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, 51 Franklin Street - Fifth Floor,
  18 Boston, MA 02110-1301, 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 /* Get a definition for size_t.  */
  34 #include <stddef.h>
  35
  36 #ifdef HAVE_STDLIB_H
  37 #include <stdlib.h>
  38 #else
  39 /* For systems with larger pointers than ints, this must be declared.  */
  40 extern PTR malloc (size_t);
  41 extern void free (PTR);
  42 #endif
  43
  44 #endif
  45
  46 /* These routines allocate space for an object.  Freeing allocated
  47    space may or may not free all more recently allocated space.
  48
  49    We handle large and small allocation requests differently.  If we
  50    don't have enough space in the current block, and the allocation
  51    request is for more than 512 bytes, we simply pass it through to
  52    malloc.  */
  53
  54 /* The objalloc structure is defined in objalloc.h.  */
  55
  56 /* This structure appears at the start of each chunk.  */
  57
  58 struct objalloc_chunk
  59 {
  60   /* Next chunk.  */
  61   struct objalloc_chunk *next;
  62   /* If this chunk contains large objects, this is the value of
  63      current_ptr when this chunk was allocated.  If this chunk
  64      contains small objects, this is NULL.  */
  65   char *current_ptr;
  66 };
  67
  68 /* The aligned size of objalloc_chunk.  */
  69
  70 #define CHUNK_HEADER_SIZE                                       \
  71   ((sizeof (struct objalloc_chunk) + OBJALLOC_ALIGN - 1)        \
  72    &~ (OBJALLOC_ALIGN - 1))
  73
  74 /* We ask for this much memory each time we create a chunk which is to
  75    hold small objects.  */
  76
  77 #define CHUNK_SIZE (4096 - 32)
  78
  79 /* A request for this amount or more is just passed through to malloc.  */
  80
  81 #define BIG_REQUEST (512)
  82
  83 /* Create an objalloc structure.  */
  84
  85 struct objalloc *
  86 objalloc_create (void)
  87 {
  88   struct objalloc *ret;
  89   struct objalloc_chunk *chunk;
  90
  91   ret = (struct objalloc *) malloc (sizeof *ret);
  92   if (ret == NULL)
  93     return NULL;
  94
  95   ret->chunks = (PTR) malloc (CHUNK_SIZE);
  96   if (ret->chunks == NULL)
  97     {
  98       free (ret);
  99       return NULL;
 100     }
 101
 102   chunk = (struct objalloc_chunk *) ret->chunks;
 103   chunk->next = NULL;
 104   chunk->current_ptr = NULL;
 105
 106   ret->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 107   ret->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 108
 109   return ret;
 110 }
 111
 112 /* Allocate space from an objalloc structure.  */
 113
 114 PTR
 115 _objalloc_alloc (struct objalloc *o, unsigned long len)
 116 {
 117   /* We avoid confusion from zero sized objects by always allocating
 118      at least 1 byte.  */
 119   if (len == 0)
 120     len = 1;
 121
 122   len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);
 123
 124   if (len <= o->current_space)
 125     {
 126       o->current_ptr += len;
 127       o->current_space -= len;
 128       return (PTR) (o->current_ptr - len);
 129     }
 130
 131   if (len >= BIG_REQUEST)
 132     {
 133       char *ret;
 134       struct objalloc_chunk *chunk;
 135
 136       ret = (char *) malloc (CHUNK_HEADER_SIZE + len);
 137       if (ret == NULL)
 138         return NULL;
 139
 140       chunk = (struct objalloc_chunk *) ret;
 141       chunk->next = (struct objalloc_chunk *) o->chunks;
 142       chunk->current_ptr = o->current_ptr;
 143
 144       o->chunks = (PTR) chunk;
 145
 146       return (PTR) (ret + CHUNK_HEADER_SIZE);
 147     }
 148   else
 149     {
 150       struct objalloc_chunk *chunk;
 151
 152       chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);
 153       if (chunk == NULL)
 154         return NULL;
 155       chunk->next = (struct objalloc_chunk *) o->chunks;
 156       chunk->current_ptr = NULL;
 157
 158       o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 159       o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 160
 161       o->chunks = (PTR) chunk;
 162
 163       return objalloc_alloc (o, len);
 164     }
 165 }
 166
 167 /* Free an entire objalloc structure.  */
 168
 169 void
 170 objalloc_free (struct objalloc *o)
 171 {
 172   struct objalloc_chunk *l;
 173
 174   l = (struct objalloc_chunk *) o->chunks;
 175   while (l != NULL)
 176     {
 177       struct objalloc_chunk *next;
 178
 179       next = l->next;
 180       free (l);
 181       l = next;
 182     }
 183
 184   free (o);
 185 }
 186
 187 /* Free a block from an objalloc structure.  This also frees all more
 188    recently allocated blocks.  */
 189
 190 void
 191 objalloc_free_block (struct objalloc *o, 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 }