net: fix data races on deadline vars

Fixes #4434.

This proposal replaces the previous CL 6855110. Due to issue 599, 64-bit atomic operations should probably be avoided, so use a sync.Mutex instead.

Benchmark comparisons against 025b9d070a85 on linux/386:

CL 6855110:

benchmark                        old ns/op    new ns/op    delta
BenchmarkTCPOneShot                 710024       727409   +2.45%
BenchmarkTCPOneShotTimeout          758178       768620   +1.38%
BenchmarkTCPPersistent              223464       228058   +2.06%
BenchmarkTCPPersistentTimeout       234494       242600   +3.46%

This proposal:

benchmark                        old ns/op    new ns/op    delta
BenchmarkTCPOneShot                 710024       718492   +1.19%
BenchmarkTCPOneShotTimeout          758178       748783   -1.24%
BenchmarkTCPPersistent              223464       227628   +1.86%
BenchmarkTCPPersistentTimeout       234494       238321   +1.63%

R=rsc, dvyukov, mikioh.mikioh, alex.brainman, bradfitz
CC=golang-dev, remyoudompheng
https://golang.org/cl/6866050

src/pkg/net/fd_posix_test.go

+// Copyright 2012 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 darwin freebsd linux netbsd openbsd windows
+
+package net
+
+import (
+	"testing"
+	"time"
+)
+
+var deadlineSetTimeTests = []struct {
+	input    time.Time
+	expected int64
+}{
+	{time.Time{}, 0},
+	{time.Date(2009, 11, 10, 23, 00, 00, 00, time.UTC), 1257894000000000000}, // 2009-11-10 23:00:00 +0000 UTC
+}
+
+func TestDeadlineSetTime(t *testing.T) {
+	for _, tt := range deadlineSetTimeTests {
+		var d deadline
+		d.setTime(tt.input)
+		actual := d.value()
+		expected := int64(0)
+		if !tt.input.IsZero() {
+			expected = tt.input.UnixNano()
+		}
+		if actual != expected {
+			t.Errorf("set/value failed: expected %v, actual %v", expected, actual)
+		}
+	}
+}
+
+var deadlineExpiredTests = []struct {
+	deadline time.Time
+	expired  bool
+}{
+	// note, times are relative to the start of the test run, not
+	// the start of TestDeadlineExpired
+	{time.Now().Add(5 * time.Minute), false},
+	{time.Now().Add(-5 * time.Minute), true},
+	{time.Time{}, false}, // no deadline set
+}
+
+func TestDeadlineExpired(t *testing.T) {
+	for _, tt := range deadlineExpiredTests {
+		var d deadline
+		d.set(tt.deadline.UnixNano())
+		expired := d.expired()
+		if expired != tt.expired {
+			t.Errorf("expire failed: expected %v, actual %v", tt.expired, expired)
+		}
+	}
+}

src/pkg/net/fd_unix.go

@@ -37,11 +37,11 @@ type netFD struct {
 	laddr       Addr
 	raddr       Addr
 
-	// owned by client
-	rdeadline int64
-	rio       sync.Mutex
-	wdeadline int64
-	wio       sync.Mutex
+	// serialize access to Read and Write methods
+	rio, wio sync.Mutex
+
+	// read and write deadlines
+	rdeadline, wdeadline deadline
 
 	// owned by fd wait server
 	ncr, ncw int
@@ -82,11 +82,11 @@ func (s *pollServer) AddFD(fd *netFD, mode int) error {
 	key := intfd << 1
 	if mode == 'r' {
 		fd.ncr++
-		t = fd.rdeadline
+		t = fd.rdeadline.value()
 	} else {
 		fd.ncw++
 		key++
-		t = fd.wdeadline
+		t = fd.wdeadline.value()
 	}
 	s.pending[key] = fd
 	doWakeup := false
@@ -153,12 +153,8 @@ func (s *pollServer) WakeFD(fd *netFD, mode int, err error) {
 	}
 }
 
-func (s *pollServer) Now() int64 {
-	return time.Now().UnixNano()
-}
-
 func (s *pollServer) CheckDeadlines() {
-	now := s.Now()
+	now := time.Now().UnixNano()
 	// TODO(rsc): This will need to be handled more efficiently,
 	// probably with a heap indexed by wakeup time.
 
