os: add deadline methods for File type

Add SetDeadline, SetReadDeadline, and SetWriteDeadline methods to os.File,
just as they exist today for the net package.

Fixes #22114

Change-Id: I4d390d739169b991175baba676010897dc8568fa
Reviewed-on: https://go-review.googlesource.com/71770
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>

src/internal/poll/fd.go

@@ -21,6 +21,10 @@ var ErrNetClosing = errors.New("use of closed network connection")
 // has been closed.
 var ErrFileClosing = errors.New("use of closed file")
 
+// ErrNoDeadline is returned when a request is made to set a deadline
+// on a file type that does not use the poller.
+var ErrNoDeadline = errors.New("file type does not support deadline")
+
 // Return the appropriate closing error based on isFile.
 func errClosing(isFile bool) error {
 	if isFile {

src/internal/poll/fd_poll_runtime.go

@@ -149,7 +149,7 @@ func setDeadlineImpl(fd *FD, t time.Time, mode int) error {
 	}
 	defer fd.decref()
 	if fd.pd.runtimeCtx == 0 {
-		return errors.New("file type does not support deadlines")
+		return ErrNoDeadline
 	}
 	runtime_pollSetDeadline(fd.pd.runtimeCtx, d, mode)
 	return nil

src/os/error.go

@@ -6,6 +6,7 @@ package os
 
 import (
 	"errors"
+	"internal/poll"
 )
 
 // Portable analogs of some common system call errors.
@@ -15,8 +16,13 @@ var (
 	ErrExist      = errors.New("file already exists")
 	ErrNotExist   = errors.New("file does not exist")
 	ErrClosed     = errors.New("file already closed")
+	ErrNoDeadline = poll.ErrNoDeadline
 )
 
+type timeout interface {
+	Timeout() bool
+}
+
 // PathError records an error and the operation and file path that caused it.
 type PathError struct {
 	Op   string
@@ -26,6 +32,12 @@ type PathError struct {
 
 func (e *PathError) Error() string { return e.Op + " " + e.Path + ": " + e.Err.Error() }
 
+// Timeout reports whether this error represents a timeout.
+func (e *PathError) Timeout() bool {
+	t, ok := e.Err.(timeout)
+	return ok && t.Timeout()
+}
+
 // SyscallError records an error from a specific system call.
 type SyscallError struct {
 	Syscall string
@@ -34,6 +46,12 @@ type SyscallError struct {
 
 func (e *SyscallError) Error() string { return e.Syscall + ": " + e.Err.Error() }
 
+// Timeout reports whether this error represents a timeout.
+func (e *SyscallError) Timeout() bool {
+	t, ok := e.Err.(timeout)
+	return ok && t.Timeout()
+}
+
 // NewSyscallError returns, as an error, a new SyscallError
 // with the given system call name and error details.
 // As a convenience, if err is nil, NewSyscallError returns nil.
@@ -65,6 +83,13 @@ func IsPermission(err error) bool {
 	return isPermission(err)
 }
 
+// IsTimeout returns a boolean indicating whether the error is known
+// to report that a timeout occurred.
+func IsTimeout(err error) bool {
+	terr, ok := underlyingError(err).(timeout)
+	return ok && terr.Timeout()
+}
+
 // underlyingError returns the underlying error for known os error types.
 func underlyingError(err error) error {
 	switch err := err.(type) {

src/os/file.go

@@ -41,6 +41,7 @@ import (
 	"internal/poll"
 	"io"
 	"syscall"
+	"time"
 )
 
