| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * Allocation of known-size blocks |
| 4 | * |
| 5 | * (c) 1998 Straylight/Edgeware |
| 6 | */ |
| 7 | |
| 8 | /*----- Licensing notice --------------------------------------------------* |
| 9 | * |
| 10 | * This file is part of the mLib utilities library. |
| 11 | * |
| 12 | * mLib is free software; you can redistribute it and/or modify |
| 13 | * it under the terms of the GNU Library General Public License as |
| 14 | * published by the Free Software Foundation; either version 2 of the |
| 15 | * License, or (at your option) any later version. |
| 16 | * |
| 17 | * mLib is distributed in the hope that it will be useful, |
| 18 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 20 | * GNU Library General Public License for more details. |
| 21 | * |
| 22 | * You should have received a copy of the GNU Library General Public |
| 23 | * License along with mLib; if not, write to the Free |
| 24 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
| 25 | * MA 02111-1307, USA. |
| 26 | */ |
| 27 | |
| 28 | /*----- The big idea ------------------------------------------------------* |
| 29 | * |
| 30 | * This file provides an extra layer over @malloc@. It provides fast |
| 31 | * turnover for small blocks, and tries to minimize the per-block overhead. |
| 32 | * |
| 33 | * To do its job, @alloc@ must place an extra restriction on you: you must |
| 34 | * know the size of a block when you free it. Usually you'll have this |
| 35 | * information encoded in some way either in the block or in the thing that |
| 36 | * referenced it, so this isn't a hardship. |
| 37 | * |
| 38 | * It works fairly simply. If a request for a big block (as defined by the |
| 39 | * constants below) comes in, it gets sent on to @malloc@ unmolested. For |
| 40 | * small blocks, it goes straight to a `bin' -- a list containing free blocks |
| 41 | * of exactly that size, or the nearest bigger size we can manage. If the |
| 42 | * bin is empty, a `chunk' is allocated from @malloc@: this has enough room |
| 43 | * for lots of blocks of the requested size, so it ets split up and each |
| 44 | * individual small block is added to the bin list. The first block in the |
| 45 | * bin list is then removed and given to the caller. In this way, @malloc@ |
| 46 | * only stores its information once for lots of little blocks, so we save |
| 47 | * memory. Because I know where the correct bin is just from the block size, |
| 48 | * and I don't need to do any searching at all in the usual case (because the |
| 49 | * list isn't empty) I can get a speed advantage too. |
| 50 | * |
| 51 | * This code is almost certainly not ANSI conformant, although I'm not |
| 52 | * actually sure. If some kind soul would let me know how seriously I've |
| 53 | * violated the standard, and whether this is easily fixable, I'd be |
| 54 | * grateful. |
| 55 | */ |
| 56 | |
| 57 | /*----- Header files ------------------------------------------------------*/ |
| 58 | |
| 59 | /* --- ANSI headers --- */ |
| 60 | |
| 61 | #include <assert.h> |
| 62 | #include <stdio.h> |
| 63 | #include <stdlib.h> |
| 64 | #include <string.h> |
| 65 | |
| 66 | /* --- Local headers --- */ |
| 67 | |
| 68 | #include "arena.h" |
| 69 | #include "exc.h" |
| 70 | #include "sub.h" |
| 71 | |
| 72 | /*----- Configuration tweaks ----------------------------------------------*/ |
| 73 | |
| 74 | /* #define SUBARENA_TRIVIAL */ |
| 75 | |
| 76 | /*----- Static variables --------------------------------------------------*/ |
| 77 | |
| 78 | static size_t sizes[SUB_BINS]; |
| 79 | |
| 80 | /*----- Global variables --------------------------------------------------*/ |
| 81 | |
| 82 | subarena sub_global; |
| 83 | |
| 84 | #ifdef SUBARENA_TRIVIAL |
| 85 | |
