src/pkg/net/fd.go - go - 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.

 // TODO(rsc): All the prints in this file should go to standard error.

 package net

 import (
 	"io"
 	"once"
 	"os"
 	"sync"
 	"syscall"
 	"time"
 )

 // Network file descriptor.
 type netFD struct {
 	// locking/lifetime of sysfd
 	sysmu   sync.Mutex
 	sysref  int
 	closing bool

 	// immutable until Close
 	sysfd   int
 	family  int
 	proto   int
 	sysfile *os.File
 	cr      chan bool
 	cw      chan bool
 	net     string
 	laddr   Addr
 	raddr   Addr

 	// owned by client
 	rdeadline_delta int64
 	rdeadline       int64
 	rio             sync.Mutex
 	wdeadline_delta int64
 	wdeadline       int64
 	wio             sync.Mutex

 	// owned by fd wait server
 	ncr, ncw int
 }

 type InvalidConnError struct{}

 func (e *InvalidConnError) String() string  { return "invalid net.Conn" }
 func (e *InvalidConnError) Temporary() bool { return false }
 func (e *InvalidConnError) Timeout() bool   { return false }

 // A pollServer helps FDs determine when to retry a non-blocking
 // read or write after they get EAGAIN.  When an FD needs to wait,
 // send the fd on s.cr (for a read) or s.cw (for a write) to pass the
 // request to the poll server.  Then receive on fd.cr/fd.cw.
 // When the pollServer finds that i/o on FD should be possible
 // again, it will send fd on fd.cr/fd.cw to wake any waiting processes.
 // This protocol is implemented as s.WaitRead() and s.WaitWrite().
 //
 // There is one subtlety: when sending on s.cr/s.cw, the
 // poll server is probably in a system call, waiting for an fd
 // to become ready.  It's not looking at the request channels.
 // To resolve this, the poll server waits not just on the FDs it has
 // been given but also its own pipe.  After sending on the
 // buffered channel s.cr/s.cw, WaitRead/WaitWrite writes a
 // byte to the pipe, causing the pollServer's poll system call to
 // return.  In response to the pipe being readable, the pollServer
 // re-polls its request channels.
 //
 // Note that the ordering is "send request" and then "wake up server".
 // If the operations were reversed, there would be a race: the poll
 // server might wake up and look at the request channel, see that it
 // was empty, and go back to sleep, all before the requester managed
 // to send the request.  Because the send must complete before the wakeup,
 // the request channel must be buffered.  A buffer of size 1 is sufficient
 // for any request load.  If many processes are trying to submit requests,
 // one will succeed, the pollServer will read the request, and then the
 // channel will be empty for the next process's request.  A larger buffer
 // might help batch requests.
 //
 // To avoid races in closing, all fd operations are locked and
 // refcounted. when netFD.Close() is called, it calls syscall.Shutdown
 // and sets a closing flag. Only when the last reference is removed
 // will the fd be closed.

 type pollServer struct {
 	cr, cw   chan *netFD // buffered >= 1
 	pr, pw   *os.File
 	pending  map[int]*netFD
 	poll     *pollster // low-level OS hooks
 	deadline int64     // next deadline (nsec since 1970)
 }

 func newPollServer() (s *pollServer, err os.Error) {
 	s = new(pollServer)
 	s.cr = make(chan *netFD, 1)
 	s.cw = make(chan *netFD, 1)
 	if s.pr, s.pw, err = os.Pipe(); err != nil {
 		return nil, err
 	}
 	var e int
 	if e = syscall.SetNonblock(s.pr.Fd(), true); e != 0 {
 	Errno:
 		err = &os.PathError{"setnonblock", s.pr.Name(), os.Errno(e)}
 	Error:
 		s.pr.Close()
 		s.pw.Close()
 		return nil, err
 	}
 	if e = syscall.SetNonblock(s.pw.Fd(), true); e != 0 {
 		goto Errno
 	}
 	if s.poll, err = newpollster(); err != nil {
 		goto Error
 	}
 	if err = s.poll.AddFD(s.pr.Fd(), 'r', true); err != nil {
 		s.poll.Close()
 		goto Error
 	}
 	s.pending = make(map[int]*netFD)
 	go s.Run()
 	return s, nil
 }

