src/os/timeout_test.go - go - Git at Google

 // Copyright 2017 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 !js
 // +build !plan9
 // +build !windows

 package os_test

 import (
 	"fmt"
 	"io"
 	"math/rand"
 	"os"
 	"os/signal"
 	"runtime"
 	"sync"
 	"syscall"
 	"testing"
 	"time"
 )

 func TestNonpollableDeadline(t *testing.T) {
 	// On BSD systems regular files seem to be pollable,
 	// so just run this test on Linux.
 	if runtime.GOOS != "linux" {
 		t.Skipf("skipping on %s", runtime.GOOS)
 	}

 	f, err := os.CreateTemp("", "ostest")
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer os.Remove(f.Name())
 	defer f.Close()
 	deadline := time.Now().Add(10 * time.Second)
 	if err := f.SetDeadline(deadline); err != os.ErrNoDeadline {
 		t.Errorf("SetDeadline on file returned %v, wanted %v", err, os.ErrNoDeadline)
 	}
 	if err := f.SetReadDeadline(deadline); err != os.ErrNoDeadline {
 		t.Errorf("SetReadDeadline on file returned %v, wanted %v", err, os.ErrNoDeadline)
 	}
 	if err := f.SetWriteDeadline(deadline); err != os.ErrNoDeadline {
 		t.Errorf("SetWriteDeadline on file returned %v, wanted %v", err, os.ErrNoDeadline)
 	}
 }

 // noDeadline is a zero time.Time value, which cancels a deadline.
 var noDeadline time.Time

 var readTimeoutTests = []struct {
 	timeout time.Duration
 	xerrs   [2]error // expected errors in transition
 }{
 	// Tests that read deadlines work, even if there's data ready
 	// to be read.
 	{-5 * time.Second, [2]error{os.ErrDeadlineExceeded, os.ErrDeadlineExceeded}},

 	{50 * time.Millisecond, [2]error{nil, os.ErrDeadlineExceeded}},
 }

 func TestReadTimeout(t *testing.T) {
 	t.Parallel()

 	r, w, err := os.Pipe()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer r.Close()
 	defer w.Close()

 	if _, err := w.Write([]byte("READ TIMEOUT TEST")); err != nil {
 		t.Fatal(err)
 	}

 	for i, tt := range readTimeoutTests {
 		if err := r.SetReadDeadline(time.Now().Add(tt.timeout)); err != nil {
 			t.Fatalf("#%d: %v", i, err)
 		}
 		var b [1]byte
 		for j, xerr := range tt.xerrs {
 			for {
 				n, err := r.Read(b[:])
 				if xerr != nil {
 					if !isDeadlineExceeded(err) {
 						t.Fatalf("#%d/%d: %v", i, j, err)
 					}
 				}
 				if err == nil {
 					time.Sleep(tt.timeout / 3)
 					continue
 				}
 				if n != 0 {
 					t.Fatalf("#%d/%d: read %d; want 0", i, j, n)
 				}
 				break
 			}
 		}
 	}
 }

 func TestReadTimeoutMustNotReturn(t *testing.T) {
 	t.Parallel()

 	r, w, err := os.Pipe()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer r.Close()
 	defer w.Close()

 	max := time.NewTimer(100 * time.Millisecond)
 	defer max.Stop()
 	ch := make(chan error)
 	go func() {
 		if err := r.SetDeadline(time.Now().Add(-5 * time.Second)); err != nil {
 			t.Error(err)
 		}
 		if err := r.SetWriteDeadline(time.Now().Add(-5 * time.Second)); err != nil {
 			t.Error(err)
 		}
 		if err := r.SetReadDeadline(noDeadline); err != nil {
 			t.Error(err)
 		}
 		var b [1]byte
 		_, err := r.Read(b[:])
 		ch <- err
 	}()

 	select {
 	case err := <-ch:
 		t.Fatalf("expected Read to not return, but it returned with %v", err)
 	case <-max.C:
 		w.Close()
 		err := <-ch // wait for tester goroutine to stop
 		if os.IsTimeout(err) {
 			t.Fatal(err)
 		}
 	}
 }

 var writeTimeoutTests = []struct {
 	timeout time.Duration
 	xerrs   [2]error // expected errors in transition
 }{
 	// Tests that write deadlines work, even if there's buffer
 	// space available to write.
 	{-5 * time.Second, [2]error{os.ErrDeadlineExceeded, os.ErrDeadlineExceeded}},

