/* Efficient caching of X GCs (graphics contexts).
   Copyright (C) 1993 Free Software Foundation, Inc.
   Copyright (C) 1994, 1995 Board of Trustees, University of Illinois.
   Copyright (C) 2010 Ben Wing.

This file is part of XEmacs.

XEmacs 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 3 of the License, or (at your
option) any later version.

XEmacs 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 XEmacs.  If not, see <http://www.gnu.org/licenses/>. */

/* Synched up with: Not in FSF. */

/* Emacs uses a lot of different display attributes; for example, assume
   that only four fonts are in use (normal, bold, italic, and bold-italic).
   Then assume that one stipple or background is used for text selections,
   and another is used for highlighting mousable regions.  That makes 16
   GCs already.  Add in the fact that another GC may be needed to display
   the text cursor in any of those regions, and you've got 32.  Add in
   more fonts, and it keeps increasing exponentially.

   We used to keep these GCs in a cache of merged (fully qualified) faces.
   However, a lot of other code in xterm.c used XChangeGC of existing GCs,
   which is kind of slow and kind of random.  Also, managing the face cache
   was tricky because it was hard to know when a face was no longer visible
   on the frame -- we had to mark all frames as garbaged whenever a face
   was changed, which caused an unpleasant amount of flicker (since faces are
   created/destroyed (= changed) whenever a frame is created/destroyed.

   So this code maintains a cache at the GC level instead of at the face
   level.  There is an upper limit on the size of the cache, after which we
   will stop creating GCs and start reusing them (reusing the least-recently-
   used ones first).  So if faces get changed, their GCs will eventually be
   recycled.  Also more sharing of GCs is possible.

   This code uses hash tables.  It could be that, if the cache size is small
   enough, a linear search might be faster; but I doubt it, since we need
   `equal' comparisons, not `eq', and I expect that the optimal cache size
   will be ~100.

   Written by jwz, 14 jun 93
 */

#include <config.h>
#include "lisp.h"
#include "hash.h"

#include "gccache-x.h"

#define GC_CACHE_SIZE 100

#define GCCACHE_HASH

struct gcv_and_mask {
  XGCValues gcv;
  unsigned long mask;
};

struct gc_cache_cell {
  GC gc;
  struct gcv_and_mask gcvm;
  struct gc_cache_cell *prev, *next;
};

struct gc_cache {
  Display *dpy;		/* used only as arg to XCreateGC/XFreeGC */
  Window window;	/* used only as arg to XCreateGC */
  int size;
  struct gc_cache_cell *head;
  struct gc_cache_cell *tail;
#ifdef GCCACHE_HASH
  struct hash_table *table;
#endif

  int create_count;
  int delete_count;
};

#ifdef GCCACHE_HASH
static Hashcode
gc_cache_hash (const void *arg)
{
  const struct gcv_and_mask *gcvm = (const struct gcv_and_mask *) arg;
  unsigned long *longs = (unsigned long *) &gcvm->gcv;
  Hashcode hash = gcvm->mask;
  int i;
  /* This could look at the mask and only use the used slots in the
     hash code.  That would win in that we wouldn't have to initialize
     every slot of the gcv when calling gc_cache_lookup.  But we need
     the hash function to be as fast as possible; some timings should
     be done. */
  for (i = 0; i < (int) (sizeof (XGCValues) / sizeof (unsigned long)); i++)
    hash = (hash << 1) ^ *longs++;
  return hash;
}