 func (s *pollServer) AddFD(fd *netFD, mode int) {
 	intfd := fd.sysfd
 	if intfd < 0 {
 		// fd closed underfoot
 		if mode == 'r' {
 			fd.cr <- true
 		} else {
 			fd.cw <- true
 		}
 		return
 	}
 	if err := s.poll.AddFD(intfd, mode, false); err != nil {
 		panic("pollServer AddFD " + err.String())
 		return
 	}

 	var t int64
 	key := intfd << 1
 	if mode == 'r' {
 		fd.ncr++
 		t = fd.rdeadline
 	} else {
 		fd.ncw++
 		key++
 		t = fd.wdeadline
 	}
 	s.pending[key] = fd
 	if t > 0 && (s.deadline == 0 || t < s.deadline) {
 		s.deadline = t
 	}
 }

 func (s *pollServer) LookupFD(fd int, mode int) *netFD {
 	key := fd << 1
 	if mode == 'w' {
 		key++
 	}
 	netfd, ok := s.pending[key]
 	if !ok {
 		return nil
 	}
 	s.pending[key] = nil, false
 	return netfd
 }

 func (s *pollServer) WakeFD(fd *netFD, mode int) {
 	if mode == 'r' {
 		for fd.ncr > 0 {
 			fd.ncr--
 			fd.cr <- true
 		}
 	} else {
 		for fd.ncw > 0 {
 			fd.ncw--
 			fd.cw <- true
 		}
 	}
 }

 func (s *pollServer) Now() int64 {
 	return time.Nanoseconds()
 }

 func (s *pollServer) CheckDeadlines() {
 	now := s.Now()
 	// TODO(rsc): This will need to be handled more efficiently,
 	// probably with a heap indexed by wakeup time.

 	var next_deadline int64
 	for key, fd := range s.pending {
 		var t int64
 		var mode int
 		if key&1 == 0 {
 			mode = 'r'
 		} else {
 			mode = 'w'
 		}
 		if mode == 'r' {
 			t = fd.rdeadline
 		} else {
 			t = fd.wdeadline
 		}
 		if t > 0 {
 			if t <= now {
 				s.pending[key] = nil, false
 				if mode == 'r' {
 					s.poll.DelFD(fd.sysfd, mode)
 					fd.rdeadline = -1
 				} else {
 					s.poll.DelFD(fd.sysfd, mode)
 					fd.wdeadline = -1
 				}
 				s.WakeFD(fd, mode)
 			} else if next_deadline == 0 || t < next_deadline {
 				next_deadline = t
 			}
 		}
 	}
 	s.deadline = next_deadline
 }

 func (s *pollServer) Run() {
 	var scratch [100]byte
 	for {
 		var t = s.deadline
 		if t > 0 {
 			t = t - s.Now()
 			if t <= 0 {
 				s.CheckDeadlines()
 				continue
 			}
 		}
 		fd, mode, err := s.poll.WaitFD(t)
 		if err != nil {
 			print("pollServer WaitFD: ", err.String(), "\n")
 			return
 		}
 		if fd < 0 {
 			// Timeout happened.
 			s.CheckDeadlines()
 			continue
 		}
 		if fd == s.pr.Fd() {
 			// Drain our wakeup pipe.
 			for nn, _ := s.pr.Read(&scratch); nn > 0; {
 				nn, _ = s.pr.Read(&scratch)
 			}
 			// Read from channels
 			for fd, ok := <-s.cr; ok; fd, ok = <-s.cr {
 				s.AddFD(fd, 'r')
 			}
 			for fd, ok := <-s.cw; ok; fd, ok = <-s.cw {
 				s.AddFD(fd, 'w')
 			}
 		} else {
 			netfd := s.LookupFD(fd, mode)
 			if netfd == nil {
 				print("pollServer: unexpected wakeup for fd=", netfd, " mode=", string(mode), "\n")
 				continue
 			}
 			s.WakeFD(netfd, mode)
 		}
 	}
 }

 var wakeupbuf [1]byte

 func (s *pollServer) Wakeup() { s.pw.Write(&wakeupbuf) }

 func (s *pollServer) WaitRead(fd *netFD) {
 	s.cr <- fd
 	s.Wakeup()
 	<-fd.cr
 }

 func (s *pollServer) WaitWrite(fd *netFD) {
 	s.cw <- fd
 	s.Wakeup()
 	<-fd.cw
 }

