Initial revision

1 files changed, 726 insertions, 0 deletions

diff --git a/gc/allchblk.c b/gc/allchblk.c
new file mode 100644
index 0000000..d8d0afd
--- /dev/null
+++ b/gc/allchblk.c
@@ -0,0 +1,726 @@
+/* 
+ * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
+ * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
+ * Copyright (c) 1998-1999 by Silicon Graphics.  All rights reserved.
+ *
+ * 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.
+ */
+
+#define DEBUG
+#undef DEBUG
+#include <stdio.h>
+#include "gc_priv.h"
+
+
+/*
+ * Free heap blocks are kept on one of several free lists,
+ * depending on the size of the block.  Each free list is doubly linked.
+ * Adjacent free blocks are coalesced.
+ */
+
+ 
+# define MAX_BLACK_LIST_ALLOC (2*HBLKSIZE)
+		/* largest block we will allocate starting on a black   */
+		/* listed block.  Must be >= HBLKSIZE.			*/
+
+
+# define UNIQUE_THRESHOLD 32
+	/* Sizes up to this many HBLKs each have their own free list    */
+# define HUGE_THRESHOLD 256
+	/* Sizes of at least this many heap blocks are mapped to a	*/
+	/* single free list.						*/
+# define FL_COMPRESSION 8
+	/* In between sizes map this many distinct sizes to a single	*/
+	/* bin.								*/
+
+# define N_HBLK_FLS (HUGE_THRESHOLD - UNIQUE_THRESHOLD)/FL_COMPRESSION \
+				 + UNIQUE_THRESHOLD
+
+struct hblk * GC_hblkfreelist[N_HBLK_FLS+1] = { 0 };
+
+/* Map a number of blocks to the appropriate large block free list index. */
+int GC_hblk_fl_from_blocks(blocks_needed)
+word blocks_needed;
+{
+    if (blocks_needed <= UNIQUE_THRESHOLD) return blocks_needed;
+    if (blocks_needed >= HUGE_THRESHOLD) return N_HBLK_FLS;
+    return (blocks_needed - UNIQUE_THRESHOLD)/FL_COMPRESSION
+					+ UNIQUE_THRESHOLD;
+    
+}
+
+# define HBLK_IS_FREE(hdr) ((hdr) -> hb_map == GC_invalid_map)
+# define PHDR(hhdr) HDR(hhdr -> hb_prev)
+# define NHDR(hhdr) HDR(hhdr -> hb_next)
+
+# ifdef USE_MUNMAP
+#   define IS_MAPPED(hhdr) (((hhdr) -> hb_flags & WAS_UNMAPPED) == 0)
+# else  /* !USE_MMAP */
+#   define IS_MAPPED(hhdr) 1
+# endif /* USE_MUNMAP */
+
+# if !defined(NO_DEBUGGING)
+void GC_print_hblkfreelist()
+{
+    struct hblk * h;
+    word total_free = 0;
+    hdr * hhdr;
+    word sz;
+    int i;
+    
+    for (i = 0; i <= N_HBLK_FLS; ++i) {
+      h = GC_hblkfreelist[i];
+      if (0 != h) GC_printf1("Free list %ld:\n", (unsigned long)i);
+      while (h != 0) {
+        hhdr = HDR(h);
+        sz = hhdr -> hb_sz;
+    	GC_printf2("\t0x%lx size %lu ", (unsigned long)h, (unsigned long)sz);
+    	total_free += sz;
+        if (GC_is_black_listed(h, HBLKSIZE) != 0) {
+             GC_printf0("start black listed\n");
+        } else if (GC_is_black_listed(h, hhdr -> hb_sz) != 0) {
+             GC_printf0("partially black listed\n");
+        } else {
+             GC_printf0("not black listed\n");
+        }
+        h = hhdr -> hb_next;
+      }
+    }
+    if (total_free != GC_large_free_bytes) {
+	GC_printf1("GC_large_free_bytes = %lu (INCONSISTENT!!)\n",
+		   (unsigned long) GC_large_free_bytes);
+    }
+    GC_printf1("Total of %lu bytes on free list\n", (unsigned long)total_free);
+}
+
