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
5This program is free software; you can redistribute it and/or modify it
6under the terms of the GNU General Public License as published by the
7Free Software Foundation; either version 2, or (at your option) any
8later version.
9
10This program is distributed in the hope that it will be useful,
11but WITHOUT ANY WARRANTY; without even the implied warranty of
12MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13GNU General Public License for more details.
14
15You should have received a copy of the GNU General Public License
16along with this program; if not, write to the Free Software
17Foundation, 51 Franklin Street - Fifth Floor,
18Boston, 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.  */
40extern PTR malloc (size_t);
41extern 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
58struct 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
85struct objalloc *
86objalloc_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
114PTR
115_objalloc_alloc (struct objalloc *o, unsigned long len)
116{
117  /* We avoid confusion from zero sized objects by always allocating
118     at least 1 byte.  */
119  if (len == 0)
120    len = 1;
121
122  len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);
123
124  if (len <= o->current_space)
125    {
126      o->current_ptr += len;
127      o->current_space -= len;
128      return (PTR) (o->current_ptr - len);
129    }
130
131  if (len >= BIG_REQUEST)
132    {
133      char *ret;
134      struct objalloc_chunk *chunk;
135
136      ret = (char *) malloc (CHUNK_HEADER_SIZE + len);
137      if (ret == NULL)
138	return NULL;
139
140      chunk = (struct objalloc_chunk *) ret;
141      chunk->next = (struct objalloc_chunk *) o->chunks;
142      chunk->current_ptr = o->current_ptr;
143
144      o->chunks = (PTR) chunk;
145
146      return (PTR) (ret + CHUNK_HEADER_SIZE);
147    }
148  else
149    {
150      struct objalloc_chunk *chunk;
151
152      chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);
153      if (chunk == NULL)
154	return NULL;
155      chunk->next = (struct objalloc_chunk *) o->chunks;
156      chunk->current_ptr = NULL;
157
158      o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
159      o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
160
161      o->chunks = (PTR) chunk;
162
163      return objalloc_alloc (o, len);
164    }
165}
166
167/* Free an entire objalloc structure.  */
168
169void
170objalloc_free (struct objalloc *o)
171{
172  struct objalloc_chunk *l;
173
174  l = (struct objalloc_chunk *) o->chunks;
175  while (l != NULL)
176    {
177      struct objalloc_chunk *next;
178
179      next = l->next;
180      free (l);
181      l = next;
182    }
183
184  free (o);
185}
186
187/* Free a block from an objalloc structure.  This also frees all more
188   recently allocated blocks.  */
189
190void
191objalloc_free_block (struct objalloc *o, PTR block)
192{
193  struct objalloc_chunk *p, *small;
194  char *b = (char *) block;
195
196  /* First set P to the chunk which contains the block we are freeing,
197     and set Q to the last small object chunk we see before P.  */
198  small = NULL;
199  for (p = (struct objalloc_chunk *) o->chunks; p != NULL; p = p->next)
200    {
201      if (p->current_ptr == NULL)
202	{
203	  if (b > (char *) p && b < (char *) p + CHUNK_SIZE)
204	    break;
205	  small = p;
206	}
207      else
208	{
209	  if (b == (char *) p + CHUNK_HEADER_SIZE)
210	    break;
211	}
212    }
213
214  /* If we can't find the chunk, the caller has made a mistake.  */
215  if (p == NULL)
216    abort ();
217
218  if (p->current_ptr == NULL)
219    {
220      struct objalloc_chunk *q;
221      struct objalloc_chunk *first;
222
223      /* The block is in a chunk containing small objects.  We can
224	 free every chunk through SMALL, because they have certainly
225	 been allocated more recently.  After SMALL, we will not see
226	 any chunks containing small objects; we can free any big
227	 chunk if the current_ptr is greater than or equal to B.  We
228	 can then reset the new current_ptr to B.  */
229
230      first = NULL;
231      q = (struct objalloc_chunk *) o->chunks;
232      while (q != p)
233	{
234	  struct objalloc_chunk *next;
235
236	  next = q->next;
237	  if (small != NULL)
238	    {
239	      if (small == q)
240		small = NULL;
241	      free (q);
242	    }
243	  else if (q->current_ptr > b)
244	    free (q);
245	  else if (first == NULL)
246	    first = q;
247
248	  q = next;
249	}
250
251      if (first == NULL)
252	first = p;
253      o->chunks = (PTR) first;
254
255      /* Now start allocating from this small block again.  */
256      o->current_ptr = b;
257      o->current_space = ((char *) p + CHUNK_SIZE) - b;
258    }
259  else
260    {
261      struct objalloc_chunk *q;
262      char *current_ptr;
263
264      /* This block is in a large chunk by itself.  We can free
265         everything on the list up to and including this block.  We
266         then start allocating from the next chunk containing small
267         objects, setting current_ptr from the value stored with the
268         large chunk we are freeing.  */
269
270      current_ptr = p->current_ptr;
271      p = p->next;
272
273      q = (struct objalloc_chunk *) o->chunks;
274      while (q != p)
275	{
276	  struct objalloc_chunk *next;
277
278	  next = q->next;
279	  free (q);
280	  q = next;
281	}
282
283      o->chunks = (PTR) p;
284
285      while (p->current_ptr != NULL)
286	p = p->next;
287
288      o->current_ptr = current_ptr;
289      o->current_space = ((char *) p + CHUNK_SIZE) - current_ptr;
290    }
291}
292