libgo/go/os/signal/signal_test.go - gofrontend - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // +build aix darwin dragonfly freebsd hurd linux netbsd openbsd solaris

 package signal

 import (
 	"bytes"
 	"flag"
 	"fmt"
 	"internal/testenv"
 	"io/ioutil"
 	"os"
 	"os/exec"
 	"runtime"
 	"strconv"
 	"sync"
 	"syscall"
 	"testing"
 	"time"
 )

 var testDeadline time.Time

 func TestMain(m *testing.M) {
 	flag.Parse()

 	// TODO(golang.org/issue/28135): Remove this setup and use t.Deadline instead.
 	timeoutFlag := flag.Lookup("test.timeout")
 	if timeoutFlag != nil {
 		if d := timeoutFlag.Value.(flag.Getter).Get().(time.Duration); d != 0 {
 			testDeadline = time.Now().Add(d)
 		}
 	}

 	os.Exit(m.Run())
 }

 func waitSig(t *testing.T, c <-chan os.Signal, sig os.Signal) {
 	waitSig1(t, c, sig, false)
 }
 func waitSigAll(t *testing.T, c <-chan os.Signal, sig os.Signal) {
 	waitSig1(t, c, sig, true)
 }

 func waitSig1(t *testing.T, c <-chan os.Signal, sig os.Signal, all bool) {
 	// Sleep multiple times to give the kernel more tries to
 	// deliver the signal.
 	for i := 0; i < 10; i++ {
 		select {
 		case s := <-c:
 			// If the caller notified for all signals on
 			// c, filter out SIGURG, which is used for
 			// runtime preemption and can come at
 			// unpredictable times.
 			if all && s == syscall.SIGURG {
 				continue
 			}
 			if s != sig {
 				t.Fatalf("signal was %v, want %v", s, sig)
 			}
 			return

 		case <-time.After(100 * time.Millisecond):
 		}
 	}
 	t.Fatalf("timeout waiting for %v", sig)
 }

 // Test that basic signal handling works.
 func TestSignal(t *testing.T) {
 	// Ask for SIGHUP
 	c := make(chan os.Signal, 1)
 	Notify(c, syscall.SIGHUP)
 	defer Stop(c)

 	// Send this process a SIGHUP
 	t.Logf("sighup...")
 	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
 	waitSig(t, c, syscall.SIGHUP)

 	// Ask for everything we can get. The buffer size has to be
 	// more than 1, since the runtime might send SIGURG signals.
 	// Using 10 is arbitrary.
 	c1 := make(chan os.Signal, 10)
 	Notify(c1)

 	// Send this process a SIGWINCH
 	t.Logf("sigwinch...")
 	syscall.Kill(syscall.Getpid(), syscall.SIGWINCH)
 	waitSigAll(t, c1, syscall.SIGWINCH)

 	// Send two more SIGHUPs, to make sure that
 	// they get delivered on c1 and that not reading
 	// from c does not block everything.
 	t.Logf("sighup...")
 	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
 	waitSigAll(t, c1, syscall.SIGHUP)
 	t.Logf("sighup...")
 	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
 	waitSigAll(t, c1, syscall.SIGHUP)

 	// The first SIGHUP should be waiting for us on c.
 	waitSig(t, c, syscall.SIGHUP)
 }

 func TestStress(t *testing.T) {
 	dur := 3 * time.Second
 	if testing.Short() {
 		dur = 100 * time.Millisecond
 	}
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
 	done := make(chan bool)
 	finished := make(chan bool)
 	go func() {
 		sig := make(chan os.Signal, 1)
 		Notify(sig, syscall.SIGUSR1)
 		defer Stop(sig)
 	Loop:
 		for {
 			select {
 			case <-sig:
 			case <-done:
 				break Loop
 			}
 		}
 		finished <- true
 	}()
 	go func() {
 	Loop:
 		for {
 			select {
 			case <-done:
 				break Loop
 			default:
 				syscall.Kill(syscall.Getpid(), syscall.SIGUSR1)
 				runtime.Gosched()
 			}
 		}
 		finished <- true
 	}()
 	time.Sleep(dur)
 	close(done)
 	<-finished
 	<-finished
 	// When run with 'go test -cpu=1,2,4' SIGUSR1 from this test can slip
 	// into subsequent TestSignal() causing failure.
 	// Sleep for a while to reduce the possibility of the failure.
 	time.Sleep(10 * time.Millisecond)
 }

 func testCancel(t *testing.T, ignore bool) {
 	// Send SIGWINCH. By default this signal should be ignored.
 	syscall.Kill(syscall.Getpid(), syscall.SIGWINCH)
 	time.Sleep(100 * time.Millisecond)

 	// Ask to be notified on c1 when a SIGWINCH is received.
 	c1 := make(chan os.Signal, 1)
 	Notify(c1, syscall.SIGWINCH)
 	defer Stop(c1)

 	// Ask to be notified on c2 when a SIGHUP is received.
 	c2 := make(chan os.Signal, 1)
 	Notify(c2, syscall.SIGHUP)
 	defer Stop(c2)

