desired libraries. The main function is provided by
_cgo_main.c:

	int main() { return 0; }
	void crosscall2(void(*fn)(void*), void *a, int c, uintptr_t ctxt) { }
	uintptr_t _cgo_wait_runtime_init_done(void) { return 0; }
	void _cgo_release_context(uintptr_t ctxt) { }
	char* _cgo_topofstack(void) { return (char*)0; }
	void _cgo_allocate(void *a, int c) { }
	void _cgo_panic(void *a, int c) { }

		return 0, err
	}

	// In case we're booting a device or emulator alongside all.bash, wait for
	// it to be ready. adb wait-for-device is not enough, we have to
	// wait for sys.boot_completed.
	if err := adb("wait-for-device", "exec-out", "while [[ -z $(getprop sys.boot_completed) ]]; do sleep 1; done;"); err != nil {
		return 0, err
	}

	// Done once per make.bash.

	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	if err := cmd.Start(); err != nil {
		return nil, fmt.Errorf("idevicedebugserverproxy: %v", err)
	}
	go func() {
		if err := cmd.Wait(); err != nil {
			if _, ok := err.(*exec.ExitError); ok {
				errChan <- fmt.Errorf("idevicedebugserverproxy: %s", stderr.Bytes())
			} else {
				errChan <- fmt.Errorf("idevicedebugserverproxy: %v", err)
			}
		}

	for i, context := range contexts {
		i, context := i, context
		wg.Add(1)
		go func() {
			defer wg.Done()
			walkers[i] = NewWalker(context, filepath.Join(testenv.GOROOT(t), "src"))
		}()
	}
	wg.Wait()

	var featureCtx = make(map[string]map[string]bool) // feature -> context name -> true
	for _, w := range walkers {
		for _, name := range w.stdPackages {
			pkg, err := w.import_(name)