#endif /* GCCACHE_HASH */

static int
gc_cache_eql (const void *arg1, const void *arg2)
{
  /* See comment in gc_cache_hash */
  return !memcmp (arg1, arg2, sizeof (struct gcv_and_mask));
}

struct gc_cache *
make_gc_cache (Display *dpy, Window window)
{
  struct gc_cache *cache = xnew (struct gc_cache);
  cache->dpy = dpy;
  cache->window = window;
  cache->size = 0;
  cache->head = cache->tail = 0;
  cache->create_count = cache->delete_count = 0;
#ifdef GCCACHE_HASH
  cache->table =
    make_general_hash_table (GC_CACHE_SIZE, gc_cache_hash, gc_cache_eql);
#endif
  return cache;
}

void
free_gc_cache (struct gc_cache *cache)
{
  struct gc_cache_cell *rest, *next;
  rest = cache->head;
  while (rest)
    {
      XFreeGC (cache->dpy, rest->gc);
      next = rest->next;
      xfree (rest);
      rest = next;
    }
#ifdef GCCACHE_HASH
  free_hash_table (cache->table);
#endif
  xfree (cache);
}

GC
gc_cache_lookup (struct gc_cache *cache, XGCValues *gcv, unsigned long mask)
{
  struct gc_cache_cell *cell, *next, *prev;
  struct gcv_and_mask gcvm;

#ifdef DEBUG_XEMACS
  (void) describe_gc_cache (cache, DGCCFLAG_DISABLE);
#endif

  assert ((!!cache->head) == (!!cache->tail));
  assert (!(cache->head && (cache->head->prev || cache->tail->next)));

  gcvm.mask = mask;
  gcvm.gcv = *gcv;	/* this copies... */

#ifdef GCCACHE_HASH

  /* The intermediate cast fools gcc into not outputting strict-aliasing
     complaints */
  if (gethash (&gcvm, cache->table, (const void **) (void *) &cell))

#else /* !GCCACHE_HASH */

  cell = cache->tail;	/* start at the end (most recently used) */
  while (cell)
    {
      if (gc_cache_eql (&gcvm, &cell->gcvm))
	break;
      else
	cell = cell->prev;
    }

  /* #### This whole file needs some serious overhauling. */
  if (!(mask | GCTile) && cell->gc->values.tile)
    cell = 0;
  else if (!(mask | GCStipple) && cell->gc->values.stipple)
    cell = 0;

  if (cell)

#endif /* !GCCACHE_HASH */

    {
      /* Found a cell.  Move this cell to the end of the list, so that it
	 will be less likely to be collected than a cell that was accessed
	 less recently.
       */
#if 0
      debug_out ("Returning cached GC: %08lx\n", XE_GCONTEXT(cell));
#endif
      if (cell == cache->tail)
	return cell->gc;

      next = cell->next;
      prev = cell->prev;
      if (prev) prev->next = next;
      if (next) next->prev = prev;
      if (cache->head == cell) cache->head = next;
      cell->next = 0;
      cell->prev = cache->tail;
      cache->tail->next = cell;
      cache->tail = cell;
      assert (cache->head != cell);
      assert (!cell->next);
      assert (!cache->head->prev);
      assert (!cache->tail->next);
      return cell->gc;
    }

  /* else, cache miss. */

  if (cache->size == GC_CACHE_SIZE)
    /* Reuse the first cell on the list (least-recently-used).
       Remove it from the list, and unhash it from the table.
     */
    {
      cell = cache->head;
      cache->head = cell->next;
      cache->head->prev = 0;
      if (cache->tail == cell) cache->tail = 0; /* only one */
#if 0
      debug_out ("Cache full, freeing GC: %08lx\n  ", XE_GCONTEXT(cell));
#endif
      XFreeGC (cache->dpy, cell->gc);
      cache->delete_count++;
#ifdef GCCACHE_HASH
      remhash (&cell->gcvm, cache->table);
#endif
    }
  else if (cache->size > GC_CACHE_SIZE)
    ABORT ();
  else
    {
      /* Allocate a new cell (don't put it in the list or table yet). */
      cell = xnew (struct gc_cache_cell);
      cache->size++;
    }

  /* Now we've got a cell (new or reused).  Fill it in. */
  memcpy (&cell->gcvm.gcv, gcv, sizeof (XGCValues));
  cell->gcvm.mask = mask;