+/* Return the free list index on which the block described by the header */
+/* appears, or -1 if it appears nowhere.				 */
+int free_list_index_of(wanted)
+hdr * wanted;
+{
+    struct hblk * h;
+    hdr * hhdr;
+    int i;
+    
+    for (i = 0; i <= N_HBLK_FLS; ++i) {
+      h = GC_hblkfreelist[i];
+      while (h != 0) {
+        hhdr = HDR(h);
+	if (hhdr == wanted) return i;
+        h = hhdr -> hb_next;
+      }
+    }
+    return -1;
+}
+
+void GC_dump_regions()
+{
+    int i;
+    ptr_t start, end;
+    ptr_t p;
+    size_t bytes;
+    hdr *hhdr;
+    for (i = 0; i < GC_n_heap_sects; ++i) {
+	start = GC_heap_sects[i].hs_start;
+	bytes = GC_heap_sects[i].hs_bytes;
+	end = start + bytes;
+	/* Merge in contiguous sections.	*/
+	  while (i+1 < GC_n_heap_sects && GC_heap_sects[i+1].hs_start == end) {
+	    ++i;
+	    end = GC_heap_sects[i].hs_start + GC_heap_sects[i].hs_bytes;
+	  }
+	GC_printf2("***Section from 0x%lx to 0x%lx\n", start, end);
+	for (p = start; p < end;) {
+	    hhdr = HDR(p);
+	    GC_printf1("\t0x%lx ", (unsigned long)p);
+	    if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
+		GC_printf1("Missing header!!\n", hhdr);
+		p += HBLKSIZE;
+		continue;
+	    }
+	    if (HBLK_IS_FREE(hhdr)) {
+                int correct_index = GC_hblk_fl_from_blocks(
+					divHBLKSZ(hhdr -> hb_sz));
+	        int actual_index;
+		
+		GC_printf1("\tfree block of size 0x%lx bytes",
+			   (unsigned long)(hhdr -> hb_sz));
+	 	if (IS_MAPPED(hhdr)) {
+		    GC_printf0("\n");
+		} else {
+		    GC_printf0("(unmapped)\n");
+		}
+		actual_index = free_list_index_of(hhdr);
+		if (-1 == actual_index) {
+		    GC_printf1("\t\tBlock not on free list %ld!!\n",
+				correct_index);
+		} else if (correct_index != actual_index) {
+		    GC_printf2("\t\tBlock on list %ld, should be on %ld!!\n",
+			       actual_index, correct_index);
+		}
+		p += hhdr -> hb_sz;
+	    } else {
+		GC_printf1("\tused for blocks of size 0x%lx bytes\n",
+			   (unsigned long)WORDS_TO_BYTES(hhdr -> hb_sz));
+		p += HBLKSIZE * OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
+	    }
+	}
+    }
+}
+
+# endif /* NO_DEBUGGING */
+
+/* Initialize hdr for a block containing the indicated size and 	*/
+/* kind of objects.							*/
+/* Return FALSE on failure.						*/
+static GC_bool setup_header(hhdr, sz, kind, flags)
+register hdr * hhdr;
+word sz;	/* object size in words */
+int kind;
+unsigned char flags;
+{
+    register word descr;
+    
+    /* Add description of valid object pointers */
+      if (!GC_add_map_entry(sz)) return(FALSE);
+      hhdr -> hb_map = GC_obj_map[sz > MAXOBJSZ? 0 : sz];
+      
+    /* Set size, kind and mark proc fields */
+      hhdr -> hb_sz = sz;
+      hhdr -> hb_obj_kind = kind;
+      hhdr -> hb_flags = flags;
+      descr = GC_obj_kinds[kind].ok_descriptor;
+      if (GC_obj_kinds[kind].ok_relocate_descr) descr += WORDS_TO_BYTES(sz);
+      hhdr -> hb_descr = descr;
+      
+    /* Clear mark bits */
+      GC_clear_hdr_marks(hhdr);
+      
+    hhdr -> hb_last_reclaimed = (unsigned short)GC_gc_no;
+    return(TRUE);
+}
+
+#define FL_UNKNOWN -1
+/*
+ * Remove hhdr from the appropriate free list.
