boehm-gc/allchblk.c

   1 /*
   2  * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
   3  * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
   4  * Copyright (c) 1998-1999 by Silicon Graphics.  All rights reserved.
   5  * Copyright (c) 1999 by Hewlett-Packard Company. All rights reserved.
   6  *
   7  * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
   8  * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
   9  *
  10  * Permission is hereby granted to use or copy this program
  11  * for any purpose,  provided the above notices are retained on all copies.
  12  * Permission to modify the code and to distribute modified code is granted,
  13  * provided the above notices are retained, and a notice that the code was
  14  * modified is included with the above copyright notice.
  15  */
  16
  17 #define DEBUG
  18 #undef DEBUG
  19 #include <stdio.h>
  20 #include "gc_priv.h"
  21
  22 GC_bool GC_use_entire_heap = 0;
  23
  24 /*
  25  * Free heap blocks are kept on one of several free lists,
  26  * depending on the size of the block.  Each free list is doubly linked.
  27  * Adjacent free blocks are coalesced.
  28  */
  29
  30
  31 # define MAX_BLACK_LIST_ALLOC (2*HBLKSIZE)
  32                 /* largest block we will allocate starting on a black   */
  33                 /* listed block.  Must be >= HBLKSIZE.                  */
  34
  35
  36 # define UNIQUE_THRESHOLD 32
  37         /* Sizes up to this many HBLKs each have their own free list    */
  38 # define HUGE_THRESHOLD 256
  39         /* Sizes of at least this many heap blocks are mapped to a      */
  40         /* single free list.                                            */
  41 # define FL_COMPRESSION 8
  42         /* In between sizes map this many distinct sizes to a single    */
  43         /* bin.                                                         */
  44
  45 # define N_HBLK_FLS (HUGE_THRESHOLD - UNIQUE_THRESHOLD)/FL_COMPRESSION \
  46                                  + UNIQUE_THRESHOLD
  47
  48 struct hblk * GC_hblkfreelist[N_HBLK_FLS+1] = { 0 };
  49
  50 /* Map a number of blocks to the appropriate large block free list index. */
  51 int GC_hblk_fl_from_blocks(blocks_needed)
  52 word blocks_needed;
  53 {
  54     if (blocks_needed <= UNIQUE_THRESHOLD) return blocks_needed;
  55     if (blocks_needed >= HUGE_THRESHOLD) return N_HBLK_FLS;
  56     return (blocks_needed - UNIQUE_THRESHOLD)/FL_COMPRESSION
  57                                         + UNIQUE_THRESHOLD;
  58
  59 }
  60
  61 # define HBLK_IS_FREE(hdr) ((hdr) -> hb_map == GC_invalid_map)
  62 # define PHDR(hhdr) HDR(hhdr -> hb_prev)
  63 # define NHDR(hhdr) HDR(hhdr -> hb_next)
  64
  65 # ifdef USE_MUNMAP
  66 #   define IS_MAPPED(hhdr) (((hhdr) -> hb_flags & WAS_UNMAPPED) == 0)
  67 # else  /* !USE_MMAP */
  68 #   define IS_MAPPED(hhdr) 1
  69 # endif /* USE_MUNMAP */
  70
  71 # if !defined(NO_DEBUGGING)
  72 void GC_print_hblkfreelist()
  73 {
  74     struct hblk * h;
  75     word total_free = 0;
  76     hdr * hhdr;
  77     word sz;
  78     int i;
  79
  80     for (i = 0; i <= N_HBLK_FLS; ++i) {
  81       h = GC_hblkfreelist[i];
  82       if (0 != h) GC_printf1("Free list %ld:\n", (unsigned long)i);
  83       while (h != 0) {
  84         hhdr = HDR(h);
  85         sz = hhdr -> hb_sz;
  86         GC_printf2("\t0x%lx size %lu ", (unsigned long)h, (unsigned long)sz);
