| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * $Id: sub.c,v 1.6 2000/06/17 10:35:51 mdw Exp $ |
| 4 | * |
| 5 | * Allocation of known-size blocks |
| 6 | * |
| 7 | * (c) 1998 Straylight/Edgeware |
| 8 | */ |
| 9 | |
| 10 | /*----- Licensing notice --------------------------------------------------* |
| 11 | * |
| 12 | * This file is part of the mLib utilities library. |
| 13 | * |
| 14 | * mLib is free software; you can redistribute it and/or modify |
| 15 | * it under the terms of the GNU Library General Public License as |
| 16 | * published by the Free Software Foundation; either version 2 of the |
| 17 | * License, or (at your option) any later version. |
| 18 | * |
| 19 | * mLib is distributed in the hope that it will be useful, |
| 20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 22 | * GNU Library General Public License for more details. |
| 23 | * |
| 24 | * You should have received a copy of the GNU Library General Public |
| 25 | * License along with mLib; if not, write to the Free |
| 26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
| 27 | * MA 02111-1307, USA. |
| 28 | */ |
| 29 | |
| 30 | /*----- Revision history --------------------------------------------------* |
| 31 | * |
| 32 | * $Log: sub.c,v $ |
| 33 | * Revision 1.6 2000/06/17 10:35:51 mdw |
| 34 | * Major overhaul for arena support. |
| 35 | * |
| 36 | * Revision 1.5 1999/05/19 20:27:11 mdw |
| 37 | * Change naming to match newer mLib conventions. |
| 38 | * |
| 39 | * Revision 1.4 1999/05/13 22:48:55 mdw |
| 40 | * Change `-ise' to `-ize' throughout. |
| 41 | * |
| 42 | * Revision 1.3 1999/05/06 19:51:35 mdw |
| 43 | * Reformatted the LGPL notice a little bit. |
| 44 | * |
| 45 | * Revision 1.2 1999/05/05 18:50:31 mdw |
| 46 | * Change licensing conditions to LGPL. |
| 47 | * |
| 48 | * Revision 1.1.1.1 1998/06/17 23:44:42 mdw |
| 49 | * Initial version of mLib |
| 50 | * |
| 51 | */ |
| 52 | |
| 53 | /*----- The big idea ------------------------------------------------------* |
| 54 | * |
| 55 | * This file provides an extra layer over @malloc@. It provides fast |
| 56 | * turnover for small blocks, and tries to minimize the per-block overhead. |
| 57 | * |
| 58 | * To do its job, @alloc@ must place an extra restriction on you: you must |
| 59 | * know the size of a block when you free it. Usually you'll have this |
| 60 | * information encoded in some way either in the block or in the thing that |
| 61 | * referenced it, so this isn't a hardship. |
| 62 | * |
| 63 | * It works fairly simply. If a request for a big block (as defined by the |
| 64 | * constants below) comes in, it gets sent on to @malloc@ unmolested. For |
| 65 | * small blocks, it goes straight to a `bin' -- a list containing free blocks |
| 66 | * of exactly that size, or the nearest bigger size we can manage. If the |
| 67 | * bin is empty, a `chunk' is allocated from @malloc@: this has enough room |
| 68 | * for lots of blocks of the requested size, so it ets split up and each |
| 69 | * individual small block is added to the bin list. The first block in the |
| 70 | * bin list is then removed and given to the caller. In this way, @malloc@ |
| 71 | * only stores its information once for lots of little blocks, so we save |
| 72 | * memory. Because I know where the correct bin is just from the block size, |
| 73 | * and I don't need to do any searching at all in the usual case (because the |
| 74 | * list isn't empty) I can get a speed advantage too. |
