libiberty/objalloc.c

   1 /* objalloc.c -- routines to allocate memory for objects
   2    Copyright 1997 Free Software Foundation, Inc.
   3    Written by Ian Lance Taylor, Cygnus Solutions.
   4
   5 This program is free software; you can redistribute it and/or modify it
   6 under the terms of the GNU General Public License as published by the
   7 Free Software Foundation; either version 2, or (at your option) any
   8 later version.
   9
  10 This program is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 GNU General Public License for more details.
  14
  15 You should have received a copy of the GNU General Public License
  16 along with this program; if not, write to the Free Software
  17 Foundation, 59 Temple Place - Suite 330,
  18 Boston, MA 02111-1307, USA.  */
  19
  20 #include "ansidecl.h"
  21 #include "objalloc.h"
  22
  23 /* Get a definition for NULL.  */
  24 #include <stdio.h>
  25
  26 #if VMS
  27 #include <stdlib.h>
  28 #include <unixlib.h>
  29 #else
  30
  31 #ifdef ANSI_PROTOTYPES
  32 /* Get a definition for size_t.  */
  33 #include <stddef.h>
  34 #endif
  35
  36 /* For systems with larger pointers than ints, this must be declared.  */
  37 extern PTR malloc PARAMS ((size_t));
  38 extern void free PARAMS ((PTR));
  39 #endif
  40
  41 /* These routines allocate space for an object.  Freeing allocated
  42    space may or may not free all more recently allocated space.
  43
  44    We handle large and small allocation requests differently.  If we
  45    don't have enough space in the current block, and the allocation
  46    request is for more than 512 bytes, we simply pass it through to
  47    malloc.  */
  48
  49 /* The objalloc structure is defined in objalloc.h.  */
  50
  51 /* This structure appears at the start of each chunk.  */
  52
  53 struct objalloc_chunk
  54 {
  55   /* Next chunk.  */
  56   struct objalloc_chunk *next;
  57   /* If this chunk contains large objects, this is the value of
  58      current_ptr when this chunk was allocated.  If this chunk
  59      contains small objects, this is NULL.  */
  60   char *current_ptr;
  61 };
  62
  63 /* The aligned size of objalloc_chunk.  */
  64
  65 #define CHUNK_HEADER_SIZE                                       \
  66   ((sizeof (struct objalloc_chunk) + OBJALLOC_ALIGN - 1)        \
  67    &~ (OBJALLOC_ALIGN - 1))
  68
  69 /* We ask for this much memory each time we create a chunk which is to
  70    hold small objects.  */
  71
  72 #define CHUNK_SIZE (4096 - 32)
  73
  74 /* A request for this amount or more is just passed through to malloc.  */
  75
  76 #define BIG_REQUEST (512)
  77
  78 /* Create an objalloc structure.  */
  79
  80 struct objalloc *
  81 objalloc_create ()
  82 {
  83   struct objalloc *ret;
  84   struct objalloc_chunk *chunk;
  85
  86   ret = (struct objalloc *) malloc (sizeof *ret);
  87   if (ret == NULL)
  88     return NULL;
  89
  90   ret->chunks = (PTR) malloc (CHUNK_SIZE);
  91   if (ret->chunks == NULL)
  92     {
  93       free (ret);
  94       return NULL;
  95     }
  96
  97   chunk = (struct objalloc_chunk *) ret->chunks;
  98   chunk->next = NULL;
  99   chunk->current_ptr = NULL;
 100
 101   ret->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 102   ret->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 103
 104   return ret;
 105 }
 106
 107 /* Allocate space from an objalloc structure.  */
 108
 109 PTR
 110 _objalloc_alloc (o, len)
 111      struct objalloc *o;
 112      unsigned long len;
 113 {
 114   /* We avoid confusion from zero sized objects by always allocating
 115      at least 1 byte.  */
 116   if (len == 0)
 117     len = 1;
 118
 119   len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);
 120
 121   if (len <= o->current_space)
 122     {
 123       o->current_ptr += len;
 124       o->current_space -= len;
 125       return (PTR) (o->current_ptr - len);
 126     }
 127
 128   if (len >= BIG_REQUEST)
 129     {
 130       char *ret;
 131       struct objalloc_chunk *chunk;
 132
 133       ret = (char *) malloc (CHUNK_HEADER_SIZE + len);
 134       if (ret == NULL)
 135         return NULL;
 136
 137       chunk = (struct objalloc_chunk *) ret;
 138       chunk->next = (struct objalloc_chunk *) o->chunks;
 139       chunk->current_ptr = o->current_ptr;
 140
 141       o->chunks = (PTR) chunk;
 142
