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 "config.h"
  21 #include "ansidecl.h"
  22
  23 #include "objalloc.h"
  24
  25 /* Get a definition for NULL.  */
  26 #include <stdio.h>
  27
  28 #if VMS
  29 #include <stdlib.h>
  30 #include <unixlib.h>
  31 #else
  32
  33 #ifdef ANSI_PROTOTYPES
  34 /* Get a definition for size_t.  */
  35 #include <stddef.h>
  36 #endif
  37
  38 #ifdef HAVE_STDLIB_H
  39 #include <stdlib.h>
  40 #else
  41 /* For systems with larger pointers than ints, this must be declared.  */
  42 extern PTR malloc (size_t);
  43 extern void free (PTR);
  44 #endif
  45
  46 #endif
  47
  48 /* These routines allocate space for an object.  Freeing allocated
  49    space may or may not free all more recently allocated space.
  50
  51    We handle large and small allocation requests differently.  If we
  52    don't have enough space in the current block, and the allocation
  53    request is for more than 512 bytes, we simply pass it through to
  54    malloc.  */
  55
  56 /* The objalloc structure is defined in objalloc.h.  */
  57
  58 /* This structure appears at the start of each chunk.  */
  59
  60 struct objalloc_chunk
  61 {
  62   /* Next chunk.  */
  63   struct objalloc_chunk *next;
  64   /* If this chunk contains large objects, this is the value of
  65      current_ptr when this chunk was allocated.  If this chunk
  66      contains small objects, this is NULL.  */
  67   char *current_ptr;
  68 };
  69
  70 /* The aligned size of objalloc_chunk.  */
  71
  72 #define CHUNK_HEADER_SIZE                                       \
  73   ((sizeof (struct objalloc_chunk) + OBJALLOC_ALIGN - 1)        \
  74    &~ (OBJALLOC_ALIGN - 1))
  75
  76 /* We ask for this much memory each time we create a chunk which is to
  77    hold small objects.  */
  78
  79 #define CHUNK_SIZE (4096 - 32)
  80
  81 /* A request for this amount or more is just passed through to malloc.  */
  82
  83 #define BIG_REQUEST (512)
  84
  85 /* Create an objalloc structure.  */
  86
  87 struct objalloc *
  88 objalloc_create (void)
  89 {
  90   struct objalloc *ret;
  91   struct objalloc_chunk *chunk;
  92
  93   ret = (struct objalloc *) malloc (sizeof *ret);
  94   if (ret == NULL)
  95     return NULL;
  96
  97   ret->chunks = (PTR) malloc (CHUNK_SIZE);
  98   if (ret->chunks == NULL)
  99     {
 100       free (ret);
 101       return NULL;
 102     }
 103
 104   chunk = (struct objalloc_chunk *) ret->chunks;
 105   chunk->next = NULL;
 106   chunk->current_ptr = NULL;
 107
 108   ret->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 109   ret->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 110
 111   return ret;
 112 }
 113
 114 /* Allocate space from an objalloc structure.  */
 115
 116 PTR
 117 _objalloc_alloc (struct objalloc *o, unsigned long len)
 118 {
 119   /* We avoid confusion from zero sized objects by always allocating
 120      at least 1 byte.  */
 121   if (len == 0)
 122     len = 1;
 123
 124   len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);
 125
 126   if (len <= o->current_space)
 127     {
 128       o->current_ptr += len;
 129       o->current_space -= len;
 130       return (PTR) (o->current_ptr - len);
 131     }
 132
 133   if (len >= BIG_REQUEST)
 134     {
 135       char *ret;
 136       struct objalloc_chunk *chunk;
 137
 138       ret = (char *) malloc (CHUNK_HEADER_SIZE + len);
 139       if (ret == NULL)
 140         return NULL;
 141
 142       chunk = (struct objalloc_chunk *) ret;
 143       chunk->next = (struct objalloc_chunk *) o->chunks;
 144       chunk->current_ptr = o->current_ptr;
 145
 146       o->chunks = (PTR) chunk;
 147
 148       return (PTR) (ret + CHUNK_HEADER_SIZE);
 149     }
 150   else
 151     {
 152       struct objalloc_chunk *chunk;
 153
 154       chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);
 155       if (chunk == NULL)
 156         return NULL;
 157       chunk->next = (struct objalloc_chunk *) o->chunks;
