guile/libguile/gc-segment.c

/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001, 2002, 2006 Free Software Foundation, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <assert.h> 
#include <stdio.h>
#include <string.h>

#include "libguile/_scm.h"
#include "libguile/pairs.h"
#include "libguile/gc.h"
#include "libguile/private-gc.h"





size_t scm_max_segment_size;

scm_t_heap_segment *
scm_i_make_empty_heap_segment (scm_t_cell_type_statistics *fl)
{
  scm_t_heap_segment * shs = malloc (sizeof (scm_t_heap_segment));

  if (!shs)
    {
      fprintf (stderr, "scm_i_get_new_heap_segment: out of memory.\n");
      abort ();
    }
  
  shs->bounds[0] = NULL;
  shs->bounds[1] = NULL;
  shs->malloced = NULL;
  shs->span = fl->span;
  shs->freelist  = fl;
  shs->next_free_card = NULL;
  
  return shs;
}


void
scm_i_heap_segment_statistics (scm_t_heap_segment *seg, SCM tab)
{
  scm_t_cell *p = seg->bounds[0];
  while (p <  seg->bounds[1])
    {
      scm_i_card_statistics (p, tab, seg); 
      p += SCM_GC_CARD_N_CELLS;
    }
}



/*
  Fill SEGMENT with memory both for data and mark bits.

  RETURN:  1 on success, 0 failure  
 */
int 
scm_i_initialize_heap_segment_data (scm_t_heap_segment * segment, size_t requested)
{
  /*
    round upwards
   */
  int card_data_cell_count = (SCM_GC_CARD_N_CELLS - SCM_GC_CARD_N_HEADER_CELLS);
  int card_count =1 + (requested / sizeof (scm_t_cell)) /  card_data_cell_count; 

  /*
    one card extra due to alignment
  */
  size_t mem_needed = (1+card_count) * SCM_GC_SIZEOF_CARD
    + SCM_GC_CARD_BVEC_SIZE_IN_LONGS * card_count * SCM_SIZEOF_LONG
    ;
  scm_t_c_bvec_long * bvec_ptr = 0;
  scm_t_cell *  memory = 0;

  /*
    We use calloc to alloc the heap. On GNU libc this is 
    equivalent to mmapping /dev/zero
   */
  SCM_SYSCALL (memory = (scm_t_cell * ) calloc (1, mem_needed));

  if (memory == NULL)
    return 0;

  segment->malloced = memory;
  segment->bounds[0] = SCM_GC_CARD_UP (memory);
  segment->bounds[1] = segment->bounds[0] + card_count * SCM_GC_CARD_N_CELLS;

  segment->freelist->heap_size += scm_i_segment_cell_count (segment);
  
  bvec_ptr = (scm_t_c_bvec_long*) segment->bounds[1];

  /*
    Don't init the mem or the bitvector. This is handled by lazy
    sweeping.
  */
  
  segment->next_free_card = segment->bounds[0];
  segment->first_time = 1;
  return 1;
}

int
scm_i_segment_card_count (scm_t_heap_segment * seg)
{
  return (seg->bounds[1] - seg->bounds[0]) / SCM_GC_CARD_N_CELLS;
}

/*
  Return the number of available single-cell data cells. 
 */
int
scm_i_segment_cell_count (scm_t_heap_segment * seg)
{
  return scm_i_segment_card_count (seg) * (SCM_GC_CARD_N_CELLS - SCM_GC_CARD_N_HEADER_CELLS)
    + ((seg->span == 2) ? -1 : 0);
}

void
scm_i_clear_segment_mark_space (scm_t_heap_segment *seg)
{
  scm_t_cell *  markspace = seg->bounds[1];

  memset (markspace, 0x00,
	  scm_i_segment_card_count (seg) *  SCM_GC_CARD_BVEC_SIZE_IN_LONGS * SCM_SIZEOF_LONG);
}

