(tags-loop-scan): Set default value to an error form.

[bpt/emacs.git] / src / xselect.c.old

/* X Selection processing for emacs
   Copyright (C) 1990, 1992 Free Software Foundation.

This file is part of GNU Emacs.

GNU Emacs is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs; see the file COPYING.  If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */

#include "config.h"
#include "lisp.h"
#include "xterm.h"
#include "buffer.h"
#include "frame.h"

#ifdef HAVE_X11

/* Macros for X Selections */
#define MAX_SELECTION(dpy) (((dpy)->max_request_size << 2) - 100)
#define SELECTION_LENGTH(len,format) ((len) * ((format) >> 2))

/* The timestamp of the last input event we received from the X server.  */
unsigned long last_event_timestamp;

/* t if a mouse button is depressed. */
extern Lisp_Object Vmouse_grabbed;

/* When emacs became the PRIMARY selection owner. */
Time x_begin_selection_own;

/* When emacs became the SECONDARY selection owner. */
Time x_begin_secondary_selection_own;

/* When emacs became the CLIPBOARD selection owner. */
Time x_begin_clipboard_own;

/* The value of the current CLIPBOARD selection. */
Lisp_Object Vx_clipboard_value;

/* The value of the current PRIMARY selection. */
Lisp_Object Vx_selection_value;

/* The value of the current SECONDARY selection. */
Lisp_Object Vx_secondary_selection_value;

/* Types of selections we may make.  */
Lisp_Object Qprimary, Qsecondary, Qclipboard;

/* Emacs' selection property identifiers. */
Atom Xatom_emacs_selection;
Atom Xatom_emacs_secondary_selection;

/* Clipboard selection atom. */
Atom Xatom_clipboard_selection;

/* Clipboard atom. */
Atom Xatom_clipboard;

/* Atom for indicating incremental selection transfer. */
Atom Xatom_incremental;

/* Atom for indicating multiple selection request list */
Atom Xatom_multiple;

/* Atom for what targets emacs handles. */
Atom Xatom_targets;

/* Atom for indicating timstamp selection request */
Atom Xatom_timestamp;

/* Atom requesting we delete our selection. */
Atom Xatom_delete;

/* Selection magic. */
Atom Xatom_insert_selection;

/* Type of property for INSERT_SELECTION. */
Atom Xatom_pair;

/* More selection magic. */
Atom Xatom_insert_property;

/* Atom for indicating property type TEXT */
Atom Xatom_text;

/* Kinds of protocol things we may receive. */
Atom Xatom_wm_take_focus;
Atom Xatom_wm_save_yourself;
Atom Xatom_wm_delete_window;

/* Communication with window managers. */
Atom Xatom_wm_protocols;

/* These are to handle incremental selection transfer. */
Window incr_requestor;
Atom incr_property;
int incr_nbytes;
unsigned char *incr_value;
unsigned char *incr_ptr;

/* Declarations for handling cut buffers.

   Whenever we set a cut buffer or read a cut buffer's value, we cache
   it in cut_buffer_value.  We look for PropertyNotify events about
   the CUT_BUFFER properties, and invalidate our cache accordingly.
   We ignore PropertyNotify events that we suspect were caused by our
   own changes to the cut buffers, so we can keep the cache valid
   longer.

   IS ALL THIS HAIR WORTH IT?  Well, these functions get called every
   time an element goes into or is retrieved from the kill ring, and
   those ought to be quick.  It's not fun in time or space to wait for
   50k cut buffers to fly back and forth across the net.  */

/* The number of CUT_BUFFER properties defined under X.  */
#define NUM_CUT_BUFFERS (8)

/* cut_buffer_atom[n] is the atom naming the nth cut buffer.  */
static Atom cut_buffer_atom[NUM_CUT_BUFFERS] = {
  XA_CUT_BUFFER0, XA_CUT_BUFFER1, XA_CUT_BUFFER2, XA_CUT_BUFFER3,
  XA_CUT_BUFFER4, XA_CUT_BUFFER5, XA_CUT_BUFFER6, XA_CUT_BUFFER7
};