+ * We assume it is on the nth free list, or on the size
+ * appropriate free list if n is FL_UNKNOWN.
+ */
+void GC_remove_from_fl(hhdr, n)
+hdr * hhdr;
+int n;
+{
+    GC_ASSERT(((hhdr -> hb_sz) & (HBLKSIZE-1)) == 0);
+    if (hhdr -> hb_prev == 0) {
+        int index;
+	if (FL_UNKNOWN == n) {
+            index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
+	} else {
+	    index = n;
+	}
+	GC_ASSERT(HDR(GC_hblkfreelist[index]) == hhdr);
+	GC_hblkfreelist[index] = hhdr -> hb_next;
+    } else {
+	PHDR(hhdr) -> hb_next = hhdr -> hb_next;
+    }
+    if (0 != hhdr -> hb_next) {
+	GC_ASSERT(!IS_FORWARDING_ADDR_OR_NIL(NHDR(hhdr)));
+	NHDR(hhdr) -> hb_prev = hhdr -> hb_prev;
+    }
+}
+
+/*
+ * Return a pointer to the free block ending just before h, if any.
+ */
+struct hblk * GC_free_block_ending_at(h)
+struct hblk *h;
+{
+    struct hblk * p = h - 1;
+    hdr * phdr = HDR(p);
+
+    while (0 != phdr && IS_FORWARDING_ADDR_OR_NIL(phdr)) {
+	p = FORWARDED_ADDR(p,phdr);
+	phdr = HDR(p);
+    }
+    if (0 != phdr && HBLK_IS_FREE(phdr)) return p;
+    p = GC_prev_block(h - 1);
+    if (0 != p) {
+      phdr = HDR(p);
+      if (HBLK_IS_FREE(phdr) && (ptr_t)p + phdr -> hb_sz == (ptr_t)h) {
+	return p;
+      }
+    }
+    return 0;
+}
+
+/*
+ * Add hhdr to the appropriate free list.
+ * We maintain individual free lists sorted by address.
+ */
+void GC_add_to_fl(h, hhdr)
+struct hblk *h;
+hdr * hhdr;
+{
+    int index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
+    struct hblk *second = GC_hblkfreelist[index];
+#   ifdef GC_ASSERTIONS
+      struct hblk *next = (struct hblk *)((word)h + hhdr -> hb_sz);
+      hdr * nexthdr = HDR(next);
+      struct hblk *prev = GC_free_block_ending_at(h);
+      hdr * prevhdr = HDR(prev);
+      GC_ASSERT(nexthdr == 0 || !HBLK_IS_FREE(nexthdr) || !IS_MAPPED(nexthdr));
+      GC_ASSERT(prev == 0 || !HBLK_IS_FREE(prevhdr) || !IS_MAPPED(prevhdr));
+#   endif
+    GC_ASSERT(((hhdr -> hb_sz) & (HBLKSIZE-1)) == 0);
+    GC_hblkfreelist[index] = h;
+    hhdr -> hb_next = second;
+    hhdr -> hb_prev = 0;
+    if (0 != second) HDR(second) -> hb_prev = h;
+    GC_invalidate_map(hhdr);
+}
+
+#ifdef USE_MUNMAP
+
+/* Unmap blocks that haven't been recently touched.  This is the only way */
+/* way blocks are ever unmapped.					  */
+void GC_unmap_old(void)
+{
+    struct hblk * h;
+    hdr * hhdr;
+    word sz;
+    unsigned short last_rec, threshold;
+    int i;
+#   define UNMAP_THRESHOLD 6
+    
+    for (i = 0; i <= N_HBLK_FLS; ++i) {
+      for (h = GC_hblkfreelist[i]; 0 != h; h = hhdr -> hb_next) {
+        hhdr = HDR(h);
+	if (!IS_MAPPED(hhdr)) continue;
+	threshold = (unsigned short)(GC_gc_no - UNMAP_THRESHOLD);
+	last_rec = hhdr -> hb_last_reclaimed;
+	if (last_rec > GC_gc_no
+	    || last_rec < threshold && threshold < GC_gc_no
+				       /* not recently wrapped */) {
+          sz = hhdr -> hb_sz;
+	  GC_unmap((ptr_t)h, sz);
+	  hhdr -> hb_flags |= WAS_UNMAPPED;
+    	}
+      }
+    }  
+}
+
+/* Merge all unmapped blocks that are adjacent to other free		*/