/* Sweep cards from SEG until we've gathered THRESHOLD cells.  On return,
   SWEEP_STATS contains the number of cells that have been visited and
   collected.  A freelist is returned, potentially empty.  */
SCM
scm_i_sweep_some_cards (scm_t_heap_segment *seg,
			scm_t_sweep_statistics *sweep_stats)
{
  SCM cells = SCM_EOL;
  int threshold = 512;
  int collected = 0;
  int (*sweeper) (scm_t_cell *, SCM *, scm_t_heap_segment* )
    = (seg->first_time) ? &scm_i_init_card_freelist : &scm_i_sweep_card;

  scm_t_cell * next_free = seg->next_free_card;
  int cards_swept = 0;

  while (collected < threshold && next_free < seg->bounds[1])
    {
      collected += (*sweeper) (next_free, &cells, seg);
      next_free += SCM_GC_CARD_N_CELLS;
      cards_swept ++;
    }

  sweep_stats->swept = cards_swept * seg->span
    * (SCM_GC_CARD_N_CELLS - SCM_GC_CARD_N_HEADER_CELLS);

  if (!seg->first_time)
    {
      /* scm_cells_allocated -= collected * seg->span; */
      sweep_stats->collected = collected * seg->span;
    }
  else
    sweep_stats->collected = 0;

  seg->freelist->collected += collected * seg->span;

  if(next_free == seg->bounds[1])
    {
      seg->first_time = 0;
    }

  seg->next_free_card = next_free;
  return cells;
}


/*
  Force a sweep of this entire segment. This doesn't modify sweep
  statistics, it just frees the memory pointed to by to-be-swept
  cells.

  Implementation is slightly ugh.

  FIXME: if you do scm_i_sweep_segment(), and then allocate from this
  segment again, the statistics are off.
 */
void
scm_i_sweep_segment (scm_t_heap_segment *seg,
		     scm_t_sweep_statistics *sweep_stats)
{
  scm_t_sweep_statistics sweep;
  scm_t_cell * p = seg->next_free_card;

  scm_i_sweep_statistics_init (sweep_stats);

  scm_i_sweep_statistics_init (&sweep);
  while (scm_i_sweep_some_cards (seg, &sweep) != SCM_EOL)
    {
      scm_i_sweep_statistics_sum (sweep_stats, sweep);
      scm_i_sweep_statistics_init (&sweep);
    }

  seg->next_free_card =p;
}

void
scm_i_sweep_all_segments (char const *reason,
			  scm_t_sweep_statistics *sweep_stats)
{
  unsigned i= 0;

  scm_i_sweep_statistics_init (sweep_stats);
  for (i = 0; i < scm_i_heap_segment_table_size; i++)
    {
      scm_t_sweep_statistics sweep;

      scm_i_sweep_segment (scm_i_heap_segment_table[i], &sweep);
      scm_i_sweep_statistics_sum (sweep_stats, sweep);
    }
}


/*
  Heap segment table.

  The table is sorted by the address of the data itself. This makes
  for easy lookups. This is not portable: according to ANSI C,
  pointers can only be compared within the same object (i.e. the same
  block of malloced memory.). For machines with weird architectures,
  this should be revised.
  
  (Apparently, for this reason 1.6 and earlier had macros for pointer
  comparison. )
  
  perhaps it is worthwhile to remove the 2nd level of indirection in
  the table, but this certainly makes for cleaner code.
*/
scm_t_heap_segment ** scm_i_heap_segment_table;
size_t scm_i_heap_segment_table_size;
scm_t_cell *lowest_cell;
scm_t_cell *highest_cell; 


void
scm_i_clear_mark_space (void)
{
  int i = 0;
  for (; i < scm_i_heap_segment_table_size; i++)
    {
      scm_i_clear_segment_mark_space (scm_i_heap_segment_table[i]);
    }
}


/*
  RETURN: index of inserted segment.
 */
int
scm_i_insert_segment (scm_t_heap_segment * seg)
{
  size_t size = (scm_i_heap_segment_table_size + 1) * sizeof (scm_t_heap_segment *);
  SCM_SYSCALL(scm_i_heap_segment_table = ((scm_t_heap_segment **)
			       realloc ((char *)scm_i_heap_segment_table, size)));

