boehm-gc/gc_hdrs.h

   1 /*
   2  * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
   3  * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
   4  *
   5  * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
   6  * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
   7  *
   8  * Permission is hereby granted to use or copy this program
   9  * for any purpose,  provided the above notices are retained on all copies.
  10  * Permission to modify the code and to distribute modified code is granted,
  11  * provided the above notices are retained, and a notice that the code was
  12  * modified is included with the above copyright notice.
  13  */
  14 /* Boehm, July 11, 1995 11:54 am PDT */
  15 # ifndef GC_HEADERS_H
  16 # define GC_HEADERS_H
  17 typedef struct hblkhdr hdr;
  18
  19 # if CPP_WORDSZ != 32 && CPP_WORDSZ < 36
  20         --> Get a real machine.
  21 # endif
  22
  23 /*
  24  * The 2 level tree data structure that is used to find block headers.
  25  * If there are more than 32 bits in a pointer, the top level is a hash
  26  * table.
  27  *
  28  * This defines HDR, GET_HDR, and SET_HDR, the main macros used to
  29  * retrieve and set object headers.  We also define some variants to
  30  * retrieve 2 unrelated headers in interleaved fashion.  This
  31  * slightly improves scheduling.
  32  *
  33  * Since 5.0 alpha 5, we can also take advantage of a header lookup
  34  * cache.  This is a locally declared direct mapped cache, used inside
  35  * the marker.  The HC_GET_HDR and HC_GET_HDR2 macros use and maintain this
  36  * cache.  Assuming we get reasonable hit rates, this shaves a few
  37  * memory references from each pointer validation.
  38  */
  39
  40 # if CPP_WORDSZ > 32
  41 #   define HASH_TL
  42 # endif
  43
  44 /* Define appropriate out-degrees for each of the two tree levels       */
  45 # ifdef SMALL_CONFIG
  46 #   define LOG_BOTTOM_SZ 11
  47         /* Keep top index size reasonable with smaller blocks. */
  48 # else
  49 #   define LOG_BOTTOM_SZ 10
  50 # endif
  51 # ifndef HASH_TL
  52 #   define LOG_TOP_SZ (WORDSZ - LOG_BOTTOM_SZ - LOG_HBLKSIZE)
  53 # else
  54 #   define LOG_TOP_SZ 11
  55 # endif
  56 # define TOP_SZ (1 << LOG_TOP_SZ)
  57 # define BOTTOM_SZ (1 << LOG_BOTTOM_SZ)
  58
  59 #ifndef SMALL_CONFIG
  60 # define USE_HDR_CACHE
  61 #endif
  62
  63 /* #define COUNT_HDR_CACHE_HITS  */
  64
  65 extern hdr * GC_invalid_header; /* header for an imaginary block        */
  66                                 /* containing no objects.               */
  67
  68
  69 /* Check whether p and corresponding hhdr point to long or invalid      */
  70 /* object.  If so, advance them to                                      */
  71 /* beginning of block, or set hhdr to GC_invalid_header.                */
  72 #define ADVANCE(p, hhdr, source) \
  73             if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) { \
  74               p = GC_FIND_START(p, hhdr, (word)source); \
  75               if (p == 0) { \
  76                 hhdr = GC_invalid_header; \
  77               } else { \
  78                 hhdr = GC_find_header(p); \
  79               } \
  80             }
  81
  82 #ifdef USE_HDR_CACHE
  83
  84 # ifdef COUNT_HDR_CACHE_HITS
  85     extern word GC_hdr_cache_hits;
  86     extern word GC_hdr_cache_misses;
  87 #   define HC_HIT() ++GC_hdr_cache_hits
  88 #   define HC_MISS() ++GC_hdr_cache_misses
  89 # else
  90 #   define HC_HIT()
  91 #   define HC_MISS()
  92 # endif
  93
  94   typedef struct hce {
  95     word block_addr;    /* right shifted by LOG_HBLKSIZE */
  96     hdr * hce_hdr;
  97   } hdr_cache_entry;
  98
  99 # define HDR_CACHE_SIZE 8  /* power of 2 */
 100
 101 # define DECLARE_HDR_CACHE \
 102         hdr_cache_entry hdr_cache[HDR_CACHE_SIZE]
 103
 104 # define INIT_HDR_CACHE BZERO(hdr_cache, sizeof(hdr_cache));
 105
 106 # define HCE(h) hdr_cache + (((word)(h) >> LOG_HBLKSIZE) & (HDR_CACHE_SIZE-1))
 107
 108 # define HCE_VALID_FOR(hce,h) ((hce) -> block_addr == \
 109                                 ((word)(h) >> LOG_HBLKSIZE))
 110
 111 # define HCE_HDR(h) ((hce) -> hce_hdr)
 112
 113