/* cut_buffer_value is an eight-element vector;
   (aref cut_buffer_value n) is the cached value of cut buffer n, or
   Qnil if cut buffer n is unset.  */
static Lisp_Object cut_buffer_value;

/* Bit N of cut_buffer_cached is true if (aref cut_buffer_value n) is
   known to be valid.  This is cleared by PropertyNotify events
   handled by x_invalidate_cut_buffer_cache.  It would be wonderful if
   that routine could just set the appropriate element of
   cut_buffer_value to some special value meaning "uncached", but that
   would lose if a GC happened to be in progress.

   Bit N of cut_buffer_just_set is true if cut buffer N has been set since
   the last PropertyNotify event; since we get an event even when we set
   the property ourselves, we should ignore one event after setting
   a cut buffer, so we don't have to throw away our cache.  */
#ifdef __STDC__
volatile
#endif
static cut_buffer_cached, cut_buffer_just_set;

\f
/* Acquiring ownership of a selection.  */


/* Request selection ownership if we do not already have it. */

static int
own_selection (selection_type, time)
     Atom selection_type;
     Time time;
{
  Window owner_window, selecting_window;

  if ((selection_type == XA_PRIMARY
       && !NILP (Vx_selection_value))
      || (selection_type == XA_SECONDARY
          && !NILP (Vx_secondary_selection_value))
      || (selection_type == Xatom_clipboard
          && !NILP (Vx_clipboard_value)))
    return 1;

  selecting_window = FRAME_X_WINDOW (selected_frame);
  XSetSelectionOwner (x_current_display, selection_type,
		      selecting_window, time);
  owner_window = XGetSelectionOwner (x_current_display, selection_type);

      if (owner_window != selecting_window)
    return 0;

  return 1;
}

/* Become the selection owner and make our data the selection value.
   If we are already the owner, merely change data and timestamp values.
   This avoids generating SelectionClear events for ourselves. */

DEFUN ("x-own-selection", Fx_own_selection, Sx_own_selection,
  1, 2, "",
  "Make STRING the selection value.  Default is the primary selection,\n\
but optional second argument TYPE may specify secondary or clipboard.\n\
\n\
TYPE may also be cut-buffer0, indicating that Emacs should set the X\n\
cut buffer 0 to STRING.  This is for compatibility with older X\n\
applications which still use the cut buffers; new applications should\n\
use X selections.")
  (string, type)
     register Lisp_Object string, type;
{
  Atom selection_type;
  Lisp_Object val;
  Time event_time = last_event_timestamp;
  CHECK_STRING (string, 0);

  val = Qnil;

  if (NILP (type) || EQ (type, Qprimary))
    {
      BLOCK_INPUT;
      if (own_selection (XA_PRIMARY, event_time))
	{
	  x_begin_selection_own = event_time;
	  val = Vx_selection_value = string;
	}
      UNBLOCK_INPUT;
    }
  else if (EQ (type, Qsecondary))
    {
      BLOCK_INPUT;
      if (own_selection (XA_SECONDARY, event_time))
	{
	  x_begin_secondary_selection_own = event_time;
	  val = Vx_secondary_selection_value = string;
	}
      UNBLOCK_INPUT;
    }
  else if (EQ (type, Qclipboard))
    {
      BLOCK_INPUT;
      if (own_selection (Xatom_clipboard, event_time))
	{
	  x_begin_clipboard_own = event_time;
	  val = Vx_clipboard_value = string;
	}
      UNBLOCK_INPUT;
    }
#if 0
  else if (EQ (type, Qcut_buffer0))
    {
      /* DECwindows and some other servers don't seem to like setting
	 properties to values larger than about 20k.  For very large
	 values, they signal an error, but for intermediate values
	 they just seem to hang.