| 86 | typedef struct sub_link { |
| 87 | struct sub_link *next; |
| 88 | void *p; |
| 89 | size_t sz; |
| 90 | } sub_link; |
| 91 | |
| 92 | #endif |
| 93 | |
| 94 | /*----- Main code ---------------------------------------------------------*/ |
| 95 | |
| 96 | /* --- @subarena_create@ --- * |
| 97 | * |
| 98 | * Arguments: @subarena *s@ = pointer to arena to initialize |
| 99 | * @arena *a@ = pointer to underlying arena block |
| 100 | * |
| 101 | * Returns: --- |
| 102 | * |
| 103 | * Use: Initialize a suballocation arena based on an underlying large |
| 104 | * blocks arena. |
| 105 | */ |
| 106 | |
| 107 | void subarena_create(subarena *s, arena *a) |
| 108 | { |
| 109 | #ifdef SUBARENA_TRIVIAL |
| 110 | s->bin[0] = 0; |
| 111 | #else |
| 112 | size_t i; |
| 113 | if (!sizes[1]) |
| 114 | sub_init(); |
| 115 | for (i = 0; i < SUB_BINS; i++) |
| 116 | s->bin[i] = 0; |
| 117 | #endif |
| 118 | s->a = a; |
| 119 | } |
| 120 | |
| 121 | /* --- @subarena_destroy@ --- * |
| 122 | * |
| 123 | * Arguments: @subarena *s@ = pointer to arena to destroy |
| 124 | * |
| 125 | * Returns: --- |
| 126 | * |
| 127 | * Use: Destroys a suballocation arena, freeing all of the memory it |
| 128 | * contains back to the underlying large blocks arena. |
| 129 | */ |
| 130 | |
| 131 | void subarena_destroy(subarena *s) |
| 132 | { |
| 133 | #ifdef SUBARENA_TRIVIAL |
| 134 | |
| 135 | sub_link *l, *ll; |
| 136 | |
| 137 | for (l = s->bin[0]; l; l = ll) { |
| 138 | ll = l; |
| 139 | a_free(s->a, l->p); |
| 140 | a_free(s->a, l); |
| 141 | } |
| 142 | s->bin[0] = 0; |
| 143 | |
| 144 | #else |
| 145 | |
| 146 | size_t i; |
| 147 | for (i = 0; i < SUB_BINS; i++) { |
| 148 | void *p = s->bin[i]; |
| 149 | while (p) { |
| 150 | void *q = p; |
| 151 | p = *(void **)q; |
| 152 | A_FREE(s->a, q); |
| 153 | } |
| 154 | s->bin[i] = 0; |
| 155 | } |
| 156 | |
| 157 | #endif |
| 158 | } |
| 159 | |
| 160 | /* --- @subarena_alloc@ --- * |
| 161 | * |
| 162 | * Arguments: @subarena *s@ = pointer to arena |
| 163 | * @size_t s@ = size of chunk wanted |
| 164 | * |
| 165 | * Returns: Pointer to a block at least as large as the one wanted. |
| 166 | * |
| 167 | * Use: Allocates a small block of memory from the given pool. The |
| 168 | * exception @EXC_NOMEM@ is raised if the underlying arena is |
| 169 | * full. |
| 170 | */ |
| 171 | |
| 172 | void *subarena_alloc(subarena *s, size_t sz) |
| 173 | { |
| 174 | #ifdef SUBARENA_TRIVIAL |
| 175 | |
| 176 | sub_link *l; |
| 177 | void *p; |
| 178 | |
| 179 | if (!s->a) |
| 180 | subarena_create(s, arena_global); |
| 181 | |
| 182 | if ((l = a_alloc(s->a, sizeof(*l))) == 0) |
| 183 | return (0); |
| 184 | if ((p = a_alloc(s->a, sz)) == 0) { |
| 185 | a_free(s->a, l); |
| 186 | return (0); |
| 187 | } |
| 188 | l->p = p; |
| 189 | l->sz = sz; |
| 190 | l->next = s->bin[0]; |
| 191 | s->bin[0] = l; |
| 192 | return (p); |
| 193 | |
| 194 | #else |
| 195 | |
| 196 | int bin; |
| 197 | void *p; |
| 198 | |
| 199 | /* --- Ensure that everything is initialized --- */ |
| 200 | |
| 201 | if (!s->a) |
| 202 | subarena_create(s, arena_global); |
| 203 | |
| 204 | /* --- Handle oversize blocks --- */ |
| 205 | |
| 206 | bin = SUB_BIN(sz); |
| 207 | if (bin >= SUB_BINS) { |
| 208 | void *p = A_ALLOC(s->a, sz); |
| 209 | if (!p) |
| 210 | THROW(EXC_NOMEM); |
| 211 | return (p); |
| 212 | } |
| 213 | |
| 214 | /* --- If the bin is empty, find some memory --- */ |
| 215 | |
| 216 | if (!s->bin[bin]) { |
| 217 | char *p, *q; |
| 218 | |
| 219 | p = A_ALLOC(s->a, sizes[bin]); |
| 220 | if (!p) |
| 221 | THROW(EXC_NOMEM); |
| 222 | q = p + sizes[bin]; |
| 223 | |
| 224 | sz = SUB_BINSZ(bin); |
| 225 | |
| 226 | q -= sz; |
| 227 | *(void **)q = 0; |
| 228 | |
| 229 | while (q > p) { |
| 230 | q -= sz; |