 	{10 * time.Millisecond, [2]error{nil, os.ErrDeadlineExceeded}},
 }

 func TestWriteTimeout(t *testing.T) {
 	t.Parallel()

 	for i, tt := range writeTimeoutTests {
 		t.Run(fmt.Sprintf("#%d", i), func(t *testing.T) {
 			r, w, err := os.Pipe()
 			if err != nil {
 				t.Fatal(err)
 			}
 			defer r.Close()
 			defer w.Close()

 			if err := w.SetWriteDeadline(time.Now().Add(tt.timeout)); err != nil {
 				t.Fatalf("%v", err)
 			}
 			for j, xerr := range tt.xerrs {
 				for {
 					n, err := w.Write([]byte("WRITE TIMEOUT TEST"))
 					if xerr != nil {
 						if !isDeadlineExceeded(err) {
 							t.Fatalf("%d: %v", j, err)
 						}
 					}
 					if err == nil {
 						time.Sleep(tt.timeout / 3)
 						continue
 					}
 					if n != 0 {
 						t.Fatalf("%d: wrote %d; want 0", j, n)
 					}
 					break
 				}
 			}
 		})
 	}
 }

 func TestWriteTimeoutMustNotReturn(t *testing.T) {
 	t.Parallel()

 	r, w, err := os.Pipe()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer r.Close()
 	defer w.Close()

 	max := time.NewTimer(100 * time.Millisecond)
 	defer max.Stop()
 	ch := make(chan error)
 	go func() {
 		if err := w.SetDeadline(time.Now().Add(-5 * time.Second)); err != nil {
 			t.Error(err)
 		}
 		if err := w.SetReadDeadline(time.Now().Add(-5 * time.Second)); err != nil {
 			t.Error(err)
 		}
 		if err := w.SetWriteDeadline(noDeadline); err != nil {
 			t.Error(err)
 		}
 		var b [1]byte
 		for {
 			if _, err := w.Write(b[:]); err != nil {
 				ch <- err
 				break
 			}
 		}
 	}()

 	select {
 	case err := <-ch:
 		t.Fatalf("expected Write to not return, but it returned with %v", err)
 	case <-max.C:
 		r.Close()
 		err := <-ch // wait for tester goroutine to stop
 		if os.IsTimeout(err) {
 			t.Fatal(err)
 		}
 	}
 }

 func timeoutReader(r *os.File, d, min, max time.Duration, ch chan<- error) {
 	var err error
 	defer func() { ch <- err }()

 	t0 := time.Now()
 	if err = r.SetReadDeadline(time.Now().Add(d)); err != nil {
 		return
 	}
 	b := make([]byte, 256)
 	var n int
 	n, err = r.Read(b)
 	t1 := time.Now()
 	if n != 0 || err == nil || !isDeadlineExceeded(err) {
 		err = fmt.Errorf("Read did not return (0, timeout): (%d, %v)", n, err)
 		return
 	}
 	if dt := t1.Sub(t0); min > dt || dt > max && !testing.Short() {
 		err = fmt.Errorf("Read took %s; expected %s", dt, d)
 		return
 	}
 }

 func TestReadTimeoutFluctuation(t *testing.T) {
 	t.Parallel()

 	r, w, err := os.Pipe()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer r.Close()
 	defer w.Close()

 	max := time.NewTimer(time.Second)
 	defer max.Stop()
 	ch := make(chan error)
 	go timeoutReader(r, 100*time.Millisecond, 50*time.Millisecond, 250*time.Millisecond, ch)

 	select {
 	case <-max.C:
 		t.Fatal("Read took over 1s; expected 0.1s")
 	case err := <-ch:
 		if !isDeadlineExceeded(err) {
 			t.Fatal(err)
 		}
 	}
 }

 func timeoutWriter(w *os.File, d, min, max time.Duration, ch chan<- error) {
 	var err error
 	defer func() { ch <- err }()