	 We could just truncate the request, but it's better to let
	 the user know that the strategy he/she's using isn't going to
	 work than to have it work partially, but incorrectly.  */
      BLOCK_INPUT;
      if (XSTRING (string)->size > MAX_SELECTION (x_current_display))
	{
	  XStoreBytes (x_current_display, (char *) 0, 0);
	  val = Qnil;
	}
      else
	{
	  XStoreBytes (x_current_display,
		       (char *) XSTRING (string)->data,
		       XSTRING (string)->size);
	  val = string;
	}
      UNBLOCK_INPUT;
    }
#endif
  else
    error ("Invalid X selection type");

  return val;
}

/* Clear our selection ownership data, as some other client has
   become the owner. */

void
x_disown_selection (old_owner, selection, changed_owner_time)
     Window *old_owner;
     Atom selection;
     Time changed_owner_time;
{
  struct frame *s = x_window_to_frame (old_owner);

  if (s)			/* We are the owner */
    {
      if (selection == XA_PRIMARY)
	{
	  x_begin_selection_own = 0;
	  Vx_selection_value = Qnil;
	}
      else if (selection == XA_SECONDARY)
	{
	  x_begin_secondary_selection_own = 0;
	  Vx_secondary_selection_value = Qnil;
	}
      else if (selection == Xatom_clipboard)
	{
	  x_begin_clipboard_own = 0;
	  Vx_clipboard_value = Qnil;
	}
      else
	abort ();
    }
  else
    abort ();			/* Inconsistent state. */
}

\f
/* Answering selection requests.  */

int x_selection_alloc_error;
int x_converting_selection;

/* Reply to some client's request for our selection data.
   Data is placed in a property supplied by the requesting window.

   If the data exceeds the maximum amount the server can send,
   then prepare to send it incrementally, and reply to the client with
   the total size of the data.

   But first, check for all the other crufty stuff we could get. */

void
x_answer_selection_request (event)
     XSelectionRequestEvent event;
{
  Time emacs_own_time;
  Lisp_Object selection_value;
  XSelectionEvent evt;
  int format = 8;		/* We have only byte sized (text) data. */

  evt.type = SelectionNotify;	/* Construct reply event */
  evt.display = event.display;
  evt.requestor = event.requestor;
  evt.selection = event.selection;
  evt.time = event.time;
  evt.target = event.target;

  if (event.selection == XA_PRIMARY)
    {
      emacs_own_time = x_begin_selection_own;
      selection_value = Vx_selection_value;
    }
  else if (event.selection == XA_SECONDARY)
    {
      emacs_own_time = x_begin_secondary_selection_own;
      selection_value = Vx_secondary_selection_value;
    }
  else if (event.selection == Xatom_clipboard)
    {
      emacs_own_time = x_begin_clipboard_own;
      selection_value = Vx_clipboard_value;
    }
  else
    abort ();

  if (event.time != CurrentTime
      && event.time < emacs_own_time)
    evt.property = None;
  else
    {
      if (event.property == None)	/* obsolete client */
	evt.property = event.target;
      else
	evt.property = event.property;
    }

  if (event.target == Xatom_targets)          /* Send List of target atoms */
    {
    }
  else if (event.target == Xatom_multiple)    /* Recvd list: <target, prop> */
    {
      Atom type;
      int return_format;
      unsigned long items, bytes_left;
      unsigned char *data;
      int result, i;

      if (event.property == 0	/* 0 == NILP */
	  || event.property == None)
	return;

      result = XGetWindowProperty (event.display, event.requestor,
				   event.property, 0L, 10000000L,
				   True, Xatom_pair, &type, &return_format,
				   &items, &bytes_left, &data);

      if (result == Success && type == Xatom_pair)
	for (i = items; i > 0; i--)
	  {
	    /* Convert each element of the list. */
	  }

      (void) XSendEvent (x_current_display, evt.requestor, False,
			 0L, (XEvent *) &evt);
      return;
    }
  else if (event.target == Xatom_timestamp)   /* Send ownership timestamp */
    {
      if (! emacs_own_time)
	abort ();

      format = 32;
      XChangeProperty (evt.display, evt.requestor, evt.property,
		       evt.target, format, PropModeReplace,
		       (unsigned char *) &emacs_own_time, 1);
      return;
    }
  else if (event.target == Xatom_delete)      /* Delete our selection. */
    {
      if (EQ (Qnil, selection_value))
	abort ();

      x_disown_selection (event.owner, event.selection, event.time);