  87         total_free += sz;
  88         if (GC_is_black_listed(h, HBLKSIZE) != 0) {
  89              GC_printf0("start black listed\n");
  90         } else if (GC_is_black_listed(h, hhdr -> hb_sz) != 0) {
  91              GC_printf0("partially black listed\n");
  92         } else {
  93              GC_printf0("not black listed\n");
  94         }
  95         h = hhdr -> hb_next;
  96       }
  97     }
  98     if (total_free != GC_large_free_bytes) {
  99         GC_printf1("GC_large_free_bytes = %lu (INCONSISTENT!!)\n",
 100                    (unsigned long) GC_large_free_bytes);
 101     }
 102     GC_printf1("Total of %lu bytes on free list\n", (unsigned long)total_free);
 103 }
 104
 105 /* Return the free list index on which the block described by the header */
 106 /* appears, or -1 if it appears nowhere.                                 */
 107 int free_list_index_of(wanted)
 108 hdr * wanted;
 109 {
 110     struct hblk * h;
 111     hdr * hhdr;
 112     int i;
 113
 114     for (i = 0; i <= N_HBLK_FLS; ++i) {
 115       h = GC_hblkfreelist[i];
 116       while (h != 0) {
 117         hhdr = HDR(h);
 118         if (hhdr == wanted) return i;
 119         h = hhdr -> hb_next;
 120       }
 121     }
 122     return -1;
 123 }
 124
 125 void GC_dump_regions()
 126 {
 127     unsigned i;
 128     ptr_t start, end;
 129     ptr_t p;
 130     size_t bytes;
 131     hdr *hhdr;
 132     for (i = 0; i < GC_n_heap_sects; ++i) {
 133         start = GC_heap_sects[i].hs_start;
 134         bytes = GC_heap_sects[i].hs_bytes;
 135         end = start + bytes;
 136         /* Merge in contiguous sections.        */
 137           while (i+1 < GC_n_heap_sects && GC_heap_sects[i+1].hs_start == end) {
 138             ++i;
 139             end = GC_heap_sects[i].hs_start + GC_heap_sects[i].hs_bytes;
 140           }
 141         GC_printf2("***Section from 0x%lx to 0x%lx\n", start, end);
 142         for (p = start; p < end;) {
 143             hhdr = HDR(p);
 144             GC_printf1("\t0x%lx ", (unsigned long)p);
 145             if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
 146                 GC_printf1("Missing header!!\n", hhdr);
 147                 p += HBLKSIZE;
 148                 continue;
 149             }
 150             if (HBLK_IS_FREE(hhdr)) {
 151                 int correct_index = GC_hblk_fl_from_blocks(
 152                                         divHBLKSZ(hhdr -> hb_sz));
 153                 int actual_index;
 154
 155                 GC_printf1("\tfree block of size 0x%lx bytes",
 156                            (unsigned long)(hhdr -> hb_sz));
 157                 if (IS_MAPPED(hhdr)) {
 158                     GC_printf0("\n");
 159                 } else {
 160                     GC_printf0("(unmapped)\n");
 161                 }
 162                 actual_index = free_list_index_of(hhdr);
 163                 if (-1 == actual_index) {
 164                     GC_printf1("\t\tBlock not on free list %ld!!\n",
 165                                 correct_index);
 166                 } else if (correct_index != actual_index) {
 167                     GC_printf2("\t\tBlock on list %ld, should be on %ld!!\n",
 168                                actual_index, correct_index);
 169                 }
 170                 p += hhdr -> hb_sz;
 171             } else {
 172                 GC_printf1("\tused for blocks of size 0x%lx bytes\n",
