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 (
 	"once";
 	"os";
 	"sync";
 	"syscall";
 )

 // Network file descriptor.
 type netFD struct {
 	// immutable until Close
 	fd	int;
 	family	int;
 	proto	int;
 	file	*os.File;
 	cr	chan *netFD;
 	cw	chan *netFD;
 	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;
 }

 // 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.

 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) {
 	// TODO(rsc): This check handles a race between
 	// one goroutine reading and another one closing,
 	// but it doesn't solve the race completely:
 	// it still could happen that one goroutine closes
 	// but we read fd.fd before it does, and then
 	// another goroutine creates a new open file with
 	// that fd, which we'd now be referring to.
 	// The fix is probably to send the Close call
 	// through the poll server too, except that
 	// not all Reads and Writes go through the poll
 	// server even now.
 	intfd := fd.fd;
 	if intfd < 0 {
 		// fd closed underfoot
 		if mode == 'r' {
 			fd.cr <- fd
 		} else {
 			fd.cw <- fd
 		}
 		return;
 	}
 	if err := s.poll.AddFD(intfd, mode, false); err != nil {
 		panicln("pollServer AddFD ", intfd, ": ", err.String(), "\n");
 		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 <- fd;
 		}
 	} else {
 		for fd.ncw > 0 {
 			fd.ncw--;
 			fd.cw <- fd;
 		}
 	}
 }

 func (s *pollServer) Now() int64 {
 	sec, nsec, err := os.Time();
 	if err != nil {
 		panic("net: os.Time: ", err.String())
 	}
 	nsec += sec * 1e9;
 	return nsec;
 }

 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.fd, mode);
 					fd.rdeadline = -1;
 				} else {
 					s.poll.DelFD(fd.fd, 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{
 		fd: 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.file = os.NewFile(fd, net+":"+ls+"->"+rs);
 	f.cr = make(chan *netFD, 1);
 	f.cw = make(chan *netFD, 1);
 	return f, nil;
 }

 func isEAGAIN(e os.Error) bool {
 	if e1, ok := e.(*os.PathError); ok {
 		return e1.Error == os.EAGAIN
 	}
 	return e == os.EAGAIN;
 }

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

 	// 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.file.Fd(), false);

 	e := fd.file.Close();
 	fd.file = nil;
 	fd.fd = -1;
 	return e;
 }

 func (fd *netFD) Read(p []byte) (n int, err os.Error) {
 	if fd == nil || fd.file == nil {
 		return 0, os.EINVAL
 	}
 	fd.rio.Lock();
 	defer fd.rio.Unlock();
 	if fd.rdeadline_delta > 0 {
 		fd.rdeadline = pollserver.Now() + fd.rdeadline_delta
 	} else {
 		fd.rdeadline = 0
 	}
 	for {
 		n, err = fd.file.Read(p);
 		if isEAGAIN(err) && fd.rdeadline >= 0 {
 			pollserver.WaitRead(fd);
 			continue;
 		}
 		break;
 	}
 	return;
 }

 func (fd *netFD) Write(p []byte) (n int, err os.Error) {
 	if fd == nil || fd.file == nil {
 		return 0, os.EINVAL
 	}
 	fd.wio.Lock();
 	defer fd.wio.Unlock();
 	if fd.wdeadline_delta > 0 {
 		fd.wdeadline = pollserver.Now() + fd.wdeadline_delta
 	} else {
 		fd.wdeadline = 0
 	}
 	err = nil;
 	nn := 0;
 	for nn < len(p) {
 		n, err = fd.file.Write(p[nn:len(p)]);
 		if n > 0 {
 			nn += n
 		}
 		if nn == len(p) {
 			break
 		}
 		if isEAGAIN(err) && fd.wdeadline >= 0 {
 			pollserver.WaitWrite(fd);
 			continue;
 		}
 		if n == 0 || err != nil {
 			break
 		}
 	}
 	return nn, err;
 }

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

 	// See ../syscall/exec.go for description of ForkLock.
 	// It is okay to hold the lock across syscall.Accept
 	// because we have put fd.fd into non-blocking mode.
 	syscall.ForkLock.RLock();
 	var s, e int;
 	var sa syscall.Sockaddr;
 	for {
 		s, sa, e = syscall.Accept(fd.fd);
 		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 (
	"once";
	"os";
	"sync";
	"syscall";
	)

	// Network file descriptor.
	type netFD struct {
	// immutable until Close
	fd int;
	family int;
	proto int;
	file *os.File;
	cr chan *netFD;
	cw chan *netFD;
	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;
	}

	// 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.