 	t0 := time.Now()
 	if err = w.SetWriteDeadline(time.Now().Add(d)); err != nil {
 		return
 	}
 	var n int
 	for {
 		n, err = w.Write([]byte("TIMEOUT WRITER"))
 		if err != nil {
 			break
 		}
 	}
 	t1 := time.Now()
 	if err == nil || !isDeadlineExceeded(err) {
 		err = fmt.Errorf("Write did not return (any, timeout): (%d, %v)", n, err)
 		return
 	}
 	if dt := t1.Sub(t0); min > dt || dt > max && !testing.Short() {
 		err = fmt.Errorf("Write took %s; expected %s", dt, d)
 		return
 	}
 }

 func TestWriteTimeoutFluctuation(t *testing.T) {
 	t.Parallel()

 	r, w, err := os.Pipe()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer r.Close()
 	defer w.Close()

 	d := time.Second
 	max := time.NewTimer(d)
 	defer max.Stop()
 	ch := make(chan error)
 	go timeoutWriter(w, 100*time.Millisecond, 50*time.Millisecond, 250*time.Millisecond, ch)

 	select {
 	case <-max.C:
 		t.Fatalf("Write took over %v; expected 0.1s", d)
 	case err := <-ch:
 		if !isDeadlineExceeded(err) {
 			t.Fatal(err)
 		}
 	}
 }

 func TestVariousDeadlines(t *testing.T) {
 	t.Parallel()
 	testVariousDeadlines(t)
 }

 func TestVariousDeadlines1Proc(t *testing.T) {
 	// Cannot use t.Parallel - modifies global GOMAXPROCS.
 	if testing.Short() {
 		t.Skip("skipping in short mode")
 	}
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
 	testVariousDeadlines(t)
 }

 func TestVariousDeadlines4Proc(t *testing.T) {
 	// Cannot use t.Parallel - modifies global GOMAXPROCS.
 	if testing.Short() {
 		t.Skip("skipping in short mode")
 	}
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
 	testVariousDeadlines(t)
 }

 type neverEnding byte

 func (b neverEnding) Read(p []byte) (int, error) {
 	for i := range p {
 		p[i] = byte(b)
 	}
 	return len(p), nil
 }

 func testVariousDeadlines(t *testing.T) {
 	type result struct {
 		n   int64
 		err error
 		d   time.Duration
 	}

 	handler := func(w *os.File, pasvch chan result) {
 		// The writer, with no timeouts of its own,
 		// sending bytes to clients as fast as it can.
 		t0 := time.Now()
 		n, err := io.Copy(w, neverEnding('a'))
 		dt := time.Since(t0)
 		pasvch <- result{n, err, dt}
 	}

 	for _, timeout := range []time.Duration{
 		1 * time.Nanosecond,
 		2 * time.Nanosecond,
 		5 * time.Nanosecond,
 		50 * time.Nanosecond,
 		100 * time.Nanosecond,
 		200 * time.Nanosecond,
 		500 * time.Nanosecond,
 		750 * time.Nanosecond,
 		1 * time.Microsecond,
 		5 * time.Microsecond,
 		25 * time.Microsecond,
 		250 * time.Microsecond,
 		500 * time.Microsecond,
 		1 * time.Millisecond,
 		5 * time.Millisecond,
 		100 * time.Millisecond,
 		250 * time.Millisecond,
 		500 * time.Millisecond,
 		1 * time.Second,
 	} {
 		numRuns := 3
 		if testing.Short() {
 			numRuns = 1
 			if timeout > 500*time.Microsecond {
 				continue
 			}
 		}
 		for run := 0; run < numRuns; run++ {
 			t.Run(fmt.Sprintf("%v-%d", timeout, run+1), func(t *testing.T) {
 				r, w, err := os.Pipe()
 				if err != nil {
 					t.Fatal(err)
 				}
 				defer r.Close()
 				defer w.Close()

 				pasvch := make(chan result)
 				go handler(w, pasvch)

 				tooLong := 5 * time.Second
 				max := time.NewTimer(tooLong)
 				defer max.Stop()
 				actvch := make(chan result)
 				go func() {
 					t0 := time.Now()
 					if err := r.SetDeadline(t0.Add(timeout)); err != nil {
 						t.Error(err)
 					}
 					n, err := io.Copy(io.Discard, r)
 					dt := time.Since(t0)
 					r.Close()
 					actvch <- result{n, err, dt}
 				}()

 				select {
 				case res := <-actvch:
 					if !isDeadlineExceeded(err) {
 						t.Logf("good client timeout after %v, reading %d bytes", res.d, res.n)
 					} else {
 						t.Fatalf("client Copy = %d, %v; want timeout", res.n, res.err)
 					}
 				case <-max.C:
 					t.Fatalf("timeout (%v) waiting for client to timeout (%v) reading", tooLong, timeout)
 				}

 				select {
 				case res := <-pasvch:
 					t.Logf("writer in %v wrote %d: %v", res.d, res.n, res.err)
 				case <-max.C:
 					t.Fatalf("timeout waiting for writer to finish writing")
 				}
 			})
 		}
 	}
 }

 func TestReadWriteDeadlineRace(t *testing.T) {
 	t.Parallel()