 	// Send this process a SIGWINCH and wait for notification on c1.
 	syscall.Kill(syscall.Getpid(), syscall.SIGWINCH)
 	waitSig(t, c1, syscall.SIGWINCH)

 	// Send this process a SIGHUP and wait for notification on c2.
 	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
 	waitSig(t, c2, syscall.SIGHUP)

 	// Ignore, or reset the signal handlers for, SIGWINCH and SIGHUP.
 	if ignore {
 		Ignore(syscall.SIGWINCH, syscall.SIGHUP)
 	} else {
 		Reset(syscall.SIGWINCH, syscall.SIGHUP)
 	}

 	// At this point we do not expect any further signals on c1.
 	// However, it is just barely possible that the initial SIGWINCH
 	// at the start of this function was delivered after we called
 	// Notify on c1. In that case the waitSig for SIGWINCH may have
 	// picked up that initial SIGWINCH, and the second SIGWINCH may
 	// then have been delivered on the channel. This sequence of events
 	// may have caused issue 15661.
 	// So, read any possible signal from the channel now.
 	select {
 	case <-c1:
 	default:
 	}

 	// Send this process a SIGWINCH. It should be ignored.
 	syscall.Kill(syscall.Getpid(), syscall.SIGWINCH)

 	// If ignoring, Send this process a SIGHUP. It should be ignored.
 	if ignore {
 		syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
 	}

 	select {
 	case s := <-c1:
 		t.Fatalf("unexpected signal %v", s)
 	case <-time.After(100 * time.Millisecond):
 		// nothing to read - good
 	}

 	select {
 	case s := <-c2:
 		t.Fatalf("unexpected signal %v", s)
 	case <-time.After(100 * time.Millisecond):
 		// nothing to read - good
 	}

 	// Reset the signal handlers for all signals.
 	Reset()
 }

 // Test that Reset cancels registration for listed signals on all channels.
 func TestReset(t *testing.T) {
 	testCancel(t, false)
 }

 // Test that Ignore cancels registration for listed signals on all channels.
 func TestIgnore(t *testing.T) {
 	testCancel(t, true)
 }

 // Test that Ignored correctly detects changes to the ignored status of a signal.
 func TestIgnored(t *testing.T) {
 	// Ask to be notified on SIGWINCH.
 	c := make(chan os.Signal, 1)
 	Notify(c, syscall.SIGWINCH)

 	// If we're being notified, then the signal should not be ignored.
 	if Ignored(syscall.SIGWINCH) {
 		t.Errorf("expected SIGWINCH to not be ignored.")
 	}
 	Stop(c)
 	Ignore(syscall.SIGWINCH)

 	// We're no longer paying attention to this signal.
 	if !Ignored(syscall.SIGWINCH) {
 		t.Errorf("expected SIGWINCH to be ignored when explicitly ignoring it.")
 	}

 	Reset()
 }

 var checkSighupIgnored = flag.Bool("check_sighup_ignored", false, "if true, TestDetectNohup will fail if SIGHUP is not ignored.")

 // Test that Ignored(SIGHUP) correctly detects whether it is being run under nohup.
 func TestDetectNohup(t *testing.T) {
 	if *checkSighupIgnored {
 		if !Ignored(syscall.SIGHUP) {
 			t.Fatal("SIGHUP is not ignored.")
 		} else {
 			t.Log("SIGHUP is ignored.")
 		}
 	} else {
 		defer Reset()
 		// Ugly: ask for SIGHUP so that child will not have no-hup set
 		// even if test is running under nohup environment.
 		// We have no intention of reading from c.
 		c := make(chan os.Signal, 1)
 		Notify(c, syscall.SIGHUP)
 		if out, err := exec.Command(os.Args[0], "-test.run=TestDetectNohup", "-check_sighup_ignored").CombinedOutput(); err == nil {
 			t.Errorf("ran test with -check_sighup_ignored and it succeeded: expected failure.\nOutput:\n%s", out)
 		}
 		Stop(c)
 		// Again, this time with nohup, assuming we can find it.
 		_, err := os.Stat("/usr/bin/nohup")
 		if err != nil {
 			t.Skip("cannot find nohup; skipping second half of test")
 		}
 		Ignore(syscall.SIGHUP)
 		os.Remove("nohup.out")
 		out, err := exec.Command("/usr/bin/nohup", os.Args[0], "-test.run=TestDetectNohup", "-check_sighup_ignored").CombinedOutput()

 		data, _ := ioutil.ReadFile("nohup.out")
 		os.Remove("nohup.out")
 		if err != nil {
 			t.Errorf("ran test with -check_sighup_ignored under nohup and it failed: expected success.\nError: %v\nOutput:\n%s%s", err, out, data)
 		}
 	}
 }

 var sendUncaughtSighup = flag.Int("send_uncaught_sighup", 0, "send uncaught SIGHUP during TestStop")