 173                            (unsigned long)WORDS_TO_BYTES(hhdr -> hb_sz));
 174                 p += HBLKSIZE * OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
 175             }
 176         }
 177     }
 178 }
 179
 180 # endif /* NO_DEBUGGING */
 181
 182 /* Initialize hdr for a block containing the indicated size and         */
 183 /* kind of objects.                                                     */
 184 /* Return FALSE on failure.                                             */
 185 static GC_bool setup_header(hhdr, sz, kind, flags)
 186 register hdr * hhdr;
 187 word sz;        /* object size in words */
 188 int kind;
 189 unsigned char flags;
 190 {
 191     register word descr;
 192
 193     /* Add description of valid object pointers */
 194       if (!GC_add_map_entry(sz)) return(FALSE);
 195       hhdr -> hb_map = GC_obj_map[sz > MAXOBJSZ? 0 : sz];
 196
 197     /* Set size, kind and mark proc fields */
 198       hhdr -> hb_sz = sz;
 199       hhdr -> hb_obj_kind = kind;
 200       hhdr -> hb_flags = flags;
 201       descr = GC_obj_kinds[kind].ok_descriptor;
 202       if (GC_obj_kinds[kind].ok_relocate_descr) descr += WORDS_TO_BYTES(sz);
 203       hhdr -> hb_descr = descr;
 204
 205     /* Clear mark bits */
 206       GC_clear_hdr_marks(hhdr);
 207
 208     hhdr -> hb_last_reclaimed = (unsigned short)GC_gc_no;
 209     return(TRUE);
 210 }
 211
 212 #define FL_UNKNOWN -1
 213 /*
 214  * Remove hhdr from the appropriate free list.
 215  * We assume it is on the nth free list, or on the size
 216  * appropriate free list if n is FL_UNKNOWN.
 217  */
 218 void GC_remove_from_fl(hhdr, n)
 219 hdr * hhdr;
 220 int n;
 221 {
 222     GC_ASSERT(((hhdr -> hb_sz) & (HBLKSIZE-1)) == 0);
 223     if (hhdr -> hb_prev == 0) {
 224         int index;
 225         if (FL_UNKNOWN == n) {
 226             index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
 227         } else {
 228             index = n;
 229         }
 230         GC_ASSERT(HDR(GC_hblkfreelist[index]) == hhdr);
 231         GC_hblkfreelist[index] = hhdr -> hb_next;
 232     } else {
 233         hdr *phdr;
 234         GET_HDR(hhdr -> hb_prev, phdr);
 235         phdr -> hb_next = hhdr -> hb_next;
 236     }
 237     if (0 != hhdr -> hb_next) {
 238         hdr * nhdr;
 239         GC_ASSERT(!IS_FORWARDING_ADDR_OR_NIL(NHDR(hhdr)));
 240         GET_HDR(hhdr -> hb_next, nhdr);
 241         nhdr -> hb_prev = hhdr -> hb_prev;
 242     }
 243 }
 244
 245 /*
 246  * Return a pointer to the free block ending just before h, if any.
 247  */
 248 struct hblk * GC_free_block_ending_at(h)
 249 struct hblk *h;
 250 {
 251     struct hblk * p = h - 1;
 252     hdr * phdr;
 253
 254     GET_HDR(p, phdr);
 255     while (0 != phdr && IS_FORWARDING_ADDR_OR_NIL(phdr)) {
 256         p = FORWARDED_ADDR(p,phdr);
 257         phdr = HDR(p);
 258     }
 259     if (0 != phdr) {
 260         if(HBLK_IS_FREE(phdr)) {
 261             return p;
 262         } else {
 263             return 0;
 264         }
 265     }
 266     p = GC_prev_block(h - 1);
 267     if (0 != p) {
 268       phdr = HDR(p);
 269       if (HBLK_IS_FREE(phdr) && (ptr_t)p + phdr -> hb_sz == (ptr_t)h) {
 270         return p;
 271       }
 272     }
 273     return 0;
 274 }
 275
 276 /*
 277  * Add hhdr to the appropriate free list.
 278  * We maintain individual free lists sorted by address.