| 231 | *(void **)q = q + sz; |
| 232 | } |
| 233 | |
| 234 | s->bin[bin] = p; |
| 235 | } |
| 236 | |
| 237 | /* --- Extract the first block in the list --- */ |
| 238 | |
| 239 | p = s->bin[bin]; |
| 240 | s->bin[bin] = *(void **)p; |
| 241 | return (p); |
| 242 | |
| 243 | #endif |
| 244 | } |
| 245 | |
| 246 | /* --- @subarena_free@ --- * |
| 247 | * |
| 248 | * Arguments: @subarena *s@ = pointer to arena |
| 249 | * @void *p@ = address of block to free |
| 250 | * @size_t s@ = size of block |
| 251 | * |
| 252 | * Returns: --- |
| 253 | * |
| 254 | * Use: Frees a block allocated by @subarena_alloc@. |
| 255 | */ |
| 256 | |
| 257 | void subarena_free(subarena *s, void *p, size_t sz) |
| 258 | { |
| 259 | #ifdef SUBARENA_TRIVIAL |
| 260 | |
| 261 | sub_link *lh = s->bin[0], **l, *ll; |
| 262 | |
| 263 | for (l = &lh; *l && (*l)->p != p; l = &(*l)->next) |
| 264 | ; |
| 265 | ll = *l; |
| 266 | assert(ll); |
| 267 | assert(ll->sz == sz); |
| 268 | *l = ll->next; |
| 269 | a_free(s->a, ll); |
| 270 | a_free(s->a, p); |
| 271 | s->bin[0] = lh; |
| 272 | |
| 273 | #else |
| 274 | |
| 275 | int bin = SUB_BIN(sz); |
| 276 | |
| 277 | if (bin >= SUB_BINS) |
| 278 | A_FREE(s->a, p); |
| 279 | else { |
| 280 | *(void **)p = s->bin[bin]; |
| 281 | s->bin[bin] = p; |
| 282 | } |
| 283 | |
| 284 | #endif |
| 285 | } |
| 286 | |
| 287 | /*----- Compatibility stuff -----------------------------------------------*/ |
| 288 | |
| 289 | /* --- @sub_alloc@ --- * |
| 290 | * |
| 291 | * Arguments: @size_t s@ = size of chunk wanted |
| 292 | * |
| 293 | * Returns: Pointer to a block at least as large as the one wanted. |
| 294 | * |
| 295 | * Use: Allocates a small block of memory from the @sub_global@ pool. |
| 296 | */ |
| 297 | |
| 298 | void *(sub_alloc)(size_t sz) { return sub_alloc(sz); } |
| 299 | |
| 300 | /* --- @sub_free@ --- * |
| 301 | * |
| 302 | * Arguments: @void *p@ = address of block to free |
| 303 | * @size_t s@ = size of block |
| 304 | * |
| 305 | * Returns: --- |
| 306 | * |
| 307 | * Use: Frees a block allocated by @sub_alloc@. |
| 308 | */ |
| 309 | |
| 310 | void (sub_free)(void *p, size_t sz) { sub_free(p, sz); } |
| 311 | |
| 312 | /* --- @sub_init@ --- * |
| 313 | * |
| 314 | * Arguments: --- |
| 315 | * |
| 316 | * Returns: --- |
| 317 | * |
| 318 | * Use: Initializes the magic allocator. |
| 319 | */ |
| 320 | |
| 321 | void sub_init(void) |
| 322 | { |
| 323 | #ifndef SUBARENA_TRIVIAL |
| 324 | int i; |
| 325 | |
| 326 | /* --- Initialize the sizes bins --- */ |
| 327 | |
| 328 | for (i = 1; i < SUB_BINS; i++) { |
| 329 | sizes[i] = ((SUB_CHUNK + SUB_BINSZ(i) - 1) / |
| 330 | SUB_BINSZ(i) * SUB_BINSZ(i)); |
| 331 | } |
| 332 | #endif |
| 333 | } |
| 334 | |
| 335 | /*----- Debugging code ----------------------------------------------------*/ |
| 336 | |
| 337 | #ifdef TEST_RIG |
| 338 | |
| 339 | #define BLOCKS 1024 |
| 340 | #define SIZE_MAX 2048 |
| 341 | #define ITERATIONS 500000 |
| 342 | |
| 343 | int main(void) |
| 344 | { |
| 345 | static void *block[BLOCKS]; |
| 346 | static size_t size[BLOCKS]; |
| 347 | size_t allocced = 0; |
| 348 | int i; |
| 349 | long count; |
| 350 | |
| 351 | sub_init(); |
| 352 | |
| 353 | for (count = 0; count < ITERATIONS; count++) { |
| 354 | i = rand() % BLOCKS; |
| 355 | if (block[i]) { |
| 356 | sub_free(block[i], size[i]); |
| 357 | block[i] = 0; |
| 358 | allocced -= size[i]; |
| 359 | } else { |
| 360 | block[i] = sub_alloc(size[i] = |
| 361 | rand() % (SUB_MAXBIN - 128) + 128); |
| 362 | allocced += size[i]; |
| 363 | memset(block[i], 0, size[i]); /* trample allocated storage */ |
| 364 | } |
| 365 | } |
| 366 | |
| 367 | return (0); |
| 368 | } |
| 369 | |
| 370 | #endif |
| 371 | |
| 372 | /*----- That's all, folks -------------------------------------------------*/ |