 // Test that Stop cancels the channel's registrations.
 func TestStop(t *testing.T) {
 	sigs := []syscall.Signal{
 		syscall.SIGWINCH,
 		syscall.SIGHUP,
 		syscall.SIGUSR1,
 	}

 	for _, sig := range sigs {
 		// Send the signal.
 		// If it's SIGWINCH, we should not see it.
 		// If it's SIGHUP, maybe we'll die. Let the flag tell us what to do.
 		if sig == syscall.SIGWINCH || (sig == syscall.SIGHUP && *sendUncaughtSighup == 1) {
 			syscall.Kill(syscall.Getpid(), sig)
 		}

 		// The kernel will deliver a signal as a thread returns
 		// from a syscall. If the only active thread is sleeping,
 		// and the system is busy, the kernel may not get around
 		// to waking up a thread to catch the signal.
 		// We try splitting up the sleep to give the kernel
 		// another chance to deliver the signal.
 		time.Sleep(50 * time.Millisecond)
 		time.Sleep(50 * time.Millisecond)

 		// Ask for signal
 		c := make(chan os.Signal, 1)
 		Notify(c, sig)
 		defer Stop(c)

 		// Send this process that signal
 		syscall.Kill(syscall.Getpid(), sig)
 		waitSig(t, c, sig)

 		Stop(c)
 		time.Sleep(50 * time.Millisecond)
 		select {
 		case s := <-c:
 			t.Fatalf("unexpected signal %v", s)
 		case <-time.After(50 * time.Millisecond):
 			// nothing to read - good
 		}

 		// Send the signal.
 		// If it's SIGWINCH, we should not see it.
 		// If it's SIGHUP, maybe we'll die. Let the flag tell us what to do.
 		if sig != syscall.SIGHUP || *sendUncaughtSighup == 2 {
 			syscall.Kill(syscall.Getpid(), sig)
 		}

 		time.Sleep(50 * time.Millisecond)
 		select {
 		case s := <-c:
 			t.Fatalf("unexpected signal %v", s)
 		case <-time.After(50 * time.Millisecond):
 			// nothing to read - good
 		}
 	}
 }

 // Test that when run under nohup, an uncaught SIGHUP does not kill the program,
 // but a
 func TestNohup(t *testing.T) {
 	// Ugly: ask for SIGHUP so that child will not have no-hup set
 	// even if test is running under nohup environment.
 	// We have no intention of reading from c.
 	c := make(chan os.Signal, 1)
 	Notify(c, syscall.SIGHUP)

 	// When run without nohup, the test should crash on an uncaught SIGHUP.
 	// When run under nohup, the test should ignore uncaught SIGHUPs,
 	// because the runtime is not supposed to be listening for them.
 	// Either way, TestStop should still be able to catch them when it wants them
 	// and then when it stops wanting them, the original behavior should resume.
 	//
 	// send_uncaught_sighup=1 sends the SIGHUP before starting to listen for SIGHUPs.
 	// send_uncaught_sighup=2 sends the SIGHUP after no longer listening for SIGHUPs.
 	//
 	// Both should fail without nohup and succeed with nohup.

 	for i := 1; i <= 2; i++ {
 		out, err := exec.Command(os.Args[0], "-test.run=TestStop", "-send_uncaught_sighup="+strconv.Itoa(i)).CombinedOutput()
 		if err == nil {
 			t.Fatalf("ran test with -send_uncaught_sighup=%d and it succeeded: expected failure.\nOutput:\n%s", i, out)
 		}
 	}

 	Stop(c)

 	// Skip the nohup test below when running in tmux on darwin, since nohup
 	// doesn't work correctly there. See issue #5135.
 	if runtime.GOOS == "darwin" && os.Getenv("TMUX") != "" {
 		t.Skip("Skipping nohup test due to running in tmux on darwin")
 	}

 	// Again, this time with nohup, assuming we can find it.
 	_, err := os.Stat("/usr/bin/nohup")
 	if err != nil {
 		t.Skip("cannot find nohup; skipping second half of test")
 	}

 	for i := 1; i <= 2; i++ {
 		os.Remove("nohup.out")
 		out, err := exec.Command("/usr/bin/nohup", os.Args[0], "-test.run=TestStop", "-send_uncaught_sighup="+strconv.Itoa(i)).CombinedOutput()

 		data, _ := ioutil.ReadFile("nohup.out")
 		os.Remove("nohup.out")
 		if err != nil {
 			t.Fatalf("ran test with -send_uncaught_sighup=%d under nohup and it failed: expected success.\nError: %v\nOutput:\n%s%s", i, err, out, data)
 		}
 	}
 }

 // Test that SIGCONT works (issue 8953).
 func TestSIGCONT(t *testing.T) {
 	c := make(chan os.Signal, 1)
 	Notify(c, syscall.SIGCONT)
 	defer Stop(c)
 	syscall.Kill(syscall.Getpid(), syscall.SIGCONT)
 	waitSig(t, c, syscall.SIGCONT)
 }