 // Name returns the name of the file as presented to Open.
@@ -316,3 +317,47 @@ func Chmod(name string, mode FileMode) error { return chmod(name, mode) }
 // Chmod changes the mode of the file to mode.
 // If there is an error, it will be of type *PathError.
 func (f *File) Chmod(mode FileMode) error { return f.chmod(mode) }
+
+// SetDeadline sets the read and write deadlines for a File.
+// It is equivalent to calling both SetReadDeadline and SetWriteDeadline.
+//
+// Only some kinds of files support setting a deadline. Calls to SetDeadline
+// for files that do not support deadlines will return ErrNoDeadline.
+// On most systems ordinary files do not support deadlines, but pipes do.
+//
+// A deadline is an absolute time after which I/O operations fail with an
+// error instead of blocking. The deadline applies to all future and pending
+// I/O, not just the immediately following call to Read or Write.
+// After a deadline has been exceeded, the connection can be refreshed
+// by setting a deadline in the future.
+//
+// An error returned after a timeout fails will implement the
+// Timeout method, and calling the Timeout method will return true.
+// The PathError and SyscallError types implement the Timeout method.
+// In general, call IsTimeout to test whether an error indicates a timeout.
+//
+// An idle timeout can be implemented by repeatedly extending
+// the deadline after successful Read or Write calls.
+//
+// A zero value for t means I/O operations will not time out.
+func (f *File) SetDeadline(t time.Time) error {
+	return f.setDeadline(t)
+}
+
+// SetReadDeadline sets the deadline for future Read calls and any
+// currently-blocked Read call.
+// A zero value for t means Read will not time out.
+// Not all files support setting deadlines; see SetDeadline.
+func (f *File) SetReadDeadline(t time.Time) error {
+	return f.setReadDeadline(t)
+}
+
+// SetWriteDeadline sets the deadline for any future Write calls and any
+// currently-blocked Write call.
+// Even if Write times out, it may return n > 0, indicating that
+// some of the data was successfully written.
+// A zero value for t means Write will not time out.
+// Not all files support setting deadlines; see SetDeadline.
+func (f *File) SetWriteDeadline(t time.Time) error {
+	return f.setWriteDeadline(t)
+}

src/os/file_plan9.go

@@ -5,6 +5,7 @@
 package os
 
 import (
+	"internal/poll"
 	"io"
 	"runtime"
 	"syscall"
@@ -491,6 +492,30 @@ func (f *File) Chdir() error {
 	return nil
 }
 
+// setDeadline sets the read and write deadline.
+func (f *File) setDeadline(time.Time) error {
+	if err := f.checkValid("SetDeadline"); err != nil {
+		return err
+	}
+	return poll.ErrNoDeadline
+}
+
+// setReadDeadline sets the read deadline.
+func (f *File) setReadDeadline(time.Time) error {
+	if err := f.checkValid("SetReadDeadline"); err != nil {
+		return err
+	}
+	return poll.ErrNoDeadline
+}
+
+// setWriteDeadline sets the write deadline.
+func (f *File) setWriteDeadline(time.Time) error {
+	if err := f.checkValid("SetWriteDeadline"); err != nil {
+		return err
+	}
+	return poll.ErrNoDeadline
+}
+
 // checkValid checks whether f is valid for use.
 // If not, it returns an appropriate error, perhaps incorporating the operation name op.
 func (f *File) checkValid(op string) error {

src/os/file_posix.go

@@ -159,6 +159,30 @@ func (f *File) Chdir() error {
 	return nil
 }
 
+// setDeadline sets the read and write deadline.
+func (f *File) setDeadline(t time.Time) error {
+	if err := f.checkValid("SetDeadline"); err != nil {
+		return err
+	}
+	return f.pfd.SetDeadline(t)
+}
+
+// setReadDeadline sets the read deadline.
+func (f *File) setReadDeadline(t time.Time) error {
+	if err := f.checkValid("SetReadDeadline"); err != nil {
+		return err
+	}
+	return f.pfd.SetReadDeadline(t)
+}
+
+// setWriteDeadline sets the write deadline.
+func (f *File) setWriteDeadline(t time.Time) error {
+	if err := f.checkValid("SetWriteDeadline"); err != nil {
+		return err
+	}
+	return f.pfd.SetWriteDeadline(t)
+}
+
 // checkValid checks whether f is valid for use.
 // If not, it returns an appropriate error, perhaps incorporating the operation name op.
 func (f *File) checkValid(op string) error {

src/os/file_unix.go

@@ -75,12 +75,22 @@ func (f *File) Fd() uintptr {
 // name. The returned value will be nil if fd is not a valid file
 // descriptor.
 func NewFile(fd uintptr, name string) *File {
-	return newFile(fd, name, false)
+	return newFile(fd, name, kindNewFile)
 }
 
