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, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  18
  19 #include "ansidecl.h"
  20 #include "objalloc.h"
  21
  22 /* Get a definition for NULL.  */
  23 #include <stdio.h>
  24
  25 #if VMS
  26 #include <stdlib.h>
  27 #include <unixlib.h>
  28 #else
  29
  30 #ifdef ANSI_PROTOTYPES
  31 /* Get a definition for size_t.  */
  32 #include <stddef.h>
  33 #endif
  34
  35 /* For systems with larger pointers than ints, this must be declared.  */
  36 extern PTR malloc PARAMS ((size_t));
  37 #endif
  38
  39 /* These routines allocate space for an object.  Freeing allocated
  40    space may or may not free all more recently allocated space.
  41
  42    We handle large and small allocation requests differently.  If we
  43    don't have enough space in the current block, and the allocation
  44    request is for more than 512 bytes, we simply pass it through to
  45    malloc.  */
  46
  47 /* The objalloc structure is defined in objalloc.h.  */
  48
  49 /* This structure appears at the start of each chunk.  */
  50
  51 struct objalloc_chunk
  52 {
  53   /* Next chunk.  */
  54   struct objalloc_chunk *next;
  55   /* If this chunk contains large objects, this is the value of
  56      current_ptr when this chunk was allocated.  If this chunk
  57      contains small objects, this is NULL.  */
  58   char *current_ptr;
  59 };
  60
  61 /* The aligned size of objalloc_chunk.  */
  62
  63 #define CHUNK_HEADER_SIZE                                       \
  64   ((sizeof (struct objalloc_chunk) + OBJALLOC_ALIGN - 1)        \
  65    &~ (OBJALLOC_ALIGN - 1))
  66
  67 /* We ask for this much memory each time we create a chunk which is to
  68    hold small objects.  */
  69
  70 #define CHUNK_SIZE (4096 - 32)
  71
  72 /* A request for this amount or more is just passed through to malloc.  */
  73
  74 #define BIG_REQUEST (512)
  75
  76 /* Create an objalloc structure.  */
  77
  78 struct objalloc *
  79 objalloc_create ()
  80 {
  81   struct objalloc *ret;
  82   struct objalloc_chunk *chunk;
  83
  84   ret = (struct objalloc *) malloc (sizeof *ret);
  85   if (ret == NULL)
  86     return NULL;
  87
  88   ret->chunks = (PTR) malloc (CHUNK_SIZE);
  89   if (ret->chunks == NULL)
  90     {
  91       free (ret);
  92       return NULL;
  93     }
  94
  95   chunk = (struct objalloc_chunk *) ret->chunks;
  96   chunk->next = NULL;
  97   chunk->current_ptr = NULL;
  98
  99   ret->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 100   ret->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 101
 102   return ret;
 103 }
 104
 105 /* Allocate space from an objalloc structure.  */
 106
 107 PTR
 108 _objalloc_alloc (o, len)
 109      struct objalloc *o;
 110      unsigned long len;
 111 {
 112   /* We avoid confusion from zero sized objects by always allocating
 113      at least 1 byte.  */
 114   if (len == 0)
 115     len = 1;
 116
 117   len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);
 118
 119   if (len <= o->current_space)
 120     {
 121       o->current_ptr += len;
 122       o->current_space -= len;
 123       return (PTR) (o->current_ptr - len);
 124     }
 125
 126   if (len >= BIG_REQUEST)
 127     {
 128       char *ret;
 129       struct objalloc_chunk *chunk;
 130
 131       ret = (char *) malloc (CHUNK_HEADER_SIZE + len);
 132       if (ret == NULL)
 133         return NULL;
 134
 135       chunk = (struct objalloc_chunk *) ret;
 136       chunk->next = (struct objalloc_chunk *) o->chunks;
 137       chunk->current_ptr = o->current_ptr;
 138
 139       o->chunks = (PTR) chunk;
 140
 141       return (PTR) (ret + CHUNK_HEADER_SIZE);
 142     }
 143   else
 144     {
 145       struct objalloc_chunk *chunk;
 146
 147       chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);
 148       if (chunk == NULL)
 149         return NULL;
 150       chunk->next = (struct objalloc_chunk *) o->chunks;
 151       chunk->current_ptr = NULL;
 152