 // Test race between stopping and receiving a signal (issue 14571).
 func TestAtomicStop(t *testing.T) {
 	if os.Getenv("GO_TEST_ATOMIC_STOP") != "" {
 		atomicStopTestProgram()
 		t.Fatal("atomicStopTestProgram returned")
 	}

 	testenv.MustHaveExec(t)

 	// Call Notify for SIGINT before starting the child process.
 	// That ensures that SIGINT is not ignored for the child.
 	// This is necessary because if SIGINT is ignored when a
 	// Go program starts, then it remains ignored, and closing
 	// the last notification channel for SIGINT will switch it
 	// back to being ignored. In that case the assumption of
 	// atomicStopTestProgram, that it will either die from SIGINT
 	// or have it be reported, breaks down, as there is a third
 	// option: SIGINT might be ignored.
 	cs := make(chan os.Signal, 1)
 	Notify(cs, syscall.SIGINT)
 	defer Stop(cs)

 	const execs = 10
 	for i := 0; i < execs; i++ {
 		timeout := "0"
 		if !testDeadline.IsZero() {
 			timeout = testDeadline.Sub(time.Now()).String()
 		}
 		cmd := exec.Command(os.Args[0], "-test.run=TestAtomicStop", "-test.timeout="+timeout)
 		cmd.Env = append(os.Environ(), "GO_TEST_ATOMIC_STOP=1")
 		out, err := cmd.CombinedOutput()
 		if err == nil {
 			if len(out) > 0 {
 				t.Logf("iteration %d: output %s", i, out)
 			}
 		} else {
 			t.Logf("iteration %d: exit status %q: output: %s", i, err, out)
 		}

 		lost := bytes.Contains(out, []byte("lost signal"))
 		if lost {
 			t.Errorf("iteration %d: lost signal", i)
 		}

 		// The program should either die due to SIGINT,
 		// or exit with success without printing "lost signal".
 		if err == nil {
 			if len(out) > 0 && !lost {
 				t.Errorf("iteration %d: unexpected output", i)
 			}
 		} else {
 			if ee, ok := err.(*exec.ExitError); !ok {
 				t.Errorf("iteration %d: error (%v) has type %T; expected exec.ExitError", i, err, err)
 			} else if ws, ok := ee.Sys().(syscall.WaitStatus); !ok {
 				t.Errorf("iteration %d: error.Sys (%v) has type %T; expected syscall.WaitStatus", i, ee.Sys(), ee.Sys())
 			} else if !ws.Signaled() || ws.Signal() != syscall.SIGINT {
 				t.Errorf("iteration %d: got exit status %v; expected SIGINT", i, ee)
 			}
 		}
 	}
 }

 // atomicStopTestProgram is run in a subprocess by TestAtomicStop.
 // It tries to trigger a signal delivery race. This function should
 // either catch a signal or die from it.
 func atomicStopTestProgram() {
 	// This test won't work if SIGINT is ignored here.
 	if Ignored(syscall.SIGINT) {
 		fmt.Println("SIGINT is ignored")
 		os.Exit(1)
 	}

 	const tries = 10

 	timeout := 2 * time.Second
 	if !testDeadline.IsZero() {
 		// Give each try an equal slice of the deadline, with one slice to spare for
 		// cleanup.
 		timeout = testDeadline.Sub(time.Now()) / (tries + 1)
 	}

 	pid := syscall.Getpid()
 	printed := false
 	for i := 0; i < tries; i++ {
 		cs := make(chan os.Signal, 1)
 		Notify(cs, syscall.SIGINT)

 		var wg sync.WaitGroup
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
 			Stop(cs)
 		}()

 		syscall.Kill(pid, syscall.SIGINT)

 		// At this point we should either die from SIGINT or
 		// get a notification on cs. If neither happens, we
 		// dropped the signal. It is given 2 seconds to
 		// deliver, as needed for gccgo on some loaded test systems.

 		select {
 		case <-cs:
 		case <-time.After(timeout):
 			if !printed {
 				fmt.Print("lost signal on tries:")
 				printed = true
 			}
 			fmt.Printf(" %d", i)
 		}

 		wg.Wait()
 	}
 	if printed {
 		fmt.Print("\n")
 	}

 	os.Exit(0)
 }

 func TestTime(t *testing.T) {
 	// Test that signal works fine when we are in a call to get time,
 	// which on some platforms is using VDSO. See issue #34391.
 	dur := 3 * time.Second
 	if testing.Short() {
 		dur = 100 * time.Millisecond
 	}
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
 	done := make(chan bool)
 	finished := make(chan bool)
 	go func() {
 		sig := make(chan os.Signal, 1)
 		Notify(sig, syscall.SIGUSR1)
 		defer Stop(sig)
 	Loop:
 		for {
 			select {
 			case <-sig:
 			case <-done:
 				break Loop
 			}
 		}
 		finished <- true
 	}()
 	go func() {
 	Loop:
 		for {
 			select {
 			case <-done:
 				break Loop
 			default:
 				syscall.Kill(syscall.Getpid(), syscall.SIGUSR1)
 				runtime.Gosched()
 			}
 		}
 		finished <- true
 	}()
 	t0 := time.Now()
 	for t1 := t0; t1.Sub(t0) < dur; t1 = time.Now() {
 	} // hammering on getting time
 	close(done)
 	<-finished
 	<-finished
 	// When run with 'go test -cpu=1,2,4' SIGUSR1 from this test can slip
 	// into subsequent TestSignal() causing failure.
 	// Sleep for a while to reduce the possibility of the failure.
 	time.Sleep(10 * time.Millisecond)
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// +build aix darwin dragonfly freebsd hurd linux netbsd openbsd solaris

