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 PARAMS ((size_t));
  43 extern void free PARAMS ((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 ()
  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 (o, len)
 118      struct objalloc *o;
 119      unsigned long len;
 120 {
 121   /* We avoid confusion from zero sized objects by always allocating
 122      at least 1 byte.  */
 123   if (len == 0)
 124     len = 1;
 125
 126   len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);
 127
 128   if (len <= o->current_space)
 129     {
 130       o->current_ptr += len;
 131       o->current_space -= len;
 132       return (PTR) (o->current_ptr - len);
 133     }
 134
 135   if (len >= BIG_REQUEST)
 136     {
 137       char *ret;
 138       struct objalloc_chunk *chunk;
 139
 140       ret = (char *) malloc (CHUNK_HEADER_SIZE + len);
 141       if (ret == NULL)
 142         return NULL;
 143
 144       chunk = (struct objalloc_chunk *) ret;
 145       chunk->next = (struct objalloc_chunk *) o->chunks;
 146       chunk->current_ptr = o->current_ptr;
 147
 148       o->chunks = (PTR) chunk;
 149
 150       return (PTR) (ret + CHUNK_HEADER_SIZE);
 151     }
 152   else
 153     {
 154       struct objalloc_chunk *chunk;
 155
 156       chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);
 157       if (chunk == NULL)
 158         return NULL;
 159       chunk->next = (struct objalloc_chunk *) o->chunks;
 160       chunk->current_ptr = NULL;
 161
 162       o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 163       o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 164
 165       o->chunks = (PTR) chunk;
 166
 167       return objalloc_alloc (o, len);
 168     }
 169 }
 170
 171 /* Free an entire objalloc structure.  */
 172
 173 void
 174 objalloc_free (o)
 175      struct objalloc *o;
 176 {
 177   struct objalloc_chunk *l;
 178
 179   l = (struct objalloc_chunk *) o->chunks;
 180   while (l != NULL)
 181     {
 182       struct objalloc_chunk *next;
 183
 184       next = l->next;
 185       free (l);
 186       l = next;
 187     }
 188
 189   free (o);
 190 }
 191
 192 /* Free a block from an objalloc structure.  This also frees all more
 193    recently allocated blocks.  */
 194
 195 void
 196 objalloc_free_block (o, block)
 197      struct objalloc *o;
 198      PTR block;
 199 {
 200   struct objalloc_chunk *p, *small;
 201   char *b = (char *) block;
 202
 203   /* First set P to the chunk which contains the block we are freeing,
 204      and set Q to the last small object chunk we see before P.  */
 205   small = NULL;
 206   for (p = (struct objalloc_chunk *) o->chunks; p != NULL; p = p->next)
 207     {
 208       if (p->current_ptr == NULL)
 209         {
 210           if (b > (char *) p && b < (char *) p + CHUNK_SIZE)
 211             break;
 212           small = p;
 213         }
 214       else
 215         {
 216           if (b == (char *) p + CHUNK_HEADER_SIZE)
 217             break;
 218         }
 219     }
 220
 221   /* If we can't find the chunk, the caller has made a mistake.  */
 222   if (p == NULL)
 223     abort ();
 224
 225   if (p->current_ptr == NULL)
 226     {
 227       struct objalloc_chunk *q;
 228       struct objalloc_chunk *first;
 229
 230       /* The block is in a chunk containing small objects.  We can
 231          free every chunk through SMALL, because they have certainly
 232          been allocated more recently.  After SMALL, we will not see
 233          any chunks containing small objects; we can free any big
 234          chunk if the current_ptr is greater than or equal to B.  We
 235          can then reset the new current_ptr to B.  */
 236
 237       first = NULL;
 238       q = (struct objalloc_chunk *) o->chunks;
 239       while (q != p)
 240         {
 241           struct objalloc_chunk *next;
 242
 243           next = q->next;
 244           if (small != NULL)
 245             {
 246               if (small == q)
 247                 small = NULL;
 248               free (q);
 249             }
 250           else if (q->current_ptr > b)
 251             free (q);
 252           else if (first == NULL)
 253             first = q;
 254
 255           q = next;
 256         }
 257
 258       if (first == NULL)
 259         first = p;
 260       o->chunks = (PTR) first;
 261
 262       /* Now start allocating from this small block again.  */
 263       o->current_ptr = b;
 264       o->current_space = ((char *) p + CHUNK_SIZE) - b;
 265     }
 266   else
 267     {
 268       struct objalloc_chunk *q;
 269       char *current_ptr;
 270
 271       /* This block is in a large chunk by itself.  We can free
 272          everything on the list up to and including this block.  We
 273          then start allocating from the next chunk containing small
 274          objects, setting current_ptr from the value stored with the
 275          large chunk we are freeing.  */
 276
 277       current_ptr = p->current_ptr;
 278       p = p->next;
 279
 280       q = (struct objalloc_chunk *) o->chunks;
 281       while (q != p)
 282         {
 283           struct objalloc_chunk *next;
 284
 285           next = q->next;
 286           free (q);
 287           q = next;
 288         }
 289
 290       o->chunks = (PTR) p;
 291
 292       while (p->current_ptr != NULL)
 293         p = p->next;
 294
 295       o->current_ptr = current_ptr;
 296       o->current_space = ((char *) p + CHUNK_SIZE) - current_ptr;
 297     }
 298 }