 	N := 1000
 	if testing.Short() {
 		N = 50
 	}

 	r, w, err := os.Pipe()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer r.Close()
 	defer w.Close()

 	var wg sync.WaitGroup
 	wg.Add(3)
 	go func() {
 		defer wg.Done()
 		tic := time.NewTicker(2 * time.Microsecond)
 		defer tic.Stop()
 		for i := 0; i < N; i++ {
 			if err := r.SetReadDeadline(time.Now().Add(2 * time.Microsecond)); err != nil {
 				break
 			}
 			if err := w.SetWriteDeadline(time.Now().Add(2 * time.Microsecond)); err != nil {
 				break
 			}
 			<-tic.C
 		}
 	}()
 	go func() {
 		defer wg.Done()
 		var b [1]byte
 		for i := 0; i < N; i++ {
 			_, err := r.Read(b[:])
 			if err != nil && !isDeadlineExceeded(err) {
 				t.Error("Read returned non-timeout error", err)
 			}
 		}
 	}()
 	go func() {
 		defer wg.Done()
 		var b [1]byte
 		for i := 0; i < N; i++ {
 			_, err := w.Write(b[:])
 			if err != nil && !isDeadlineExceeded(err) {
 				t.Error("Write returned non-timeout error", err)
 			}
 		}
 	}()
 	wg.Wait() // wait for tester goroutine to stop
 }

 // TestRacyRead tests that it is safe to mutate the input Read buffer
 // immediately after cancellation has occurred.
 func TestRacyRead(t *testing.T) {
 	t.Parallel()

 	r, w, err := os.Pipe()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer r.Close()
 	defer w.Close()

 	var wg sync.WaitGroup
 	defer wg.Wait()

 	go io.Copy(w, rand.New(rand.NewSource(0)))

 	r.SetReadDeadline(time.Now().Add(time.Millisecond))
 	for i := 0; i < 10; i++ {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()

 			b1 := make([]byte, 1024)
 			b2 := make([]byte, 1024)
 			for j := 0; j < 100; j++ {
 				_, err := r.Read(b1)
 				copy(b1, b2) // Mutate b1 to trigger potential race
 				if err != nil {
 					if !isDeadlineExceeded(err) {
 						t.Error(err)
 					}
 					r.SetReadDeadline(time.Now().Add(time.Millisecond))
 				}
 			}
 		}()
 	}
 }

 // TestRacyWrite tests that it is safe to mutate the input Write buffer
 // immediately after cancellation has occurred.
 func TestRacyWrite(t *testing.T) {
 	t.Parallel()

 	r, w, err := os.Pipe()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer r.Close()
 	defer w.Close()

 	var wg sync.WaitGroup
 	defer wg.Wait()

 	go io.Copy(io.Discard, r)

 	w.SetWriteDeadline(time.Now().Add(time.Millisecond))
 	for i := 0; i < 10; i++ {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()

 			b1 := make([]byte, 1024)
 			b2 := make([]byte, 1024)
 			for j := 0; j < 100; j++ {
 				_, err := w.Write(b1)
 				copy(b1, b2) // Mutate b1 to trigger potential race
 				if err != nil {
 					if !isDeadlineExceeded(err) {
 						t.Error(err)
 					}
 					w.SetWriteDeadline(time.Now().Add(time.Millisecond))
 				}
 			}
 		}()
 	}
 }

 // Closing a TTY while reading from it should not hang.  Issue 23943.
 func TestTTYClose(t *testing.T) {
 	// Ignore SIGTTIN in case we are running in the background.
 	signal.Ignore(syscall.SIGTTIN)
 	defer signal.Reset(syscall.SIGTTIN)

 	f, err := os.Open("/dev/tty")
 	if err != nil {
 		t.Skipf("skipping because opening /dev/tty failed: %v", err)
 	}

 	go func() {
 		var buf [1]byte
 		f.Read(buf[:])
 	}()

