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1 | /* -*-c-*- |
2 | * |
3 | * $Id: sub.c,v 1.1 1998/06/17 23:44:42 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 General Public License as published by |
16 | * the Free Software Foundation; either version 2 of the License, or |
17 | * (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 General Public License for more details. |
23 | * |
24 | * You should have received a copy of the GNU General Public License |
25 | * along with mLib; if not, write to the Free Software Foundation, |
26 | * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
27 | */ |
28 | |
29 | /*----- Revision history --------------------------------------------------* |
30 | * |
31 | * $Log: sub.c,v $ |
32 | * Revision 1.1 1998/06/17 23:44:42 mdw |
33 | * Initial revision |
34 | * |
35 | */ |
36 | |
37 | /*----- The big idea ------------------------------------------------------* |
38 | * |
39 | * This file provides an extra layer over @malloc@. It provides fast |
40 | * turnover for small blocks, and tries to minimise the per-block overhead. |
41 | * |
42 | * To do its job, @alloc@ must place an extra restriction on you: you must |
43 | * know the size of a block when you free it. Usually you'll have this |
44 | * information encoded in some way either in the block or in the thing that |
45 | * referenced it, so this isn't a hardship. |
46 | * |
47 | * It works fairly simply. If a request for a big block (as defined by the |
48 | * constants below) comes in, it gets sent on to @malloc@ unmolested. For |
49 | * small blocks, it goes straight to a `bin' -- a list containing free blocks |
50 | * of exactly that size, or the nearest bigger size we can manage. If the |
51 | * bin is empty, a `chunk' is allocated from @malloc@: this has enough room |
52 | * for lots of blocks of the requested size, so it ets split up and each |
53 | * individual small block is added to the bin list. The first block in the |
54 | * bin list is then removed and given to the caller. In this way, @malloc@ |
55 | * only stores its information once for lots of little blocks, so we save |
56 | * memory. Because I know where the correct bin is just from the block size, |
57 | * and I don't need to do any searching at all in the usual case (because the |
58 | * list isn't empty) I can get a speed advantage too. |
59 | * |
60 | * This code is almost certainly not ANSI conformant, although I'm not |
61 | * actually sure. If some kind soul would let me know how seriously I've |
62 | * violated the standard, and whether this is easily fixable, I'd be |
63 | * grateful. |
64 | */ |
65 | |
66 | /*----- Header files ------------------------------------------------------*/ |
67 | |
68 | /* --- ANSI headers --- */ |
69 | |
70 | #include <stdio.h> |
71 | #include <stdlib.h> |
72 | #include <string.h> |
73 | |
74 | /* --- Local headers --- */ |
75 | |
76 | #undef TRACK_ENABLE /* Can't track suballoc routines */ |
77 | #include "alloc.h" |
78 | |
79 | /*----- Configuration and tuning ------------------------------------------*/ |
80 | |
81 | /* --- The largest block I'll handle here --- * |
82 | * |
83 | * Anything larger will be handed on to @malloc@. |
84 | */ |
85 | |
86 | #define SUB_MAXBIN 256 |
87 | |
88 | /* --- Preferred chunk size --- * |
89 | * |
90 | * When a bin is empty, I'll allocate a large chunk of approximately this |
91 | * size and divvy it up into small bin-sized blocks. |
92 | */ |
93 | |
94 | #define SUB_CHUNK 4096 |
95 | |
96 | /*----- Other useful macros -----------------------------------------------*/ |
97 | |
98 | /* --- The granularity of bin buffers --- * |
99 | * |
100 | * All blocks allocated by the binner are a multiple of this size. I've |
101 | * chosen @void *@ because I need to store @void *@ things in here. |
102 | */ |
103 | |
104 | #define SUB_GRANULE sizeof(void *) |
105 | |
106 | /* --- Finding the right bin for a given size --- * |
107 | * |