+/* blocks.  This may involve remapping, since all blocks are either	*/
+/* fully mapped or fully unmapped.					*/
+void GC_merge_unmapped(void)
+{
+    struct hblk * h, *next;
+    hdr * hhdr, *nexthdr;
+    word size, nextsize;
+    int i;
+    
+    for (i = 0; i <= N_HBLK_FLS; ++i) {
+      h = GC_hblkfreelist[i];
+      while (h != 0) {
+	hhdr = HDR(h);
+	size = hhdr->hb_sz;
+	next = (struct hblk *)((word)h + size);
+	nexthdr = HDR(next);
+	/* Coalesce with successor, if possible */
+	  if (0 != nexthdr && HBLK_IS_FREE(nexthdr)) {
+	    nextsize = nexthdr -> hb_sz;
+	    if (IS_MAPPED(hhdr)) {
+	      GC_ASSERT(!IS_MAPPED(nexthdr));
+	      /* make both consistent, so that we can merge */
+	        if (size > nextsize) {
+		  GC_remap((ptr_t)next, nextsize);
+		} else {
+		  GC_unmap((ptr_t)h, size);
+		  hhdr -> hb_flags |= WAS_UNMAPPED;
+		}
+	    } else if (IS_MAPPED(nexthdr)) {
+	      GC_ASSERT(!IS_MAPPED(hhdr));
+	      if (size > nextsize) {
+		GC_unmap((ptr_t)next, nextsize);
+	      } else {
+		GC_remap((ptr_t)h, size);
+		hhdr -> hb_flags &= ~WAS_UNMAPPED;
+	      }
+	    } else {
+	      /* Unmap any gap in the middle */
+		GC_unmap_gap((ptr_t)h, size, (ptr_t)next, nexthdr -> hb_sz);
+	    }
+	    /* If they are both unmapped, we merge, but leave unmapped. */
+	    GC_remove_from_fl(hhdr, i);
+	    GC_remove_from_fl(nexthdr, FL_UNKNOWN);
+	    hhdr -> hb_sz += nexthdr -> hb_sz; 
+	    GC_remove_header(next);
+	    GC_add_to_fl(h, hhdr); 
+	    /* Start over at beginning of list */
+	    h = GC_hblkfreelist[i];
+	  } else /* not mergable with successor */ {
+	    h = hhdr -> hb_next;
+	  }
+      } /* while (h != 0) ... */
+    } /* for ... */
+}
+
+#endif /* USE_MUNMAP */
+
+/*
+ * Return a pointer to a block starting at h of length bytes.
+ * Memory for the block is mapped.
+ * Remove the block from its free list, and return the remainder (if any)
+ * to its appropriate free list.
+ * May fail by returning 0.
+ * The header for the returned block must be set up by the caller.
+ * If the return value is not 0, then hhdr is the header for it.
+ */
+struct hblk * GC_get_first_part(h, hhdr, bytes, index)
+struct hblk *h;
+hdr * hhdr;
+word bytes;
+int index;
+{
+    word total_size = hhdr -> hb_sz;
+    struct hblk * rest;
+    hdr * rest_hdr;
+
+    GC_ASSERT((total_size & (HBLKSIZE-1)) == 0);
+    GC_remove_from_fl(hhdr, index);
+    if (total_size == bytes) return h;
+    rest = (struct hblk *)((word)h + bytes);
+    if (!GC_install_header(rest)) return(0);
+    rest_hdr = HDR(rest);
+    rest_hdr -> hb_sz = total_size - bytes;
+    rest_hdr -> hb_flags = 0;
+#   ifdef GC_ASSERTIONS
+      // Mark h not free, to avoid assertion about adjacent free blocks.
+        hhdr -> hb_map = 0;
+#   endif
+    GC_add_to_fl(rest, rest_hdr);
+    return h;
+}
+
+/*
+ * H is a free block.  N points at an address inside it.
+ * A new header for n has already been set up.  Fix up h's header
+ * to reflect the fact that it is being split, move it to the
+ * appropriate free list.