 279  */
 280 void GC_add_to_fl(h, hhdr)
 281 struct hblk *h;
 282 hdr * hhdr;
 283 {
 284     int index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
 285     struct hblk *second = GC_hblkfreelist[index];
 286     hdr * second_hdr;
 287 #   ifdef GC_ASSERTIONS
 288       struct hblk *next = (struct hblk *)((word)h + hhdr -> hb_sz);
 289       hdr * nexthdr = HDR(next);
 290       struct hblk *prev = GC_free_block_ending_at(h);
 291       hdr * prevhdr = HDR(prev);
 292       GC_ASSERT(nexthdr == 0 || !HBLK_IS_FREE(nexthdr) || !IS_MAPPED(nexthdr));
 293       GC_ASSERT(prev == 0 || !HBLK_IS_FREE(prevhdr) || !IS_MAPPED(prevhdr));
 294 #   endif
 295     GC_ASSERT(((hhdr -> hb_sz) & (HBLKSIZE-1)) == 0);
 296     GC_hblkfreelist[index] = h;
 297     hhdr -> hb_next = second;
 298     hhdr -> hb_prev = 0;
 299     if (0 != second) {
 300       GET_HDR(second, second_hdr);
 301       second_hdr -> hb_prev = h;
 302     }
 303     GC_invalidate_map(hhdr);
 304 }
 305
 306 #ifdef USE_MUNMAP
 307
 308 /* Unmap blocks that haven't been recently touched.  This is the only way */
 309 /* way blocks are ever unmapped.                                          */
 310 void GC_unmap_old(void)
 311 {
 312     struct hblk * h;
 313     hdr * hhdr;
 314     word sz;
 315     unsigned short last_rec, threshold;
 316     int i;
 317 #   define UNMAP_THRESHOLD 6
 318
 319     for (i = 0; i <= N_HBLK_FLS; ++i) {
 320       for (h = GC_hblkfreelist[i]; 0 != h; h = hhdr -> hb_next) {
 321         hhdr = HDR(h);
 322         if (!IS_MAPPED(hhdr)) continue;
 323         threshold = (unsigned short)(GC_gc_no - UNMAP_THRESHOLD);
 324         last_rec = hhdr -> hb_last_reclaimed;
 325         if (last_rec > GC_gc_no
 326             || last_rec < threshold && threshold < GC_gc_no
 327                                        /* not recently wrapped */) {
 328           sz = hhdr -> hb_sz;
 329           GC_unmap((ptr_t)h, sz);
 330           hhdr -> hb_flags |= WAS_UNMAPPED;
 331         }
 332       }
 333     }
 334 }
 335
 336 /* Merge all unmapped blocks that are adjacent to other free            */
 337 /* blocks.  This may involve remapping, since all blocks are either     */
 338 /* fully mapped or fully unmapped.                                      */
 339 void GC_merge_unmapped(void)
 340 {
 341     struct hblk * h, *next;
 342     hdr * hhdr, *nexthdr;
 343     word size, nextsize;
 344     int i;
 345
 346     for (i = 0; i <= N_HBLK_FLS; ++i) {
 347       h = GC_hblkfreelist[i];
 348       while (h != 0) {
 349         GET_HDR(h, hhdr);
 350         size = hhdr->hb_sz;
 351         next = (struct hblk *)((word)h + size);
 352         GET_HDR(next, nexthdr);
 353         /* Coalesce with successor, if possible */
 354           if (0 != nexthdr && HBLK_IS_FREE(nexthdr)) {
 355             nextsize = nexthdr -> hb_sz;
 356             if (IS_MAPPED(hhdr)) {
 357               GC_ASSERT(!IS_MAPPED(nexthdr));
 358               /* make both consistent, so that we can merge */
 359                 if (size > nextsize) {
 360                   GC_remap((ptr_t)next, nextsize);
 361                 } else {
 362                   GC_unmap((ptr_t)h, size);
 363                   hhdr -> hb_flags |= WAS_UNMAPPED;
 364                 }
 365             } else if (IS_MAPPED(nexthdr)) {
 366               GC_ASSERT(!IS_MAPPED(hhdr));
 367               if (size > nextsize) {
 368                 GC_unmap((ptr_t)next, nextsize);
 369               } else {
 370                 GC_remap((ptr_t)h, size);
 371                 hhdr -> hb_flags &= ~WAS_UNMAPPED;
 372               }
 373             } else {
 374               /* Unmap any gap in the middle */
 375                 GC_unmap_gap((ptr_t)h, size, (ptr_t)next, nexthdr -> hb_sz);
 376             }
 377             /* If they are both unmapped, we merge, but leave unmapped. */
 378             GC_remove_from_fl(hhdr, i);
 379             GC_remove_from_fl(nexthdr, FL_UNKNOWN);
 380             hhdr -> hb_sz += nexthdr -> hb_sz;
 381             GC_remove_header(next);
 382             GC_add_to_fl(h, hhdr);
 383             /* Start over at beginning of list */
 384             h = GC_hblkfreelist[i];
 385           } else /* not mergable with successor */ {
 386             h = hhdr -> hb_next;
 387           }
 388       } /* while (h != 0) ... */
 389     } /* for ... */
 390 }
 391
 392 #endif /* USE_MUNMAP */
 393
 394 /*
 395  * Return a pointer to a block starting at h of length bytes.
