if pd.closing {
		return errClosing(isFile)
	}
	return nil
}

func (pd *pollDesc) prepareRead(isFile bool) error { return pd.prepare('r', isFile) }

func (pd *pollDesc) prepareWrite(isFile bool) error { return pd.prepare('w', isFile) }

func (pd *pollDesc) wait(mode int, isFile bool) error {
	if pd.closing {
		return errClosing(isFile)
	}

func runtime_Semrelease(sema *uint32)

// incref adds a reference to fd.
// It returns an error when fd cannot be used.
func (fd *FD) incref() error {
	if !fd.fdmu.incref() {
		return errClosing(fd.isFile)
	}
	return nil
}

// decref removes a reference from fd.
// It also closes fd when the state of fd is set to closed and there
// is no remaining reference.
func (fd *FD) decref() error {

// 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 {
		return ErrFileClosing
	}
	return ErrNetClosing
}

// ErrDeadlineExceeded is returned for an expired deadline.
// This is exported by the os package as os.ErrDeadlineExceeded.

	pollErrTimeout     = 2
	pollErrNotPollable = 3
)

func convertErr(res int, isFile bool) error {
	switch res {
	case pollNoError:
		return nil
	case pollErrClosing:
		return errClosing(isFile)
	case pollErrTimeout:
		return ErrDeadlineExceeded
	case pollErrNotPollable:
		return ErrNotPollable
	}
	println("unreachable: ", res)
	panic("unreachable")
}

		fd.Destroy()
	}
	return nil
}

// Close handles the locking for closing an FD. The real operation
// is in the net package.
func (fd *FD) Close() error {
	if !fd.fdmu.increfAndClose() {
		return errClosing(fd.isFile)
	}
	return nil
}

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

	if !fd.fdmu.increfAndClose() {
		return errClosing(fd.isFile)
	}

	// Unblock any I/O.  Once it all unblocks and returns,
	// so that it cannot be referring to fd.sysfd anymore,
	// the final decref will close fd.sysfd. This should happen
	// fairly quickly, since all the I/O is non-blocking, and any
	// attempts to block in the pollDesc will return errClosing(fd.isFile).
	fd.pd.evict()

}

// 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)
	}
	if fd.kind == kindPipe {
		syscall.CancelIoEx(fd.Sysfd, nil)
	}
	// unblock pending reader and writer
	fd.pd.evict()
	err := fd.decref()