      /* Now return property of type NILP, length 0. */
      XChangeProperty (event.display, event.requestor, event.property,
		       0, format, PropModeReplace, (unsigned char *) 0, 0);
      return;
    }
  else if (event.target == Xatom_insert_selection)
    {
      Atom type;
      int return_format;
      unsigned long items, bytes_left;
      unsigned char *data;
      int result = XGetWindowProperty (event.display, event.requestor,
				       event.property, 0L, 10000000L,
				       True, Xatom_pair, &type, &return_format,
				       &items, &bytes_left, &data);
      if (result == Success && type == Xatom_pair)
	{
	  /* Convert the first atom to (a selection) to the target
	     indicated by the second atom. */
	}
    }
  else if (event.target == Xatom_insert_property)
    {
      Atom type;
      int return_format;
      unsigned long items, bytes_left;
      unsigned char *data;
      int result = XGetWindowProperty (event.display, event.requestor,
				       event.property, 0L, 10000000L,
				       True, XA_STRING, &type, &return_format,
				       &items, &bytes_left, &data);

      if (result == Success && type == XA_STRING && return_format == 8)
	{
	  if (event.selection == Xatom_emacs_selection)
	    Vx_selection_value = make_string (data);
	  else if (event.selection == Xatom_emacs_secondary_selection)
	    Vx_secondary_selection_value = make_string (data);
	  else if (event.selection == Xatom_clipboard_selection)
	    Vx_clipboard_value = make_string (data);
	  else
	    abort ();
	}

      return;
    }
  else if ((event.target == Xatom_text
	    || event.target == XA_STRING))
    {
      int size = XSTRING (selection_value)->size;
      unsigned char *data = XSTRING (selection_value)->data;
		
      if (EQ (Qnil, selection_value))
	abort ();

      /* Place data on requestor window's property. */
      if (SELECTION_LENGTH (size, format)
	  <= MAX_SELECTION (x_current_display))
	{
	  x_converting_selection = 1;
	  XChangeProperty (evt.display, evt.requestor, evt.property,
			   evt.target, format, PropModeReplace,
			   data, size);
	  if (x_selection_alloc_error)
	    {
	      x_selection_alloc_error = 0;
	      abort ();
	    }
	  x_converting_selection = 0;
	}
      else  /* Send incrementally */
	{
	  evt.target = Xatom_incremental;
	  incr_requestor = evt.requestor;
	  incr_property = evt.property;
	  x_converting_selection = 1;

	  /* Need to handle Alloc errors on these requests. */
	  XChangeProperty (evt.display, incr_requestor, incr_property,
			   Xatom_incremental, 32,
			   PropModeReplace,
			   (unsigned char *) &size, 1);
	  if (x_selection_alloc_error)
	    {
	      x_selection_alloc_error = 0;
	      x_converting_selection = 0;
	      abort ();
	      /* Now abort the send. */
	    }

	  incr_nbytes = size;
	  incr_value = data;
	  incr_ptr = data;

	  /* Ask for notification when requestor deletes property. */
	  XSelectInput (x_current_display, incr_requestor, PropertyChangeMask);

	  /* If we're sending incrementally, perhaps block here
	     until all sent? */
	}
    }
  else
    evt.property = None;

  /* Don't do this if there was an Alloc error:  abort the transfer
     by sending None. */
  (void) XSendEvent (x_current_display, evt.requestor, False,
		     0L, (XEvent *) &evt);
}

/* Send an increment of selection data in response to a PropertyNotify event.
   The increment is placed in a property on the requestor's window.
   When the requestor has processed the increment, it deletes the property,
   which sends us another PropertyNotify event.

