libgo: update to go1.9

[official-gcc.git] / libgo / go / internal / poll / fd_windows.go

// 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.

package poll

import (
        "errors"
        "internal/race"
        "io"
        "runtime"
        "sync"
        "syscall"
        "unicode/utf16"
        "unicode/utf8"
        "unsafe"
)

var (
        initErr error
        ioSync  uint64
)

// CancelIo Windows API cancels all outstanding IO for a particular
// socket on current thread. To overcome that limitation, we run
// special goroutine, locked to OS single thread, that both starts
// and cancels IO. It means, there are 2 unavoidable thread switches
// for every IO.
// Some newer versions of Windows has new CancelIoEx API, that does
// not have that limitation and can be used from any thread. This
// package uses CancelIoEx API, if present, otherwise it fallback
// to CancelIo.

var (
        canCancelIO                               bool // determines if CancelIoEx API is present
        skipSyncNotif                             bool
        hasLoadSetFileCompletionNotificationModes bool
)

func init() {
        var d syscall.WSAData
        e := syscall.WSAStartup(uint32(0x202), &d)
        if e != nil {
                initErr = e
        }
        canCancelIO = syscall.LoadCancelIoEx() == nil
        hasLoadSetFileCompletionNotificationModes = syscall.LoadSetFileCompletionNotificationModes() == nil
        if hasLoadSetFileCompletionNotificationModes {
                // It's not safe to use FILE_SKIP_COMPLETION_PORT_ON_SUCCESS if non IFS providers are installed:
                // http://support.microsoft.com/kb/2568167
                skipSyncNotif = true
                protos := [2]int32{syscall.IPPROTO_TCP, 0}
                var buf [32]syscall.WSAProtocolInfo
                len := uint32(unsafe.Sizeof(buf))
                n, err := syscall.WSAEnumProtocols(&protos[0], &buf[0], &len)
                if err != nil {
                        skipSyncNotif = false
                } else {
                        for i := int32(0); i < n; i++ {
                                if buf[i].ServiceFlags1&syscall.XP1_IFS_HANDLES == 0 {
                                        skipSyncNotif = false
                                        break
                                }
                        }
                }
        }
}

// operation contains superset of data necessary to perform all async IO.
type operation struct {
        // Used by IOCP interface, it must be first field
        // of the struct, as our code rely on it.
        o syscall.Overlapped

        // fields used by runtime.netpoll
        runtimeCtx uintptr
        mode       int32
        errno      int32
        qty        uint32

        // fields used only by net package
        fd     *FD
        errc   chan error
        buf    syscall.WSABuf
        sa     syscall.Sockaddr
        rsa    *syscall.RawSockaddrAny
        rsan   int32
        handle syscall.Handle
        flags  uint32
        bufs   []syscall.WSABuf
}

func (o *operation) InitBuf(buf []byte) {
        o.buf.Len = uint32(len(buf))
        o.buf.Buf = nil
        if len(buf) != 0 {
                o.buf.Buf = &buf[0]
        }
}

func (o *operation) InitBufs(buf *[][]byte) {
        if o.bufs == nil {
                o.bufs = make([]syscall.WSABuf, 0, len(*buf))
        } else {
                o.bufs = o.bufs[:0]
        }
        for _, b := range *buf {
                var p *byte
                if len(b) > 0 {
                        p = &b[0]
                }
                o.bufs = append(o.bufs, syscall.WSABuf{Len: uint32(len(b)), Buf: p})
        }
}

// ClearBufs clears all pointers to Buffers parameter captured
// by InitBufs, so it can be released by garbage collector.
func (o *operation) ClearBufs() {
        for i := range o.bufs {
                o.bufs[i].Buf = nil
        }
        o.bufs = o.bufs[:0]
}

// ioSrv executes net IO requests.
type ioSrv struct {
        req chan ioSrvReq
}

type ioSrvReq struct {
        o      *operation
        submit func(o *operation) error // if nil, cancel the operation
}