 396  * Memory for the block is mapped.
 397  * Remove the block from its free list, and return the remainder (if any)
 398  * to its appropriate free list.
 399  * May fail by returning 0.
 400  * The header for the returned block must be set up by the caller.
 401  * If the return value is not 0, then hhdr is the header for it.
 402  */
 403 struct hblk * GC_get_first_part(h, hhdr, bytes, index)
 404 struct hblk *h;
 405 hdr * hhdr;
 406 word bytes;
 407 int index;
 408 {
 409     word total_size = hhdr -> hb_sz;
 410     struct hblk * rest;
 411     hdr * rest_hdr;
 412
 413     GC_ASSERT((total_size & (HBLKSIZE-1)) == 0);
 414     GC_remove_from_fl(hhdr, index);
 415     if (total_size == bytes) return h;
 416     rest = (struct hblk *)((word)h + bytes);
 417     rest_hdr = GC_install_header(rest);
 418     if (0 == rest_hdr) return(0);
 419     rest_hdr -> hb_sz = total_size - bytes;
 420     rest_hdr -> hb_flags = 0;
 421 #   ifdef GC_ASSERTIONS
 422       // Mark h not free, to avoid assertion about adjacent free blocks.
 423         hhdr -> hb_map = 0;
 424 #   endif
 425     GC_add_to_fl(rest, rest_hdr);
 426     return h;
 427 }
 428
 429 /*
 430  * H is a free block.  N points at an address inside it.
 431  * A new header for n has already been set up.  Fix up h's header
 432  * to reflect the fact that it is being split, move it to the
 433  * appropriate free list.
 434  * N replaces h in the original free list.
 435  *
 436  * Nhdr is not completely filled in, since it is about to allocated.
 437  * It may in fact end up on the wrong free list for its size.
 438  * (Hence adding it to a free list is silly.  But this path is hopefully
 439  * rare enough that it doesn't matter.  The code is cleaner this way.)
 440  */
 441 void GC_split_block(h, hhdr, n, nhdr, index)
 442 struct hblk *h;
 443 hdr * hhdr;
 444 struct hblk *n;
 445 hdr * nhdr;
 446 int index;      /* Index of free list */
 447 {
 448     word total_size = hhdr -> hb_sz;
 449     word h_size = (word)n - (word)h;
 450     struct hblk *prev = hhdr -> hb_prev;
 451     struct hblk *next = hhdr -> hb_next;
 452
 453     /* Replace h with n on its freelist */
 454       nhdr -> hb_prev = prev;
 455       nhdr -> hb_next = next;
 456       nhdr -> hb_sz = total_size - h_size;
 457       nhdr -> hb_flags = 0;
 458       if (0 != prev) {
 459         HDR(prev) -> hb_next = n;
 460       } else {
 461         GC_hblkfreelist[index] = n;
 462       }
 463       if (0 != next) {
 464         HDR(next) -> hb_prev = n;
 465       }
 466 #     ifdef GC_ASSERTIONS
 467         nhdr -> hb_map = 0;     /* Don't fail test for consecutive      */
 468                                 /* free blocks in GC_add_to_fl.         */
 469 #     endif
 470 #   ifdef USE_MUNMAP
 471       hhdr -> hb_last_reclaimed = GC_gc_no;
 472 #   endif
 473     hhdr -> hb_sz = h_size;
 474     GC_add_to_fl(h, hhdr);
 475     GC_invalidate_map(nhdr);
 476 }
 477
 478 struct hblk * GC_allochblk_nth();
 479
 480 /*
 481  * Allocate (and return pointer to) a heap block
 482  *   for objects of size sz words, searching the nth free list.
