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 } 292