  /*
    We can't alloc 4 more bytes. This is hopeless.
   */
  if (!scm_i_heap_segment_table)
    {
      fprintf (stderr, "scm_i_get_new_heap_segment: Could not grow heap segment table.\n");
      abort ();
    }

  if (!lowest_cell)
    {
      lowest_cell = seg->bounds[0];
      highest_cell = seg->bounds[1];
    }
  else
    {
      lowest_cell = SCM_MIN (lowest_cell, seg->bounds[0]);
      highest_cell = SCM_MAX (highest_cell, seg->bounds[1]);
    }


  {
    int i = 0;
    int j = 0;

    while (i < scm_i_heap_segment_table_size
	   && scm_i_heap_segment_table[i]->bounds[0] <= seg->bounds[0])
      i++;

    /*
      We insert a new entry; if that happens to be before the
      "current" segment of a freelist, we must move the freelist index
      as well.
    */
    if (scm_i_master_freelist.heap_segment_idx >= i)
      scm_i_master_freelist.heap_segment_idx ++;
    if (scm_i_master_freelist2.heap_segment_idx >= i)
      scm_i_master_freelist2.heap_segment_idx ++;

    for (j = scm_i_heap_segment_table_size; j > i; --j)
      scm_i_heap_segment_table[j] = scm_i_heap_segment_table[j - 1];

    scm_i_heap_segment_table [i] = seg;
    scm_i_heap_segment_table_size ++;

    return i;
  }
}

SCM
scm_i_sweep_some_segments (scm_t_cell_type_statistics *fl,
			   scm_t_sweep_statistics *sweep_stats)
{
  int i = fl->heap_segment_idx;
  SCM collected = SCM_EOL;

  scm_i_sweep_statistics_init (sweep_stats);
  if (i == -1)
    i++;

  for (;
       i < scm_i_heap_segment_table_size; i++)
    {
      scm_t_sweep_statistics sweep;

      if (scm_i_heap_segment_table[i]->freelist != fl)
	continue;

      scm_i_sweep_statistics_init (&sweep);
      collected = scm_i_sweep_some_cards (scm_i_heap_segment_table[i],
					  &sweep);

      scm_i_sweep_statistics_sum (sweep_stats, sweep);

      if (collected != SCM_EOL)       /* Don't increment i */
	break;
    }

  fl->heap_segment_idx = i;

  return collected;
}


void
scm_i_reset_segments (void)
{
  int i = 0;
  for (; i < scm_i_heap_segment_table_size; i++)
    {
      scm_t_heap_segment * seg = scm_i_heap_segment_table[i];
      seg->next_free_card = seg->bounds[0];
    }
}

/*
  Return a hashtab with counts of live objects, with tags as keys.
 */


SCM
scm_i_all_segments_statistics (SCM tab)
{
  int i = 0;
  for (; i < scm_i_heap_segment_table_size; i++)
    {
      scm_t_heap_segment * seg = scm_i_heap_segment_table[i];
      scm_i_heap_segment_statistics (seg, tab);
    }

  return tab;
}




/*
  Determine whether the given value does actually represent a cell in
  some heap segment.  If this is the case, the number of the heap
  segment is returned.  Otherwise, -1 is returned.  Binary search is
  used to determine the heap segment that contains the cell.


  I think this function is too long to be inlined. --hwn
*/
long int
scm_i_find_heap_segment_containing_object (SCM obj)
{
  if (!CELL_P (obj))
    return -1;

  if ((scm_t_cell* ) obj < lowest_cell || (scm_t_cell*) obj >= highest_cell)
    return -1;