 	// Give the goroutine a chance to enter the read.
 	// It doesn't matter much if it occasionally fails to do so,
 	// we won't be testing what we want to test but the test will pass.
 	time.Sleep(time.Millisecond)

 	c := make(chan bool)
 	go func() {
 		defer close(c)
 		f.Close()
 	}()

 	select {
 	case <-c:
 	case <-time.After(time.Second):
 		t.Error("timed out waiting for close")
 	}

 	// On some systems the goroutines may now be hanging.
 	// There's not much we can do about that.
 }
	// Copyright 2017 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 !js
	// +build !plan9
	// +build !windows

	package os_test

	import (
	"fmt"
	"io"
	"math/rand"
	"os"
	"os/signal"
	"runtime"
	"sync"
	"syscall"
	"testing"
	"time"
	)

	func TestNonpollableDeadline(t *testing.T) {
	// On BSD systems regular files seem to be pollable,
	// so just run this test on Linux.
	if runtime.GOOS != "linux" {
	t.Skipf("skipping on %s", runtime.GOOS)
	}

	f, err := os.CreateTemp("", "ostest")
	if err != nil {
	t.Fatal(err)
	}
	defer os.Remove(f.Name())
	defer f.Close()
	deadline := time.Now().Add(10 * time.Second)
	if err := f.SetDeadline(deadline); err != os.ErrNoDeadline {
	t.Errorf("SetDeadline on file returned %v, wanted %v", err, os.ErrNoDeadline)
	}
	if err := f.SetReadDeadline(deadline); err != os.ErrNoDeadline {
	t.Errorf("SetReadDeadline on file returned %v, wanted %v", err, os.ErrNoDeadline)
	}
	if err := f.SetWriteDeadline(deadline); err != os.ErrNoDeadline {
	t.Errorf("SetWriteDeadline on file returned %v, wanted %v", err, os.ErrNoDeadline)
	}
	}

	// noDeadline is a zero time.Time value, which cancels a deadline.
	var noDeadline time.Time

	var readTimeoutTests = []struct {
	timeout time.Duration
	xerrs [2]error // expected errors in transition
	}{
	// Tests that read deadlines work, even if there's data ready
	// to be read.
	{-5 * time.Second, [2]error{os.ErrDeadlineExceeded, os.ErrDeadlineExceeded}},

	{50 * time.Millisecond, [2]error{nil, os.ErrDeadlineExceeded}},
	}

	func TestReadTimeout(t *testing.T) {
	t.Parallel()

	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer r.Close()
	defer w.Close()

	if _, err := w.Write([]byte("READ TIMEOUT TEST")); err != nil {
	t.Fatal(err)
	}

	for i, tt := range readTimeoutTests {
	if err := r.SetReadDeadline(time.Now().Add(tt.timeout)); err != nil {
	t.Fatalf("#%d: %v", i, err)
	}
	var b [1]byte
	for j, xerr := range tt.xerrs {
	for {
	n, err := r.Read(b[:])
	if xerr != nil {
	if !isDeadlineExceeded(err) {
	t.Fatalf("#%d/%d: %v", i, j, err)
	}
	}
	if err == nil {
	time.Sleep(tt.timeout / 3)
	continue
	}
	if n != 0 {
	t.Fatalf("#%d/%d: read %d; want 0", i, j, n)
	}
	break
	}
	}
	}
	}

	func TestReadTimeoutMustNotReturn(t *testing.T) {
	t.Parallel()

	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer r.Close()
	defer w.Close()

	max := time.NewTimer(100 * time.Millisecond)
	defer max.Stop()
	ch := make(chan error)
	go func() {
	if err := r.SetDeadline(time.Now().Add(-5 * time.Second)); err != nil {
	t.Error(err)
	}
	if err := r.SetWriteDeadline(time.Now().Add(-5 * time.Second)); err != nil {
	t.Error(err)
	}
	if err := r.SetReadDeadline(noDeadline); err != nil {
	t.Error(err)
	}
	var b [1]byte
	_, err := r.Read(b[:])
	ch <- err
	}()

	select {
	case err := <-ch:
	t.Fatalf("expected Read to not return, but it returned with %v", err)
	case <-max.C:
	w.Close()
	err := <-ch // wait for tester goroutine to stop
	if os.IsTimeout(err) {
	t.Fatal(err)
	}
	}
	}

	var writeTimeoutTests = []struct {
	timeout time.Duration
	xerrs [2]error // expected errors in transition
	}{
	// Tests that write deadlines work, even if there's buffer
	// space available to write.
	{-5 * time.Second, [2]error{os.ErrDeadlineExceeded, os.ErrDeadlineExceeded}},

