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")

	-->
	<script src="wasm_exec.js"></script>
	<script>
		if (!WebAssembly.instantiateStreaming) { // polyfill
			WebAssembly.instantiateStreaming = async (resp, importObject) => {
				const source = await (await resp).arrayBuffer();
				return await WebAssembly.instantiate(source, importObject);
			};
		}

		const go = new Go();
		let mod, inst;
		WebAssembly.instantiateStreaming(fetch("test.wasm"), go.importObject).then((result) => {

			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))
		}
	}

	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.

	CLDEMOTE BX                      // ERROR "invalid instruction"
	// WAITPKG instructions:
	TPAUSE (BX)                      // ERROR "invalid instruction"
	UMONITOR (BX)                    // ERROR "invalid instruction"
	UMWAIT (BX)                      // ERROR "invalid instruction"
	// .Z instructions
	VMOVDQA32.Z Z0, Z1               // ERROR "mask register must be specified for .Z instructions"