reclaim.c

/*
 * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
 * Copyright (c) 1991-1996 by Xerox Corporation.  All rights reserved.
 * Copyright (c) 1996-1999 by Silicon Graphics.  All rights reserved.
 * Copyright (c) 1999-2004 Hewlett-Packard Development Company, L.P.
 * Copyright (c) 2009-2021 Ivan Maidanski
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose,  provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 */

#include "private/gc_priv.h"

#ifdef ENABLE_DISCLAIM
#  include "gc/gc_disclaim.h"
#endif

#include <stdio.h>

GC_INNER signed_word GC_bytes_found = 0;
                        /* Number of bytes of memory reclaimed     */
                        /* minus the number of bytes originally    */
                        /* on free lists which we had to drop.     */

#if defined(PARALLEL_MARK)
  GC_INNER signed_word GC_fl_builder_count = 0;
        /* Number of threads currently building free lists without      */
        /* holding GC lock.  It is not safe to collect if this is       */
        /* nonzero.  Also, together with the mark lock, it is used as   */
        /* a semaphore during marker threads startup.                   */
#endif /* PARALLEL_MARK */

/* We defer printing of leaked objects until we're done with the GC     */
/* cycle, since the routine for printing objects needs to run outside   */
/* the collector, e.g. without the allocation lock.                     */
#ifndef MAX_LEAKED
# define MAX_LEAKED 40
#endif
STATIC ptr_t GC_leaked[MAX_LEAKED] = { NULL };
STATIC unsigned GC_n_leaked = 0;

GC_INNER GC_bool GC_have_errors = FALSE;

#if !defined(EAGER_SWEEP) && defined(ENABLE_DISCLAIM)
  STATIC void GC_reclaim_unconditionally_marked(void);
#endif

GC_INLINE void GC_add_leaked(ptr_t leaked)
{
#  ifndef SHORT_DBG_HDRS
     if (GC_findleak_delay_free && !GC_check_leaked(leaked))
       return;
#  endif

    GC_have_errors = TRUE;
    if (GC_n_leaked < MAX_LEAKED) {
      GC_leaked[GC_n_leaked++] = leaked;
      /* Make sure it's not reclaimed this cycle */
      GC_set_mark_bit(leaked);
    }
}

/* Print all objects on the list after printing any smashed objects.    */
/* Clear both lists.  Called without the allocation lock held.          */
GC_INNER void GC_print_all_errors(void)
{
    static GC_bool printing_errors = FALSE;
    GC_bool have_errors;
    unsigned i, n_leaked;
    ptr_t leaked[MAX_LEAKED];
    DCL_LOCK_STATE;

    LOCK();
    if (printing_errors) {
        UNLOCK();
        return;
    }
    have_errors = GC_have_errors;
    printing_errors = TRUE;
    n_leaked = GC_n_leaked;
    if (n_leaked > 0) {
      GC_ASSERT(n_leaked <= MAX_LEAKED);
      BCOPY(GC_leaked, leaked, n_leaked * sizeof(ptr_t));
      GC_n_leaked = 0;
      BZERO(GC_leaked, n_leaked * sizeof(ptr_t));
    }
    UNLOCK();

    if (GC_debugging_started) {
      GC_print_all_smashed();
    } else {
      have_errors = FALSE;
    }

    if (n_leaked > 0) {
        GC_err_printf("Found %u leaked objects:\n", n_leaked);
        have_errors = TRUE;
    }
    for (i = 0; i < n_leaked; i++) {
        ptr_t p = leaked[i];
#       ifndef SKIP_LEAKED_OBJECTS_PRINTING
          GC_print_heap_obj(p);
#       endif
        GC_free(p);
    }

    if (have_errors
#       ifndef GC_ABORT_ON_LEAK
          && GETENV("GC_ABORT_ON_LEAK") != NULL
#       endif
        ) {
      ABORT("Leaked or smashed objects encountered");
    }