+ * N replaces h in the original free list.
+ *
+ * Nhdr is not completely filled in, since it is about to allocated.
+ * It may in fact end up on the wrong free list for its size.
+ * (Hence adding it to a free list is silly.  But this path is hopefully
+ * rare enough that it doesn't matter.  The code is cleaner this way.)
+ */
+void GC_split_block(h, hhdr, n, nhdr, index)
+struct hblk *h;
+hdr * hhdr;
+struct hblk *n;
+hdr * nhdr;
+int index;	/* Index of free list */
+{
+    word total_size = hhdr -> hb_sz;
+    word h_size = (word)n - (word)h;
+    struct hblk *prev = hhdr -> hb_prev;
+    struct hblk *next = hhdr -> hb_next;
+
+    /* Replace h with n on its freelist */
+      nhdr -> hb_prev = prev;
+      nhdr -> hb_next = next;
+      nhdr -> hb_sz = total_size - h_size;
+      nhdr -> hb_flags = 0;
+      if (0 != prev) {
+	HDR(prev) -> hb_next = n;
+      } else {
+        GC_hblkfreelist[index] = n;
+      }
+      if (0 != next) {
+	HDR(next) -> hb_prev = n;
+      }
+#     ifdef GC_ASSERTIONS
+	nhdr -> hb_map = 0;	/* Don't fail test for consecutive	*/
+				/* free blocks in GC_add_to_fl.		*/
+#     endif
+#   ifdef USE_MUNMAP
+      hhdr -> hb_last_reclaimed = GC_gc_no;
+#   endif
+    hhdr -> hb_sz = h_size;
+    GC_add_to_fl(h, hhdr);
+    GC_invalidate_map(nhdr);
+}
+	
+struct hblk * GC_allochblk_nth();
+
+/*
+ * Allocate (and return pointer to) a heap block
+ *   for objects of size sz words, searching the nth free list.
+ *
+ * NOTE: We set obj_map field in header correctly.
+ *       Caller is responsible for building an object freelist in block.
+ *
+ * We clear the block if it is destined for large objects, and if
+ * kind requires that newly allocated objects be cleared.
+ */
+struct hblk *
+GC_allochblk(sz, kind, flags)
+word sz;
+int kind;
+unsigned char flags;  /* IGNORE_OFF_PAGE or 0 */
+{
+    int start_list = GC_hblk_fl_from_blocks(OBJ_SZ_TO_BLOCKS(sz));
+    int i;
+    for (i = start_list; i <= N_HBLK_FLS; ++i) {
+	struct hblk * result = GC_allochblk_nth(sz, kind, flags, i);
+	if (0 != result) return result;
+    }
+    return 0;
+}
+/*
+ * The same, but with search restricted to nth free list.
+ */
+struct hblk *
+GC_allochblk_nth(sz, kind, flags, n)
+word sz;
+int kind;
+unsigned char flags;  /* IGNORE_OFF_PAGE or 0 */
+int n;
+{
+    register struct hblk *hbp;
+    register hdr * hhdr;		/* Header corr. to hbp */
+    register struct hblk *thishbp;
+    register hdr * thishdr;		/* Header corr. to hbp */
+    signed_word size_needed;    /* number of bytes in requested objects */
+    signed_word size_avail;	/* bytes available in this block	*/
+
+    size_needed = HBLKSIZE * OBJ_SZ_TO_BLOCKS(sz);
+
+    /* search for a big enough block in free list */
+	hbp = GC_hblkfreelist[n];
+	hhdr = HDR(hbp);
+	for(; 0 != hbp; hbp = hhdr -> hb_next, hhdr = HDR(hbp)) {
+	    size_avail = hhdr->hb_sz;
+	    if (size_avail < size_needed) continue;
+#	    ifdef PRESERVE_LAST
+		if (size_avail != size_needed
+		    && !GC_incremental && GC_should_collect()) {
+		    continue;
+		} 
+#	    endif
+	    /* If the next heap block is obviously better, go on.	*/
+	    /* This prevents us from disassembling a single large block */
+	    /* to get tiny blocks.					*/
+	    {
+	      signed_word next_size;
+	      
+	      thishbp = hhdr -> hb_next;
+	      if (thishbp != 0) {
+	        thishdr = HDR(thishbp);
+	        next_size = (signed_word)(thishdr -> hb_sz);
+	        if (next_size < size_avail
+	          && next_size >= size_needed
+	          && !GC_is_black_listed(thishbp, (word)size_needed)) {
+	          continue;
+	        }
+	      }
+	    }
+	    if ( !IS_UNCOLLECTABLE(kind) &&
+	         (kind != PTRFREE || size_needed > MAX_BLACK_LIST_ALLOC)) {
+	      struct hblk * lasthbp = hbp;
+	      ptr_t search_end = (ptr_t)hbp + size_avail - size_needed;
+	      signed_word orig_avail = size_avail;
+	      signed_word eff_size_needed = ((flags & IGNORE_OFF_PAGE)?