   When there is no more data to send, we send a zero-length increment. */

void
x_send_incremental (event)
     XPropertyEvent event;
{
  if (incr_requestor
      && incr_requestor == event.window
      && incr_property == event.atom
      && event.state == PropertyDelete)
    {
      int format = 8;
      int length = MAX_SELECTION (x_current_display);
      int bytes_left = (incr_nbytes - (incr_ptr - incr_value));
		
      if (length > bytes_left)	/* Also sends 0 len when finished. */
	length = bytes_left;
      XChangeProperty (x_current_display, incr_requestor,
		       incr_property, XA_STRING, format,
		       PropModeAppend, incr_ptr, length);
      if (x_selection_alloc_error)
	{
	  x_selection_alloc_error = 0;
	  x_converting_selection = 0;
	  /* Abandon the transmission. */
	  abort ();
	}
      if (length > 0)
	incr_ptr += length;
      else
	{			/* Everything's sent */
	  XSelectInput (x_current_display, incr_requestor, 0L);
	  incr_requestor = (Window) 0;
	  incr_property = (Atom) 0;
	  incr_nbytes = 0;
	  incr_value = (unsigned char *) 0;
	  incr_ptr = (unsigned char *) 0;
	  x_converting_selection = 0;
	}
    }
}

\f
/* Requesting the value of a selection.  */

static Lisp_Object x_selection_arrival ();

/* Predicate function used to match a requested event. */

Bool
XCheckSelectionEvent (dpy, event, window)
     Display *dpy;
     XEvent *event;
     char *window;
{
  if (event->type == SelectionNotify)
    if (event->xselection.requestor == (Window) window)
      return True;

  return False;
}

/* Request a selection value from its owner.  This will block until
   all the data is arrived. */

static Lisp_Object
get_selection_value (type)
     Atom type;
{
  XEvent event;
  Lisp_Object val;
  Time requestor_time;		/* Timestamp of selection request. */
  Window requestor_window;

  BLOCK_INPUT;
  requestor_time = last_event_timestamp;
  requestor_window = FRAME_X_WINDOW (selected_frame);
  XConvertSelection (x_current_display, type, XA_STRING,
		     Xatom_emacs_selection, requestor_window, requestor_time);
  XIfEvent (x_current_display,
	    &event,
	    XCheckSelectionEvent,
	    (char *) requestor_window);
  val = x_selection_arrival (&event, requestor_window, requestor_time);
  UNBLOCK_INPUT;

  return val;
}

/* Request a selection value from the owner.  If we are the owner,
   simply return our selection value.  If we are not the owner, this
   will block until all of the data has arrived. */

DEFUN ("x-selection-value", Fx_selection_value, Sx_selection_value,
  0, 1, "",
  "Return the value of one of the selections.  Default is the primary\n\
selection, but optional argument TYPE may specify secondary or clipboard.")
  (type)
     register Lisp_Object type;
{
  Atom selection_type;

  if (NILP (type) || EQ (type, Qprimary))
    {
      if (!NILP (Vx_selection_value))
	return Vx_selection_value;

      return get_selection_value (XA_PRIMARY);
    }
  else if (EQ (type, Qsecondary))
    {
      if (!NILP (Vx_secondary_selection_value))
	return Vx_secondary_selection_value;

      return get_selection_value (XA_SECONDARY);
    }
  else if (EQ (type, Qclipboard))
    {
      if (!NILP (Vx_clipboard_value))
	return Vx_clipboard_value;

      return get_selection_value (Xatom_clipboard);
    }
#if 0
  else if (EQ (type, Qcut_buffer0))
    {
      char *data;
      int size;
      Lisp_Object string;