    LOCK();
    printing_errors = FALSE;
    UNLOCK();
}


/*
 * reclaim phase
 *
 */

/* Test whether a block is completely empty, i.e. contains no marked    */
/* objects.  This does not require the block to be in physical memory.  */
GC_INNER GC_bool GC_block_empty(hdr *hhdr)
{
    return (hhdr -> hb_n_marks == 0);
}

STATIC GC_bool GC_block_nearly_full(hdr *hhdr, word sz)
{
    return hhdr -> hb_n_marks > HBLK_OBJS(sz) * 7 / 8;
}

/* TODO: This should perhaps again be specialized for USE_MARK_BYTES    */
/* and USE_MARK_BITS cases.                                             */

GC_INLINE word *GC_clear_block(word *p, word sz, signed_word *count)
{
  word *q = (word *)((ptr_t)p + sz);

  /* Clear object, advance p to next object in the process.     */
# ifdef USE_MARK_BYTES
    GC_ASSERT((sz & 1) == 0);
    GC_ASSERT(((word)p & (2 * sizeof(word) - 1)) == 0);
    p[1] = 0;
    p += 2;
    while ((word)p < (word)q) {
      CLEAR_DOUBLE(p);
      p += 2;
    }
# else
    p++; /* Skip link field */
    while ((word)p < (word)q) {
      *p++ = 0;
    }
# endif
  *count += sz;
  return p;
}

/*
 * Restore unmarked small objects in h of size sz to the object
 * free list.  Returns the new list.
 * Clears unmarked objects.  Sz is in bytes.
 */
STATIC ptr_t GC_reclaim_clear(struct hblk *hbp, hdr *hhdr, word sz,
                              ptr_t list, signed_word *count)
{
    word bit_no = 0;
    ptr_t p, plim;

    GC_ASSERT(hhdr == GC_find_header((ptr_t)hbp));
#   ifndef THREADS
      GC_ASSERT(sz == hhdr -> hb_sz);
#   else
      /* Skip the assertion because of a potential race with GC_realloc. */
#   endif
    GC_ASSERT((sz & (BYTES_PER_WORD-1)) == 0);
    p = hbp->hb_body;
    plim = p + HBLKSIZE - sz;

    /* go through all words in block */
        while ((word)p <= (word)plim) {
            if (mark_bit_from_hdr(hhdr, bit_no)) {
                p += sz;
            } else {
                /* Object is available - put it on list. */
                obj_link(p) = list;
                list = p;

                p = (ptr_t)GC_clear_block((word *)p, sz, count);
            }
            bit_no += MARK_BIT_OFFSET(sz);
        }
    return list;
}

/* The same thing, but don't clear objects: */
STATIC ptr_t GC_reclaim_uninit(struct hblk *hbp, hdr *hhdr, word sz,
                               ptr_t list, signed_word *count)
{
    word bit_no = 0;
    word *p, *plim;
    signed_word n_bytes_found = 0;

#   ifndef THREADS
      GC_ASSERT(sz == hhdr -> hb_sz);
#   endif
    p = (word *)(hbp->hb_body);
    plim = (word *)((ptr_t)hbp + HBLKSIZE - sz);

    /* go through all words in block */
        while ((word)p <= (word)plim) {
            if (!mark_bit_from_hdr(hhdr, bit_no)) {
                n_bytes_found += sz;
                /* object is available - put on list */
                    obj_link(p) = list;
                    list = ((ptr_t)p);
            }
            p = (word *)((ptr_t)p + sz);
            bit_no += MARK_BIT_OFFSET(sz);
        }
    *count += n_bytes_found;
    return(list);
}

