1 /* -*- mode: C; c-file-style: "gnu" -*- */
2 /* dbus-mempool.h Memory pools
4 * Copyright (C) 2002, 2003 Red Hat, Inc.
6 * Licensed under the Academic Free License version 1.2
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
24 #include "dbus-mempool.h"
27 * @defgroup DBusMemPool memory pools
28 * @ingroup DBusInternals
29 * @brief DBusMemPool object
31 * Types and functions related to DBusMemPool. A memory pool is used
32 * to decrease memory fragmentation/overhead and increase speed for
33 * blocks of small uniformly-sized objects. The main point is to avoid
34 * the overhead of a malloc block for each small object, speed is
39 * @defgroup DBusMemPoolInternals Memory pool implementation details
40 * @ingroup DBusInternals
41 * @brief DBusMemPool implementation details
43 * The guts of DBusMemPool.
49 * typedef so DBusFreedElement struct can refer to itself.
51 typedef struct DBusFreedElement DBusFreedElement;
54 * struct representing an element on the free list.
55 * We just cast freed elements to this so we can
56 * make a list out of them.
58 struct DBusFreedElement
60 DBusFreedElement *next; /**< next element of the free list */
64 * The dummy size of the variable-length "elements"
65 * field in DBusMemBlock
67 #define ELEMENT_PADDING 4
70 * Typedef for DBusMemBlock so the struct can recursively
73 typedef struct DBusMemBlock DBusMemBlock;
76 * DBusMemBlock object represents a single malloc()-returned
77 * block that gets chunked up into objects in the memory pool.
81 DBusMemBlock *next; /**< next block in the list, which is already used up;
82 * only saved so we can free all the blocks
83 * when we free the mem pool.
86 int used_so_far; /**< bytes of this block already allocated as elements. */
88 unsigned char elements[ELEMENT_PADDING]; /**< the block data, actually allocated to required size */
92 * Internals fields of DBusMemPool
96 int element_size; /**< size of a single object in the pool */
97 int block_size; /**< size of most recently allocated block */
98 unsigned int zero_elements : 1; /**< whether to zero-init allocated elements */
100 DBusFreedElement *free_elements; /**< a free list of elements to recycle */
101 DBusMemBlock *blocks; /**< blocks of memory from malloc() */
107 * @addtogroup DBusMemPool
113 * @typedef DBusMemPool
115 * Opaque object representing a memory pool. Memory pools allow
116 * avoiding per-malloc-block memory overhead when allocating a lot of
117 * small objects that are all the same size. They are slightly
118 * faster than calling malloc() also.
122 * Creates a new memory pool, or returns #NULL on failure. Objects in
123 * the pool must be at least sizeof(void*) bytes each, due to the way
124 * memory pools work. To avoid creating 64 bit problems, this means at
125 * least 8 bytes on all platforms, unless you are 4 bytes on 32-bit
126 * and 8 bytes on 64-bit.
128 * @param element_size size of an element allocated from the pool.
129 * @param zero_elements whether to zero-initialize elements
130 * @returns the new pool or #NULL
133 _dbus_mem_pool_new (int element_size,
134 dbus_bool_t zero_elements)
138 pool = dbus_new0 (DBusMemPool, 1);
142 /* these assertions are equivalent but the first is more clear
143 * to programmers that see it fail.
145 _dbus_assert (element_size >= (int) sizeof (void*));
146 _dbus_assert (element_size >= (int) sizeof (DBusFreedElement));
148 /* align the element size to a pointer boundary so we won't get bus
149 * errors under other architectures.
151 pool->element_size = _DBUS_ALIGN_VALUE (element_size, sizeof (void *));
153 pool->zero_elements = zero_elements != FALSE;
155 /* pick a size for the first block; it increases
156 * for each block we need to allocate. This is
157 * actually half the initial block size
158 * since _dbus_mem_pool_alloc() unconditionally
159 * doubles it prior to creating a new block. */
160 pool->block_size = pool->element_size * 8;
162 _dbus_assert ((pool->block_size %
163 pool->element_size) == 0);
169 * Frees a memory pool (and all elements allocated from it).
171 * @param pool the memory pool.
174 _dbus_mem_pool_free (DBusMemPool *pool)
178 block = pool->blocks;
179 while (block != NULL)
181 DBusMemBlock *next = block->next;
192 * Allocates an object from the memory pool.
193 * The object must be freed with _dbus_mem_pool_dealloc().
195 * @param pool the memory pool
196 * @returns the allocated object or #NULL if no memory.
