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 "objalloc.h" 22 23 /* Get a definition for NULL. */ 24 #include <stdio.h> 25 26 #if VMS 27 #include <stdlib.h> 28 #include <unixlib.h> 29 #else 30 31 #ifdef ANSI_PROTOTYPES 32 /* Get a definition for size_t. */ 33 #include <stddef.h> 34 #endif 35 36 /* For systems with larger pointers than ints, this must be declared. */ 37 extern PTR malloc PARAMS ((size_t)); 38 extern void free PARAMS ((PTR)); 39 #endif 40 41 /* These routines allocate space for an object. Freeing allocated 42 space may or may not free all more recently allocated space. 43 44 We handle large and small allocation requests differently. If we 45 don't have enough space in the current block, and the allocation 46 request is for more than 512 bytes, we simply pass it through to 47 malloc. */ 48 49 /* The objalloc structure is defined in objalloc.h. */ 50 51 /* This structure appears at the start of each chunk. */ 52 53 struct objalloc_chunk 54 { 55 /* Next chunk. */ 56 struct objalloc_chunk *next; 57 /* If this chunk contains large objects, this is the value of 58 current_ptr when this chunk was allocated. If this chunk 59 contains small objects, this is NULL. */ 60 char *current_ptr; 61 }; 62 63 /* The aligned size of objalloc_chunk. */ 64 65 #define CHUNK_HEADER_SIZE \ 66 ((sizeof (struct objalloc_chunk) + OBJALLOC_ALIGN - 1) \ 67 &~ (OBJALLOC_ALIGN - 1)) 68 69 /* We ask for this much memory each time we create a chunk which is to 70 hold small objects. */ 71 72 #define CHUNK_SIZE (4096 - 32) 73 74 /* A request for this amount or more is just passed through to malloc. */ 75 76 #define BIG_REQUEST (512) 77 78 /* Create an objalloc structure. */ 79 80 struct objalloc * 81 objalloc_create () 82 { 83 struct objalloc *ret; 84 struct objalloc_chunk *chunk; 85 86 ret = (struct objalloc *) malloc (sizeof *ret); 87 if (ret == NULL) 88 return NULL; 89 90 ret->chunks = (PTR) malloc (CHUNK_SIZE); 91 if (ret->chunks == NULL) 92 { 93 free (ret); 94 return NULL; 95 } 96 97 chunk = (struct objalloc_chunk *) ret->chunks; 98 chunk->next = NULL; 99 chunk->current_ptr = NULL; 100 101 ret->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE; 102 ret->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE; 103 104 return ret; 105 } 106 107 /* Allocate space from an objalloc structure. */ 108 109 PTR 110 _objalloc_alloc (o, len) 111 struct objalloc *o; 112 unsigned long len; 113 { 114 /* We avoid confusion from zero sized objects by always allocating 115 at least 1 byte. */ 116 if (len == 0) 117 len = 1; 118 119 len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1); 120 121 if (len <= o->current_space) 122 { 123 o->current_ptr += len; 124 o->current_space -= len; 125 return (PTR) (o->current_ptr - len); 126 } 127 128 if (len >= BIG_REQUEST) 129 { 130 char *ret; 131 struct objalloc_chunk *chunk; 132 133 ret = (char *) malloc (CHUNK_HEADER_SIZE + len); 134 if (ret == NULL) 135 return NULL; 136 137 chunk = (struct objalloc_chunk *) ret; 138 chunk->next = (struct objalloc_chunk *) o->chunks; 139 chunk->current_ptr = o->current_ptr; 140 141 o->chunks = (PTR) chunk; 142 143 return (PTR) (ret + CHUNK_HEADER_SIZE); 144 } 145 else 146 { 147 struct objalloc_chunk *chunk; 148 149 chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE); 150 if (chunk == NULL) 151 return NULL; 152 chunk->next = (struct objalloc_chunk *) o->chunks; 153 chunk->current_ptr = NULL; 154 155 o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE; 156 o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE; 157 158 o->chunks = (PTR) chunk; 159 160 return objalloc_alloc (o, len); 161 } 162 } 163 164 /* Free an entire objalloc structure. */ 165 166 void 167 objalloc_free (o) 168 struct objalloc *o; 169 { 170 struct objalloc_chunk *l; 171 172 l = (struct objalloc_chunk *) o->chunks; 173 while (l != NULL) 174 { 175 struct objalloc_chunk *next; 176 177 next = l->next; 178 free (l); 179 l = next; 180 } 181 182 free (o); 183 } 184 185 /* Free a block from an objalloc structure. This also frees all more 186 recently allocated blocks. */ 187 188 void 189 objalloc_free_block (o, block) 190 struct objalloc *o; 191 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