#ifdef ENABLE_DISCLAIM
  /* Call reclaim notifier for block's kind on each unmarked object in  */
  /* block, all within a pair of corresponding enter/leave callbacks.   */
  STATIC ptr_t GC_disclaim_and_reclaim(struct hblk *hbp, hdr *hhdr, word sz,
                                       ptr_t list, signed_word *count)
  {
    word bit_no = 0;
    ptr_t p, plim;
    struct obj_kind *ok = &GC_obj_kinds[hhdr->hb_obj_kind];
    int (GC_CALLBACK *disclaim)(void *) = ok->ok_disclaim_proc;

#   ifndef THREADS
      GC_ASSERT(sz == hhdr -> hb_sz);
#   endif
    p = hbp->hb_body;
    plim = p + HBLKSIZE - sz;

    for (; (word)p <= (word)plim; bit_no += MARK_BIT_OFFSET(sz)) {
        if (mark_bit_from_hdr(hhdr, bit_no)) {
            p += sz;
        } else if ((*disclaim)(p)) {
            set_mark_bit_from_hdr(hhdr, bit_no);
            hhdr -> hb_n_marks++;
            p += sz;
        } else {
            obj_link(p) = list;
            list = p;
            p = (ptr_t)GC_clear_block((word *)p, sz, count);
        }
    }
    return list;
  }
#endif /* ENABLE_DISCLAIM */

/* Don't really reclaim objects, just check for unmarked ones: */
STATIC void GC_reclaim_check(struct hblk *hbp, hdr *hhdr, word sz)
{
    word bit_no;
    ptr_t p, plim;

#   ifndef THREADS
      GC_ASSERT(sz == hhdr -> hb_sz);
#   endif
    /* go through all words in block */
    p = hbp->hb_body;
    plim = p + HBLKSIZE - sz;
    for (bit_no = 0; (word)p <= (word)plim;
         p += sz, bit_no += MARK_BIT_OFFSET(sz)) {
      if (!mark_bit_from_hdr(hhdr, bit_no)) {
        GC_add_leaked(p);
      }
    }
}

/* Is a pointer-free block?  Same as IS_PTRFREE macro (in os_dep.c) but */
/* uses unordered atomic access to avoid racing with GC_realloc.        */
#ifdef AO_HAVE_load
# define IS_PTRFREE_SAFE(hhdr) \
                (AO_load((volatile AO_t *)&(hhdr)->hb_descr) == 0)
#else
  /* No race as GC_realloc holds the lock while updating hb_descr.      */
# define IS_PTRFREE_SAFE(hhdr) ((hhdr)->hb_descr == 0)
#endif

/*
 * Generic procedure to rebuild a free list in hbp.
 * Also called directly from GC_malloc_many.
 * Sz is now in bytes.
 */
GC_INNER ptr_t GC_reclaim_generic(struct hblk * hbp, hdr *hhdr, size_t sz,
                                  GC_bool init, ptr_t list,
                                  signed_word *count)
{
    ptr_t result;

    GC_ASSERT(GC_find_header((ptr_t)hbp) == hhdr);
#   ifndef GC_DISABLE_INCREMENTAL
      GC_remove_protection(hbp, 1, IS_PTRFREE_SAFE(hhdr));
#   endif
#   ifdef ENABLE_DISCLAIM
      if ((hhdr -> hb_flags & HAS_DISCLAIM) != 0) {
        result = GC_disclaim_and_reclaim(hbp, hhdr, sz, list, count);
      } else
#   endif
    /* else */ if (init || GC_debugging_started) {
      result = GC_reclaim_clear(hbp, hhdr, sz, list, count);
    } else {
      GC_ASSERT(IS_PTRFREE_SAFE(hhdr));
      result = GC_reclaim_uninit(hbp, hhdr, sz, list, count);
    }
    if (IS_UNCOLLECTABLE(hhdr -> hb_obj_kind)) GC_set_hdr_marks(hhdr);
    return result;
}

