1 /* objalloc.c -- routines to allocate memory for objects
2    Copyright 1997-2012 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 /* Get a definition for size_t.  */
34 #include <stddef.h>
35 
36 #ifdef HAVE_STDLIB_H
37 #include <stdlib.h>
38 #else
39 /* For systems with larger pointers than ints, this must be declared.  */
40 extern PTR malloc (size_t);
41 extern void free (PTR);
42 #endif
43 
44 #endif
45 
46 /* These routines allocate space for an object.  Freeing allocated
47    space may or may not free all more recently allocated space.
48 
49    We handle large and small allocation requests differently.  If we
50    don't have enough space in the current block, and the allocation
51    request is for more than 512 bytes, we simply pass it through to
52    malloc.  */
53 
54 /* The objalloc structure is defined in objalloc.h.  */
55 
56 /* This structure appears at the start of each chunk.  */
57 
58 struct objalloc_chunk
59 {
60   /* Next chunk.  */
61   struct objalloc_chunk *next;
62   /* If this chunk contains large objects, this is the value of
63      current_ptr when this chunk was allocated.  If this chunk
64      contains small objects, this is NULL.  */
65   char *current_ptr;
66 };
67 
68 /* The aligned size of objalloc_chunk.  */
69 
70 #define CHUNK_HEADER_SIZE					\
71   ((sizeof (struct objalloc_chunk) + OBJALLOC_ALIGN - 1)	\
72    &~ (OBJALLOC_ALIGN - 1))
73 
74 /* We ask for this much memory each time we create a chunk which is to
75    hold small objects.  */
76 
77 #define CHUNK_SIZE (4096 - 32)
78 
79 /* A request for this amount or more is just passed through to malloc.  */
80 
81 #define BIG_REQUEST (512)
82 
83 /* Create an objalloc structure.  */
84 
85 struct objalloc *
objalloc_create(void)86 objalloc_create (void)
87 {
88   struct objalloc *ret;
89   struct objalloc_chunk *chunk;
90 
91   ret = (struct objalloc *) malloc (sizeof *ret);
92   if (ret == NULL)
93     return NULL;
94 
95   ret->chunks = (PTR) malloc (CHUNK_SIZE);
96   if (ret->chunks == NULL)
97     {
98       free (ret);
99       return NULL;
100     }
101 
102   chunk = (struct objalloc_chunk *) ret->chunks;
103   chunk->next = NULL;
104   chunk->current_ptr = NULL;
105 
106   ret->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
107   ret->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
108 
109   return ret;
110 }
111 
112 /* Allocate space from an objalloc structure.  */
113 
114 PTR
_objalloc_alloc(struct objalloc * o,unsigned long original_len)115 _objalloc_alloc (struct objalloc *o, unsigned long original_len)
116 {
117   unsigned long len = original_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   /* Check for overflow in the alignment operation above and the
127      malloc argument below. */
128   if (len + CHUNK_HEADER_SIZE < original_len)
129     return NULL;
130 
131   if (len <= o->current_space)
132     {
133       o->current_ptr += len;
134       o->current_space -= len;
135       return (PTR) (o->current_ptr - len);
136     }
137 
138   if (len >= BIG_REQUEST)
139     {
140       char *ret;
141       struct objalloc_chunk *chunk;
142 
143       ret = (char *) malloc (CHUNK_HEADER_SIZE + len);
144       if (ret == NULL)
145 	return NULL;
146 
147       chunk = (struct objalloc_chunk *) ret;
148       chunk->next = (struct objalloc_chunk *) o->chunks;
149       chunk->current_ptr = o->current_ptr;
150 
151       o->chunks = (PTR) chunk;
152 
153       return (PTR) (ret + CHUNK_HEADER_SIZE);
154     }
155   else
156     {
157       struct objalloc_chunk *chunk;
158 
159       chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);
160       if (chunk == NULL)
161 	return NULL;
162       chunk->next = (struct objalloc_chunk *) o->chunks;