	package signal

	import (
	"bytes"
	"flag"
	"fmt"
	"internal/testenv"
	"io/ioutil"
	"os"
	"os/exec"
	"runtime"
	"strconv"
	"sync"
	"syscall"
	"testing"
	"time"
	)

	var testDeadline time.Time

	func TestMain(m *testing.M) {
	flag.Parse()

	// TODO(golang.org/issue/28135): Remove this setup and use t.Deadline instead.
	timeoutFlag := flag.Lookup("test.timeout")
	if timeoutFlag != nil {
	if d := timeoutFlag.Value.(flag.Getter).Get().(time.Duration); d != 0 {
	testDeadline = time.Now().Add(d)
	}
	}

	os.Exit(m.Run())
	}

	func waitSig(t *testing.T, c <-chan os.Signal, sig os.Signal) {
	waitSig1(t, c, sig, false)
	}
	func waitSigAll(t *testing.T, c <-chan os.Signal, sig os.Signal) {
	waitSig1(t, c, sig, true)
	}

	func waitSig1(t *testing.T, c <-chan os.Signal, sig os.Signal, all bool) {
	// Sleep multiple times to give the kernel more tries to
	// deliver the signal.
	for i := 0; i < 10; i++ {
	select {
	case s := <-c:
	// If the caller notified for all signals on
	// c, filter out SIGURG, which is used for
	// runtime preemption and can come at
	// unpredictable times.
	if all && s == syscall.SIGURG {
	continue
	}
	if s != sig {
	t.Fatalf("signal was %v, want %v", s, sig)
	}
	return

	case <-time.After(100 * time.Millisecond):
	}
	}
	t.Fatalf("timeout waiting for %v", sig)
	}

	// Test that basic signal handling works.
	func TestSignal(t *testing.T) {
	// Ask for SIGHUP
	c := make(chan os.Signal, 1)
	Notify(c, syscall.SIGHUP)
	defer Stop(c)

	// Send this process a SIGHUP
	t.Logf("sighup...")
	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
	waitSig(t, c, syscall.SIGHUP)

	// Ask for everything we can get. The buffer size has to be
	// more than 1, since the runtime might send SIGURG signals.
	// Using 10 is arbitrary.
	c1 := make(chan os.Signal, 10)
	Notify(c1)

	// Send this process a SIGWINCH
	t.Logf("sigwinch...")
	syscall.Kill(syscall.Getpid(), syscall.SIGWINCH)
	waitSigAll(t, c1, syscall.SIGWINCH)

	// Send two more SIGHUPs, to make sure that
	// they get delivered on c1 and that not reading
	// from c does not block everything.
	t.Logf("sighup...")
	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
	waitSigAll(t, c1, syscall.SIGHUP)
	t.Logf("sighup...")
	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
	waitSigAll(t, c1, syscall.SIGHUP)

	// The first SIGHUP should be waiting for us on c.
	waitSig(t, c, syscall.SIGHUP)
	}

	func TestStress(t *testing.T) {
	dur := 3 * time.Second
	if testing.Short() {
	dur = 100 * time.Millisecond
	}
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
	done := make(chan bool)
	finished := make(chan bool)
	go func() {
	sig := make(chan os.Signal, 1)
	Notify(sig, syscall.SIGUSR1)
	defer Stop(sig)
	Loop:
	for {
	select {
	case <-sig:
	case <-done:
	break Loop
	}
	}
	finished <- true
	}()
	go func() {
	Loop:
	for {
	select {
	case <-done:
	break Loop
	default:
	syscall.Kill(syscall.Getpid(), syscall.SIGUSR1)
	runtime.Gosched()
	}
	}
	finished <- true
	}()
	time.Sleep(dur)
	close(done)
	<-finished
	<-finished
	// When run with 'go test -cpu=1,2,4' SIGUSR1 from this test can slip
	// into subsequent TestSignal() causing failure.
	// Sleep for a while to reduce the possibility of the failure.
	time.Sleep(10 * time.Millisecond)
	}

	func testCancel(t *testing.T, ignore bool) {
	// Send SIGWINCH. By default this signal should be ignored.
	syscall.Kill(syscall.Getpid(), syscall.SIGWINCH)
	time.Sleep(100 * time.Millisecond)