 // Network FD methods.
 // All the network FDs use a single pollServer.

 var pollserver *pollServer

 func startServer() {
 	p, err := newPollServer()
 	if err != nil {
 		print("Start pollServer: ", err.String(), "\n")
 	}
 	pollserver = p
 }

 func newFD(fd, family, proto int, net string, laddr, raddr Addr) (f *netFD, err os.Error) {
 	once.Do(startServer)
 	if e := syscall.SetNonblock(fd, true); e != 0 {
 		return nil, &OpError{"setnonblock", net, laddr, os.Errno(e)}
 	}
 	f = &netFD{
 		sysfd:  fd,
 		family: family,
 		proto:  proto,
 		net:    net,
 		laddr:  laddr,
 		raddr:  raddr,
 	}
 	var ls, rs string
 	if laddr != nil {
 		ls = laddr.String()
 	}
 	if raddr != nil {
 		rs = raddr.String()
 	}
 	f.sysfile = os.NewFile(fd, net+":"+ls+"->"+rs)
 	f.cr = make(chan bool, 1)
 	f.cw = make(chan bool, 1)
 	return f, nil
 }

 // Add a reference to this fd.
 func (fd *netFD) incref() {
 	fd.sysmu.Lock()
 	fd.sysref++
 	fd.sysmu.Unlock()
 }

 // Remove a reference to this FD and close if we've been asked to do so (and
 // there are no references left.
 func (fd *netFD) decref() {
 	fd.sysmu.Lock()
 	fd.sysref--
 	if fd.closing && fd.sysref == 0 && fd.sysfd >= 0 {
 		// In case the user has set linger, switch to blocking mode so
 		// the close blocks.  As long as this doesn't happen often, we
 		// can handle the extra OS processes.  Otherwise we'll need to
 		// use the pollserver for Close too.  Sigh.
 		syscall.SetNonblock(fd.sysfd, false)
 		fd.sysfile.Close()
 		fd.sysfile = nil
 		fd.sysfd = -1
 	}
 	fd.sysmu.Unlock()
 }

 func (fd *netFD) Close() os.Error {
 	if fd == nil || fd.sysfile == nil {
 		return os.EINVAL
 	}

 	fd.incref()
 	syscall.Shutdown(fd.sysfd, syscall.SHUT_RDWR)
 	fd.closing = true
 	fd.decref()
 	return nil
 }

 func (fd *netFD) Read(p []byte) (n int, err os.Error) {
 	if fd == nil || fd.sysfile == nil {
 		return 0, os.EINVAL
 	}
 	fd.rio.Lock()
 	defer fd.rio.Unlock()
 	fd.incref()
 	defer fd.decref()
 	if fd.rdeadline_delta > 0 {
 		fd.rdeadline = pollserver.Now() + fd.rdeadline_delta
 	} else {
 		fd.rdeadline = 0
 	}
 	var oserr os.Error
 	for {
 		var errno int
 		n, errno = syscall.Read(fd.sysfile.Fd(), p)
 		if errno == syscall.EAGAIN && fd.rdeadline >= 0 {
 			pollserver.WaitRead(fd)
 			continue
 		}
 		if errno != 0 {
 			n = 0
 			oserr = os.Errno(errno)
 		} else if n == 0 && errno == 0 && fd.proto != syscall.SOCK_DGRAM {
 			err = os.EOF
 		}
 		break
 	}
 	if oserr != nil {
 		err = &OpError{"read", fd.net, fd.raddr, oserr}
 	}
 	return
 }