@@ -172,9 +168,9 @@ func (s *pollServer) CheckDeadlines() {
 			mode = 'w'
 		}
 		if mode == 'r' {
-			t = fd.rdeadline
+			t = fd.rdeadline.value()
 		} else {
-			t = fd.wdeadline
+			t = fd.wdeadline.value()
 		}
 		if t > 0 {
 			if t <= now {
@@ -198,15 +194,15 @@ func (s *pollServer) Run() {
 	s.Lock()
 	defer s.Unlock()
 	for {
-		var t = s.deadline
-		if t > 0 {
-			t = t - s.Now()
-			if t <= 0 {
+		var timeout int64 // nsec to wait for or 0 for none
+		if s.deadline > 0 {
+			timeout = s.deadline - time.Now().UnixNano()
+			if timeout <= 0 {
 				s.CheckDeadlines()
 				continue
 			}
 		}
-		fd, mode, err := s.poll.WaitFD(s, t)
+		fd, mode, err := s.poll.WaitFD(s, timeout)
 		if err != nil {
 			print("pollServer WaitFD: ", err.Error(), "\n")
 			return
@@ -418,11 +414,9 @@ func (fd *netFD) Read(p []byte) (n int, err error) {
 	}
 	defer fd.decref()
 	for {
-		if fd.rdeadline > 0 {
-			if time.Now().UnixNano() >= fd.rdeadline {
-				err = errTimeout
-				break
-			}
+		if fd.rdeadline.expired() {
+			err = errTimeout
+			break
 		}
 		n, err = syscall.Read(int(fd.sysfd), p)
 		if err != nil {
@@ -450,11 +444,9 @@ func (fd *netFD) ReadFrom(p []byte) (n int, sa syscall.Sockaddr, err error) {
 	}
 	defer fd.decref()
 	for {
-		if fd.rdeadline > 0 {
-			if time.Now().UnixNano() >= fd.rdeadline {
-				err = errTimeout
-				break
-			}
+		if fd.rdeadline.expired() {
+			err = errTimeout
+			break
 		}
 		n, sa, err = syscall.Recvfrom(fd.sysfd, p, 0)
 		if err != nil {
@@ -482,15 +474,13 @@ func (fd *netFD) ReadMsg(p []byte, oob []byte) (n, oobn, flags int, sa syscall.S
 	}
 	defer fd.decref()
 	for {
-		if fd.rdeadline > 0 {
-			if time.Now().UnixNano() >= fd.rdeadline {
-				err = errTimeout
-				break
-			}
+		if fd.rdeadline.expired() {
+			err = errTimeout
+			break
 		}
 		n, oobn, flags, sa, err = syscall.Recvmsg(fd.sysfd, p, oob, 0)
 		if err != nil {
-			// TODO(dfc) should n and oobn be set to nil
+			// TODO(dfc) should n and oobn be set to 0
 			if err == syscall.EAGAIN {
 				if err = fd.pollServer.WaitRead(fd); err == nil {
 					continue
@@ -513,21 +503,17 @@ func chkReadErr(n int, err error, fd *netFD) error {
 	return err
 }
 