	{10 * time.Millisecond, [2]error{nil, os.ErrDeadlineExceeded}},
	}

	func TestWriteTimeout(t *testing.T) {
	t.Parallel()

	for i, tt := range writeTimeoutTests {
	t.Run(fmt.Sprintf("#%d", i), func(t *testing.T) {
	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer r.Close()
	defer w.Close()

	if err := w.SetWriteDeadline(time.Now().Add(tt.timeout)); err != nil {
	t.Fatalf("%v", err)
	}
	for j, xerr := range tt.xerrs {
	for {
	n, err := w.Write([]byte("WRITE TIMEOUT TEST"))
	if xerr != nil {
	if !isDeadlineExceeded(err) {
	t.Fatalf("%d: %v", j, err)
	}
	}
	if err == nil {
	time.Sleep(tt.timeout / 3)
	continue
	}
	if n != 0 {
	t.Fatalf("%d: wrote %d; want 0", j, n)
	}
	break
	}
	}
	})
	}
	}

	func TestWriteTimeoutMustNotReturn(t *testing.T) {
	t.Parallel()

	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer r.Close()
	defer w.Close()

	max := time.NewTimer(100 * time.Millisecond)
	defer max.Stop()
	ch := make(chan error)
	go func() {
	if err := w.SetDeadline(time.Now().Add(-5 * time.Second)); err != nil {
	t.Error(err)
	}
	if err := w.SetReadDeadline(time.Now().Add(-5 * time.Second)); err != nil {
	t.Error(err)
	}
	if err := w.SetWriteDeadline(noDeadline); err != nil {
	t.Error(err)
	}
	var b [1]byte
	for {
	if _, err := w.Write(b[:]); err != nil {
	ch <- err
	break
	}
	}
	}()

	select {
	case err := <-ch:
	t.Fatalf("expected Write to not return, but it returned with %v", err)
	case <-max.C:
	r.Close()
	err := <-ch // wait for tester goroutine to stop
	if os.IsTimeout(err) {
	t.Fatal(err)
	}
	}
	}

	func timeoutReader(r *os.File, d, min, max time.Duration, ch chan<- error) {
	var err error
	defer func() { ch <- err }()

	t0 := time.Now()
	if err = r.SetReadDeadline(time.Now().Add(d)); err != nil {
	return
	}
	b := make([]byte, 256)
	var n int
	n, err = r.Read(b)
	t1 := time.Now()
	if n != 0 \|\| err == nil \|\| !isDeadlineExceeded(err) {
	err = fmt.Errorf("Read did not return (0, timeout): (%d, %v)", n, err)
	return
	}
	if dt := t1.Sub(t0); min > dt \|\| dt > max && !testing.Short() {
	err = fmt.Errorf("Read took %s; expected %s", dt, d)
	return
	}
	}

	func TestReadTimeoutFluctuation(t *testing.T) {
	t.Parallel()

	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer r.Close()
	defer w.Close()

	max := time.NewTimer(time.Second)
	defer max.Stop()
	ch := make(chan error)
	go timeoutReader(r, 100time.Millisecond, 50time.Millisecond, 250*time.Millisecond, ch)

	select {
	case <-max.C:
	t.Fatal("Read took over 1s; expected 0.1s")
	case err := <-ch:
	if !isDeadlineExceeded(err) {
	t.Fatal(err)
	}
	}
	}

	func timeoutWriter(w *os.File, d, min, max time.Duration, ch chan<- error) {
	var err error
	defer func() { ch <- err }()

	t0 := time.Now()
	if err = w.SetWriteDeadline(time.Now().Add(d)); err != nil {
	return
	}
	var n int
	for {
	n, err = w.Write([]byte("TIMEOUT WRITER"))
	if err != nil {
	break
	}
	}
	t1 := time.Now()
	if err == nil \|\| !isDeadlineExceeded(err) {
	err = fmt.Errorf("Write did not return (any, timeout): (%d, %v)", n, err)
	return
	}
	if dt := t1.Sub(t0); min > dt \|\| dt > max && !testing.Short() {
	err = fmt.Errorf("Write took %s; expected %s", dt, d)
	return
	}
	}

	func TestWriteTimeoutFluctuation(t *testing.T) {
	t.Parallel()