 func (fd *netFD) ReadFrom(p []byte) (n int, sa syscall.Sockaddr, err os.Error) {
 	if fd == nil || fd.sysfile == nil {
 		return 0, nil, os.EINVAL
 	}
 	fd.rio.Lock()
 	defer fd.rio.Unlock()
 	fd.incref()
 	defer fd.decref()
 	if fd.rdeadline_delta > 0 {
 		fd.rdeadline = pollserver.Now() + fd.rdeadline_delta
 	} else {
 		fd.rdeadline = 0
 	}
 	var oserr os.Error
 	for {
 		var errno int
 		n, sa, errno = syscall.Recvfrom(fd.sysfd, p, 0)
 		if errno == syscall.EAGAIN && fd.rdeadline >= 0 {
 			pollserver.WaitRead(fd)
 			continue
 		}
 		if errno != 0 {
 			n = 0
 			oserr = os.Errno(errno)
 		}
 		break
 	}
 	if oserr != nil {
 		err = &OpError{"read", fd.net, fd.laddr, oserr}
 	}
 	return
 }

 func (fd *netFD) Write(p []byte) (n int, err os.Error) {
 	if fd == nil || fd.sysfile == nil {
 		return 0, os.EINVAL
 	}
 	fd.wio.Lock()
 	defer fd.wio.Unlock()
 	fd.incref()
 	defer fd.decref()
 	if fd.wdeadline_delta > 0 {
 		fd.wdeadline = pollserver.Now() + fd.wdeadline_delta
 	} else {
 		fd.wdeadline = 0
 	}
 	nn := 0
 	var oserr os.Error
 	for {
 		n, errno := syscall.Write(fd.sysfile.Fd(), p[nn:])
 		if n > 0 {
 			nn += n
 		}
 		if nn == len(p) {
 			break
 		}
 		if errno == syscall.EAGAIN && fd.wdeadline >= 0 {
 			pollserver.WaitWrite(fd)
 			continue
 		}
 		if errno != 0 {
 			n = 0
 			oserr = os.Errno(errno)
 			break
 		}
 		if n == 0 {
 			oserr = io.ErrUnexpectedEOF
 			break
 		}
 	}
 	if oserr != nil {
 		err = &OpError{"write", fd.net, fd.raddr, oserr}
 	}
 	return nn, err
 }

 func (fd *netFD) WriteTo(p []byte, sa syscall.Sockaddr) (n int, err os.Error) {
 	if fd == nil || fd.sysfile == nil {
 		return 0, os.EINVAL
 	}
 	fd.wio.Lock()
 	defer fd.wio.Unlock()
 	fd.incref()
 	defer fd.decref()
 	if fd.wdeadline_delta > 0 {
 		fd.wdeadline = pollserver.Now() + fd.wdeadline_delta
 	} else {
 		fd.wdeadline = 0
 	}
 	var oserr os.Error
 	for {
 		errno := syscall.Sendto(fd.sysfd, p, 0, sa)
 		if errno == syscall.EAGAIN && fd.wdeadline >= 0 {
 			pollserver.WaitWrite(fd)
 			continue
 		}
 		if errno != 0 {
 			oserr = os.Errno(errno)
 		}
 		break
 	}
 	if oserr == nil {
 		n = len(p)
 	} else {
 		err = &OpError{"write", fd.net, fd.raddr, oserr}
 	}
 	return
 }

 func (fd *netFD) accept(toAddr func(syscall.Sockaddr) Addr) (nfd *netFD, err os.Error) {
 	if fd == nil || fd.sysfile == nil {
 		return nil, os.EINVAL
 	}

 	fd.incref()
 	defer fd.decref()

 	// See ../syscall/exec.go for description of ForkLock.
 	// It is okay to hold the lock across syscall.Accept
 	// because we have put fd.sysfd into non-blocking mode.
 	syscall.ForkLock.RLock()
 	var s, e int
 	var sa syscall.Sockaddr
 	for {
 		s, sa, e = syscall.Accept(fd.sysfd)
 		if e != syscall.EAGAIN {
 			break
 		}
 		syscall.ForkLock.RUnlock()
 		pollserver.WaitRead(fd)
 		syscall.ForkLock.RLock()
 	}
 	if e != 0 {
 		syscall.ForkLock.RUnlock()
 		return nil, &OpError{"accept", fd.net, fd.laddr, os.Errno(e)}
 	}
 	syscall.CloseOnExec(s)
 	syscall.ForkLock.RUnlock()

 	if nfd, err = newFD(s, fd.family, fd.proto, fd.net, fd.laddr, toAddr(sa)); err != nil {
 		syscall.Close(s)
 		return nil, err
 	}
 	return nfd, nil
 }
	// 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.