| 75 | * |
| 76 | * This code is almost certainly not ANSI conformant, although I'm not |
| 77 | * actually sure. If some kind soul would let me know how seriously I've |
| 78 | * violated the standard, and whether this is easily fixable, I'd be |
| 79 | * grateful. |
| 80 | */ |
| 81 | |
| 82 | /*----- Header files ------------------------------------------------------*/ |
| 83 | |
| 84 | /* --- ANSI headers --- */ |
| 85 | |
| 86 | #include <stdio.h> |
| 87 | #include <stdlib.h> |
| 88 | #include <string.h> |
| 89 | |
| 90 | /* --- Local headers --- */ |
| 91 | |
| 92 | #include "arena.h" |
| 93 | #include "exc.h" |
| 94 | #include "sub.h" |
| 95 | |
| 96 | /*----- Static variables --------------------------------------------------*/ |
| 97 | |
| 98 | static size_t sizes[SUB_BINS]; |
| 99 | |
| 100 | /*----- Global variables --------------------------------------------------*/ |
| 101 | |
| 102 | subarena sub_global; |
| 103 | |
| 104 | /*----- Main code ---------------------------------------------------------*/ |
| 105 | |
| 106 | /* --- @subarena_create@ --- * |
| 107 | * |
| 108 | * Arguments: @subarena *s@ = pointer to arena to initialize |
| 109 | * @arena *a@ = pointer to underlying arena block |
| 110 | * |
| 111 | * Returns: --- |
| 112 | * |
| 113 | * Use: Initialize a suballocation arena based on an underlying large |
| 114 | * blocks arena. |
| 115 | */ |
| 116 | |
| 117 | void subarena_create(subarena *s, arena *a) |
| 118 | { |
| 119 | size_t i; |
| 120 | if (!sizes[1]) |
| 121 | sub_init(); |
| 122 | for (i = 0; i < SUB_BINS; i++) |
| 123 | s->bin[i] = 0; |
| 124 | s->a = a; |
| 125 | } |
| 126 | |
| 127 | /* --- @subarena_destroy@ --- * |
| 128 | * |
| 129 | * Arguments: @subarena *s@ = pointer to arena to destroy |
| 130 | * |
| 131 | * Returns: --- |
| 132 | * |
| 133 | * Use: Destroys a suballocation arena, freeing all of the memory it |
| 134 | * contains back to the underlying large blocks arena. |
| 135 | */ |
| 136 | |
| 137 | void subarena_destroy(subarena *s) |
| 138 | { |
| 139 | size_t i; |
| 140 | for (i = 0; i < SUB_BINS; i++) { |
| 141 | void *p = s->bin[i]; |
| 142 | while (p) { |
| 143 | void *q = p; |
| 144 | p = *(void **)q; |
| 145 | A_FREE(s->a, q); |
| 146 | } |
| 147 | } |
| 148 | } |
| 149 | |
| 150 | /* --- @subarena_alloc@ --- * |
| 151 | * |
| 152 | * Arguments: @subarena *s@ = pointer to arena |
| 153 | * @size_t s@ = size of chunk wanted |
| 154 | * |
| 155 | * Returns: Pointer to a block at least as large as the one wanted. |
| 156 | * |
| 157 | * Use: Allocates a small block of memory from the given pool. The |
| 158 | * exception @EXC_NOMEM@ is raised if the underlying arena is |
| 159 | * full. |
| 160 | */ |
| 161 | |
| 162 | void *subarena_alloc(subarena *s, size_t sz) |
| 163 | { |
| 164 | int bin; |
| 165 | void *p; |
| 166 | |
| 167 | /* --- Ensure that everything is initialized --- */ |
| 168 | |
| 169 | if (!s->a) |
| 170 | subarena_create(s, arena_global); |
| 171 | bin = SUB_BIN(sz); |
| 172 | |
| 173 | /* --- Handle oversize blocks --- */ |
| 174 | |
| 175 | if (bin >= SUB_BINS) { |
| 176 | void *p = A_ALLOC(s->a, sz); |
| 177 | if (!p) |
| 178 | THROW(EXC_NOMEM); |
| 179 | return (p); |
| 180 | } |
| 181 | |
| 182 | /* --- If the bin is empty, find some memory --- */ |
| 183 | |
| 184 | if (!s->bin[bin]) { |
| 185 | char *p, *q; |
| 186 | |
| 187 | p = A_ALLOC(s->a, sizes[bin]); |
| 188 | if (!p) |
| 189 | THROW(EXC_NOMEM); |