163       chunk->current_ptr = NULL;
164 
165       o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
166       o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
167 
168       o->chunks = (PTR) chunk;
169 
170       return objalloc_alloc (o, len);
171     }
172 }
173 
174 /* Free an entire objalloc structure.  */
175 
176 void
objalloc_free(struct objalloc * o)177 objalloc_free (struct objalloc *o)
178 {
179   struct objalloc_chunk *l;
180 
181   l = (struct objalloc_chunk *) o->chunks;
182   while (l != NULL)
183     {
184       struct objalloc_chunk *next;
185 
186       next = l->next;
187       free (l);
188       l = next;
189     }
190 
191   free (o);
192 }
193 
194 /* Free a block from an objalloc structure.  This also frees all more
195    recently allocated blocks.  */
196 
197 void
objalloc_free_block(struct objalloc * o,PTR block)198 objalloc_free_block (struct objalloc *o, PTR block)
199 {
200   struct objalloc_chunk *p, *small;
201   char *b = (char *) block;
202 
203   /* First set P to the chunk which contains the block we are freeing,
204      and set Q to the last small object chunk we see before P.  */
205   small = NULL;
206   for (p = (struct objalloc_chunk *) o->chunks; p != NULL; p = p->next)
207     {
208       if (p->current_ptr == NULL)
209 	{
210 	  if (b > (char *) p && b < (char *) p + CHUNK_SIZE)
211 	    break;
212 	  small = p;
213 	}
214       else
215 	{
216 	  if (b == (char *) p + CHUNK_HEADER_SIZE)
217 	    break;
218 	}
219     }
220 
221   /* If we can't find the chunk, the caller has made a mistake.  */
222   if (p == NULL)
223     abort ();
224 
225   if (p->current_ptr == NULL)
226     {
227       struct objalloc_chunk *q;
228       struct objalloc_chunk *first;
229 
230       /* The block is in a chunk containing small objects.  We can
231 	 free every chunk through SMALL, because they have certainly
232 	 been allocated more recently.  After SMALL, we will not see
233 	 any chunks containing small objects; we can free any big
234 	 chunk if the current_ptr is greater than or equal to B.  We
235 	 can then reset the new current_ptr to B.  */
236 
237       first = NULL;
238       q = (struct objalloc_chunk *) o->chunks;
239       while (q != p)
240 	{
241 	  struct objalloc_chunk *next;
242 
243 	  next = q->next;
244 	  if (small != NULL)
245 	    {
246 	      if (small == q)
247 		small = NULL;
248 	      free (q);
249 	    }
250 	  else if (q->current_ptr > b)
251 	    free (q);
252 	  else if (first == NULL)
253 	    first = q;
254 
255 	  q = next;
256 	}
257 
258       if (first == NULL)
259 	first = p;
260       o->chunks = (PTR) first;
261 
262       /* Now start allocating from this small block again.  */
263       o->current_ptr = b;
264       o->current_space = ((char *) p + CHUNK_SIZE) - b;
265     }
266   else
267     {
268       struct objalloc_chunk *q;
269       char *current_ptr;
270 
271       /* This block is in a large chunk by itself.  We can free
272          everything on the list up to and including this block.  We
273          then start allocating from the next chunk containing small
274          objects, setting current_ptr from the value stored with the
275          large chunk we are freeing.  */
276 
277       current_ptr = p->current_ptr;
278       p = p->next;
279 
280       q = (struct objalloc_chunk *) o->chunks;
281       while (q != p)
282 	{
283 	  struct objalloc_chunk *next;
284 
285 	  next = q->next;
286 	  free (q);
287 	  q = next;
288 	}
289 
290       o->chunks = (PTR) p;
291 
292       while (p->current_ptr != NULL)
293 	p = p->next;
294 
295       o->current_ptr = current_ptr;
296       o->current_space = ((char *) p + CHUNK_SIZE) - current_ptr;
297     }
298 }
299