	// TODO(rsc): All the prints in this file should go to standard error.

	package net

	import (
	"io"
	"once"
	"os"
	"sync"
	"syscall"
	"time"
	)

	// Network file descriptor.
	type netFD struct {
	// locking/lifetime of sysfd
	sysmu sync.Mutex
	sysref int
	closing bool

	// immutable until Close
	sysfd int
	family int
	proto int
	sysfile *os.File
	cr chan bool
	cw chan bool
	net string
	laddr Addr
	raddr Addr

	// owned by client
	rdeadline_delta int64
	rdeadline int64
	rio sync.Mutex
	wdeadline_delta int64
	wdeadline int64
	wio sync.Mutex

	// owned by fd wait server
	ncr, ncw int
	}

	type InvalidConnError struct{}

	func (e *InvalidConnError) String() string { return "invalid net.Conn" }
	func (e *InvalidConnError) Temporary() bool { return false }
	func (e *InvalidConnError) Timeout() bool { return false }

	// A pollServer helps FDs determine when to retry a non-blocking
	// read or write after they get EAGAIN. When an FD needs to wait,
	// send the fd on s.cr (for a read) or s.cw (for a write) to pass the
	// request to the poll server. Then receive on fd.cr/fd.cw.
	// When the pollServer finds that i/o on FD should be possible
	// again, it will send fd on fd.cr/fd.cw to wake any waiting processes.
	// This protocol is implemented as s.WaitRead() and s.WaitWrite().
	//
	// There is one subtlety: when sending on s.cr/s.cw, the
	// poll server is probably in a system call, waiting for an fd
	// to become ready. It's not looking at the request channels.
	// To resolve this, the poll server waits not just on the FDs it has
	// been given but also its own pipe. After sending on the
	// buffered channel s.cr/s.cw, WaitRead/WaitWrite writes a
	// byte to the pipe, causing the pollServer's poll system call to
	// return. In response to the pipe being readable, the pollServer
	// re-polls its request channels.
	//
	// Note that the ordering is "send request" and then "wake up server".
	// If the operations were reversed, there would be a race: the poll
	// server might wake up and look at the request channel, see that it
	// was empty, and go back to sleep, all before the requester managed
	// to send the request. Because the send must complete before the wakeup,
	// the request channel must be buffered. A buffer of size 1 is sufficient
	// for any request load. If many processes are trying to submit requests,
	// one will succeed, the pollServer will read the request, and then the
	// channel will be empty for the next process's request. A larger buffer
	// might help batch requests.
	//
	// To avoid races in closing, all fd operations are locked and
	// refcounted. when netFD.Close() is called, it calls syscall.Shutdown
	// and sets a closing flag. Only when the last reference is removed
	// will the fd be closed.

	type pollServer struct {
	cr, cw chan *netFD // buffered >= 1
	pr, pw *os.File
	pending map[int]*netFD
	poll *pollster // low-level OS hooks
	deadline int64 // next deadline (nsec since 1970)
	}

	func newPollServer() (s *pollServer, err os.Error) {
	s = new(pollServer)
	s.cr = make(chan *netFD, 1)
	s.cw = make(chan *netFD, 1)
	if s.pr, s.pw, err = os.Pipe(); err != nil {
	return nil, err
	}
	var e int
	if e = syscall.SetNonblock(s.pr.Fd(), true); e != 0 {
	Errno:
	err = &os.PathError{"setnonblock", s.pr.Name(), os.Errno(e)}
	Error:
	s.pr.Close()
	s.pw.Close()
	return nil, err
	}
	if e = syscall.SetNonblock(s.pw.Fd(), true); e != 0 {
	goto Errno
	}
	if s.poll, err = newpollster(); err != nil {
	goto Error
	}
	if err = s.poll.AddFD(s.pr.Fd(), 'r', true); err != nil {
	s.poll.Close()
	goto Error
	}
	s.pending = make(map[int]*netFD)
	go s.Run()
	return s, nil
	}