| 190 | q = p + sizes[bin]; |
| 191 | |
| 192 | sz = SUB_BINSZ(bin); |
| 193 | |
| 194 | q -= sz; |
| 195 | *(void **)q = 0; |
| 196 | |
| 197 | while (q > p) { |
| 198 | q -= sz; |
| 199 | *(void **)q = q + sz; |
| 200 | } |
| 201 | |
| 202 | s->bin[bin] = p; |
| 203 | } |
| 204 | |
| 205 | /* --- Extract the first block in the list --- */ |
| 206 | |
| 207 | p = s->bin[bin]; |
| 208 | s->bin[bin] = *(void **)p; |
| 209 | return (p); |
| 210 | } |
| 211 | |
| 212 | /* --- @subarena_free@ --- * |
| 213 | * |
| 214 | * Arguments: @subarena *s@ = pointer to arena |
| 215 | * @void *p@ = address of block to free |
| 216 | * @size_t s@ = size of block |
| 217 | * |
| 218 | * Returns: --- |
| 219 | * |
| 220 | * Use: Frees a block allocated by @subarena_alloc@. |
| 221 | */ |
| 222 | |
| 223 | void subarena_free(subarena *s, void *p, size_t sz) |
| 224 | { |
| 225 | int bin = SUB_BIN(sz); |
| 226 | |
| 227 | if (bin >= SUB_BINS) |
| 228 | A_FREE(s->a, p); |
| 229 | else { |
| 230 | *(void **)p = s->bin[bin]; |
| 231 | s->bin[bin] = p; |
| 232 | } |
| 233 | } |
| 234 | |
| 235 | /*----- Compatibility stuff -----------------------------------------------*/ |
| 236 | |
| 237 | /* --- @sub_alloc@ --- * |
| 238 | * |
| 239 | * Arguments: @size_t s@ = size of chunk wanted |
| 240 | * |
| 241 | * Returns: Pointer to a block at least as large as the one wanted. |
| 242 | * |
| 243 | * Use: Allocates a small block of memory from the @sub_global@ pool. |
| 244 | */ |
| 245 | |
| 246 | void *(sub_alloc)(size_t sz) { return sub_alloc(sz); } |
| 247 | |
| 248 | /* --- @sub_free@ --- * |
| 249 | * |
| 250 | * Arguments: @void *p@ = address of block to free |
| 251 | * @size_t s@ = size of block |
| 252 | * |
| 253 | * Returns: --- |
| 254 | * |
| 255 | * Use: Frees a block allocated by @sub_alloc@. |
| 256 | */ |
| 257 | |
| 258 | void (sub_free)(void *p, size_t sz) { sub_free(p, sz); } |
| 259 | |
| 260 | /* --- @sub_init@ --- * |
| 261 | * |
| 262 | * Arguments: --- |
| 263 | * |
| 264 | * Returns: --- |
| 265 | * |
| 266 | * Use: Initializes the magic allocator. |
| 267 | */ |
| 268 | |
| 269 | void sub_init(void) |
| 270 | { |
| 271 | int i; |
| 272 | |
| 273 | /* --- Initialize the sizes bins --- */ |
| 274 | |
| 275 | for (i = 1; i < SUB_BINS; i++) { |
| 276 | sizes[i] = ((SUB_CHUNK + SUB_BINSZ(i) - 1) / |
| 277 | SUB_BINSZ(i) * SUB_BINSZ(i)); |
| 278 | } |
| 279 | } |
| 280 | |
| 281 | /*----- Debugging code ----------------------------------------------------*/ |
| 282 | |
| 283 | #ifdef TEST_RIG |
| 284 | |
| 285 | #define BLOCKS 1024 |
| 286 | #define SIZE_MAX 2048 |
| 287 | #define ITERATIONS 500000 |
| 288 | |
| 289 | int main(void) |
| 290 | { |
| 291 | static void *block[BLOCKS]; |
| 292 | static size_t size[BLOCKS]; |
| 293 | size_t allocced = 0; |
| 294 | int i; |
| 295 | long count; |
| 296 | |
| 297 | sub_init(); |
| 298 | |
| 299 | for (count = 0; count < ITERATIONS; count++) { |
| 300 | i = rand() % BLOCKS; |
| 301 | if (block[i]) { |
| 302 | sub_free(block[i], size[i]); |
| 303 | block[i] = 0; |
| 304 | allocced -= size[i]; |
| 305 | } else { |
| 306 | block[i] = sub_alloc(size[i] = |
| 307 | rand() % (SUB_MAXBIN - 128) + 128); |
| 308 | allocced += size[i]; |
| 309 | memset(block[i], 0, size[i]); /* trample allocated storage */ |
| 310 | } |
| 311 | } |
| 312 | |
| 313 | return (0); |
| 314 | } |
| 315 | |
| 316 | #endif |
| 317 | |
| 318 | /*----- That's all, folks -------------------------------------------------*/ |