// ProcessRemoteIO will execute submit IO requests on behalf
// of other goroutines, all on a single os thread, so it can
// cancel them later. Results of all operations will be sent
// back to their requesters via channel supplied in request.
// It is used only when the CancelIoEx API is unavailable.
func (s *ioSrv) ProcessRemoteIO() {
        runtime.LockOSThread()
        defer runtime.UnlockOSThread()
        for r := range s.req {
                if r.submit != nil {
                        r.o.errc <- r.submit(r.o)
                } else {
                        r.o.errc <- syscall.CancelIo(r.o.fd.Sysfd)
                }
        }
}

// ExecIO executes a single IO operation o. It submits and cancels
// IO in the current thread for systems where Windows CancelIoEx API
// is available. Alternatively, it passes the request onto
// runtime netpoll and waits for completion or cancels request.
func (s *ioSrv) ExecIO(o *operation, submit func(o *operation) error) (int, error) {
        if o.fd.pd.runtimeCtx == 0 {
                return 0, errors.New("internal error: polling on unsupported descriptor type")
        }

        if !canCancelIO {
                onceStartServer.Do(startServer)
        }

        fd := o.fd
        // Notify runtime netpoll about starting IO.
        err := fd.pd.prepare(int(o.mode), fd.isFile)
        if err != nil {
                return 0, err
        }
        // Start IO.
        if canCancelIO {
                err = submit(o)
        } else {
                // Send request to a special dedicated thread,
                // so it can stop the IO with CancelIO later.
                s.req <- ioSrvReq{o, submit}
                err = <-o.errc
        }
        switch err {
        case nil:
                // IO completed immediately
                if o.fd.skipSyncNotif {
                        // No completion message will follow, so return immediately.
                        return int(o.qty), nil
                }
                // Need to get our completion message anyway.
        case syscall.ERROR_IO_PENDING:
                // IO started, and we have to wait for its completion.
                err = nil
        default:
                return 0, err
        }
        // Wait for our request to complete.
        err = fd.pd.wait(int(o.mode), fd.isFile)
        if err == nil {
                // All is good. Extract our IO results and return.
                if o.errno != 0 {
                        err = syscall.Errno(o.errno)
                        return 0, err
                }
                return int(o.qty), nil
        }
        // IO is interrupted by "close" or "timeout"
        netpollErr := err
        switch netpollErr {
        case ErrNetClosing, ErrFileClosing, ErrTimeout:
                // will deal with those.
        default:
                panic("unexpected runtime.netpoll error: " + netpollErr.Error())
        }
        // Cancel our request.
        if canCancelIO {
                err := syscall.CancelIoEx(fd.Sysfd, &o.o)
                // Assuming ERROR_NOT_FOUND is returned, if IO is completed.
                if err != nil && err != syscall.ERROR_NOT_FOUND {
                        // TODO(brainman): maybe do something else, but panic.
                        panic(err)
                }
        } else {
                s.req <- ioSrvReq{o, nil}
                <-o.errc
        }
        // Wait for cancelation to complete.
        fd.pd.waitCanceled(int(o.mode))
        if o.errno != 0 {
                err = syscall.Errno(o.errno)
                if err == syscall.ERROR_OPERATION_ABORTED { // IO Canceled
                        err = netpollErr
                }
                return 0, err
        }
        // We issued a cancelation request. But, it seems, IO operation succeeded
        // before the cancelation request run. We need to treat the IO operation as
        // succeeded (the bytes are actually sent/recv from network).
        return int(o.qty), nil
}

// Start helper goroutines.
var rsrv, wsrv ioSrv
var onceStartServer sync.Once

func startServer() {
        // This is called, once, when only the CancelIo API is available.
        // Start two special goroutines, both locked to an OS thread,
        // that start and cancel IO requests.
        // One will process read requests, while the other will do writes.
        rsrv.req = make(chan ioSrvReq)
        go rsrv.ProcessRemoteIO()
        wsrv.req = make(chan ioSrvReq)
        go wsrv.ProcessRemoteIO()
}

// FD is a file descriptor. The net and os packages embed this type in
// a larger type representing a network connection or OS file.
type FD struct {
        // Lock sysfd and serialize access to Read and Write methods.
        fdmu fdMutex

        // System file descriptor. Immutable until Close.
        Sysfd syscall.Handle

        // Read operation.
        rop operation
        // Write operation.
        wop operation