108 | * This chooses the correct bin for an allocation. Input is the size of |
109 | * block wanted; result is the bin index. |
110 | */ |
111 | |
112 | #define SUB_BIN(x) (((x) + SUB_GRANULE - 1) / SUB_GRANULE) |
113 | |
114 | /* --- Convert a bin back to the block size --- * |
115 | * |
116 | * This gives the size of block contained in a given bin. |
117 | */ |
118 | |
119 | #define SUB_BINSZ(x) ((x) * SUB_GRANULE) |
120 | |
121 | /* --- Number of bins required --- */ |
122 | |
123 | #define SUB_BINS (SUB_MAXBIN / SUB_GRANULE + 1) |
124 | |
125 | /*----- Static variables --------------------------------------------------*/ |
126 | |
127 | static void *sub__bins[SUB_BINS]; |
128 | static size_t sub__sizes[SUB_BINS]; |
129 | |
130 | /*----- Main code ---------------------------------------------------------*/ |
131 | |
132 | /* --- @sub_alloc@ --- * |
133 | * |
134 | * Arguments: @size_t s@ = size of chunk wanted |
135 | * |
136 | * Returns: Pointer to a block at least as large as the one wanted. |
137 | * |
138 | * Use: Allocates a small block of memory. If there is no more |
139 | * memory left, the exception @EXC_NOMEM@ is raised. |
140 | */ |
141 | |
142 | void *sub_alloc(size_t s) |
143 | { |
144 | int bin = SUB_BIN(s); |
145 | void *p; |
146 | |
147 | /* --- Handle oversize blocks --- */ |
148 | |
149 | if (bin >= SUB_BINS) |
150 | return (xmalloc(s)); |
151 | |
152 | /* --- If the bin is empty, find some memory --- */ |
153 | |
154 | if (!sub__bins[bin]) { |
155 | char *p, *q; |
156 | |
157 | p = xmalloc(sub__sizes[bin]); |
158 | q = p + sub__sizes[bin]; |
159 | |
160 | s = SUB_BINSZ(bin); |
161 | |
162 | q -= s; |
163 | *(void **)q = 0; |
164 | |
165 | while (q > p) { |
166 | q -= s; |
167 | *(void **)q = q + s; |
168 | } |
169 | |
170 | sub__bins[bin] = p; |
171 | } |
172 | |
173 | /* --- Extract the first block in the list --- */ |
174 | |
175 | p = sub__bins[bin]; |
176 | sub__bins[bin] = *(void **)p; |
177 | return (p); |
178 | } |
179 | |
180 | /* --- @sub_free@ --- * |
181 | * |
182 | * Arguments: @void *p@ = address of block to free |
183 | * @size_t s@ = size of block |
184 | * |
185 | * Returns: --- |
186 | * |
187 | * Use: Frees a block allocated by @sub_alloc@. |
188 | */ |
189 | |
190 | void sub_free(void *p, size_t s) |
191 | { |
192 | int bin = SUB_BIN(s); |
193 | |
194 | if (bin >= SUB_BINS) |
195 | free(p); |
196 | else { |
197 | *(void **)p = sub__bins[bin]; |
198 | sub__bins[bin] = p; |
199 | } |
200 | } |
201 | |
202 | /* --- @sub_init@ --- * |
203 | * |
204 | * Arguments: --- |
205 | * |
206 | * Returns: --- |
207 | * |
208 | * Use: Initialises the magic allocator. |
209 | */ |
210 | |
211 | void sub_init(void) |
212 | { |
213 | int i; |
214 | |
215 | /* --- Initialise the sizes bins --- */ |
216 | |
217 | for (i = 1; i < SUB_BINS; i++) { |
218 | sub__sizes[i] = ((SUB_CHUNK + SUB_BINSZ(i) - 1) / |
219 | SUB_BINSZ(i) * SUB_BINSZ(i)); |
220 | } |
221 | } |
222 | |
223 | /*----- Debugging code ----------------------------------------------------*/ |
224 | |
225 | #ifdef TEST_RIG |
226 | |
227 | #define BLOCKS 1024 |
228 | #define SIZE_MAX 2048 |
229 | #define ITERATIONS 500000 |
230 | |
231 | int main(void) |
232 | { |
233 | static void *block[BLOCKS]; |
234 | static size_t size[BLOCKS]; |
235 | size_t allocced = 0; |
236 | int i; |
237 | long count; |
238 | |
239 | sub_init(); |
240 | |
241 | for (count = 0; count < ITERATIONS; count++) { |
242 | i = rand() % BLOCKS; |
243 | if (block[i]) { |
244 | sub_free(block[i], size[i]); |
245 | block[i] = 0; |
246 | allocced -= size[i]; |
247 | } else { |
248 | block[i] = sub_alloc(size[i] = |
249 | rand() % (SUB_MAXBIN - 128) + 128); |
250 | allocced += size[i]; |
251 | memset(block[i], 0, size[i]); /* trample allocated storage */ |
252 | } |
253 | } |
254 | |
255 | return (0); |
256 | } |
257 | |
258 | #endif |
259 | |
260 | /*----- That's all, folks -------------------------------------------------*/ |