	func (s pollServer) AddFD(fd netFD, mode int) {
	intfd := fd.sysfd
	if intfd < 0 {
	// fd closed underfoot
	if mode == 'r' {
	fd.cr <- true
	} else {
	fd.cw <- true
	}
	return
	}
	if err := s.poll.AddFD(intfd, mode, false); err != nil {
	panic("pollServer AddFD " + err.String())
	return
	}

	var t int64
	key := intfd << 1
	if mode == 'r' {
	fd.ncr++
	t = fd.rdeadline
	} else {
	fd.ncw++
	key++
	t = fd.wdeadline
	}
	s.pending[key] = fd
	if t > 0 && (s.deadline == 0 \|\| t < s.deadline) {
	s.deadline = t
	}
	}

	func (s pollServer) LookupFD(fd int, mode int) netFD {
	key := fd << 1
	if mode == 'w' {
	key++
	}
	netfd, ok := s.pending[key]
	if !ok {
	return nil
	}
	s.pending[key] = nil, false
	return netfd
	}

	func (s pollServer) WakeFD(fd netFD, mode int) {
	if mode == 'r' {
	for fd.ncr > 0 {
	fd.ncr--
	fd.cr <- true
	}
	} else {
	for fd.ncw > 0 {
	fd.ncw--
	fd.cw <- true
	}
	}
	}

	func (s *pollServer) Now() int64 {
	return time.Nanoseconds()
	}

	func (s *pollServer) CheckDeadlines() {
	now := s.Now()
	// TODO(rsc): This will need to be handled more efficiently,
	// probably with a heap indexed by wakeup time.

	var next_deadline int64
	for key, fd := range s.pending {
	var t int64
	var mode int
	if key&1 == 0 {
	mode = 'r'
	} else {
	mode = 'w'
	}
	if mode == 'r' {
	t = fd.rdeadline
	} else {
	t = fd.wdeadline
	}
	if t > 0 {
	if t <= now {
	s.pending[key] = nil, false
	if mode == 'r' {
	s.poll.DelFD(fd.sysfd, mode)
	fd.rdeadline = -1
	} else {
	s.poll.DelFD(fd.sysfd, mode)
	fd.wdeadline = -1
	}
	s.WakeFD(fd, mode)
	} else if next_deadline == 0 \|\| t < next_deadline {
	next_deadline = t
	}
	}
	}
	s.deadline = next_deadline
	}

	func (s *pollServer) Run() {
	var scratch [100]byte
	for {
	var t = s.deadline
	if t > 0 {
	t = t - s.Now()
	if t <= 0 {
	s.CheckDeadlines()
	continue
	}
	}
	fd, mode, err := s.poll.WaitFD(t)
	if err != nil {
	print("pollServer WaitFD: ", err.String(), "\n")
	return
	}
	if fd < 0 {
	// Timeout happened.
	s.CheckDeadlines()
	continue
	}
	if fd == s.pr.Fd() {
	// Drain our wakeup pipe.
	for nn, _ := s.pr.Read(&scratch); nn > 0; {
	nn, _ = s.pr.Read(&scratch)
	}
	// Read from channels
	for fd, ok := <-s.cr; ok; fd, ok = <-s.cr {
	s.AddFD(fd, 'r')
	}
	for fd, ok := <-s.cw; ok; fd, ok = <-s.cw {
	s.AddFD(fd, 'w')
	}
	} else {
	netfd := s.LookupFD(fd, mode)
	if netfd == nil {
	print("pollServer: unexpected wakeup for fd=", netfd, " mode=", string(mode), "\n")
	continue
	}
	s.WakeFD(netfd, mode)
	}
	}
	}

	var wakeupbuf [1]byte

	func (s *pollServer) Wakeup() { s.pw.Write(&wakeupbuf) }

	func (s pollServer) WaitRead(fd netFD) {
	s.cr <- fd
	s.Wakeup()
	<-fd.cr
	}

	func (s pollServer) WaitWrite(fd netFD) {
	s.cw <- fd
	s.Wakeup()
	<-fd.cw
	}

	// Network FD methods.
	// All the network FDs use a single pollServer.