+	      					HBLKSIZE
+	      					: size_needed);
+	      
+	      
+	      while ((ptr_t)lasthbp <= search_end
+	             && (thishbp = GC_is_black_listed(lasthbp,
+	             				      (word)eff_size_needed))) {
+	        lasthbp = thishbp;
+	      }
+	      size_avail -= (ptr_t)lasthbp - (ptr_t)hbp;
+	      thishbp = lasthbp;
+	      if (size_avail >= size_needed) {
+	        if (thishbp != hbp && GC_install_header(thishbp)) {
+		  /* Make sure it's mapped before we mangle it. */
+#		    ifdef USE_MUNMAP
+		      if (!IS_MAPPED(hhdr)) {
+		        GC_remap((ptr_t)hbp, size_avail);
+		        hhdr -> hb_flags &= ~WAS_UNMAPPED;
+		      }
+#		    endif
+	          /* Split the block at thishbp */
+	              thishdr = HDR(thishbp);
+		      GC_split_block(hbp, hhdr, thishbp, thishdr, n);
+		  /* Advance to thishbp */
+		      hbp = thishbp;
+		      hhdr = thishdr;
+		      /* We must now allocate thishbp, since it may	*/
+		      /* be on the wrong free list.			*/
+		}
+	      } else if (size_needed > (signed_word)BL_LIMIT
+	                 && orig_avail - size_needed
+			    > (signed_word)BL_LIMIT) {
+	        /* Punt, since anything else risks unreasonable heap growth. */
+	        WARN("Needed to allocate blacklisted block at 0x%lx\n",
+		     (word)hbp);
+	        size_avail = orig_avail;
+	      } else if (size_avail == 0 && size_needed == HBLKSIZE
+			 && IS_MAPPED(hhdr)) {
+		if (!GC_find_leak) {
+	      	  static unsigned count = 0;
+	      	  
+	      	  /* The block is completely blacklisted.  We need 	*/
+	      	  /* to drop some such blocks, since otherwise we spend */
+	      	  /* all our time traversing them if pointerfree	*/
+	      	  /* blocks are unpopular.				*/
+	          /* A dropped block will be reconsidered at next GC.	*/
+	          if ((++count & 3) == 0) {
+	            /* Allocate and drop the block in small chunks, to	*/
+	            /* maximize the chance that we will recover some	*/
+	            /* later.						*/
+		      word total_size = hhdr -> hb_sz;
+	              struct hblk * limit = hbp + divHBLKSZ(total_size);
+	              struct hblk * h;
+		      struct hblk * prev = hhdr -> hb_prev;
+	              
+		      GC_words_wasted += total_size;
+		      GC_large_free_bytes -= total_size;
+		      GC_remove_from_fl(hhdr, n);
+	              for (h = hbp; h < limit; h++) {
+	                if (h == hbp || GC_install_header(h)) {
+	                  hhdr = HDR(h);
+	                  (void) setup_header(
+	                	  hhdr,
+	              		  BYTES_TO_WORDS(HBLKSIZE - HDR_BYTES),
+	              		  PTRFREE, 0); /* Cant fail */
+	              	  if (GC_debugging_started) {
+	              	    BZERO(h + HDR_BYTES, HBLKSIZE - HDR_BYTES);
+	              	  }
+	                }
+	              }
+	            /* Restore hbp to point at free block */
+		      hbp = prev;
+		      if (0 == hbp) {