/*
 * Restore unmarked small objects in the block pointed to by hbp
 * to the appropriate object free list.
 * If entirely empty blocks are to be completely deallocated, then
 * caller should perform that check.
 */
STATIC void GC_reclaim_small_nonempty_block(struct hblk *hbp, word sz,
                                            GC_bool report_if_found)
{
    hdr *hhdr = HDR(hbp);
    struct obj_kind * ok = &GC_obj_kinds[hhdr -> hb_obj_kind];
    void **flh = &(ok -> ok_freelist[BYTES_TO_GRANULES(sz)]);

    hhdr -> hb_last_reclaimed = (unsigned short) GC_gc_no;

    if (report_if_found) {
        GC_reclaim_check(hbp, hhdr, sz);
    } else {
        *flh = GC_reclaim_generic(hbp, hhdr, sz, ok -> ok_init,
                                  (ptr_t)(*flh), &GC_bytes_found);
    }
}

#ifdef ENABLE_DISCLAIM
  STATIC void GC_disclaim_and_reclaim_or_free_small_block(struct hblk *hbp)
  {
    hdr *hhdr = HDR(hbp);
    word sz = hhdr -> hb_sz;
    struct obj_kind * ok = &GC_obj_kinds[hhdr -> hb_obj_kind];
    void **flh = &(ok -> ok_freelist[BYTES_TO_GRANULES(sz)]);
    void *flh_next;

    hhdr -> hb_last_reclaimed = (unsigned short) GC_gc_no;
    flh_next = GC_reclaim_generic(hbp, hhdr, sz, ok -> ok_init,
                                  (ptr_t)(*flh), &GC_bytes_found);
    if (hhdr -> hb_n_marks)
        *flh = flh_next;
    else {
        GC_bytes_found += HBLKSIZE;
        GC_freehblk(hbp);
    }
  }
#endif /* ENABLE_DISCLAIM */

/*
 * Restore an unmarked large object or an entirely empty blocks of small objects
 * to the heap block free list.
 * Otherwise enqueue the block for later processing
 * by GC_reclaim_small_nonempty_block.
 * If report_if_found is TRUE, then process any block immediately, and
 * simply report free objects; do not actually reclaim them.
 */
STATIC void GC_reclaim_block(struct hblk *hbp, word report_if_found)
{
    hdr * hhdr = HDR(hbp);
    word sz;    /* size of objects in current block */
    struct obj_kind * ok = &GC_obj_kinds[hhdr -> hb_obj_kind];

#   ifdef AO_HAVE_load
        /* Atomic access is used to avoid racing with GC_realloc.       */
        sz = (word)AO_load((volatile AO_t *)&hhdr->hb_sz);
#   else
        /* No race as GC_realloc holds the lock while updating hb_sz.   */
        sz = hhdr -> hb_sz;
#   endif
    if( sz > MAXOBJBYTES ) {  /* 1 big object */
        if( !mark_bit_from_hdr(hhdr, 0) ) {
            if (report_if_found) {
              GC_add_leaked((ptr_t)hbp);
            } else {
              word blocks;