 153       o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 154       o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 155
 156       o->chunks = (PTR) chunk;
 157
 158       return objalloc_alloc (o, len);
 159     }
 160 }
 161
 162 /* Free an entire objalloc structure.  */
 163
 164 void
 165 objalloc_free (o)
 166      struct objalloc *o;
 167 {
 168   struct objalloc_chunk *l;
 169
 170   l = (struct objalloc_chunk *) o->chunks;
 171   while (l != NULL)
 172     {
 173       struct objalloc_chunk *next;
 174
 175       next = l->next;
 176       free (l);
 177       l = next;
 178     }
 179
 180   free (o);
 181 }
 182
 183 /* Free a block from an objalloc structure.  This also frees all more
 184    recently allocated blocks.  */
 185
 186 void
 187 objalloc_free_block (o, block)
 188      struct objalloc *o;
 189      PTR block;
 190 {
 191   struct objalloc_chunk *p, *small;
 192   char *b = (char *) block;
 193
 194   /* First set P to the chunk which contains the block we are freeing,
 195      and set Q to the last small object chunk we see before P.  */
 196   small = NULL;
 197   for (p = (struct objalloc_chunk *) o->chunks; p != NULL; p = p->next)
 198     {
 199       if (p->current_ptr == NULL)
 200         {
 201           if (b > (char *) p && b < (char *) p + CHUNK_SIZE)
 202             break;
 203           small = p;
 204         }
 205       else
 206         {
 207           if (b == (char *) p + CHUNK_HEADER_SIZE)
 208             break;
 209         }
 210     }
 211
 212   /* If we can't find the chunk, the caller has made a mistake.  */
 213   if (p == NULL)
 214     abort ();
 215
 216   if (p->current_ptr == NULL)
 217     {
 218       struct objalloc_chunk *q;
 219       struct objalloc_chunk *first;
 220
 221       /* The block is in a chunk containing small objects.  We can
 222          free every chunk through SMALL, because they have certainly
 223          been allocated more recently.  After SMALL, we will not see
 224          any chunks containing small objects; we can free any big
 225          chunk if the current_ptr is greater than or equal to B.  We
 226          can then reset the new current_ptr to B.  */
 227
 228       first = NULL;
 229       q = (struct objalloc_chunk *) o->chunks;
 230       while (q != p)
 231         {
 232           struct objalloc_chunk *next;
 233
 234           next = q->next;
 235           if (small != NULL)
 236             {
 237               if (small == q)
 238                 small = NULL;
 239               free (q);
 240             }
 241           else if (q->current_ptr > b)
 242             free (q);
 243           else if (first == NULL)
 244             first = q;
 245
 246           q = next;
 247         }
 248
 249       if (first == NULL)
 250         first = p;
 251       o->chunks = (PTR) first;
 252
 253       /* Now start allocating from this small block again.  */
 254       o->current_ptr = b;
 255       o->current_space = ((char *) p + CHUNK_SIZE) - b;
 256     }
 257   else
 258     {
 259       struct objalloc_chunk *q;
 260       char *current_ptr;
 261
 262       /* This block is in a large chunk by itself.  We can free
 263          everything on the list up to and including this block.  We
 264          then start allocating from the next chunk containing small
 265          objects, setting current_ptr from the value stored with the
 266          large chunk we are freeing.  */
 267
 268       current_ptr = p->current_ptr;
 269       p = p->next;
 270
 271       q = (struct objalloc_chunk *) o->chunks;
 272       while (q != p)
 273         {
 274           struct objalloc_chunk *next;
 275
 276           next = q->next;
 277           free (q);
 278           q = next;
 279         }
 280
 281       o->chunks = (PTR) p;
 282
 283       while (p->current_ptr != NULL)
 284         p = p->next;
 285
 286       o->current_ptr = current_ptr;
 287       o->current_space = ((char *) p + CHUNK_SIZE) - current_ptr;
 288     }
 289 }