+			return GC_allochblk_nth(sz, kind, flags, n);
+		      }
+	   	      hhdr = HDR(hbp);
+	          }
+		}
+	      }
+	    }
+	    if( size_avail >= size_needed ) {
+#		ifdef USE_MUNMAP
+		  if (!IS_MAPPED(hhdr)) {
+		    GC_remap((ptr_t)hbp, size_avail);
+		    hhdr -> hb_flags &= ~WAS_UNMAPPED;
+		  }
+#	        endif
+		/* hbp may be on the wrong freelist; the parameter n	*/
+		/* is important.					*/
+		hbp = GC_get_first_part(hbp, hhdr, size_needed, n);
+		break;
+	    }
+	}
+
+    if (0 == hbp) return 0;
+	
+    /* Notify virtual dirty bit implementation that we are about to write. */
+    	GC_write_hint(hbp);
+    
+    /* Add it to map of valid blocks */
+    	if (!GC_install_counts(hbp, (word)size_needed)) return(0);
+    	/* This leaks memory under very rare conditions. */
+    		
+    /* Set up header */
+        if (!setup_header(hhdr, sz, kind, flags)) {
+            GC_remove_counts(hbp, (word)size_needed);
+            return(0); /* ditto */
+        }
+        
+    /* Clear block if necessary */
+	if (GC_debugging_started
+	    || sz > MAXOBJSZ && GC_obj_kinds[kind].ok_init) {
+	    BZERO(hbp + HDR_BYTES,  size_needed - HDR_BYTES);
+	}
+
+    /* We just successfully allocated a block.  Restart count of	*/
+    /* consecutive failures.						*/
+    {
+	extern unsigned GC_fail_count;
+	
+	GC_fail_count = 0;
+    }
+
+    GC_large_free_bytes -= size_needed;
+    
+    GC_ASSERT(IS_MAPPED(hhdr));
+    return( hbp );
+}
+ 
+struct hblk * GC_freehblk_ptr = 0;  /* Search position hint for GC_freehblk */
+
+/*
+ * Free a heap block.
+ *
+ * Coalesce the block with its neighbors if possible.
+ *
+ * All mark words are assumed to be cleared.
+ */
+void
+GC_freehblk(hbp)
+struct hblk *hbp;
+{
+struct hblk *next, *prev;
+hdr *hhdr, *prevhdr, *nexthdr;
+signed_word size;
+
+
+    hhdr = HDR(hbp);
+    size = hhdr->hb_sz;
+    size = HBLKSIZE * OBJ_SZ_TO_BLOCKS(size);
+    GC_remove_counts(hbp, (word)size);
+    hhdr->hb_sz = size;
+    
+    /* Check for duplicate deallocation in the easy case */
+      if (HBLK_IS_FREE(hhdr)) {
+        GC_printf1("Duplicate large block deallocation of 0x%lx\n",
+        	   (unsigned long) hbp);
+      }
+
+    GC_ASSERT(IS_MAPPED(hhdr));
+    GC_invalidate_map(hhdr);
+    next = (struct hblk *)((word)hbp + size);
+    nexthdr = HDR(next);
+    prev = GC_free_block_ending_at(hbp);
+    /* Coalesce with successor, if possible */
+      if(0 != nexthdr && HBLK_IS_FREE(nexthdr) && IS_MAPPED(nexthdr)) {
+	GC_remove_from_fl(nexthdr, FL_UNKNOWN);
+	hhdr -> hb_sz += nexthdr -> hb_sz; 
+	GC_remove_header(next);
+      }
+    /* Coalesce with predecessor, if possible. */
+      if (0 != prev) {
+	prevhdr = HDR(prev);
+	if (IS_MAPPED(prevhdr)) {
+	  GC_remove_from_fl(prevhdr, FL_UNKNOWN);
+	  prevhdr -> hb_sz += hhdr -> hb_sz;
+	  GC_remove_header(hbp);
+	  hbp = prev;
+	  hhdr = prevhdr;
+	}
+      }
+
+    GC_large_free_bytes += size;
+    GC_add_to_fl(hbp, hhdr);    
+}
+