      BLOCK_INPUT;
      data = XFetchBytes (x_current_display, &size);
      if (data == 0)
	string = Qnil;
      else
	string = make_string (data, size);
      UNBLOCK_INPUT;
      
      return string;
    }
#endif
  else
    error ("Invalid X selection type");
}

static Lisp_Object
x_selection_arrival (event, requestor_window, requestor_time)
     register XSelectionEvent *event;
     Window requestor_window;
     Time requestor_time;
{
  int result;
  Atom type, selection;
  int format;
  unsigned long items;
  unsigned long bytes_left;
  unsigned char *data = 0;
  int offset = 0;

  if (event->selection == XA_PRIMARY)
    selection = Xatom_emacs_selection;
  else if (event->selection == XA_SECONDARY)
    selection = Xatom_emacs_secondary_selection;
  else if (event->selection == Xatom_clipboard)
    selection = Xatom_clipboard_selection;
  else
    abort ();

  if (event->requestor == requestor_window
      && event->time == requestor_time
      && event->property != None)
    if (event->target != Xatom_incremental)
      {
	unsigned char *return_string =
	  (unsigned char *) alloca (MAX_SELECTION (x_current_display));

	do
	  {
	    result = XGetWindowProperty (x_current_display, requestor_window,
					 event->property, 0L,
					 10000000L, True, XA_STRING,
					 &type, &format, &items,
					 &bytes_left, &data);
	    if (result == Success && type == XA_STRING && format == 8
		&& offset < MAX_SELECTION (x_current_display))
	      {
		bcopy (data, return_string + offset, items);
		offset += items;
	      }
	    XFree ((char *) data);
	  }
	while (bytes_left);

	return make_string (return_string, offset);
      }
    else  /* Prepare incremental transfer. */
      {
	unsigned char *increment_value;
	unsigned char *increment_ptr;
	int total_size;
	int *increment_nbytes = 0;

	result = XGetWindowProperty (x_current_display, requestor_window,
				     selection, 0L, 10000000L, False,
				     event->property, &type, &format,
				     &items, &bytes_left,
				     (unsigned char **) &increment_nbytes);
	if (result == Success)
	  {
	    XPropertyEvent property_event;

	    total_size = *increment_nbytes;
	    increment_value = (unsigned char *) alloca (total_size);
	    increment_ptr = increment_value;

	    XDeleteProperty (x_current_display, event->requestor,
			     event->property);
	    XFlush (x_current_display);
	    XFree ((char *) increment_nbytes);

	    do
	      {			/* NOTE: this blocks. */
		XWindowEvent (x_current_display, requestor_window,
			      PropertyChangeMask,
			      (XEvent *) &property_event);

		if (property_event.atom == selection
		    && property_event.state == PropertyNewValue)
		  do
		    {
		      result = XGetWindowProperty (x_current_display,
						   requestor_window,
						   selection, 0L,
						   10000000L, True,
						   AnyPropertyType,
						   &type, &format,
						   &items, &bytes_left,
						   &data);
		      if (result == Success && type == XA_STRING
			  && format == 8)
			{
			  bcopy (data, increment_ptr, items);
			  increment_ptr += items;
			}
		    }
		while (bytes_left);

	      }
	    while (increment_ptr < (increment_value + total_size));

	    return make_string (increment_value,
				(increment_ptr - increment_value));
	  }
      }

  return Qnil;
}

\f
/* Cut buffer management.  */

DEFUN ("x-get-cut-buffer", Fx_get_cut_buffer, Sx_get_cut_buffer, 0, 1, "",
  "Return the value of cut buffer N, or nil if it is unset.\n\
If N is omitted, it defaults to zero.\n\
Note that cut buffers have some problems that selections don't; try to\n\
write your code to use cut buffers only for backward compatibility,\n\
and use selections for the serious work.")
  (n)
     Lisp_Object n;
{
  int buf_num;

  if (NILP (n))
    buf_num = 0;
  else
    {
      CHECK_NUMBER (n, 0);
      buf_num = XINT (n);
    }

  if (buf_num < 0 || buf_num >= NUM_CUT_BUFFERS)
    error ("cut buffer numbers must be from zero to seven");

  {
    Lisp_Object value;

    /* Note that no PropertyNotify events will be processed while
       input is blocked.  */
    BLOCK_INPUT;

    if (cut_buffer_cached & (1 << buf_num))
      value = XVECTOR (cut_buffer_value)->contents[buf_num];
    else
      {
	/* Our cache is invalid; retrieve the property's value from
	   the server.  */
	int buf_len;
	char *buf = XFetchBuffer (x_current_display, &buf_len, buf_num);

	if (buf_len == 0)
	  value = Qnil;
	else
	  value = make_string (buf, buf_len);