	var pollserver *pollServer

	func startServer() {
	p, err := newPollServer()
	if err != nil {
	print("Start pollServer: ", err.String(), "\n")
	}
	pollserver = p
	}

	func newFD(fd, family, proto int, net string, laddr, raddr Addr) (f *netFD, err os.Error) {
	once.Do(startServer)
	if e := syscall.SetNonblock(fd, true); e != 0 {
	return nil, &OpError{"setnonblock", net, laddr, os.Errno(e)}
	}
	f = &netFD{
	sysfd: fd,
	family: family,
	proto: proto,
	net: net,
	laddr: laddr,
	raddr: raddr,
	}
	var ls, rs string
	if laddr != nil {
	ls = laddr.String()
	}
	if raddr != nil {
	rs = raddr.String()
	}
	f.sysfile = os.NewFile(fd, net+":"+ls+"->"+rs)
	f.cr = make(chan bool, 1)
	f.cw = make(chan bool, 1)
	return f, nil
	}

	// Add a reference to this fd.
	func (fd *netFD) incref() {
	fd.sysmu.Lock()
	fd.sysref++
	fd.sysmu.Unlock()
	}

	// Remove a reference to this FD and close if we've been asked to do so (and
	// there are no references left.
	func (fd *netFD) decref() {
	fd.sysmu.Lock()
	fd.sysref--
	if fd.closing && fd.sysref == 0 && fd.sysfd >= 0 {
	// In case the user has set linger, switch to blocking mode so
	// the close blocks. As long as this doesn't happen often, we
	// can handle the extra OS processes. Otherwise we'll need to
	// use the pollserver for Close too. Sigh.
	syscall.SetNonblock(fd.sysfd, false)
	fd.sysfile.Close()
	fd.sysfile = nil
	fd.sysfd = -1
	}
	fd.sysmu.Unlock()
	}

	func (fd *netFD) Close() os.Error {
	if fd == nil \|\| fd.sysfile == nil {
	return os.EINVAL
	}

	fd.incref()
	syscall.Shutdown(fd.sysfd, syscall.SHUT_RDWR)
	fd.closing = true
	fd.decref()
	return nil
	}

	func (fd *netFD) Read(p []byte) (n int, err os.Error) {
	if fd == nil \|\| fd.sysfile == nil {
	return 0, os.EINVAL
	}
	fd.rio.Lock()
	defer fd.rio.Unlock()
	fd.incref()
	defer fd.decref()
	if fd.rdeadline_delta > 0 {
	fd.rdeadline = pollserver.Now() + fd.rdeadline_delta
	} else {
	fd.rdeadline = 0
	}
	var oserr os.Error
	for {
	var errno int
	n, errno = syscall.Read(fd.sysfile.Fd(), p)
	if errno == syscall.EAGAIN && fd.rdeadline >= 0 {
	pollserver.WaitRead(fd)
	continue
	}
	if errno != 0 {
	n = 0
	oserr = os.Errno(errno)
	} else if n == 0 && errno == 0 && fd.proto != syscall.SOCK_DGRAM {
	err = os.EOF
	}
	break
	}
	if oserr != nil {
	err = &OpError{"read", fd.net, fd.raddr, oserr}
	}
	return
	}

