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 "ansidecl.h" 21 #include "config.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 } 299