-func (fd *netFD) Write(p []byte) (int, error) {
+func (fd *netFD) Write(p []byte) (nn int, err error) {
 	fd.wio.Lock()
 	defer fd.wio.Unlock()
 	if err := fd.incref(false); err != nil {
 		return 0, err
 	}
 	defer fd.decref()
-	var err error
-	nn := 0
 	for {
-		if fd.wdeadline > 0 {
-			if time.Now().UnixNano() >= fd.wdeadline {
-				err = errTimeout
-				break
-			}
+		if fd.wdeadline.expired() {
+			err = errTimeout
+			break
 		}
 		var n int
 		n, err = syscall.Write(int(fd.sysfd), p[nn:])
@@ -565,11 +551,9 @@ func (fd *netFD) WriteTo(p []byte, sa syscall.Sockaddr) (n int, err error) {
 	}
 	defer fd.decref()
 	for {
-		if fd.wdeadline > 0 {
-			if time.Now().UnixNano() >= fd.wdeadline {
-				err = errTimeout
-				break
-			}
+		if fd.wdeadline.expired() {
+			err = errTimeout
+			break
 		}
 		err = syscall.Sendto(fd.sysfd, p, 0, sa)
 		if err == syscall.EAGAIN {
@@ -595,11 +579,9 @@ func (fd *netFD) WriteMsg(p []byte, oob []byte, sa syscall.Sockaddr) (n int, oob
 	}
 	defer fd.decref()
 	for {
-		if fd.wdeadline > 0 {
-			if time.Now().UnixNano() >= fd.wdeadline {
-				err = errTimeout
-				break
-			}
+		if fd.wdeadline.expired() {
+			err = errTimeout
+			break
 		}
 		err = syscall.Sendmsg(fd.sysfd, p, oob, sa, 0)
 		if err == syscall.EAGAIN {

src/pkg/net/fd_windows.go

@@ -285,11 +285,11 @@ type netFD struct {
 	errnoc      [2]chan error    // read/write submit or cancel operation errors
 	closec      chan bool        // used by Close to cancel pending IO
 
-	// owned by client
-	rdeadline int64
-	rio       sync.Mutex
-	wdeadline int64
-	wio       sync.Mutex
+	// serialize access to Read and Write methods
+	rio, wio sync.Mutex
+
+	// read and write deadlines
+	rdeadline, wdeadline deadline
 }
 
 func allocFD(fd syscall.Handle, family, sotype int, net string) *netFD {
@@ -426,7 +426,7 @@ func (fd *netFD) Read(buf []byte) (int, error) {
 	defer fd.rio.Unlock()
 	var o readOp
 	o.Init(fd, buf, 'r')
-	n, err := iosrv.ExecIO(&o, fd.rdeadline)
+	n, err := iosrv.ExecIO(&o, fd.rdeadline.value())
 	if err == nil && n == 0 {
 		err = io.EOF
 	}
@@ -463,7 +463,7 @@ func (fd *netFD) ReadFrom(buf []byte) (n int, sa syscall.Sockaddr, err error) {
 	var o readFromOp
 	o.Init(fd, buf, 'r')
 	o.rsan = int32(unsafe.Sizeof(o.rsa))
-	n, err = iosrv.ExecIO(&o, fd.rdeadline)
+	n, err = iosrv.ExecIO(&o, fd.rdeadline.value())
 	if err != nil {
 		return 0, nil, err
 	}
@@ -495,7 +495,7 @@ func (fd *netFD) Write(buf []byte) (int, error) {
 	defer fd.wio.Unlock()
 	var o writeOp
 	o.Init(fd, buf, 'w')
-	return iosrv.ExecIO(&o, fd.wdeadline)
+	return iosrv.ExecIO(&o, fd.wdeadline.value())
 }
 
 // WriteTo to network.
@@ -527,7 +527,7 @@ func (fd *netFD) WriteTo(buf []byte, sa syscall.Sockaddr) (int, error) {
 	var o writeToOp
 	o.Init(fd, buf, 'w')
 	o.sa = sa
-	return iosrv.ExecIO(&o, fd.wdeadline)
+	return iosrv.ExecIO(&o, fd.wdeadline.value())
 }
 