 483  *
 484  * NOTE: We set obj_map field in header correctly.
 485  *       Caller is responsible for building an object freelist in block.
 486  *
 487  * We clear the block if it is destined for large objects, and if
 488  * kind requires that newly allocated objects be cleared.
 489  */
 490 struct hblk *
 491 GC_allochblk(sz, kind, flags)
 492 word sz;
 493 int kind;
 494 unsigned char flags;  /* IGNORE_OFF_PAGE or 0 */
 495 {
 496     int start_list = GC_hblk_fl_from_blocks(OBJ_SZ_TO_BLOCKS(sz));
 497     int i;
 498     for (i = start_list; i <= N_HBLK_FLS; ++i) {
 499         struct hblk * result = GC_allochblk_nth(sz, kind, flags, i);
 500         if (0 != result) return result;
 501     }
 502     return 0;
 503 }
 504 /*
 505  * The same, but with search restricted to nth free list.
 506  */
 507 struct hblk *
 508 GC_allochblk_nth(sz, kind, flags, n)
 509 word sz;
 510 int kind;
 511 unsigned char flags;  /* IGNORE_OFF_PAGE or 0 */
 512 int n;
 513 {
 514     register struct hblk *hbp;
 515     register hdr * hhdr;                /* Header corr. to hbp */
 516     register struct hblk *thishbp;
 517     register hdr * thishdr;             /* Header corr. to hbp */
 518     signed_word size_needed;    /* number of bytes in requested objects */
 519     signed_word size_avail;     /* bytes available in this block        */
 520
 521     size_needed = HBLKSIZE * OBJ_SZ_TO_BLOCKS(sz);
 522
 523     /* search for a big enough block in free list */
 524         hbp = GC_hblkfreelist[n];
 525         for(; 0 != hbp; hbp = hhdr -> hb_next) {
 526             GET_HDR(hbp, hhdr);
 527             size_avail = hhdr->hb_sz;
 528             if (size_avail < size_needed) continue;
 529             if (!GC_use_entire_heap) {
 530                 if (size_avail != size_needed
 531                     && USED_HEAP_SIZE >= GC_requested_heapsize
 532                     && !GC_incremental && GC_should_collect()) {
 533                     continue;
 534                 }
 535             }
 536             /* If the next heap block is obviously better, go on.       */
 537             /* This prevents us from disassembling a single large block */
 538             /* to get tiny blocks.                                      */
 539             {
 540               signed_word next_size;
 541
 542               thishbp = hhdr -> hb_next;
 543               if (thishbp != 0) {
 544                 GET_HDR(thishbp, thishdr);
 545                 next_size = (signed_word)(thishdr -> hb_sz);
 546                 if (next_size < size_avail
 547                   && next_size >= size_needed
 548                   && !GC_is_black_listed(thishbp, (word)size_needed)) {
 549                   continue;
 550                 }
 551               }
 552             }
 553             if ( !IS_UNCOLLECTABLE(kind) &&
 554                  (kind != PTRFREE || size_needed > MAX_BLACK_LIST_ALLOC)) {
 555               struct hblk * lasthbp = hbp;
 556               ptr_t search_end = (ptr_t)hbp + size_avail - size_needed;
 557               signed_word orig_avail = size_avail;
 558               signed_word eff_size_needed = ((flags & IGNORE_OFF_PAGE)?