	// Ask to be notified on c1 when a SIGWINCH is received.
	c1 := make(chan os.Signal, 1)
	Notify(c1, syscall.SIGWINCH)
	defer Stop(c1)

	// Ask to be notified on c2 when a SIGHUP is received.
	c2 := make(chan os.Signal, 1)
	Notify(c2, syscall.SIGHUP)
	defer Stop(c2)

	// Send this process a SIGWINCH and wait for notification on c1.
	syscall.Kill(syscall.Getpid(), syscall.SIGWINCH)
	waitSig(t, c1, syscall.SIGWINCH)

	// Send this process a SIGHUP and wait for notification on c2.
	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
	waitSig(t, c2, syscall.SIGHUP)

	// Ignore, or reset the signal handlers for, SIGWINCH and SIGHUP.
	if ignore {
	Ignore(syscall.SIGWINCH, syscall.SIGHUP)
	} else {
	Reset(syscall.SIGWINCH, syscall.SIGHUP)
	}

	// At this point we do not expect any further signals on c1.
	// However, it is just barely possible that the initial SIGWINCH
	// at the start of this function was delivered after we called
	// Notify on c1. In that case the waitSig for SIGWINCH may have
	// picked up that initial SIGWINCH, and the second SIGWINCH may
	// then have been delivered on the channel. This sequence of events
	// may have caused issue 15661.
	// So, read any possible signal from the channel now.
	select {
	case <-c1:
	default:
	}

	// Send this process a SIGWINCH. It should be ignored.
	syscall.Kill(syscall.Getpid(), syscall.SIGWINCH)

	// If ignoring, Send this process a SIGHUP. It should be ignored.
	if ignore {
	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
	}

	select {
	case s := <-c1:
	t.Fatalf("unexpected signal %v", s)
	case <-time.After(100 * time.Millisecond):
	// nothing to read - good
	}

	select {
	case s := <-c2:
	t.Fatalf("unexpected signal %v", s)
	case <-time.After(100 * time.Millisecond):
	// nothing to read - good
	}

	// Reset the signal handlers for all signals.
	Reset()
	}

	// Test that Reset cancels registration for listed signals on all channels.
	func TestReset(t *testing.T) {
	testCancel(t, false)
	}

	// Test that Ignore cancels registration for listed signals on all channels.
	func TestIgnore(t *testing.T) {
	testCancel(t, true)
	}

	// Test that Ignored correctly detects changes to the ignored status of a signal.
	func TestIgnored(t *testing.T) {
	// Ask to be notified on SIGWINCH.
	c := make(chan os.Signal, 1)
	Notify(c, syscall.SIGWINCH)

	// If we're being notified, then the signal should not be ignored.
	if Ignored(syscall.SIGWINCH) {
	t.Errorf("expected SIGWINCH to not be ignored.")
	}
	Stop(c)
	Ignore(syscall.SIGWINCH)

	// We're no longer paying attention to this signal.
	if !Ignored(syscall.SIGWINCH) {
	t.Errorf("expected SIGWINCH to be ignored when explicitly ignoring it.")
	}

	Reset()
	}

	var checkSighupIgnored = flag.Bool("check_sighup_ignored", false, "if true, TestDetectNohup will fail if SIGHUP is not ignored.")

	// Test that Ignored(SIGHUP) correctly detects whether it is being run under nohup.
	func TestDetectNohup(t *testing.T) {
	if *checkSighupIgnored {
	if !Ignored(syscall.SIGHUP) {
	t.Fatal("SIGHUP is not ignored.")
	} else {
	t.Log("SIGHUP is ignored.")
	}
	} else {
	defer Reset()
	// Ugly: ask for SIGHUP so that child will not have no-hup set
	// even if test is running under nohup environment.
	// We have no intention of reading from c.
	c := make(chan os.Signal, 1)
	Notify(c, syscall.SIGHUP)
	if out, err := exec.Command(os.Args[0], "-test.run=TestDetectNohup", "-check_sighup_ignored").CombinedOutput(); err == nil {
	t.Errorf("ran test with -check_sighup_ignored and it succeeded: expected failure.\nOutput:\n%s", out)
	}
	Stop(c)
	// Again, this time with nohup, assuming we can find it.
	_, err := os.Stat("/usr/bin/nohup")
	if err != nil {
	t.Skip("cannot find nohup; skipping second half of test")
	}
	Ignore(syscall.SIGHUP)
	os.Remove("nohup.out")
	out, err := exec.Command("/usr/bin/nohup", os.Args[0], "-test.run=TestDetectNohup", "-check_sighup_ignored").CombinedOutput()

	data, _ := ioutil.ReadFile("nohup.out")
	os.Remove("nohup.out")
	if err != nil {
	t.Errorf("ran test with -check_sighup_ignored under nohup and it failed: expected success.\nError: %v\nOutput:\n%s%s", err, out, data)
	}
	}
	}

	var sendUncaughtSighup = flag.Int("send_uncaught_sighup", 0, "send uncaught SIGHUP during TestStop")