#             ifdef ENABLE_DISCLAIM
                if (EXPECT(hhdr->hb_flags & HAS_DISCLAIM, 0)) {
                  if ((*ok->ok_disclaim_proc)(hbp)) {
                    /* Not disclaimed => resurrect the object. */
                    set_mark_bit_from_hdr(hhdr, 0);
                    goto in_use;
                  }
                }
#             endif
              blocks = OBJ_SZ_TO_BLOCKS(sz);
#             if defined(CPPCHECK)
                GC_noop1((word)&blocks);
#             endif
              if (blocks > 1) {
                GC_large_allocd_bytes -= blocks * HBLKSIZE;
              }
              GC_bytes_found += sz;
              GC_freehblk(hbp);
            }
        } else {
#        ifdef ENABLE_DISCLAIM
           in_use:
#        endif
            if (IS_PTRFREE_SAFE(hhdr)) {
              GC_atomic_in_use += sz;
            } else {
              GC_composite_in_use += sz;
            }
        }
    } else {
        GC_bool empty = GC_block_empty(hhdr);
#       ifdef PARALLEL_MARK
          /* Count can be low or one too high because we sometimes      */
          /* have to ignore decrements.  Objects can also potentially   */
          /* be repeatedly marked by each marker.                       */
          /* Here we assume 3 markers at most, but this is extremely    */
          /* unlikely to fail spuriously with more.  And if it does, it */
          /* should be looked at.                                       */
          GC_ASSERT(sz != 0 && (GC_markers_m1 > 1 ? 3 : GC_markers_m1 + 1)
                                * (HBLKSIZE/sz + 1) + 16 >= hhdr->hb_n_marks);
#       else
          GC_ASSERT(sz * hhdr -> hb_n_marks <= HBLKSIZE);
#       endif
        if (report_if_found) {
          GC_reclaim_small_nonempty_block(hbp, sz,
                                          TRUE /* report_if_found */);
        } else if (empty) {
#       ifdef ENABLE_DISCLAIM
          if ((hhdr -> hb_flags & HAS_DISCLAIM) != 0) {
            GC_disclaim_and_reclaim_or_free_small_block(hbp);
          } else
#       endif
          /* else */ {
            GC_bytes_found += HBLKSIZE;
            GC_freehblk(hbp);
          }
        } else if (GC_find_leak || !GC_block_nearly_full(hhdr, sz)) {
          /* group of smaller objects, enqueue the real work */
          struct hblk **rlh = ok -> ok_reclaim_list;

          if (rlh != NULL) {
            rlh += BYTES_TO_GRANULES(sz);
            hhdr -> hb_next = *rlh;
            *rlh = hbp;
          }
        } /* else not worth salvaging. */
        /* We used to do the nearly_full check later, but we    */
        /* already have the right cache context here.  Also     */
        /* doing it here avoids some silly lock contention in   */
        /* GC_malloc_many.                                      */
        if (IS_PTRFREE_SAFE(hhdr)) {
          GC_atomic_in_use += sz * hhdr -> hb_n_marks;
        } else {
          GC_composite_in_use += sz * hhdr -> hb_n_marks;
        }
    }
}

#if !defined(NO_DEBUGGING)
/* Routines to gather and print heap block info         */
/* intended for debugging.  Otherwise should be called  */
/* with lock.                                           */

struct Print_stats
{
        size_t number_of_blocks;
        size_t total_bytes;
};

#ifdef USE_MARK_BYTES

/* Return the number of set mark bits in the given header.      */
/* Remains externally visible as used by GNU GCJ currently.     */
unsigned GC_n_set_marks(hdr *hhdr)
{
    unsigned result = 0;
    word i;
    word offset = MARK_BIT_OFFSET(hhdr -> hb_sz);
    word limit = FINAL_MARK_BIT(hhdr -> hb_sz);

    for (i = 0; i < limit; i += offset) {
        result += hhdr -> hb_marks[i];
    }
    GC_ASSERT(hhdr -> hb_marks[limit]); /* the one set past the end */
    return(result);
}

#else

/* Number of set bits in a word.  Not performance critical.     */
static unsigned count_ones(word n)
{
    unsigned result = 0;

    for (; n > 0; n >>= 1)
        if (n & 1) result++;

    return result;
}

unsigned GC_n_set_marks(hdr *hhdr)
{
    unsigned result = 0;
    word sz = hhdr -> hb_sz;
    word i;
#   ifdef MARK_BIT_PER_OBJ
      word n_objs = HBLK_OBJS(sz);
      word n_mark_words = divWORDSZ(n_objs > 0 ? n_objs : 1); /* round down */

      for (i = 0; i <= n_mark_words; i++) {
          result += count_ones(hhdr -> hb_marks[i]);
      }
#   else /* MARK_BIT_PER_GRANULE */

      for (i = 0; i < MARK_BITS_SZ; i++) {
          result += count_ones(hhdr -> hb_marks[i]);
      }
#   endif
    GC_ASSERT(result > 0);
    result--; /* exclude the one bit set past the end */
#   ifndef MARK_BIT_PER_OBJ
      if (IS_UNCOLLECTABLE(hhdr -> hb_obj_kind)) {
        unsigned ngranules = (unsigned)BYTES_TO_GRANULES(sz);