 559                                                 HBLKSIZE
 560                                                 : size_needed);
 561
 562
 563               while ((ptr_t)lasthbp <= search_end
 564                      && (thishbp = GC_is_black_listed(lasthbp,
 565                                                       (word)eff_size_needed))) {
 566                 lasthbp = thishbp;
 567               }
 568               size_avail -= (ptr_t)lasthbp - (ptr_t)hbp;
 569               thishbp = lasthbp;
 570               if (size_avail >= size_needed) {
 571                 if (thishbp != hbp &&
 572                     0 != (thishdr = GC_install_header(thishbp))) {
 573                   /* Make sure it's mapped before we mangle it. */
 574 #                   ifdef USE_MUNMAP
 575                       if (!IS_MAPPED(hhdr)) {
 576                         GC_remap((ptr_t)hbp, size_avail);
 577                         hhdr -> hb_flags &= ~WAS_UNMAPPED;
 578                       }
 579 #                   endif
 580                   /* Split the block at thishbp */
 581                       GC_split_block(hbp, hhdr, thishbp, thishdr, n);
 582                   /* Advance to thishbp */
 583                       hbp = thishbp;
 584                       hhdr = thishdr;
 585                       /* We must now allocate thishbp, since it may     */
 586                       /* be on the wrong free list.                     */
 587                 }
 588               } else if (size_needed > (signed_word)BL_LIMIT
 589                          && orig_avail - size_needed
 590                             > (signed_word)BL_LIMIT) {
 591                 /* Punt, since anything else risks unreasonable heap growth. */
 592                 WARN("Needed to allocate blacklisted block at 0x%lx\n",
 593                      (word)hbp);
 594                 size_avail = orig_avail;
 595               } else if (size_avail == 0 && size_needed == HBLKSIZE
 596                          && IS_MAPPED(hhdr)) {
 597                 if (!GC_find_leak) {
 598                   static unsigned count = 0;
 599
 600                   /* The block is completely blacklisted.  We need      */
 601                   /* to drop some such blocks, since otherwise we spend */
 602                   /* all our time traversing them if pointerfree        */
 603                   /* blocks are unpopular.                              */
 604                   /* A dropped block will be reconsidered at next GC.   */
 605                   if ((++count & 3) == 0) {
 606                     /* Allocate and drop the block in small chunks, to  */
 607                     /* maximize the chance that we will recover some    */
 608                     /* later.                                           */
 609                       word total_size = hhdr -> hb_sz;
 610                       struct hblk * limit = hbp + divHBLKSZ(total_size);
 611                       struct hblk * h;
 612                       struct hblk * prev = hhdr -> hb_prev;
 613
 614                       GC_words_wasted += total_size;
 615                       GC_large_free_bytes -= total_size;
 616                       GC_remove_from_fl(hhdr, n);
 617                       for (h = hbp; h < limit; h++) {
 618                         if (h == hbp || 0 != (hhdr = GC_install_header(h))) {
 619                           (void) setup_header(
 620                                   hhdr,
 621                                   BYTES_TO_WORDS(HBLKSIZE - HDR_BYTES),
 622                                   PTRFREE, 0); /* Cant fail */
 623                           if (GC_debugging_started) {
 624                             BZERO(h + HDR_BYTES, HBLKSIZE - HDR_BYTES);
 625                           }
 626                         }
 627                       }
 628                     /* Restore hbp to point at free block */