199 _dbus_mem_pool_alloc (DBusMemPool *pool)
201 if (_dbus_decrement_fail_alloc_counter ())
204 if (pool->free_elements)
206 DBusFreedElement *element = pool->free_elements;
208 pool->free_elements = pool->free_elements->next;
210 if (pool->zero_elements)
211 memset (element, '\0', pool->element_size);
219 if (pool->blocks == NULL ||
220 pool->blocks->used_so_far == pool->block_size)
222 /* Need a new block */
225 #ifdef DBUS_BUILD_TESTS
229 if (pool->block_size <= _DBUS_INT_MAX / 4) /* avoid overflow */
231 /* use a larger block size for our next block */
232 pool->block_size *= 2;
233 _dbus_assert ((pool->block_size %
234 pool->element_size) == 0);
237 alloc_size = sizeof (DBusMemBlock) - ELEMENT_PADDING + pool->block_size;
239 #ifdef DBUS_BUILD_TESTS
240 /* We save/restore the counter, so that memory pools won't
241 * cause a given function to have different number of
242 * allocations on different invocations. i.e. when testing
243 * we want consistent alloc patterns. So we skip our
244 * malloc here for purposes of failed alloc simulation.
246 saved_counter = _dbus_get_fail_alloc_counter ();
247 _dbus_set_fail_alloc_counter (_DBUS_INT_MAX);
250 if (pool->zero_elements)
251 block = dbus_malloc0 (alloc_size);
253 block = dbus_malloc (alloc_size);
255 #ifdef DBUS_BUILD_TESTS
256 _dbus_set_fail_alloc_counter (saved_counter);
262 block->used_so_far = 0;
263 block->next = pool->blocks;
264 pool->blocks = block;
267 element = &pool->blocks->elements[pool->blocks->used_so_far];
269 pool->blocks->used_so_far += pool->element_size;
276 * Deallocates an object previously created with
277 * _dbus_mem_pool_alloc(). The previous object
278 * must have come from this same pool.
279 * @param pool the memory pool
280 * @param element the element earlier allocated.
283 _dbus_mem_pool_dealloc (DBusMemPool *pool,
286 DBusFreedElement *freed;
289 freed->next = pool->free_elements;
290 pool->free_elements = freed;
295 #ifdef DBUS_BUILD_TESTS
296 #include "dbus-test.h"
301 time_for_size (int size)
307 #define FREE_ARRAY_SIZE 512
308 #define N_ITERATIONS FREE_ARRAY_SIZE * 512
309 void *to_free[FREE_ARRAY_SIZE];
312 _dbus_verbose ("Timings for size %d\n", size);
314 _dbus_verbose (" malloc\n");
320 while (i < N_ITERATIONS)
322 to_free[j] = dbus_malloc (size);
323 _dbus_assert (to_free[j] != NULL); /* in a real app of course this is wrong */
327 if (j == FREE_ARRAY_SIZE)
330 while (j < FREE_ARRAY_SIZE)
332 dbus_free (to_free[j]);
344 _dbus_verbose (" created/destroyed %d elements in %g seconds\n",
345 N_ITERATIONS, (end - start) / (double) CLOCKS_PER_SEC);
349 _dbus_verbose (" mempools\n");
353 pool = _dbus_mem_pool_new (size, FALSE);
357 while (i < N_ITERATIONS)
359 to_free[j] = _dbus_mem_pool_alloc (pool);
360 _dbus_assert (to_free[j] != NULL); /* in a real app of course this is wrong */
364 if (j == FREE_ARRAY_SIZE)
367 while (j < FREE_ARRAY_SIZE)
369 _dbus_mem_pool_dealloc (pool, to_free[j]);
379 _dbus_mem_pool_free (pool);
383 _dbus_verbose (" created/destroyed %d elements in %g seconds\n",
384 N_ITERATIONS, (end - start) / (double) CLOCKS_PER_SEC);
386 _dbus_verbose (" zeroed malloc\n");
392 while (i < N_ITERATIONS)
394 to_free[j] = dbus_malloc0 (size);
395 _dbus_assert (to_free[j] != NULL); /* in a real app of course this is wrong */
399 if (j == FREE_ARRAY_SIZE)
402 while (j < FREE_ARRAY_SIZE)
404 dbus_free (to_free[j]);
416 _dbus_verbose (" created/destroyed %d elements in %g seconds\n",
417 N_ITERATIONS, (end - start) / (double) CLOCKS_PER_SEC);
419 _dbus_verbose (" zeroed mempools\n");
423 pool = _dbus_mem_pool_new (size, TRUE);
427 while (i < N_ITERATIONS)
429 to_free[j] = _dbus_mem_pool_alloc (pool);
430 _dbus_assert (to_free[j] != NULL); /* in a real app of course this is wrong */
434 if (j == FREE_ARRAY_SIZE)
437 while (j < FREE_ARRAY_SIZE)
439 _dbus_mem_pool_dealloc (pool, to_free[j]);
449 _dbus_mem_pool_free (pool);
453 _dbus_verbose (" created/destroyed %d elements in %g seconds\n",
454 N_ITERATIONS, (end - start) / (double) CLOCKS_PER_SEC);
458 * @ingroup DBusMemPoolInternals
459 * Unit test for DBusMemPool
460 * @returns #TRUE on success.
463 _dbus_mem_pool_test (void)
466 int element_sizes[] = { 4, 8, 16, 50, 124 };
469 while (i < _DBUS_N_ELEMENTS (element_sizes))
471 time_for_size (element_sizes[i]);
478 #endif /* DBUS_BUILD_TESTS */