	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer r.Close()
	defer w.Close()

	d := time.Second
	max := time.NewTimer(d)
	defer max.Stop()
	ch := make(chan error)
	go timeoutWriter(w, 100time.Millisecond, 50time.Millisecond, 250*time.Millisecond, ch)

	select {
	case <-max.C:
	t.Fatalf("Write took over %v; expected 0.1s", d)
	case err := <-ch:
	if !isDeadlineExceeded(err) {
	t.Fatal(err)
	}
	}
	}

	func TestVariousDeadlines(t *testing.T) {
	t.Parallel()
	testVariousDeadlines(t)
	}

	func TestVariousDeadlines1Proc(t *testing.T) {
	// Cannot use t.Parallel - modifies global GOMAXPROCS.
	if testing.Short() {
	t.Skip("skipping in short mode")
	}
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
	testVariousDeadlines(t)
	}

	func TestVariousDeadlines4Proc(t *testing.T) {
	// Cannot use t.Parallel - modifies global GOMAXPROCS.
	if testing.Short() {
	t.Skip("skipping in short mode")
	}
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
	testVariousDeadlines(t)
	}

	type neverEnding byte

	func (b neverEnding) Read(p []byte) (int, error) {
	for i := range p {
	p[i] = byte(b)
	}
	return len(p), nil
	}

	func testVariousDeadlines(t *testing.T) {
	type result struct {
	n int64
	err error
	d time.Duration
	}

	handler := func(w *os.File, pasvch chan result) {
	// The writer, with no timeouts of its own,
	// sending bytes to clients as fast as it can.
	t0 := time.Now()
	n, err := io.Copy(w, neverEnding('a'))
	dt := time.Since(t0)
	pasvch <- result{n, err, dt}
	}

	for _, timeout := range []time.Duration{
	1 * time.Nanosecond,
	2 * time.Nanosecond,
	5 * time.Nanosecond,
	50 * time.Nanosecond,
	100 * time.Nanosecond,
	200 * time.Nanosecond,
	500 * time.Nanosecond,
	750 * time.Nanosecond,
	1 * time.Microsecond,
	5 * time.Microsecond,
	25 * time.Microsecond,
	250 * time.Microsecond,
	500 * time.Microsecond,
	1 * time.Millisecond,
	5 * time.Millisecond,
	100 * time.Millisecond,
	250 * time.Millisecond,
	500 * time.Millisecond,
	1 * time.Second,
	} {
	numRuns := 3
	if testing.Short() {
	numRuns = 1
	if timeout > 500*time.Microsecond {
	continue
	}
	}
	for run := 0; run < numRuns; run++ {
	t.Run(fmt.Sprintf("%v-%d", timeout, run+1), func(t *testing.T) {
	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer r.Close()
	defer w.Close()

	pasvch := make(chan result)
	go handler(w, pasvch)

	tooLong := 5 * time.Second
	max := time.NewTimer(tooLong)
	defer max.Stop()
	actvch := make(chan result)
	go func() {
	t0 := time.Now()
	if err := r.SetDeadline(t0.Add(timeout)); err != nil {
	t.Error(err)
	}
	n, err := io.Copy(io.Discard, r)
	dt := time.Since(t0)
	r.Close()
	actvch <- result{n, err, dt}
	}()

	select {
	case res := <-actvch:
	if !isDeadlineExceeded(err) {
	t.Logf("good client timeout after %v, reading %d bytes", res.d, res.n)
	} else {
	t.Fatalf("client Copy = %d, %v; want timeout", res.n, res.err)
	}
	case <-max.C:
	t.Fatalf("timeout (%v) waiting for client to timeout (%v) reading", tooLong, timeout)
	}

	select {
	case res := <-pasvch:
	t.Logf("writer in %v wrote %d: %v", res.d, res.n, res.err)
	case <-max.C:
	t.Fatalf("timeout waiting for writer to finish writing")
	}
	})
	}
	}
	}

	func TestReadWriteDeadlineRace(t *testing.T) {
	t.Parallel()