        /* As mentioned in GC_set_hdr_marks(), all the bits are set     */
        /* instead of every n-th, thus the result should be adjusted.   */
        GC_ASSERT(ngranules > 0 && result % ngranules == 0);
        result /= ngranules;
      }
#   endif
    return result;
}

#endif /* !USE_MARK_BYTES  */

STATIC void GC_print_block_descr(struct hblk *h,
                                 word /* struct PrintStats */ raw_ps)
{
    hdr *hhdr = HDR(h);
    word sz = hhdr -> hb_sz;
    struct Print_stats *ps = (struct Print_stats *)raw_ps;
    unsigned n_marks = GC_n_set_marks(hhdr);
    unsigned n_objs = (unsigned)HBLK_OBJS(sz);

#   ifndef PARALLEL_MARK
        GC_ASSERT(hhdr -> hb_n_marks == n_marks);
#   endif
    GC_ASSERT((n_objs > 0 ? n_objs : 1) >= n_marks);
    GC_printf("%u,%u,%u,%u\n",
              hhdr -> hb_obj_kind, (unsigned)sz, n_marks, n_objs);
    ps -> number_of_blocks++;
    ps -> total_bytes += (sz + (HBLKSIZE-1)) & ~(HBLKSIZE-1); /* round up */
}

void GC_print_block_list(void)
{
    struct Print_stats pstats;

    GC_printf("kind(0=ptrfree/1=normal/2=unc.),"
              "obj_sz,#marks_set,#objs_in_block\n");
    BZERO(&pstats, sizeof(pstats));
    GC_apply_to_all_blocks(GC_print_block_descr, (word)&pstats);
    GC_printf("blocks= %lu, total_bytes= %lu\n",
              (unsigned long)pstats.number_of_blocks,
              (unsigned long)pstats.total_bytes);
}

#include "gc/gc_inline.h" /* for GC_print_free_list prototype */

/* Currently for debugger use only: */
GC_API void GC_CALL GC_print_free_list(int kind, size_t sz_in_granules)
{
    void *flh_next;
    int n;

    GC_ASSERT(kind < MAXOBJKINDS);
    GC_ASSERT(sz_in_granules <= MAXOBJGRANULES);
    flh_next = GC_obj_kinds[kind].ok_freelist[sz_in_granules];
    for (n = 0; flh_next; n++) {
        GC_printf("Free object in heap block %p [%d]: %p\n",
                  (void *)HBLKPTR(flh_next), n, flh_next);
        flh_next = obj_link(flh_next);
    }
}

#endif /* !NO_DEBUGGING */

/*
 * Clear all obj_link pointers in the list of free objects *flp.
 * Clear *flp.
 * This must be done before dropping a list of free gcj-style objects,
 * since may otherwise end up with dangling "descriptor" pointers.
 * It may help for other pointer-containing objects.
 */
STATIC void GC_clear_fl_links(void **flp)
{
    void *next = *flp;

    while (0 != next) {
       *flp = 0;
       flp = &(obj_link(next));
       next = *flp;
    }
}

/*
 * Perform GC_reclaim_block on the entire heap, after first clearing
 * small object free lists (if we are not just looking for leaks).
 */
GC_INNER void GC_start_reclaim(GC_bool report_if_found)
{
    unsigned kind;