 143       return (PTR) (ret + CHUNK_HEADER_SIZE);
 144     }
 145   else
 146     {
 147       struct objalloc_chunk *chunk;
 148
 149       chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);
 150       if (chunk == NULL)
 151         return NULL;
 152       chunk->next = (struct objalloc_chunk *) o->chunks;
 153       chunk->current_ptr = NULL;
 154
 155       o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 156       o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 157
 158       o->chunks = (PTR) chunk;
 159
 160       return objalloc_alloc (o, len);
 161     }
 162 }
 163
 164 /* Free an entire objalloc structure.  */
 165
 166 void
 167 objalloc_free (o)
 168      struct objalloc *o;
 169 {
 170   struct objalloc_chunk *l;
 171
 172   l = (struct objalloc_chunk *) o->chunks;
 173   while (l != NULL)
 174     {
 175       struct objalloc_chunk *next;
 176
 177       next = l->next;
 178       free (l);
 179       l = next;
 180     }
 181
 182   free (o);
 183 }
 184
 185 /* Free a block from an objalloc structure.  This also frees all more
 186    recently allocated blocks.  */
 187
 188 void
 189 objalloc_free_block (o, block)
 190      struct objalloc *o;
 191      PTR block;
 192 {
 193   struct objalloc_chunk *p, *small;
 194   char *b = (char *) block;
 195
 196   /* First set P to the chunk which contains the block we are freeing,
 197      and set Q to the last small object chunk we see before P.  */
 198   small = NULL;
 199   for (p = (struct objalloc_chunk *) o->chunks; p != NULL; p = p->next)
 200     {
 201       if (p->current_ptr == NULL)
 202         {
 203           if (b > (char *) p && b < (char *) p + CHUNK_SIZE)
 204             break;
 205           small = p;
 206         }
 207       else
 208         {
 209           if (b == (char *) p + CHUNK_HEADER_SIZE)
 210             break;
 211         }
 212     }
 213
 214   /* If we can't find the chunk, the caller has made a mistake.  */
 215   if (p == NULL)
 216     abort ();
 217
 218   if (p->current_ptr == NULL)
 219     {
 220       struct objalloc_chunk *q;
 221       struct objalloc_chunk *first;
 222
 223       /* The block is in a chunk containing small objects.  We can
 224          free every chunk through SMALL, because they have certainly
 225          been allocated more recently.  After SMALL, we will not see
 226          any chunks containing small objects; we can free any big
 227          chunk if the current_ptr is greater than or equal to B.  We
 228          can then reset the new current_ptr to B.  */
 229
 230       first = NULL;
 231       q = (struct objalloc_chunk *) o->chunks;
 232       while (q != p)
 233         {
 234           struct objalloc_chunk *next;
 235
 236           next = q->next;
 237           if (small != NULL)
 238             {
 239               if (small == q)
 240                 small = NULL;
 241               free (q);
 242             }
 243           else if (q->current_ptr > b)
 244             free (q);
 245           else if (first == NULL)
 246             first = q;
 247
 248           q = next;
 249         }
 250
 251       if (first == NULL)
 252         first = p;
 253       o->chunks = (PTR) first;
 254
 255       /* Now start allocating from this small block again.  */
 256       o->current_ptr = b;
 257       o->current_space = ((char *) p + CHUNK_SIZE) - b;
 258     }
 259   else
 260     {
 261       struct objalloc_chunk *q;
 262       char *current_ptr;
 263
 264       /* This block is in a large chunk by itself.  We can free
 265          everything on the list up to and including this block.  We
 266          then start allocating from the next chunk containing small
 267          objects, setting current_ptr from the value stored with the
 268          large chunk we are freeing.  */
 269
 270       current_ptr = p->current_ptr;
 271       p = p->next;
 272
 273       q = (struct objalloc_chunk *) o->chunks;
 274       while (q != p)
 275         {
 276           struct objalloc_chunk *next;
 277
 278           next = q->next;
 279           free (q);
 280           q = next;
 281         }
 282
 283       o->chunks = (PTR) p;
 284
 285       while (p->current_ptr != NULL)
 286         p = p->next;
 287
 288       o->current_ptr = current_ptr;
 289       o->current_space = ((char *) p + CHUNK_SIZE) - current_ptr;
 290     }
 291 }