 158       chunk->current_ptr = NULL;
 159
 160       o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 161       o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 162
 163       o->chunks = (PTR) chunk;
 164
 165       return objalloc_alloc (o, len);
 166     }
 167 }
 168
 169 /* Free an entire objalloc structure.  */
 170
 171 void
 172 objalloc_free (struct objalloc *o)
 173 {
 174   struct objalloc_chunk *l;
 175
 176   l = (struct objalloc_chunk *) o->chunks;
 177   while (l != NULL)
 178     {
 179       struct objalloc_chunk *next;
 180
 181       next = l->next;
 182       free (l);
 183       l = next;
 184     }
 185
 186   free (o);
 187 }
 188
 189 /* Free a block from an objalloc structure.  This also frees all more
 190    recently allocated blocks.  */
 191
 192 void
 193 objalloc_free_block (struct objalloc *o, PTR block)
 194 {
 195   struct objalloc_chunk *p, *small;
 196   char *b = (char *) block;
 197
 198   /* First set P to the chunk which contains the block we are freeing,
 199      and set Q to the last small object chunk we see before P.  */
 200   small = NULL;
 201   for (p = (struct objalloc_chunk *) o->chunks; p != NULL; p = p->next)
 202     {
 203       if (p->current_ptr == NULL)
 204         {
 205           if (b > (char *) p && b < (char *) p + CHUNK_SIZE)
 206             break;
 207           small = p;
 208         }
 209       else
 210         {
 211           if (b == (char *) p + CHUNK_HEADER_SIZE)
 212             break;
 213         }
 214     }
 215
 216   /* If we can't find the chunk, the caller has made a mistake.  */
 217   if (p == NULL)
 218     abort ();
 219
 220   if (p->current_ptr == NULL)
 221     {
 222       struct objalloc_chunk *q;
 223       struct objalloc_chunk *first;
 224
 225       /* The block is in a chunk containing small objects.  We can
 226          free every chunk through SMALL, because they have certainly
 227          been allocated more recently.  After SMALL, we will not see
 228          any chunks containing small objects; we can free any big
 229          chunk if the current_ptr is greater than or equal to B.  We
 230          can then reset the new current_ptr to B.  */
 231
 232       first = NULL;
 233       q = (struct objalloc_chunk *) o->chunks;
 234       while (q != p)
 235         {
 236           struct objalloc_chunk *next;
 237
 238           next = q->next;
 239           if (small != NULL)
 240             {
 241               if (small == q)
 242                 small = NULL;
 243               free (q);
 244             }
 245           else if (q->current_ptr > b)
 246             free (q);
 247           else if (first == NULL)
 248             first = q;
 249
 250           q = next;
 251         }
 252
 253       if (first == NULL)
 254         first = p;
 255       o->chunks = (PTR) first;
 256
 257       /* Now start allocating from this small block again.  */
 258       o->current_ptr = b;
 259       o->current_space = ((char *) p + CHUNK_SIZE) - b;
 260     }
 261   else
 262     {
 263       struct objalloc_chunk *q;
 264       char *current_ptr;
 265
 266       /* This block is in a large chunk by itself.  We can free
 267          everything on the list up to and including this block.  We
 268          then start allocating from the next chunk containing small
 269          objects, setting current_ptr from the value stored with the
 270          large chunk we are freeing.  */
 271
 272       current_ptr = p->current_ptr;
 273       p = p->next;
 274
 275       q = (struct objalloc_chunk *) o->chunks;
 276       while (q != p)
 277         {
 278           struct objalloc_chunk *next;
 279
 280           next = q->next;
 281           free (q);
 282           q = next;
 283         }
 284
 285       o->chunks = (PTR) p;
 286
 287       while (p->current_ptr != NULL)
 288         p = p->next;
 289
 290       o->current_ptr = current_ptr;
 291       o->current_space = ((char *) p + CHUNK_SIZE) - current_ptr;
 292     }
 293 }