	func (fd *netFD) ReadFrom(p []byte) (n int, sa syscall.Sockaddr, err os.Error) {
	if fd == nil \|\| fd.sysfile == nil {
	return 0, nil, os.EINVAL
	}
	fd.rio.Lock()
	defer fd.rio.Unlock()
	fd.incref()
	defer fd.decref()
	if fd.rdeadline_delta > 0 {
	fd.rdeadline = pollserver.Now() + fd.rdeadline_delta
	} else {
	fd.rdeadline = 0
	}
	var oserr os.Error
	for {
	var errno int
	n, sa, errno = syscall.Recvfrom(fd.sysfd, p, 0)
	if errno == syscall.EAGAIN && fd.rdeadline >= 0 {
	pollserver.WaitRead(fd)
	continue
	}
	if errno != 0 {
	n = 0
	oserr = os.Errno(errno)
	}
	break
	}
	if oserr != nil {
	err = &OpError{"read", fd.net, fd.laddr, oserr}
	}
	return
	}

	func (fd *netFD) Write(p []byte) (n int, err os.Error) {
	if fd == nil \|\| fd.sysfile == nil {
	return 0, os.EINVAL
	}
	fd.wio.Lock()
	defer fd.wio.Unlock()
	fd.incref()
	defer fd.decref()
	if fd.wdeadline_delta > 0 {
	fd.wdeadline = pollserver.Now() + fd.wdeadline_delta
	} else {
	fd.wdeadline = 0
	}
	nn := 0
	var oserr os.Error
	for {
	n, errno := syscall.Write(fd.sysfile.Fd(), p[nn:])
	if n > 0 {
	nn += n
	}
	if nn == len(p) {
	break
	}
	if errno == syscall.EAGAIN && fd.wdeadline >= 0 {
	pollserver.WaitWrite(fd)
	continue
	}
	if errno != 0 {
	n = 0
	oserr = os.Errno(errno)
	break
	}
	if n == 0 {
	oserr = io.ErrUnexpectedEOF
	break
	}
	}
	if oserr != nil {
	err = &OpError{"write", fd.net, fd.raddr, oserr}
	}
	return nn, err
	}

	func (fd *netFD) WriteTo(p []byte, sa syscall.Sockaddr) (n int, err os.Error) {
	if fd == nil \|\| fd.sysfile == nil {
	return 0, os.EINVAL
	}
	fd.wio.Lock()
	defer fd.wio.Unlock()
	fd.incref()
	defer fd.decref()
	if fd.wdeadline_delta > 0 {
	fd.wdeadline = pollserver.Now() + fd.wdeadline_delta
	} else {
	fd.wdeadline = 0
	}
	var oserr os.Error
	for {
	errno := syscall.Sendto(fd.sysfd, p, 0, sa)
	if errno == syscall.EAGAIN && fd.wdeadline >= 0 {
	pollserver.WaitWrite(fd)
	continue
	}
	if errno != 0 {
	oserr = os.Errno(errno)
	}
	break
	}
	if oserr == nil {
	n = len(p)
	} else {
	err = &OpError{"write", fd.net, fd.raddr, oserr}
	}
	return
	}

	func (fd netFD) accept(toAddr func(syscall.Sockaddr) Addr) (nfd netFD, err os.Error) {
	if fd == nil \|\| fd.sysfile == nil {
	return nil, os.EINVAL
	}

	fd.incref()
	defer fd.decref()

	// See ../syscall/exec.go for description of ForkLock.
	// It is okay to hold the lock across syscall.Accept
	// because we have put fd.sysfd into non-blocking mode.
	syscall.ForkLock.RLock()
	var s, e int
	var sa syscall.Sockaddr
	for {
	s, sa, e = syscall.Accept(fd.sysfd)
	if e != syscall.EAGAIN {
	break
	}
	syscall.ForkLock.RUnlock()
	pollserver.WaitRead(fd)
	syscall.ForkLock.RLock()
	}
	if e != 0 {
	syscall.ForkLock.RUnlock()
	return nil, &OpError{"accept", fd.net, fd.laddr, os.Errno(e)}
	}
	syscall.CloseOnExec(s)
	syscall.ForkLock.RUnlock()

	if nfd, err = newFD(s, fd.family, fd.proto, fd.net, fd.laddr, toAddr(sa)); err != nil {
	syscall.Close(s)
	return nil, err
	}
	return nfd, nil
	}