	// Test that Stop cancels the channel's registrations.
	func TestStop(t *testing.T) {
	sigs := []syscall.Signal{
	syscall.SIGWINCH,
	syscall.SIGHUP,
	syscall.SIGUSR1,
	}

	for _, sig := range sigs {
	// Send the signal.
	// If it's SIGWINCH, we should not see it.
	// If it's SIGHUP, maybe we'll die. Let the flag tell us what to do.
	if sig == syscall.SIGWINCH \|\| (sig == syscall.SIGHUP && *sendUncaughtSighup == 1) {
	syscall.Kill(syscall.Getpid(), sig)
	}

	// The kernel will deliver a signal as a thread returns
	// from a syscall. If the only active thread is sleeping,
	// and the system is busy, the kernel may not get around
	// to waking up a thread to catch the signal.
	// We try splitting up the sleep to give the kernel
	// another chance to deliver the signal.
	time.Sleep(50 * time.Millisecond)
	time.Sleep(50 * time.Millisecond)

	// Ask for signal
	c := make(chan os.Signal, 1)
	Notify(c, sig)
	defer Stop(c)

	// Send this process that signal
	syscall.Kill(syscall.Getpid(), sig)
	waitSig(t, c, sig)

	Stop(c)
	time.Sleep(50 * time.Millisecond)
	select {
	case s := <-c:
	t.Fatalf("unexpected signal %v", s)
	case <-time.After(50 * time.Millisecond):
	// nothing to read - good
	}

	// Send the signal.
	// If it's SIGWINCH, we should not see it.
	// If it's SIGHUP, maybe we'll die. Let the flag tell us what to do.
	if sig != syscall.SIGHUP \|\| *sendUncaughtSighup == 2 {
	syscall.Kill(syscall.Getpid(), sig)
	}

	time.Sleep(50 * time.Millisecond)
	select {
	case s := <-c:
	t.Fatalf("unexpected signal %v", s)
	case <-time.After(50 * time.Millisecond):
	// nothing to read - good
	}
	}
	}

	// Test that when run under nohup, an uncaught SIGHUP does not kill the program,
	// but a
	func TestNohup(t *testing.T) {
	// Ugly: ask for SIGHUP so that child will not have no-hup set
	// even if test is running under nohup environment.
	// We have no intention of reading from c.
	c := make(chan os.Signal, 1)
	Notify(c, syscall.SIGHUP)

	// When run without nohup, the test should crash on an uncaught SIGHUP.
	// When run under nohup, the test should ignore uncaught SIGHUPs,
	// because the runtime is not supposed to be listening for them.
	// Either way, TestStop should still be able to catch them when it wants them
	// and then when it stops wanting them, the original behavior should resume.
	//
	// send_uncaught_sighup=1 sends the SIGHUP before starting to listen for SIGHUPs.
	// send_uncaught_sighup=2 sends the SIGHUP after no longer listening for SIGHUPs.
	//
	// Both should fail without nohup and succeed with nohup.

	for i := 1; i <= 2; i++ {
	out, err := exec.Command(os.Args[0], "-test.run=TestStop", "-send_uncaught_sighup="+strconv.Itoa(i)).CombinedOutput()
	if err == nil {
	t.Fatalf("ran test with -send_uncaught_sighup=%d and it succeeded: expected failure.\nOutput:\n%s", i, out)
	}
	}

	Stop(c)

	// Skip the nohup test below when running in tmux on darwin, since nohup
	// doesn't work correctly there. See issue #5135.
	if runtime.GOOS == "darwin" && os.Getenv("TMUX") != "" {
	t.Skip("Skipping nohup test due to running in tmux on darwin")
	}

	// Again, this time with nohup, assuming we can find it.
	_, err := os.Stat("/usr/bin/nohup")
	if err != nil {
	t.Skip("cannot find nohup; skipping second half of test")
	}

	for i := 1; i <= 2; i++ {
	os.Remove("nohup.out")
	out, err := exec.Command("/usr/bin/nohup", os.Args[0], "-test.run=TestStop", "-send_uncaught_sighup="+strconv.Itoa(i)).CombinedOutput()

	data, _ := ioutil.ReadFile("nohup.out")
	os.Remove("nohup.out")
	if err != nil {
	t.Fatalf("ran test with -send_uncaught_sighup=%d under nohup and it failed: expected success.\nError: %v\nOutput:\n%s%s", i, err, out, data)
	}
	}
	}

	// Test that SIGCONT works (issue 8953).
	func TestSIGCONT(t *testing.T) {
	c := make(chan os.Signal, 1)
	Notify(c, syscall.SIGCONT)
	defer Stop(c)
	syscall.Kill(syscall.Getpid(), syscall.SIGCONT)
	waitSig(t, c, syscall.SIGCONT)
	}

	// Test race between stopping and receiving a signal (issue 14571).
	func TestAtomicStop(t *testing.T) {
	if os.Getenv("GO_TEST_ATOMIC_STOP") != "" {
	atomicStopTestProgram()
	t.Fatal("atomicStopTestProgram returned")
	}

	testenv.MustHaveExec(t)