#   if defined(PARALLEL_MARK)
      GC_ASSERT(0 == GC_fl_builder_count);
#   endif
    /* Reset in use counters.  GC_reclaim_block recomputes them. */
      GC_composite_in_use = 0;
      GC_atomic_in_use = 0;
    /* Clear reclaim- and free-lists */
      for (kind = 0; kind < GC_n_kinds; kind++) {
        struct hblk ** rlist = GC_obj_kinds[kind].ok_reclaim_list;
        GC_bool should_clobber = (GC_obj_kinds[kind].ok_descriptor != 0);

        if (rlist == 0) continue;       /* This kind not used.  */
        if (!report_if_found) {
            void **fop;
            void **lim = &(GC_obj_kinds[kind].ok_freelist[MAXOBJGRANULES+1]);

            for (fop = GC_obj_kinds[kind].ok_freelist;
                 (word)fop < (word)lim; (*(word **)&fop)++) {
              if (*fop != 0) {
                if (should_clobber) {
                  GC_clear_fl_links(fop);
                } else {
                  *fop = 0;
                }
              }
            }
        } /* otherwise free list objects are marked,    */
          /* and its safe to leave them                 */
        BZERO(rlist, (MAXOBJGRANULES + 1) * sizeof(void *));
      }


  /* Go through all heap blocks (in hblklist) and reclaim unmarked objects */
  /* or enqueue the block for later processing.                            */
    GC_apply_to_all_blocks(GC_reclaim_block, (word)report_if_found);

# ifdef EAGER_SWEEP
    /* This is a very stupid thing to do.  We make it possible anyway,  */
    /* so that you can convince yourself that it really is very stupid. */
    GC_reclaim_all((GC_stop_func)0, FALSE);
# elif defined(ENABLE_DISCLAIM)
    /* However, make sure to clear reclaimable objects of kinds with    */
    /* unconditional marking enabled before we do any significant       */
    /* marking work.                                                    */
    GC_reclaim_unconditionally_marked();
# endif
# if defined(PARALLEL_MARK)
    GC_ASSERT(0 == GC_fl_builder_count);
# endif

}

/*
 * Sweep blocks of the indicated object size and kind until either the
 * appropriate free list is nonempty, or there are no more blocks to
 * sweep.
 */
GC_INNER void GC_continue_reclaim(word sz /* granules */, int kind)
{
    hdr * hhdr;
    struct hblk * hbp;
    struct obj_kind * ok = &(GC_obj_kinds[kind]);
    struct hblk ** rlh = ok -> ok_reclaim_list;
    void **flh = &(ok -> ok_freelist[sz]);

    if (NULL == rlh)
        return; /* No blocks of this kind.      */

    for (rlh += sz; (hbp = *rlh) != NULL; ) {
        hhdr = HDR(hbp);
        *rlh = hhdr -> hb_next;
        GC_reclaim_small_nonempty_block(hbp, hhdr -> hb_sz, FALSE);
        if (*flh != 0)
            break;
    }
}

/*
 * Reclaim all small blocks waiting to be reclaimed.
 * Abort and return FALSE when/if (*stop_func)() returns TRUE.
 * If this returns TRUE, then it's safe to restart the world
 * with incorrectly cleared mark bits.
 * If ignore_old is TRUE, then reclaim only blocks that have been
 * recently reclaimed, and discard the rest.
 * Stop_func may be 0.
 */
GC_INNER GC_bool GC_reclaim_all(GC_stop_func stop_func, GC_bool ignore_old)
{
    word sz;
    unsigned kind;
    hdr * hhdr;
    struct hblk * hbp;
    struct obj_kind * ok;
    struct hblk ** rlp;
    struct hblk ** rlh;
#   ifndef NO_CLOCK
      CLOCK_TYPE start_time = CLOCK_TYPE_INITIALIZER;