 // Accept new network connections.
@@ -577,7 +577,7 @@ func (fd *netFD) accept(toAddr func(syscall.Sockaddr) Addr) (*netFD, error) {
 	var o acceptOp
 	o.Init(fd, 'r')
 	o.newsock = s
-	_, err = iosrv.ExecIO(&o, fd.rdeadline)
+	_, err = iosrv.ExecIO(&o, fd.rdeadline.value())
 	if err != nil {
 		closesocket(s)
 		return nil, err

src/pkg/net/net.go

@@ -46,6 +46,7 @@ import (
 	"errors"
 	"io"
 	"os"
+	"sync"
 	"syscall"
 	"time"
 )
@@ -375,3 +376,36 @@ func genericReadFrom(w io.Writer, r io.Reader) (n int64, err error) {
 	// Use wrapper to hide existing r.ReadFrom from io.Copy.
 	return io.Copy(writerOnly{w}, r)
 }
+
+// deadline is an atomically-accessed number of nanoseconds since 1970
+// or 0, if no deadline is set.
+type deadline struct {
+	sync.Mutex
+	val int64
+}
+
+func (d *deadline) expired() bool {
+	t := d.value()
+	return t > 0 && time.Now().UnixNano() >= t
+}
+
+func (d *deadline) value() (v int64) {
+	d.Lock()
+	v = d.val
+	d.Unlock()
+	return
+}
+
+func (d *deadline) set(v int64) {
+	d.Lock()
+	d.val = v
+	d.Unlock()
+}
+
+func (d *deadline) setTime(t time.Time) {
+	if t.IsZero() {
+		d.set(0)
+	} else {
+		d.set(t.UnixNano())
+	}
+}

src/pkg/net/sendfile_freebsd.go

@@ -82,7 +82,7 @@ func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
 		if n == 0 && err1 == nil {
 			break
 		}
-		if err1 == syscall.EAGAIN && c.wdeadline >= 0 {
+		if err1 == syscall.EAGAIN {
 			if err1 = c.pollServer.WaitWrite(c); err1 == nil {
 				continue
 			}

src/pkg/net/sendfile_linux.go

@@ -58,7 +58,7 @@ func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
 		if n == 0 && err1 == nil {
 			break
 		}
-		if err1 == syscall.EAGAIN && c.wdeadline >= 0 {
+		if err1 == syscall.EAGAIN {
 			if err1 = c.pollServer.WaitWrite(c); err1 == nil {
 				continue
 			}

src/pkg/net/sock_posix.go

@@ -56,15 +56,13 @@ func socket(net string, f, t, p int, ipv6only bool, ulsa, ursa syscall.Sockaddr,
 	}
 
 	if ursa != nil {
-		if !deadline.IsZero() {
-			fd.wdeadline = deadline.UnixNano()
-		}
+		fd.wdeadline.setTime(deadline)
 		if err = fd.connect(ursa); err != nil {
 			closesocket(s)
 			return nil, err
 		}
 		fd.isConnected = true
-		fd.wdeadline = 0
+		fd.wdeadline.set(0)
 	}
 
 	lsa, _ := syscall.Getsockname(s)

src/pkg/net/sockopt_posix.go

@@ -119,29 +119,22 @@ func setWriteBuffer(fd *netFD, bytes int) error {
 	return os.NewSyscallError("setsockopt", syscall.SetsockoptInt(fd.sysfd, syscall.SOL_SOCKET, syscall.SO_SNDBUF, bytes))
 }
 
+// TODO(dfc) these unused error returns could be removed
+
 func setReadDeadline(fd *netFD, t time.Time) error {
-	if t.IsZero() {
-		fd.rdeadline = 0
-	} else {
-		fd.rdeadline = t.UnixNano()
-	}
+	fd.rdeadline.setTime(t)
 	return nil
 }
 
 func setWriteDeadline(fd *netFD, t time.Time) error {
-	if t.IsZero() {
-		fd.wdeadline = 0
-	} else {
-		fd.wdeadline = t.UnixNano()
-	}
+	fd.wdeadline.setTime(t)
 	return nil
 }
 
 func setDeadline(fd *netFD, t time.Time) error {
-	if err := setReadDeadline(fd, t); err != nil {
-		return err
-	}
-	return setWriteDeadline(fd, t)
+	setReadDeadline(fd, t)
+	setWriteDeadline(fd, t)
+	return nil
 }
 
 func setKeepAlive(fd *netFD, keepalive bool) error {