	XVECTOR (cut_buffer_value)->contents[buf_num] = value;
	cut_buffer_cached |= (1 << buf_num);

	XFree (buf);
      }

    UNBLOCK_INPUT;

    return value;
  }
}

DEFUN ("x-set-cut-buffer", Fx_set_cut_buffer, Sx_set_cut_buffer, 2, 2, "",
  "Set the value of cut buffer N to STRING.\n\
Note that cut buffers have some problems that selections don't; try to\n\
write your code to use cut buffers only for backward compatibility,\n\
and use selections for the serious work.")
  (n, string)
     Lisp_Object n, string;
{
  int buf_num;

  CHECK_NUMBER (n, 0);
  CHECK_STRING (string, 1);

  buf_num = XINT (n);

  if (buf_num < 0 || buf_num >= NUM_CUT_BUFFERS)
    error ("cut buffer numbers must be from zero to seven");

  BLOCK_INPUT;

  /* DECwindows and some other servers don't seem to like setting
     properties to values larger than about 20k.  For very large
     values, they signal an error, but for intermediate values they
     just seem to hang.

     We could just truncate the request, but it's better to let the
     user know that the strategy he/she's using isn't going to work
     than to have it work partially, but incorrectly.  */

  if (XSTRING (string)->size == 0
      || XSTRING (string)->size > MAX_SELECTION (x_current_display))
    {
      XStoreBuffer (x_current_display, (char *) 0, 0, buf_num);
      string = Qnil;
    }
  else
    {
      XStoreBuffer (x_current_display,
		    (char *) XSTRING (string)->data, XSTRING (string)->size,
		    buf_num);
    }

  XVECTOR (cut_buffer_value)->contents[buf_num] = string;
  cut_buffer_cached |= (1 << buf_num);
  cut_buffer_just_set |= (1 << buf_num);

  UNBLOCK_INPUT;

  return string;
}

/* Ask the server to send us an event if any cut buffer is modified.  */

void
x_watch_cut_buffer_cache ()
{
  XSelectInput (x_current_display, ROOT_WINDOW, PropertyChangeMask);
}

/* The server has told us that a cut buffer has been modified; deal with that.
   Note that this function is called at interrupt level.  */
void
x_invalidate_cut_buffer_cache (XPropertyEvent *event)
{
  int i;

  /* See which cut buffer this is about, if any.  */
  for (i = 0; i < NUM_CUT_BUFFERS; i++)
    if (event->atom == cut_buffer_atom[i])
      {
	int mask = (1 << i);

	if (cut_buffer_just_set & mask)
	  cut_buffer_just_set &= ~mask;
	else
	  cut_buffer_cached &= ~mask;

	break;
      }
}

\f
/* Bureaucracy.  */

void
syms_of_xselect ()
{
  DEFVAR_LISP ("x-selection-value", &Vx_selection_value,
	       "The value of emacs' last cut-string.");
  Vx_selection_value = Qnil;

  DEFVAR_LISP ("x-secondary-selection-value", &Vx_secondary_selection_value,
	       "The value of emacs' last secondary cut-string.");
  Vx_secondary_selection_value = Qnil;

  DEFVAR_LISP ("x-clipboard-value", &Vx_clipboard_value,
	       "The string emacs last sent to the clipboard.");
  Vx_clipboard_value = Qnil;

  Qprimary = intern ("primary");
  staticpro (&Qprimary);
  Qsecondary = intern ("secondary");
  staticpro (&Qsecondary);
  Qclipboard = intern ("clipboard");
  staticpro (&Qclipboard);

  defsubr (&Sx_own_selection);
  defsubr (&Sx_selection_value);

  cut_buffer_value = Fmake_vector (make_number (NUM_CUT_BUFFERS), Qnil);
  staticpro (&cut_buffer_value);

  defsubr (&Sx_get_cut_buffer);
  defsubr (&Sx_set_cut_buffer);
}
#endif	/* X11 */