1 /* objalloc.c -- routines to allocate memory for objects 2 Copyright 1997-2012 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 original_len) 116 { 117 unsigned long len = original_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 /* Check for overflow in the alignment operation above and the 127 malloc argument below. */ 128 if (len + CHUNK_HEADER_SIZE < original_len) 129 return NULL; 130 131 if (len <= o->current_space) 132 { 133 o->current_ptr += len; 134 o->current_space -= len; 135 return (PTR) (o->current_ptr - len); 136 } 137 138 if (len >= BIG_REQUEST) 139 { 140 char *ret; 141 struct objalloc_chunk *chunk; 142 143 ret = (char *) malloc (CHUNK_HEADER_SIZE + len); 144 if (ret == NULL) 145 return NULL; 146 147 chunk = (struct objalloc_chunk *) ret; 148 chunk->next = (struct objalloc_chunk *) o->chunks; 149 chunk->current_ptr = o->current_ptr; 150 151 o->chunks = (PTR) chunk; 152 153 return (PTR) (ret + CHUNK_HEADER_SIZE); 154 } 155 else 156 { 157 struct objalloc_chunk *chunk; 158 159 chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE); 160 if (chunk == NULL) 161 return NULL; 162 chunk->next = (struct objalloc_chunk *) o->chunks; 163 chunk->current_ptr = NULL; 164 165 o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE; 166 o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE; 167 168 o->chunks = (PTR) chunk; 169 170 return objalloc_alloc (o, len); 171 } 172 } 173 174 /* Free an entire objalloc structure. */ 175 176 void 177 objalloc_free (struct objalloc *o) 178 { 179 struct objalloc_chunk *l; 180 181 l = (struct objalloc_chunk *) o->chunks; 182 while (l != NULL) 183 { 184 struct objalloc_chunk *next; 185 186 next = l->next; 187 free (l); 188 l = next; 189 } 190 191 free (o); 192 } 193 194 /* Free a block from an objalloc structure. This also frees all more 195 recently allocated blocks. */ 196 197 void 198 objalloc_free_block (struct objalloc *o, 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 } 299