        // I/O poller.
        pd pollDesc

        // Used to implement pread/pwrite.
        l sync.Mutex

        // For console I/O.
        isConsole      bool
        lastbits       []byte   // first few bytes of the last incomplete rune in last write
        readuint16     []uint16 // buffer to hold uint16s obtained with ReadConsole
        readbyte       []byte   // buffer to hold decoding of readuint16 from utf16 to utf8
        readbyteOffset int      // readbyte[readOffset:] is yet to be consumed with file.Read

        skipSyncNotif bool

        // Whether this is a streaming descriptor, as opposed to a
        // packet-based descriptor like a UDP socket.
        IsStream bool

        // Whether a zero byte read indicates EOF. This is false for a
        // message based socket connection.
        ZeroReadIsEOF bool

        // Whether this is a normal file.
        isFile bool

        // Whether this is a directory.
        isDir bool
}

// Init initializes the FD. The Sysfd field should already be set.
// This can be called multiple times on a single FD.
// The net argument is a network name from the net package (e.g., "tcp"),
// or "file" or "console" or "dir".
func (fd *FD) Init(net string) (string, error) {
        if initErr != nil {
                return "", initErr
        }

        switch net {
        case "file":
                fd.isFile = true
        case "console":
                fd.isConsole = true
        case "dir":
                fd.isDir = true
        case "tcp", "tcp4", "tcp6":
        case "udp", "udp4", "udp6":
        case "ip", "ip4", "ip6":
        case "unix", "unixgram", "unixpacket":
        default:
                return "", errors.New("internal error: unknown network type " + net)
        }

        if !fd.isFile && !fd.isConsole && !fd.isDir {
                // Only call init for a network socket.
                // This means that we don't add files to the runtime poller.
                // Adding files to the runtime poller can confuse matters
                // if the user is doing their own overlapped I/O.
                // See issue #21172.
                //
                // In general the code below avoids calling the ExecIO
                // method for non-network sockets. If some method does
                // somehow call ExecIO, then ExecIO, and therefore the
                // calling method, will return an error, because
                // fd.pd.runtimeCtx will be 0.
                if err := fd.pd.init(fd); err != nil {
                        return "", err
                }
        }
        if hasLoadSetFileCompletionNotificationModes {
                // We do not use events, so we can skip them always.
                flags := uint8(syscall.FILE_SKIP_SET_EVENT_ON_HANDLE)
                // It's not safe to skip completion notifications for UDP:
                // http://blogs.technet.com/b/winserverperformance/archive/2008/06/26/designing-applications-for-high-performance-part-iii.aspx
                if skipSyncNotif && (net == "tcp" || net == "file") {
                        flags |= syscall.FILE_SKIP_COMPLETION_PORT_ON_SUCCESS
                }
                err := syscall.SetFileCompletionNotificationModes(fd.Sysfd, flags)
                if err == nil && flags&syscall.FILE_SKIP_COMPLETION_PORT_ON_SUCCESS != 0 {
                        fd.skipSyncNotif = true
                }
        }
        // Disable SIO_UDP_CONNRESET behavior.
        // http://support.microsoft.com/kb/263823
        switch net {
        case "udp", "udp4", "udp6":
                ret := uint32(0)
                flag := uint32(0)
                size := uint32(unsafe.Sizeof(flag))
                err := syscall.WSAIoctl(fd.Sysfd, syscall.SIO_UDP_CONNRESET, (*byte)(unsafe.Pointer(&flag)), size, nil, 0, &ret, nil, 0)
                if err != nil {
                        return "wsaioctl", err
                }
        }
        fd.rop.mode = 'r'
        fd.wop.mode = 'w'
        fd.rop.fd = fd
        fd.wop.fd = fd
        fd.rop.runtimeCtx = fd.pd.runtimeCtx
        fd.wop.runtimeCtx = fd.pd.runtimeCtx
        if !canCancelIO {
                fd.rop.errc = make(chan error)
                fd.wop.errc = make(chan error)
        }
        return "", nil
}

func (fd *FD) destroy() error {
        if fd.Sysfd == syscall.InvalidHandle {
                return syscall.EINVAL
        }
        // Poller may want to unregister fd in readiness notification mechanism,
        // so this must be executed before fd.CloseFunc.
        fd.pd.close()
        var err error
        if fd.isFile || fd.isConsole {
                err = syscall.CloseHandle(fd.Sysfd)
        } else if fd.isDir {
                err = syscall.FindClose(fd.Sysfd)
        } else {
                // The net package uses the CloseFunc variable for testing.
                err = CloseFunc(fd.Sysfd)
        }
        fd.Sysfd = syscall.InvalidHandle
        return err
}