	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) {
	// TODO(rsc): This check handles a race between
	// one goroutine reading and another one closing,
	// but it doesn't solve the race completely:
	// it still could happen that one goroutine closes
	// but we read fd.fd before it does, and then
	// another goroutine creates a new open file with
	// that fd, which we'd now be referring to.
	// The fix is probably to send the Close call
	// through the poll server too, except that
	// not all Reads and Writes go through the poll
	// server even now.
	intfd := fd.fd;
	if intfd < 0 {
	// fd closed underfoot
	if mode == 'r' {
	fd.cr <- fd
	} else {
	fd.cw <- fd
	}
	return;
	}
	if err := s.poll.AddFD(intfd, mode, false); err != nil {
	panicln("pollServer AddFD ", intfd, ": ", err.String(), "\n");
	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 <- fd;
	}
	} else {
	for fd.ncw > 0 {
	fd.ncw--;
	fd.cw <- fd;
	}
	}
	}

	func (s *pollServer) Now() int64 {
	sec, nsec, err := os.Time();
	if err != nil {
	panic("net: os.Time: ", err.String())
	}
	nsec += sec * 1e9;
	return nsec;
	}

	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.fd, mode);
	fd.rdeadline = -1;
	} else {
	s.poll.DelFD(fd.fd, 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{
	fd: 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.file = os.NewFile(fd, net+":"+ls+"->"+rs);
	f.cr = make(chan *netFD, 1);
	f.cw = make(chan *netFD, 1);
	return f, nil;
	}

	func isEAGAIN(e os.Error) bool {
	if e1, ok := e.(*os.PathError); ok {
	return e1.Error == os.EAGAIN
	}
	return e == os.EAGAIN;
	}

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

	// 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.file.Fd(), false);

	e := fd.file.Close();
	fd.file = nil;
	fd.fd = -1;
	return e;
	}

	func (fd *netFD) Read(p []byte) (n int, err os.Error) {
	if fd == nil \|\| fd.file == nil {
	return 0, os.EINVAL
	}
	fd.rio.Lock();
	defer fd.rio.Unlock();
	if fd.rdeadline_delta > 0 {
	fd.rdeadline = pollserver.Now() + fd.rdeadline_delta
	} else {
	fd.rdeadline = 0
	}
	for {
	n, err = fd.file.Read(p);
	if isEAGAIN(err) && fd.rdeadline >= 0 {
	pollserver.WaitRead(fd);
	continue;
	}
	break;
	}
	return;
	}

	func (fd *netFD) Write(p []byte) (n int, err os.Error) {
	if fd == nil \|\| fd.file == nil {
	return 0, os.EINVAL
	}
	fd.wio.Lock();
	defer fd.wio.Unlock();
	if fd.wdeadline_delta > 0 {
	fd.wdeadline = pollserver.Now() + fd.wdeadline_delta
	} else {
	fd.wdeadline = 0
	}
	err = nil;
	nn := 0;
	for nn < len(p) {
	n, err = fd.file.Write(p[nn:len(p)]);
	if n > 0 {
	nn += n
	}
	if nn == len(p) {
	break
	}
	if isEAGAIN(err) && fd.wdeadline >= 0 {
	pollserver.WaitWrite(fd);
	continue;
	}
	if n == 0 \|\| err != nil {
	break
	}
	}
	return nn, err;
	}

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

	// See ../syscall/exec.go for description of ForkLock.
	// It is okay to hold the lock across syscall.Accept
	// because we have put fd.fd into non-blocking mode.
	syscall.ForkLock.RLock();
	var s, e int;
	var sa syscall.Sockaddr;
	for {
	s, sa, e = syscall.Accept(fd.fd);
	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;
	}