-// newFile is like NewFile, but if pollable is true it tries to add the
-// file to the runtime poller.
-func newFile(fd uintptr, name string, pollable bool) *File {
+// newFileKind describes the kind of file to newFile.
+type newFileKind int
+
+const (
+	kindNewFile newFileKind = iota
+	kindOpenFile
+	kindPipe
+)
+
+// newFile is like NewFile, but if called from OpenFile or Pipe
+// (as passed in the kind parameter) it tries to add the file to
+// the runtime poller.
+func newFile(fd uintptr, name string, kind newFileKind) *File {
 	fdi := int(fd)
 	if fdi < 0 {
 		return nil
@@ -98,10 +108,11 @@ func newFile(fd uintptr, name string, pollable bool) *File {
 	// Don't try to use kqueue with regular files on FreeBSD.
 	// It crashes the system unpredictably while running all.bash.
 	// Issue 19093.
-	if runtime.GOOS == "freebsd" {
-		pollable = false
+	if runtime.GOOS == "freebsd" && kind == kindOpenFile {
+		kind = kindNewFile
 	}
 
+	pollable := kind == kindOpenFile || kind == kindPipe
 	if err := f.pfd.Init("file", pollable); err != nil {
 		// An error here indicates a failure to register
 		// with the netpoll system. That can happen for
@@ -183,7 +194,7 @@ func OpenFile(name string, flag int, perm FileMode) (*File, error) {
 		syscall.CloseOnExec(r)
 	}
 
-	return newFile(uintptr(r), name, true), nil
+	return newFile(uintptr(r), name, kindOpenFile), nil
 }
 
 // Close closes the File, rendering it unusable for I/O.

src/os/pipe_bsd.go

@@ -24,5 +24,5 @@ func Pipe() (r *File, w *File, err error) {
 	syscall.CloseOnExec(p[1])
 	syscall.ForkLock.RUnlock()
 
-	return newFile(uintptr(p[0]), "|0", true), newFile(uintptr(p[1]), "|1", true), nil
+	return newFile(uintptr(p[0]), "|0", kindPipe), newFile(uintptr(p[1]), "|1", kindPipe), nil
 }

src/os/pipe_freebsd.go

@@ -30,5 +30,5 @@ func Pipe() (r *File, w *File, err error) {
 		syscall.ForkLock.RUnlock()
 	}
 
-	return newFile(uintptr(p[0]), "|0", true), newFile(uintptr(p[1]), "|1", true), nil
+	return newFile(uintptr(p[0]), "|0", kindPipe), newFile(uintptr(p[1]), "|1", kindPipe), nil
 }

src/os/pipe_linux.go

@@ -29,5 +29,5 @@ func Pipe() (r *File, w *File, err error) {
 		return nil, nil, NewSyscallError("pipe2", e)
 	}
 
-	return newFile(uintptr(p[0]), "|0", true), newFile(uintptr(p[1]), "|1", true), nil
+	return newFile(uintptr(p[0]), "|0", kindPipe), newFile(uintptr(p[1]), "|1", kindPipe), nil
 }

src/os/timeout_test.go

@@ -0,0 +1,589 @@
+// 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 !nacl
+// +build !plan9
+// +build !windows
+
+package os_test
+
+import (
+	"fmt"
+	"internal/poll"
+	"io"
+	"io/ioutil"
+	"math/rand"
+	"os"
+	"runtime"
+	"sync"
+	"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 := ioutil.TempFile("", "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{poll.ErrTimeout, poll.ErrTimeout}},
+
+	{50 * time.Millisecond, [2]error{nil, poll.ErrTimeout}},
+}
+
+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 !os.IsTimeout(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{poll.ErrTimeout, poll.ErrTimeout}},
+
+	{10 * time.Millisecond, [2]error{nil, poll.ErrTimeout}},
+}
+
+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 !os.IsTimeout(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 || !os.IsTimeout(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 !os.IsTimeout(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 || !os.IsTimeout(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 !os.IsTimeout(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(ioutil.Discard, r)
+					dt := time.Since(t0)
+					r.Close()
+					actvch <- result{n, err, dt}
+				}()
+
+				select {
+				case res := <-actvch:
+					if os.IsTimeout(res.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 && !os.IsTimeout(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 && !os.IsTimeout(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 cancelation 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 !os.IsTimeout(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 cancelation 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(ioutil.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 !os.IsTimeout(err) {
+						t.Error(err)
+					}
+					w.SetWriteDeadline(time.Now().Add(time.Millisecond))
+				}
+			}
+		}()
+	}
+}