// Close closes the FD. The underlying file descriptor is closed by
// the destroy method when there are no remaining references.
func (fd *FD) Close() error {
        if !fd.fdmu.increfAndClose() {
                return errClosing(fd.isFile)
        }
        // unblock pending reader and writer
        fd.pd.evict()
        return fd.decref()
}

// Shutdown wraps the shutdown network call.
func (fd *FD) Shutdown(how int) error {
        if err := fd.incref(); err != nil {
                return err
        }
        defer fd.decref()
        return syscall.Shutdown(fd.Sysfd, how)
}

// Read implements io.Reader.
func (fd *FD) Read(buf []byte) (int, error) {
        if err := fd.readLock(); err != nil {
                return 0, err
        }
        defer fd.readUnlock()

        var n int
        var err error
        if fd.isFile || fd.isDir || fd.isConsole {
                fd.l.Lock()
                defer fd.l.Unlock()
                if fd.isConsole {
                        n, err = fd.readConsole(buf)
                } else {
                        n, err = syscall.Read(fd.Sysfd, buf)
                }
                if err != nil {
                        n = 0
                }
        } else {
                o := &fd.rop
                o.InitBuf(buf)
                n, err = rsrv.ExecIO(o, func(o *operation) error {
                        return syscall.WSARecv(o.fd.Sysfd, &o.buf, 1, &o.qty, &o.flags, &o.o, nil)
                })
                if race.Enabled {
                        race.Acquire(unsafe.Pointer(&ioSync))
                }
        }
        if len(buf) != 0 {
                err = fd.eofError(n, err)
        }
        return n, err
}

var ReadConsole = syscall.ReadConsole // changed for testing

// readConsole reads utf16 characters from console File,
// encodes them into utf8 and stores them in buffer b.
// It returns the number of utf8 bytes read and an error, if any.
func (fd *FD) readConsole(b []byte) (int, error) {
        if len(b) == 0 {
                return 0, nil
        }

        if fd.readuint16 == nil {
                // Note: syscall.ReadConsole fails for very large buffers.
                // The limit is somewhere around (but not exactly) 16384.
                // Stay well below.
                fd.readuint16 = make([]uint16, 0, 10000)
                fd.readbyte = make([]byte, 0, 4*cap(fd.readuint16))
        }

        for fd.readbyteOffset >= len(fd.readbyte) {
                n := cap(fd.readuint16) - len(fd.readuint16)
                if n > len(b) {
                        n = len(b)
                }
                var nw uint32
                err := ReadConsole(fd.Sysfd, &fd.readuint16[:len(fd.readuint16)+1][len(fd.readuint16)], uint32(n), &nw, nil)
                if err != nil {
                        return 0, err
                }
                uint16s := fd.readuint16[:len(fd.readuint16)+int(nw)]
                fd.readuint16 = fd.readuint16[:0]
                buf := fd.readbyte[:0]
                for i := 0; i < len(uint16s); i++ {
                        r := rune(uint16s[i])
                        if utf16.IsSurrogate(r) {
                                if i+1 == len(uint16s) {
                                        if nw > 0 {
                                                // Save half surrogate pair for next time.
                                                fd.readuint16 = fd.readuint16[:1]
                                                fd.readuint16[0] = uint16(r)
                                                break
                                        }
                                        r = utf8.RuneError
                                } else {
                                        r = utf16.DecodeRune(r, rune(uint16s[i+1]))
                                        if r != utf8.RuneError {
                                                i++
                                        }
                                }
                        }
                        n := utf8.EncodeRune(buf[len(buf):cap(buf)], r)
                        buf = buf[:len(buf)+n]
                }
                fd.readbyte = buf
                fd.readbyteOffset = 0
                if nw == 0 {
                        break
                }
        }

        src := fd.readbyte[fd.readbyteOffset:]
        var i int
        for i = 0; i < len(src) && i < len(b); i++ {
                x := src[i]
                if x == 0x1A { // Ctrl-Z
                        if i == 0 {
                                fd.readbyteOffset++
                        }
                        break
                }
                b[i] = x
        }
        fd.readbyteOffset += i
        return i, nil
}