      if (GC_print_stats == VERBOSE)
        GET_TIME(start_time);
#   endif

    for (kind = 0; kind < GC_n_kinds; kind++) {
        ok = &(GC_obj_kinds[kind]);
        rlp = ok -> ok_reclaim_list;
        if (rlp == 0) continue;
        for (sz = 1; sz <= MAXOBJGRANULES; sz++) {
            for (rlh = rlp + sz; (hbp = *rlh) != NULL; ) {
                if (stop_func != (GC_stop_func)0 && (*stop_func)()) {
                    return(FALSE);
                }
                hhdr = HDR(hbp);
                *rlh = hhdr -> hb_next;
                if (!ignore_old
                    || (word)hhdr->hb_last_reclaimed == GC_gc_no - 1) {
                    /* It's likely we'll need it this time, too */
                    /* It's been touched recently, so this      */
                    /* shouldn't trigger paging.                */
                    GC_reclaim_small_nonempty_block(hbp, hhdr->hb_sz, FALSE);
                }
            }
        }
    }
#   ifndef NO_CLOCK
      if (GC_print_stats == VERBOSE) {
        CLOCK_TYPE done_time;

        GET_TIME(done_time);
        GC_verbose_log_printf(
                        "Disposing of reclaim lists took %lu ms %lu ns\n",
                        MS_TIME_DIFF(done_time, start_time),
                        NS_FRAC_TIME_DIFF(done_time, start_time));
      }
#   endif
    return(TRUE);
}

#if !defined(EAGER_SWEEP) && defined(ENABLE_DISCLAIM)
/* We do an eager sweep on heap blocks where unconditional marking has  */
/* been enabled, so that any reclaimable objects have been reclaimed    */
/* before we start marking.  This is a simplified GC_reclaim_all        */
/* restricted to kinds where ok_mark_unconditionally is true.           */
  STATIC void GC_reclaim_unconditionally_marked(void)
  {
    word sz;
    unsigned kind;
    hdr * hhdr;
    struct hblk * hbp;
    struct obj_kind * ok;
    struct hblk ** rlp;
    struct hblk ** rlh;

    for (kind = 0; kind < GC_n_kinds; kind++) {
        ok = &(GC_obj_kinds[kind]);
        if (!ok->ok_mark_unconditionally)
          continue;
        rlp = ok->ok_reclaim_list;
        if (rlp == 0)
          continue;
        for (sz = 1; sz <= MAXOBJGRANULES; sz++) {
            rlh = rlp + sz;
            while ((hbp = *rlh) != 0) {
                hhdr = HDR(hbp);
                *rlh = hhdr->hb_next;
                GC_reclaim_small_nonempty_block(hbp, hhdr->hb_sz, FALSE);
            }
        }
    }
  }
#endif /* !EAGER_SWEEP && ENABLE_DISCLAIM */

struct enumerate_reachable_s {
  GC_reachable_object_proc proc;
  void *client_data;
};

STATIC void GC_do_enumerate_reachable_objects(struct hblk *hbp, word ped)
{
  struct hblkhdr *hhdr = HDR(hbp);
  size_t sz = (size_t)hhdr->hb_sz;
  size_t bit_no;
  char *p, *plim;

  if (GC_block_empty(hhdr)) {
    return;
  }

  p = hbp->hb_body;
  if (sz > MAXOBJBYTES) { /* one big object */
    plim = p;
  } else {
    plim = hbp->hb_body + HBLKSIZE - sz;
  }
  /* Go through all words in block. */
  for (bit_no = 0; p <= plim; bit_no += MARK_BIT_OFFSET(sz), p += sz) {
    if (mark_bit_from_hdr(hhdr, bit_no)) {
      ((struct enumerate_reachable_s *)ped)->proc(p, sz,
                        ((struct enumerate_reachable_s *)ped)->client_data);
    }
  }
}

GC_API void GC_CALL GC_enumerate_reachable_objects_inner(
                                                GC_reachable_object_proc proc,
                                                void *client_data)
{
  struct enumerate_reachable_s ed;

  GC_ASSERT(I_HOLD_LOCK());
  ed.proc = proc;
  ed.client_data = client_data;
  GC_apply_to_all_blocks(GC_do_enumerate_reachable_objects, (word)&ed);
}