  
    {
      scm_t_cell *  ptr = SCM2PTR (obj);
      unsigned long int i = 0;
      unsigned long int j = scm_i_heap_segment_table_size - 1;

      if (ptr < scm_i_heap_segment_table[i]->bounds[0])
	return -1;
      else if (scm_i_heap_segment_table[j]->bounds[1] <= ptr)
	return -1;
      else
	{
	  while (i < j)
	    {
	      if (ptr < scm_i_heap_segment_table[i]->bounds[1])
		{
		  break;
		}
	      else if (scm_i_heap_segment_table[j]->bounds[0] <= ptr)
		{
		  i = j;
		  break;
		}
	      else
		{
		  unsigned long int k = (i + j) / 2;

		  if (k == i)
		    return -1;
		  else if (ptr <  scm_i_heap_segment_table[k]->bounds[1])
		    {
		      j = k;
		      ++i;
		      if (ptr <  scm_i_heap_segment_table[i]->bounds[0])
			return -1;
		    }
		  else if (scm_i_heap_segment_table[k]->bounds[0] <= ptr)
		    {
		      i = k;
		      --j;
		      if (scm_i_heap_segment_table[j]->bounds[1] <= ptr)
			return -1;
		    }
		}
	    }

	  if (!SCM_DOUBLECELL_ALIGNED_P (obj) && scm_i_heap_segment_table[i]->span == 2)
	    return -1;
	  else if (SCM_GC_IN_CARD_HEADERP (ptr))
	    return -1;
	  else
	    return i;
	}
    }
}


/* Important entry point: try to grab some memory, and make it into a
   segment; return the index of the segment.  SWEEP_STATS should contain
   global GC sweep statistics collected since the last full GC.  */
int
scm_i_get_new_heap_segment (scm_t_cell_type_statistics *freelist,
			    scm_t_sweep_statistics sweep_stats,
			    policy_on_error error_policy)
{
  size_t len;

  {
    /* Assure that the new segment is predicted to be large enough.
     *
     * New yield should at least equal GC fraction of new heap size, i.e.
     *
     *   y + dh > f * (h + dh)
     *
     *    y : yield
     *    f : min yield fraction
     *    h : heap size
     *   dh : size of new heap segment
     *
     * This gives dh > (f * h - y) / (1 - f)
     */
    float f = freelist->min_yield_fraction / 100.0;
    float h = SCM_HEAP_SIZE;
    float min_cells = (f * h - sweep_stats.collected) / (1.0 - f);

    /* Make heap grow with factor 1.5 */
    len =  freelist->heap_size / 2;
#ifdef DEBUGINFO
    fprintf (stderr, "(%ld < %ld)", (long) len, (long) min_cells);
#endif

    if (len < min_cells)
      len = (unsigned long) min_cells;  
    len *= sizeof (scm_t_cell);
    /* force new sampling */
    freelist->collected = LONG_MAX;
  }

  if (len > scm_max_segment_size)
    len = scm_max_segment_size;
  if (len < SCM_MIN_HEAP_SEG_SIZE)
    len = SCM_MIN_HEAP_SEG_SIZE;

  {
    scm_t_heap_segment * seg = scm_i_make_empty_heap_segment (freelist);

    /* Allocate with decaying ambition. */
    while (len >= SCM_MIN_HEAP_SEG_SIZE)
      {
	if (scm_i_initialize_heap_segment_data (seg, len))
	  {
	    return scm_i_insert_segment (seg);
	  }
	
	len /= 2;
      }
  }

  if (error_policy == abort_on_error)
    {
      fprintf (stderr, "scm_i_get_new_heap_segment: Could not grow heap.\n");
      abort ();
    }
  return -1;
}

void
scm_i_make_initial_segment (int init_heap_size, scm_t_cell_type_statistics *freelist)
{
  scm_t_heap_segment * seg = scm_i_make_empty_heap_segment (freelist);

  if (init_heap_size < 1)
    {
      init_heap_size =  SCM_DEFAULT_INIT_HEAP_SIZE_1;
    }
 
  if (scm_i_initialize_heap_segment_data (seg, init_heap_size))
    {
      freelist->heap_segment_idx = scm_i_insert_segment (seg);
    }

  /*
    Why the fuck  try twice? --hwn
   */
  if (!seg->malloced)
    {
      scm_i_initialize_heap_segment_data (seg, SCM_HEAP_SEG_SIZE);
    }

  if (freelist->min_yield_fraction)
    freelist->min_yield = (freelist->heap_size * freelist->min_yield_fraction
			    / 100);
}