 629                       hbp = prev;
 630                       if (0 == hbp) {
 631                         return GC_allochblk_nth(sz, kind, flags, n);
 632                       }
 633                       hhdr = HDR(hbp);
 634                   }
 635                 }
 636               }
 637             }
 638             if( size_avail >= size_needed ) {
 639 #               ifdef USE_MUNMAP
 640                   if (!IS_MAPPED(hhdr)) {
 641                     GC_remap((ptr_t)hbp, size_avail);
 642                     hhdr -> hb_flags &= ~WAS_UNMAPPED;
 643                   }
 644 #               endif
 645                 /* hbp may be on the wrong freelist; the parameter n    */
 646                 /* is important.                                        */
 647                 hbp = GC_get_first_part(hbp, hhdr, size_needed, n);
 648                 break;
 649             }
 650         }
 651
 652     if (0 == hbp) return 0;
 653
 654     /* Notify virtual dirty bit implementation that we are about to write. */
 655         GC_write_hint(hbp);
 656
 657     /* Add it to map of valid blocks */
 658         if (!GC_install_counts(hbp, (word)size_needed)) return(0);
 659         /* This leaks memory under very rare conditions. */
 660
 661     /* Set up header */
 662         if (!setup_header(hhdr, sz, kind, flags)) {
 663             GC_remove_counts(hbp, (word)size_needed);
 664             return(0); /* ditto */
 665         }
 666
 667     /* Clear block if necessary */
 668         if (GC_debugging_started
 669             || sz > MAXOBJSZ && GC_obj_kinds[kind].ok_init) {
 670             BZERO(hbp + HDR_BYTES,  size_needed - HDR_BYTES);
 671         }
 672
 673     /* We just successfully allocated a block.  Restart count of        */
 674     /* consecutive failures.                                            */
 675     {
 676         extern unsigned GC_fail_count;
 677
 678         GC_fail_count = 0;
 679     }
 680
 681     GC_large_free_bytes -= size_needed;
 682
 683     GC_ASSERT(IS_MAPPED(hhdr));
 684     return( hbp );
 685 }
 686
 687 struct hblk * GC_freehblk_ptr = 0;  /* Search position hint for GC_freehblk */
 688
 689 /*
 690  * Free a heap block.
 691  *
 692  * Coalesce the block with its neighbors if possible.
 693  *
 694  * All mark words are assumed to be cleared.
 695  */
 696 void
 697 GC_freehblk(hbp)
 698 struct hblk *hbp;
 699 {
 700 struct hblk *next, *prev;
 701 hdr *hhdr, *prevhdr, *nexthdr;
 702 signed_word size;
 703
 704
 705     GET_HDR(hbp, hhdr);
 706     size = hhdr->hb_sz;
 707     size = HBLKSIZE * OBJ_SZ_TO_BLOCKS(size);
 708     GC_remove_counts(hbp, (word)size);
 709     hhdr->hb_sz = size;
 710
 711     /* Check for duplicate deallocation in the easy case */
 712       if (HBLK_IS_FREE(hhdr)) {
 713         GC_printf1("Duplicate large block deallocation of 0x%lx\n",
 714                    (unsigned long) hbp);
 715       }
 716
 717     GC_ASSERT(IS_MAPPED(hhdr));
 718     GC_invalidate_map(hhdr);
 719     next = (struct hblk *)((word)hbp + size);
 720     GET_HDR(next, nexthdr);
 721     prev = GC_free_block_ending_at(hbp);
 722     /* Coalesce with successor, if possible */
 723       if(0 != nexthdr && HBLK_IS_FREE(nexthdr) && IS_MAPPED(nexthdr)) {
 724         GC_remove_from_fl(nexthdr, FL_UNKNOWN);
 725         hhdr -> hb_sz += nexthdr -> hb_sz;
 726         GC_remove_header(next);
 727       }
 728     /* Coalesce with predecessor, if possible. */
 729       if (0 != prev) {
 730         prevhdr = HDR(prev);
 731         if (IS_MAPPED(prevhdr)) {
 732           GC_remove_from_fl(prevhdr, FL_UNKNOWN);
 733           prevhdr -> hb_sz += hhdr -> hb_sz;
 734           GC_remove_header(hbp);
 735           hbp = prev;
 736           hhdr = prevhdr;
 737         }
 738       }
 739
 740     GC_large_free_bytes += size;
 741     GC_add_to_fl(hbp, hhdr);
 742 }
 743