  /* Put the cell on the end of the list. */
  cell->next = 0;
  cell->prev = cache->tail;
  if (cache->tail) cache->tail->next = cell;
  cache->tail = cell;
  if (! cache->head) cache->head = cell;

  cache->create_count++;
#ifdef GCCACHE_HASH
  /* Hash it in the table */
  puthash (&cell->gcvm, cell, cache->table);
#endif

  /* Now make and return the GC. */
  cell->gc = XCreateGC (cache->dpy, cache->window, mask, gcv);

  /* debug */
  assert (cell->gc == gc_cache_lookup (cache, gcv, mask));

#if 0
  debug_out ("Returning new GC: %08lx\n  ", XE_GCONTEXT(cell));
#endif
  return cell->gc;
}


#ifdef DEBUG_XEMACS

/* FLAGS
   The flags argument is a bitwise or of any of the following:

   DGCCFLAG_SUMMARY		Summary statistics for cache
   DGCCFLAG_LIST_CELLS		If summary is being printed, print cell IDs too.
   DGCCFLAG_CELL_DETAILS	If cell IDs are being printed, additionally
				print the internal fields used and values.

   DGCCFLAG_DEFAULT		A predefined combination giving whatever the
				maintainers are currently interested in seeing.
*/
void
describe_gc_cache (struct gc_cache *cache, int flags)
{
  int count = 0;
  struct gc_cache_cell *cell = cache->head;

  if (! flags & DGCCFLAG_SUMMARY) return;

  stderr_out ("\nsize:    %d", cache->size);
  stderr_out ("\ncreated: %d", cache->create_count);
  stderr_out ("\ndeleted: %d", cache->delete_count);

  if (flags & DGCCFLAG_LIST_CELLS)
    while (cell)
      {
	struct gc_cache_cell *cell2;
	int i = 0;
	stderr_out ("\n%d:\t0x%lx  GC: 0x%08lx  hash: 0x%08lx\n",
		    count, (long) cell, (long) XE_GCONTEXT(cell),
		    gc_cache_hash (&cell->gcvm));

	for (cell2 = cache->head; cell2; cell2 = cell2->next, i++)
	  if (count != i &&
	      gc_cache_hash (&cell->gcvm) == gc_cache_hash (&cell2->gcvm))
	    stderr_out ("\tHASH COLLISION with cell %d\n", i);
	stderr_out ("\tmask:       %8lx\n", cell->gcvm.mask);

	if (flags & DGCCFLAG_CELL_DETAILS)
	  {
#define FROB(field) do {						\
  if ((int)cell->gcvm.gcv.field != (~0))				\
    stderr_out ("\t%-12s%8x\n", #field ":", (int)cell->gcvm.gcv.field);	\
} while (0)
	    FROB (function);
	    FROB (plane_mask);
	    FROB (foreground);
	    FROB (background);
	    FROB (line_width);
	    FROB (line_style);
	    FROB (cap_style);
	    FROB (join_style);
	    FROB (fill_style);
	    FROB (fill_rule);
	    FROB (arc_mode);
	    FROB (tile);
	    FROB (stipple);
	    FROB (ts_x_origin);
	    FROB (ts_y_origin);
	    FROB (font);
	    FROB (subwindow_mode);
	    FROB (graphics_exposures);
	    FROB (clip_x_origin);
	    FROB (clip_y_origin);
	    FROB (clip_mask);
	    FROB (dash_offset);
#undef FROB
	  }

	count++;
	if (cell->next && cell == cache->tail)
	  stderr_out ("\nERROR!  tail is here!\n\n");
	else if (!cell->next && cell != cache->tail)
	  stderr_out ("\nERROR!  tail is not at the end\n\n");
	cell = cell->next;
      }	/* while (cell) */

  if (count != cache->size)
    stderr_out ("\nERROR!  count should be %d\n\n", cache->size);
}

#endif /* DEBUG_XEMACS */