// Pread emulates the Unix pread system call.
func (fd *FD) Pread(b []byte, off int64) (int, error) {
        // Call incref, not readLock, because since pread specifies the
        // offset it is independent from other reads.
        if err := fd.incref(); err != nil {
                return 0, err
        }
        defer fd.decref()

        fd.l.Lock()
        defer fd.l.Unlock()
        curoffset, e := syscall.Seek(fd.Sysfd, 0, io.SeekCurrent)
        if e != nil {
                return 0, e
        }
        defer syscall.Seek(fd.Sysfd, curoffset, io.SeekStart)
        o := syscall.Overlapped{
                OffsetHigh: uint32(off >> 32),
                Offset:     uint32(off),
        }
        var done uint32
        e = syscall.ReadFile(fd.Sysfd, b, &done, &o)
        if e != nil {
                done = 0
                if e == syscall.ERROR_HANDLE_EOF {
                        e = io.EOF
                }
        }
        if len(b) != 0 {
                e = fd.eofError(int(done), e)
        }
        return int(done), e
}

// ReadFrom wraps the recvfrom network call.
func (fd *FD) ReadFrom(buf []byte) (int, syscall.Sockaddr, error) {
        if len(buf) == 0 {
                return 0, nil, nil
        }
        if err := fd.readLock(); err != nil {
                return 0, nil, err
        }
        defer fd.readUnlock()
        o := &fd.rop
        o.InitBuf(buf)
        n, err := rsrv.ExecIO(o, func(o *operation) error {
                if o.rsa == nil {
                        o.rsa = new(syscall.RawSockaddrAny)
                }
                o.rsan = int32(unsafe.Sizeof(*o.rsa))
                return syscall.WSARecvFrom(o.fd.Sysfd, &o.buf, 1, &o.qty, &o.flags, o.rsa, &o.rsan, &o.o, nil)
        })
        err = fd.eofError(n, err)
        if err != nil {
                return n, nil, err
        }
        sa, _ := o.rsa.Sockaddr()
        return n, sa, nil
}

// Write implements io.Writer.
func (fd *FD) Write(buf []byte) (int, error) {
        if err := fd.writeLock(); err != nil {
                return 0, err
        }
        defer fd.writeUnlock()

        var n int
        var err error
        if fd.isFile || fd.isDir || fd.isConsole {
                fd.l.Lock()
                defer fd.l.Unlock()
                if fd.isConsole {
                        n, err = fd.writeConsole(buf)
                } else {
                        n, err = syscall.Write(fd.Sysfd, buf)
                }
                if err != nil {
                        n = 0
                }
        } else {
                if race.Enabled {
                        race.ReleaseMerge(unsafe.Pointer(&ioSync))
                }
                o := &fd.wop
                o.InitBuf(buf)
                n, err = wsrv.ExecIO(o, func(o *operation) error {
                        return syscall.WSASend(o.fd.Sysfd, &o.buf, 1, &o.qty, 0, &o.o, nil)
                })
        }
        return n, err
}

// writeConsole writes len(b) bytes to the console File.
// It returns the number of bytes written and an error, if any.
func (fd *FD) writeConsole(b []byte) (int, error) {
        n := len(b)
        runes := make([]rune, 0, 256)
        if len(fd.lastbits) > 0 {
                b = append(fd.lastbits, b...)
                fd.lastbits = nil