	N := 1000
	if testing.Short() {
	N = 50
	}

	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer r.Close()
	defer w.Close()

	var wg sync.WaitGroup
	wg.Add(3)
	go func() {
	defer wg.Done()
	tic := time.NewTicker(2 * time.Microsecond)
	defer tic.Stop()
	for i := 0; i < N; i++ {
	if err := r.SetReadDeadline(time.Now().Add(2 * time.Microsecond)); err != nil {
	break
	}
	if err := w.SetWriteDeadline(time.Now().Add(2 * time.Microsecond)); err != nil {
	break
	}
	<-tic.C
	}
	}()
	go func() {
	defer wg.Done()
	var b [1]byte
	for i := 0; i < N; i++ {
	_, err := r.Read(b[:])
	if err != nil && !isDeadlineExceeded(err) {
	t.Error("Read returned non-timeout error", err)
	}
	}
	}()
	go func() {
	defer wg.Done()
	var b [1]byte
	for i := 0; i < N; i++ {
	_, err := w.Write(b[:])
	if err != nil && !isDeadlineExceeded(err) {
	t.Error("Write returned non-timeout error", err)
	}
	}
	}()
	wg.Wait() // wait for tester goroutine to stop
	}

	// TestRacyRead tests that it is safe to mutate the input Read buffer
	// immediately after cancellation has occurred.
	func TestRacyRead(t *testing.T) {
	t.Parallel()

	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer r.Close()
	defer w.Close()

	var wg sync.WaitGroup
	defer wg.Wait()

	go io.Copy(w, rand.New(rand.NewSource(0)))

	r.SetReadDeadline(time.Now().Add(time.Millisecond))
	for i := 0; i < 10; i++ {
	wg.Add(1)
	go func() {
	defer wg.Done()

	b1 := make([]byte, 1024)
	b2 := make([]byte, 1024)
	for j := 0; j < 100; j++ {
	_, err := r.Read(b1)
	copy(b1, b2) // Mutate b1 to trigger potential race
	if err != nil {
	if !isDeadlineExceeded(err) {
	t.Error(err)
	}
	r.SetReadDeadline(time.Now().Add(time.Millisecond))
	}
	}
	}()
	}
	}

	// TestRacyWrite tests that it is safe to mutate the input Write buffer
	// immediately after cancellation has occurred.
	func TestRacyWrite(t *testing.T) {
	t.Parallel()

	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer r.Close()
	defer w.Close()

	var wg sync.WaitGroup
	defer wg.Wait()

	go io.Copy(io.Discard, r)

	w.SetWriteDeadline(time.Now().Add(time.Millisecond))
	for i := 0; i < 10; i++ {
	wg.Add(1)
	go func() {
	defer wg.Done()

	b1 := make([]byte, 1024)
	b2 := make([]byte, 1024)
	for j := 0; j < 100; j++ {
	_, err := w.Write(b1)
	copy(b1, b2) // Mutate b1 to trigger potential race
	if err != nil {
	if !isDeadlineExceeded(err) {
	t.Error(err)
	}
	w.SetWriteDeadline(time.Now().Add(time.Millisecond))
	}
	}
	}()
	}
	}

	// Closing a TTY while reading from it should not hang. Issue 23943.
	func TestTTYClose(t *testing.T) {
	// Ignore SIGTTIN in case we are running in the background.
	signal.Ignore(syscall.SIGTTIN)
	defer signal.Reset(syscall.SIGTTIN)

	f, err := os.Open("/dev/tty")
	if err != nil {
	t.Skipf("skipping because opening /dev/tty failed: %v", err)
	}

	go func() {
	var buf [1]byte
	f.Read(buf[:])
	}()

	// Give the goroutine a chance to enter the read.
	// It doesn't matter much if it occasionally fails to do so,
	// we won't be testing what we want to test but the test will pass.
	time.Sleep(time.Millisecond)

	c := make(chan bool)
	go func() {
	defer close(c)
	f.Close()
	}()

	select {
	case <-c:
	case <-time.After(time.Second):
	t.Error("timed out waiting for close")
	}

	// On some systems the goroutines may now be hanging.
	// There's not much we can do about that.
	}