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 #ifdef ANSI_PROTOTYPES
34 /* Get a definition for size_t. */
35 #include <stddef.h>
36 #endif
37
38 #ifdef HAVE_STDLIB_H
39 #include <stdlib.h>
40 #else
41 /* For systems with larger pointers than ints, this must be declared. */
42 extern PTR malloc (size_t);
43 extern void free (PTR);
44 #endif
45
46 #endif
47
48 /* These routines allocate space for an object. Freeing allocated
49 space may or may not free all more recently allocated space.
50
51 We handle large and small allocation requests differently. If we
52 don't have enough space in the current block, and the allocation
53 request is for more than 512 bytes, we simply pass it through to
54 malloc. */
55
56 /* The objalloc structure is defined in objalloc.h. */
57
58 /* This structure appears at the start of each chunk. */
59
60 struct objalloc_chunk
61 {
62 /* Next chunk. */
63 struct objalloc_chunk *next;
64 /* If this chunk contains large objects, this is the value of
65 current_ptr when this chunk was allocated. If this chunk
66 contains small objects, this is NULL. */
67 char *current_ptr;
68 };
69
70 /* The aligned size of objalloc_chunk. */
71
72 #define CHUNK_HEADER_SIZE \
73 ((sizeof (struct objalloc_chunk) + OBJALLOC_ALIGN - 1) \
74 &~ (OBJALLOC_ALIGN - 1))
75
76 /* We ask for this much memory each time we create a chunk which is to
77 hold small objects. */
78
79 #define CHUNK_SIZE (4096 - 32)
80
81 /* A request for this amount or more is just passed through to malloc. */
82
83 #define BIG_REQUEST (512)
84
85 /* Create an objalloc structure. */
86
87 struct objalloc *
objalloc_create(void)88 objalloc_create (void)
89 {
90 struct objalloc *ret;
91 struct objalloc_chunk *chunk;
92
93 ret = (struct objalloc *) malloc (sizeof *ret);
94 if (ret == NULL)
95 return NULL;
96
97 ret->chunks = (PTR) malloc (CHUNK_SIZE);
98 if (ret->chunks == NULL)
99 {
100 free (ret);
101 return NULL;
102 }
103
104 chunk = (struct objalloc_chunk *) ret->chunks;
105 chunk->next = NULL;
106 chunk->current_ptr = NULL;
107
108 ret->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
109 ret->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
110
111 return ret;
112 }
113
114 /* Allocate space from an objalloc structure. */
115
116 PTR
_objalloc_alloc(struct objalloc * o,unsigned long len)117 _objalloc_alloc (struct objalloc *o, unsigned long len)
118 {
119 /* We avoid confusion from zero sized objects by always allocating
120 at least 1 byte. */
121 if (len == 0)
122 len = 1;
123
124 len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);
125
126 if (len <= o->current_space)
127 {
128 o->current_ptr += len;
129 o->current_space -= len;
130 return (PTR) (o->current_ptr - len);
131 }
132
133 if (len >= BIG_REQUEST)
134 {
135 char *ret;
136 struct objalloc_chunk *chunk;
137
138 ret = (char *) malloc (CHUNK_HEADER_SIZE + len);
139 if (ret == NULL)
140 return NULL;
141
142 chunk = (struct objalloc_chunk *) ret;
143 chunk->next = (struct objalloc_chunk *) o->chunks;
144 chunk->current_ptr = o->current_ptr;
145
146 o->chunks = (PTR) chunk;
147
148 return (PTR) (ret + CHUNK_HEADER_SIZE);
149 }
150 else
151 {
152 struct objalloc_chunk *chunk;
153
154 chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);
155 if (chunk == NULL)
156 return NULL;
157 chunk->next = (struct objalloc_chunk *) o->chunks;
158 chunk->current_ptr = NULL;
159
160 o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
161 o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
162
163 o->chunks = (PTR) chunk;
164
165 return objalloc_alloc (o, len);
166 }
167 }
168
169 /* Free an entire objalloc structure. */
170
171 void
objalloc_free(struct objalloc * o)172 objalloc_free (struct objalloc *o)
173 {
174 struct objalloc_chunk *l;
175
176 l = (struct objalloc_chunk *) o->chunks;
177 while (l != NULL)
178 {
179 struct objalloc_chunk *next;
180
181 next = l->next;
182 free (l);
183 l = next;
184 }
185
186 free (o);
187 }
188
189 /* Free a block from an objalloc structure. This also frees all more
190 recently allocated blocks. */
191
192 void
objalloc_free_block(struct objalloc * o,PTR block)193 objalloc_free_block (struct objalloc *o, PTR block)
194 {
195 struct objalloc_chunk *p, *small;
196 char *b = (char *) block;
197
198 /* First set P to the chunk which contains the block we are freeing,
199 and set Q to the last small object chunk we see before P. */
200 small = NULL;
201 for (p = (struct objalloc_chunk *) o->chunks; p != NULL; p = p->next)
202 {
203 if (p->current_ptr == NULL)
204 {
205 if (b > (char *) p && b < (char *) p + CHUNK_SIZE)
206 break;
207 small = p;
208 }
209 else
210 {
211 if (b == (char *) p + CHUNK_HEADER_SIZE)
212 break;
213 }
214 }
215
216 /* If we can't find the chunk, the caller has made a mistake. */
217 if (p == NULL)
218 abort ();
219
220 if (p->current_ptr == NULL)
221 {
222 struct objalloc_chunk *q;
223 struct objalloc_chunk *first;
224
225 /* The block is in a chunk containing small objects. We can
226 free every chunk through SMALL, because they have certainly
227 been allocated more recently. After SMALL, we will not see
228 any chunks containing small objects; we can free any big
229 chunk if the current_ptr is greater than or equal to B. We
230 can then reset the new current_ptr to B. */
231
232 first = NULL;
233 q = (struct objalloc_chunk *) o->chunks;
234 while (q != p)
235 {
236 struct objalloc_chunk *next;
237
238 next = q->next;
239 if (small != NULL)
240 {
241 if (small == q)
242 small = NULL;
243 free (q);
244 }
245 else if (q->current_ptr > b)
246 free (q);
247 else if (first == NULL)
248 first = q;
249
250 q = next;
251 }
252
253 if (first == NULL)
254 first = p;
255 o->chunks = (PTR) first;
256
257 /* Now start allocating from this small block again. */
258 o->current_ptr = b;
259 o->current_space = ((char *) p + CHUNK_SIZE) - b;
260 }
261 else
262 {
263 struct objalloc_chunk *q;
264 char *current_ptr;
265
266 /* This block is in a large chunk by itself. We can free
267 everything on the list up to and including this block. We
268 then start allocating from the next chunk containing small
269 objects, setting current_ptr from the value stored with the
270 large chunk we are freeing. */
271
272 current_ptr = p->current_ptr;
273 p = p->next;
274
275 q = (struct objalloc_chunk *) o->chunks;
276 while (q != p)
277 {
278 struct objalloc_chunk *next;
279
280 next = q->next;
281 free (q);
282 q = next;
283 }
284
285 o->chunks = (PTR) p;
286
287 while (p->current_ptr != NULL)
288 p = p->next;
289
290 o->current_ptr = current_ptr;
291 o->current_space = ((char *) p + CHUNK_SIZE) - current_ptr;
292 }
293 }
294