        }
        for len(b) >= utf8.UTFMax || utf8.FullRune(b) {
                r, l := utf8.DecodeRune(b)
                runes = append(runes, r)
                b = b[l:]
        }
        if len(b) > 0 {
                fd.lastbits = make([]byte, len(b))
                copy(fd.lastbits, b)
        }
        // syscall.WriteConsole seems to fail, if given large buffer.
        // So limit the buffer to 16000 characters. This number was
        // discovered by experimenting with syscall.WriteConsole.
        const maxWrite = 16000
        for len(runes) > 0 {
                m := len(runes)
                if m > maxWrite {
                        m = maxWrite
                }
                chunk := runes[:m]
                runes = runes[m:]
                uint16s := utf16.Encode(chunk)
                for len(uint16s) > 0 {
                        var written uint32
                        err := syscall.WriteConsole(fd.Sysfd, &uint16s[0], uint32(len(uint16s)), &written, nil)
                        if err != nil {
                                return 0, err
                        }
                        uint16s = uint16s[written:]
                }
        }
        return n, nil
}

// Pwrite emulates the Unix pwrite system call.
func (fd *FD) Pwrite(b []byte, off int64) (int, error) {
        // Call incref, not writeLock, because since pwrite specifies the
        // offset it is independent from other writes.
        if err := fd.incref(); err != nil {
                return 0, err
        }
        defer fd.decref()

        fd.l.Lock()
        defer fd.l.Unlock()
        curoffset, e := syscall.Seek(fd.Sysfd, 0, io.SeekCurrent)
        if e != nil {
                return 0, e
        }
        defer syscall.Seek(fd.Sysfd, curoffset, io.SeekStart)
        o := syscall.Overlapped{
                OffsetHigh: uint32(off >> 32),
                Offset:     uint32(off),
        }
        var done uint32
        e = syscall.WriteFile(fd.Sysfd, b, &done, &o)
        if e != nil {
                return 0, e
        }
        return int(done), nil
}

// Writev emulates the Unix writev system call.
func (fd *FD) Writev(buf *[][]byte) (int64, error) {
        if len(*buf) == 0 {
                return 0, nil
        }
        if err := fd.writeLock(); err != nil {
                return 0, err
        }
        defer fd.writeUnlock()
        if race.Enabled {
                race.ReleaseMerge(unsafe.Pointer(&ioSync))
        }
        o := &fd.wop
        o.InitBufs(buf)
        n, err := wsrv.ExecIO(o, func(o *operation) error {
                return syscall.WSASend(o.fd.Sysfd, &o.bufs[0], uint32(len(o.bufs)), &o.qty, 0, &o.o, nil)
        })
        o.ClearBufs()
        TestHookDidWritev(n)
        consume(buf, int64(n))
        return int64(n), err
}

// WriteTo wraps the sendto network call.
func (fd *FD) WriteTo(buf []byte, sa syscall.Sockaddr) (int, error) {
        if len(buf) == 0 {
                return 0, nil
        }
        if err := fd.writeLock(); err != nil {
                return 0, err
        }
        defer fd.writeUnlock()
        o := &fd.wop
        o.InitBuf(buf)
        o.sa = sa
        n, err := wsrv.ExecIO(o, func(o *operation) error {
                return syscall.WSASendto(o.fd.Sysfd, &o.buf, 1, &o.qty, 0, o.sa, &o.o, nil)
        })
        return n, err
}

// Call ConnectEx. This doesn't need any locking, since it is only
// called when the descriptor is first created. This is here rather
// than in the net package so that it can use fd.wop.
func (fd *FD) ConnectEx(ra syscall.Sockaddr) error {
        o := &fd.wop
        o.sa = ra
        _, err := wsrv.ExecIO(o, func(o *operation) error {
                return ConnectExFunc(o.fd.Sysfd, o.sa, nil, 0, nil, &o.o)
        })
        return err
}

func (fd *FD) acceptOne(s syscall.Handle, rawsa []syscall.RawSockaddrAny, o *operation) (string, error) {
        // Submit accept request.
        o.handle = s
        o.rsan = int32(unsafe.Sizeof(rawsa[0]))
        _, err := rsrv.ExecIO(o, func(o *operation) error {
                return AcceptFunc(o.fd.Sysfd, o.handle, (*byte)(unsafe.Pointer(&rawsa[0])), 0, uint32(o.rsan), uint32(o.rsan), &o.qty, &o.o)
        })
        if err != nil {
                CloseFunc(s)
                return "acceptex", err
        }