 114 /* Analogous to GET_HDR, except that in the case of large objects, it   */
 115 /* Returns the header for the object beginning, and updates p.          */
 116 /* Returns &GC_bad_header instead of 0.  All of this saves a branch     */
 117 /* in the fast path.                                                    */
 118 # define HC_GET_HDR(p, hhdr, source) \
 119         { \
 120           hdr_cache_entry * hce = HCE(p); \
 121           if (HCE_VALID_FOR(hce, p)) { \
 122             HC_HIT(); \
 123             hhdr = hce -> hce_hdr; \
 124           } else { \
 125             HC_MISS(); \
 126             GET_HDR(p, hhdr); \
 127             ADVANCE(p, hhdr, source); \
 128             hce -> block_addr = (word)(p) >> LOG_HBLKSIZE; \
 129             hce -> hce_hdr = hhdr; \
 130           } \
 131         }
 132
 133 # define HC_GET_HDR2(p1, hhdr1, source1, p2, hhdr2, source2) \
 134         { \
 135           hdr_cache_entry * hce1 = HCE(p1); \
 136           hdr_cache_entry * hce2 = HCE(p2); \
 137           if (HCE_VALID_FOR(hce1, p1)) { \
 138             HC_HIT(); \
 139             hhdr1 = hce1 -> hce_hdr; \
 140           } else { \
 141             HC_MISS(); \
 142             GET_HDR(p1, hhdr1); \
 143             ADVANCE(p1, hhdr1, source1); \
 144             hce1 -> block_addr = (word)(p1) >> LOG_HBLKSIZE; \
 145             hce1 -> hce_hdr = hhdr1; \
 146           } \
 147           if (HCE_VALID_FOR(hce2, p2)) { \
 148             HC_HIT(); \
 149             hhdr2 = hce2 -> hce_hdr; \
 150           } else { \
 151             HC_MISS(); \
 152             GET_HDR(p2, hhdr2); \
 153             ADVANCE(p2, hhdr2, source2); \
 154             hce2 -> block_addr = (word)(p2) >> LOG_HBLKSIZE; \
 155             hce2 -> hce_hdr = hhdr2; \
 156           } \
 157         }
 158
 159 #else /* !USE_HDR_CACHE */
 160
 161 # define DECLARE_HDR_CACHE
 162
 163 # define INIT_HDR_CACHE
 164
 165 # define HC_GET_HDR(p, hhdr, source) \
 166         { \
 167           GET_HDR(p, hhdr); \
 168           ADVANCE(p, hhdr, source); \
 169         }
 170
 171 # define HC_GET_HDR2(p1, hhdr1, source1, p2, hhdr2, source2) \
 172         { \
 173           GET_HDR2(p1, hhdr1, p2, hhdr2); \
 174           ADVANCE(p1, hhdr1, source1); \
 175           ADVANCE(p2, hhdr2, source2); \
 176         }
 177
 178 #endif
 179
 180 typedef struct bi {
 181     hdr * index[BOTTOM_SZ];
 182         /*
 183          * The bottom level index contains one of three kinds of values:
 184          * 0 means we're not responsible for this block,
 185          *   or this is a block other than the first one in a free block.
 186          * 1 < (long)X <= MAX_JUMP means the block starts at least
 187          *        X * HBLKSIZE bytes before the current address.
 188          * A valid pointer points to a hdr structure. (The above can't be
 189          * valid pointers due to the GET_MEM return convention.)
 190          */
 191     struct bi * asc_link;       /* All indices are linked in    */
 192                                 /* ascending order...           */
 193     struct bi * desc_link;      /* ... and in descending order. */
 194     word key;                   /* high order address bits.     */
 195 # ifdef HASH_TL
 196     struct bi * hash_link;      /* Hash chain link.             */
 197 # endif
 198 } bottom_index;
 199
 200 /* extern bottom_index GC_all_nils; - really part of GC_arrays */
 201
 202 /* extern bottom_index * GC_top_index []; - really part of GC_arrays */
 203                                 /* Each entry points to a bottom_index. */
 204                                 /* On a 32 bit machine, it points to    */
 205                                 /* the index for a set of high order    */
 206                                 /* bits equal to the index.  For longer */
 207                                 /* addresses, we hash the high order    */
 208                                 /* bits to compute the index in         */
 209                                 /* GC_top_index, and each entry points  */
 210                                 /* to a hash chain.                     */
 211                                 /* The last entry in each chain is      */