	// Call Notify for SIGINT before starting the child process.
	// That ensures that SIGINT is not ignored for the child.
	// This is necessary because if SIGINT is ignored when a
	// Go program starts, then it remains ignored, and closing
	// the last notification channel for SIGINT will switch it
	// back to being ignored. In that case the assumption of
	// atomicStopTestProgram, that it will either die from SIGINT
	// or have it be reported, breaks down, as there is a third
	// option: SIGINT might be ignored.
	cs := make(chan os.Signal, 1)
	Notify(cs, syscall.SIGINT)
	defer Stop(cs)

	const execs = 10
	for i := 0; i < execs; i++ {
	timeout := "0"
	if !testDeadline.IsZero() {
	timeout = testDeadline.Sub(time.Now()).String()
	}
	cmd := exec.Command(os.Args[0], "-test.run=TestAtomicStop", "-test.timeout="+timeout)
	cmd.Env = append(os.Environ(), "GO_TEST_ATOMIC_STOP=1")
	out, err := cmd.CombinedOutput()
	if err == nil {
	if len(out) > 0 {
	t.Logf("iteration %d: output %s", i, out)
	}
	} else {
	t.Logf("iteration %d: exit status %q: output: %s", i, err, out)
	}

	lost := bytes.Contains(out, []byte("lost signal"))
	if lost {
	t.Errorf("iteration %d: lost signal", i)
	}

	// The program should either die due to SIGINT,
	// or exit with success without printing "lost signal".
	if err == nil {
	if len(out) > 0 && !lost {
	t.Errorf("iteration %d: unexpected output", i)
	}
	} else {
	if ee, ok := err.(*exec.ExitError); !ok {
	t.Errorf("iteration %d: error (%v) has type %T; expected exec.ExitError", i, err, err)
	} else if ws, ok := ee.Sys().(syscall.WaitStatus); !ok {
	t.Errorf("iteration %d: error.Sys (%v) has type %T; expected syscall.WaitStatus", i, ee.Sys(), ee.Sys())
	} else if !ws.Signaled() \|\| ws.Signal() != syscall.SIGINT {
	t.Errorf("iteration %d: got exit status %v; expected SIGINT", i, ee)
	}
	}
	}
	}

	// atomicStopTestProgram is run in a subprocess by TestAtomicStop.
	// It tries to trigger a signal delivery race. This function should
	// either catch a signal or die from it.
	func atomicStopTestProgram() {
	// This test won't work if SIGINT is ignored here.
	if Ignored(syscall.SIGINT) {
	fmt.Println("SIGINT is ignored")
	os.Exit(1)
	}

	const tries = 10

	timeout := 2 * time.Second
	if !testDeadline.IsZero() {
	// Give each try an equal slice of the deadline, with one slice to spare for
	// cleanup.
	timeout = testDeadline.Sub(time.Now()) / (tries + 1)
	}

	pid := syscall.Getpid()
	printed := false
	for i := 0; i < tries; i++ {
	cs := make(chan os.Signal, 1)
	Notify(cs, syscall.SIGINT)

	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
	defer wg.Done()
	Stop(cs)
	}()

	syscall.Kill(pid, syscall.SIGINT)

	// At this point we should either die from SIGINT or
	// get a notification on cs. If neither happens, we
	// dropped the signal. It is given 2 seconds to
	// deliver, as needed for gccgo on some loaded test systems.

	select {
	case <-cs:
	case <-time.After(timeout):
	if !printed {
	fmt.Print("lost signal on tries:")
	printed = true
	}
	fmt.Printf(" %d", i)
	}

	wg.Wait()
	}
	if printed {
	fmt.Print("\n")
	}

	os.Exit(0)
	}

	func TestTime(t *testing.T) {
	// Test that signal works fine when we are in a call to get time,
	// which on some platforms is using VDSO. See issue #34391.
	dur := 3 * time.Second
	if testing.Short() {
	dur = 100 * time.Millisecond
	}
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
	done := make(chan bool)
	finished := make(chan bool)
	go func() {
	sig := make(chan os.Signal, 1)
	Notify(sig, syscall.SIGUSR1)
	defer Stop(sig)
	Loop:
	for {
	select {
	case <-sig:
	case <-done:
	break Loop
	}
	}
	finished <- true
	}()
	go func() {
	Loop:
	for {
	select {
	case <-done:
	break Loop
	default:
	syscall.Kill(syscall.Getpid(), syscall.SIGUSR1)
	runtime.Gosched()
	}
	}
	finished <- true
	}()
	t0 := time.Now()
	for t1 := t0; t1.Sub(t0) < dur; t1 = time.Now() {
	} // hammering on getting time
	close(done)
	<-finished
	<-finished
	// When run with 'go test -cpu=1,2,4' SIGUSR1 from this test can slip
	// into subsequent TestSignal() causing failure.
	// Sleep for a while to reduce the possibility of the failure.
	time.Sleep(10 * time.Millisecond)
	}