        // Inherit properties of the listening socket.
        err = syscall.Setsockopt(s, syscall.SOL_SOCKET, syscall.SO_UPDATE_ACCEPT_CONTEXT, (*byte)(unsafe.Pointer(&fd.Sysfd)), int32(unsafe.Sizeof(fd.Sysfd)))
        if err != nil {
                CloseFunc(s)
                return "setsockopt", err
        }

        return "", nil
}

// Accept handles accepting a socket. The sysSocket parameter is used
// to allocate the net socket.
func (fd *FD) Accept(sysSocket func() (syscall.Handle, error)) (syscall.Handle, []syscall.RawSockaddrAny, uint32, string, error) {
        if err := fd.readLock(); err != nil {
                return syscall.InvalidHandle, nil, 0, "", err
        }
        defer fd.readUnlock()

        o := &fd.rop
        var rawsa [2]syscall.RawSockaddrAny
        for {
                s, err := sysSocket()
                if err != nil {
                        return syscall.InvalidHandle, nil, 0, "", err
                }

                errcall, err := fd.acceptOne(s, rawsa[:], o)
                if err == nil {
                        return s, rawsa[:], uint32(o.rsan), "", nil
                }

                // Sometimes we see WSAECONNRESET and ERROR_NETNAME_DELETED is
                // returned here. These happen if connection reset is received
                // before AcceptEx could complete. These errors relate to new
                // connection, not to AcceptEx, so ignore broken connection and
                // try AcceptEx again for more connections.
                errno, ok := err.(syscall.Errno)
                if !ok {
                        return syscall.InvalidHandle, nil, 0, errcall, err
                }
                switch errno {
                case syscall.ERROR_NETNAME_DELETED, syscall.WSAECONNRESET:
                        // ignore these and try again
                default:
                        return syscall.InvalidHandle, nil, 0, errcall, err
                }
        }
}

// Seek wraps syscall.Seek.
func (fd *FD) Seek(offset int64, whence int) (int64, error) {
        if err := fd.incref(); err != nil {
                return 0, err
        }
        defer fd.decref()

        fd.l.Lock()
        defer fd.l.Unlock()

        return syscall.Seek(fd.Sysfd, offset, whence)
}

// FindNextFile wraps syscall.FindNextFile.
func (fd *FD) FindNextFile(data *syscall.Win32finddata) error {
        if err := fd.incref(); err != nil {
                return err
        }
        defer fd.decref()
        return syscall.FindNextFile(fd.Sysfd, data)
}

// Fchdir wraps syscall.Fchdir.
func (fd *FD) Fchdir() error {
        if err := fd.incref(); err != nil {
                return err
        }
        defer fd.decref()
        return syscall.Fchdir(fd.Sysfd)
}

// GetFileType wraps syscall.GetFileType.
func (fd *FD) GetFileType() (uint32, error) {
        if err := fd.incref(); err != nil {
                return 0, err
        }
        defer fd.decref()
        return syscall.GetFileType(fd.Sysfd)
}

// GetFileInformationByHandle wraps GetFileInformationByHandle.
func (fd *FD) GetFileInformationByHandle(data *syscall.ByHandleFileInformation) error {
        if err := fd.incref(); err != nil {
                return err
        }
        defer fd.decref()
        return syscall.GetFileInformationByHandle(fd.Sysfd, data)
}

// RawControl invokes the user-defined function f for a non-IO
// operation.
func (fd *FD) RawControl(f func(uintptr)) error {
        if err := fd.incref(); err != nil {
                return err
        }
        defer fd.decref()
        f(uintptr(fd.Sysfd))
        return nil
}

// RawRead invokes the user-defined function f for a read operation.
func (fd *FD) RawRead(f func(uintptr) bool) error {
        return errors.New("not implemented")
}

// RawWrite invokes the user-defined function f for a write operation.
func (fd *FD) RawWrite(f func(uintptr) bool) error {
        return errors.New("not implemented")
}