 212                                 /* GC_all_nils.                         */
 213
 214
 215 # define MAX_JUMP (HBLKSIZE - 1)
 216
 217 # define HDR_FROM_BI(bi, p) \
 218                 ((bi)->index[((word)(p) >> LOG_HBLKSIZE) & (BOTTOM_SZ - 1)])
 219 # ifndef HASH_TL
 220 #   define BI(p) (GC_top_index \
 221                 [(word)(p) >> (LOG_BOTTOM_SZ + LOG_HBLKSIZE)])
 222 #   define HDR_INNER(p) HDR_FROM_BI(BI(p),p)
 223 #   ifdef SMALL_CONFIG
 224 #       define HDR(p) GC_find_header((ptr_t)(p))
 225 #   else
 226 #       define HDR(p) HDR_INNER(p)
 227 #   endif
 228 #   define GET_BI(p, bottom_indx) (bottom_indx) = BI(p)
 229 #   define GET_HDR(p, hhdr) (hhdr) = HDR(p)
 230 #   define SET_HDR(p, hhdr) HDR_INNER(p) = (hhdr)
 231 #   define GET_HDR_ADDR(p, ha) (ha) = &(HDR_INNER(p))
 232 #   define GET_HDR2(p1, hhdr1, p2, hhdr2) \
 233         { GET_HDR(p1, hhdr1); GET_HDR(p2, hhdr2); }
 234 # else /* hash */
 235 /*  Hash function for tree top level */
 236 #   define TL_HASH(hi) ((hi) & (TOP_SZ - 1))
 237 /*  Set bottom_indx to point to the bottom index for address p */
 238 #   define GET_BI(p, bottom_indx) \
 239         { \
 240             register word hi = \
 241                 (word)(p) >> (LOG_BOTTOM_SZ + LOG_HBLKSIZE); \
 242             register bottom_index * _bi = GC_top_index[TL_HASH(hi)]; \
 243             \
 244             while (_bi -> key != hi && _bi != GC_all_nils) \
 245                 _bi = _bi -> hash_link; \
 246             (bottom_indx) = _bi; \
 247         }
 248 #   define GET_HDR_ADDR(p, ha) \
 249         { \
 250             register bottom_index * bi; \
 251             \
 252             GET_BI(p, bi);      \
 253             (ha) = &(HDR_FROM_BI(bi, p)); \
 254         }
 255 #   define GET_HDR(p, hhdr) { register hdr ** _ha; GET_HDR_ADDR(p, _ha); \
 256                               (hhdr) = *_ha; }
 257 #   define SET_HDR(p, hhdr) { register hdr ** _ha; GET_HDR_ADDR(p, _ha); \
 258                               *_ha = (hhdr); }
 259 #   define HDR(p) GC_find_header((ptr_t)(p))
 260     /* And some interleaved versions for two pointers at once.          */
 261     /* This hopefully helps scheduling on processors like IA64.         */
 262 #   define GET_BI2(p1, bottom_indx1, p2, bottom_indx2) \
 263         { \
 264             register word hi1 = \
 265                 (word)(p1) >> (LOG_BOTTOM_SZ + LOG_HBLKSIZE); \
 266             register word hi2 = \
 267                 (word)(p2) >> (LOG_BOTTOM_SZ + LOG_HBLKSIZE); \
 268             register bottom_index * _bi1 = GC_top_index[TL_HASH(hi1)]; \
 269             register bottom_index * _bi2 = GC_top_index[TL_HASH(hi2)]; \
 270             \
 271             while (_bi1 -> key != hi1 && _bi1 != GC_all_nils) \
 272                 _bi1 = _bi1 -> hash_link; \
 273             while (_bi2 -> key != hi2 && _bi2 != GC_all_nils) \
 274                 _bi2 = _bi2 -> hash_link; \
 275             (bottom_indx1) = _bi1; \
 276             (bottom_indx2) = _bi2; \
 277         }
 278 #   define GET_HDR_ADDR2(p1, ha1, p2, ha2) \
 279         { \
 280             register bottom_index * bi1; \
 281             register bottom_index * bi2; \
 282             \
 283             GET_BI2(p1, bi1, p2, bi2);  \
 284             (ha1) = &(HDR_FROM_BI(bi1, p1)); \
 285             (ha2) = &(HDR_FROM_BI(bi2, p2)); \
 286         }
 287 #   define GET_HDR2(p1, hhdr1, p2, hhdr2) \
 288         { register hdr ** _ha1;  \
 289           register hdr ** _ha2;  \
 290           GET_HDR_ADDR2(p1, _ha1, p2, _ha2); \
 291           (hhdr1) = *_ha1;  \
 292           (hhdr2) = *_ha2;  \
 293         }
 294 # endif
 295
 296 /* Is the result a forwarding address to someplace closer to the        */
 297 /* beginning of the block or NIL?                                       */
 298 # define IS_FORWARDING_ADDR_OR_NIL(hhdr) ((unsigned long) (hhdr) <= MAX_JUMP)
 299
 300 /* Get an HBLKSIZE aligned address closer to the beginning of the block */
 301 /* h.  Assumes hhdr == HDR(h) and IS_FORWARDING_ADDR(hhdr).             */
 302 # define FORWARDED_ADDR(h, hhdr) ((struct hblk *)(h) - (unsigned long)(hhdr))
 303 # endif /*  GC_HEADERS_H */