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 pool->element_size = element_size;
149 pool->zero_elements = zero_elements != FALSE;
151 /* pick a size for the first block; it increases
152 * for each block we need to allocate. This is
153 * actually half the initial block size
154 * since _dbus_mem_pool_alloc() unconditionally
155 * doubles it prior to creating a new block.
157 pool->block_size = element_size * 8;
159 _dbus_assert ((pool->block_size %
160 pool->element_size) == 0);
166 * Frees a memory pool (and all elements allocated from it).
168 * @param pool the memory pool.
171 _dbus_mem_pool_free (DBusMemPool *pool)
175 block = pool->blocks;
176 while (block != NULL)
178 DBusMemBlock *next = block->next;
189 * Allocates an object from the memory pool.
190 * The object must be freed with _dbus_mem_pool_dealloc().
192 * @param pool the memory pool
193 * @returns the allocated object or #NULL if no memory.
196 _dbus_mem_pool_alloc (DBusMemPool *pool)
198 if (_dbus_decrement_fail_alloc_counter ())
201 if (pool->free_elements)
203 DBusFreedElement *element = pool->free_elements;
205 pool->free_elements = pool->free_elements->next;
207 if (pool->zero_elements)
208 memset (element, '\0', pool->element_size);
216 if (pool->blocks == NULL ||
217 pool->blocks->used_so_far == pool->block_size)
219 /* Need a new block */
222 #ifdef DBUS_BUILD_TESTS
226 if (pool->block_size <= _DBUS_INT_MAX / 4) /* avoid overflow */
228 /* use a larger block size for our next block */
229 pool->block_size *= 2;
230 _dbus_assert ((pool->block_size %
231 pool->element_size) == 0);
234 alloc_size = sizeof (DBusMemBlock) - ELEMENT_PADDING + pool->block_size;
236 #ifdef DBUS_BUILD_TESTS
237 /* We save/restore the counter, so that memory pools won't
238 * cause a given function to have different number of
239 * allocations on different invocations. i.e. when testing
240 * we want consistent alloc patterns. So we skip our
241 * malloc here for purposes of failed alloc simulation.
243 saved_counter = _dbus_get_fail_alloc_counter ();
244 _dbus_set_fail_alloc_counter (_DBUS_INT_MAX);
247 if (pool->zero_elements)
248 block = dbus_malloc0 (alloc_size);
250 block = dbus_malloc (alloc_size);
252 #ifdef DBUS_BUILD_TESTS
253 _dbus_set_fail_alloc_counter (saved_counter);
259 block->used_so_far = 0;
260 block->next = pool->blocks;
261 pool->blocks = block;
264 element = &pool->blocks->elements[pool->blocks->used_so_far];
266 pool->blocks->used_so_far += pool->element_size;
273 * Deallocates an object previously created with
274 * _dbus_mem_pool_alloc(). The previous object
275 * must have come from this same pool.
276 * @param pool the memory pool
277 * @param element the element earlier allocated.
280 _dbus_mem_pool_dealloc (DBusMemPool *pool,
283 DBusFreedElement *freed;
286 freed->next = pool->free_elements;
287 pool->free_elements = freed;
292 #ifdef DBUS_BUILD_TESTS
293 #include "dbus-test.h"
298 time_for_size (int size)
304 #define FREE_ARRAY_SIZE 512
305 #define N_ITERATIONS FREE_ARRAY_SIZE * 512
306 void *to_free[FREE_ARRAY_SIZE];
309 _dbus_verbose ("Timings for size %d\n", size);
311 _dbus_verbose (" malloc\n");
317 while (i < N_ITERATIONS)
319 to_free[j] = dbus_malloc (size);
320 _dbus_assert (to_free[j] != NULL); /* in a real app of course this is wrong */
324 if (j == FREE_ARRAY_SIZE)
327 while (j < FREE_ARRAY_SIZE)
329 dbus_free (to_free[j]);
341 _dbus_verbose (" created/destroyed %d elements in %g seconds\n",
342 N_ITERATIONS, (end - start) / (double) CLOCKS_PER_SEC);
346 _dbus_verbose (" mempools\n");
350 pool = _dbus_mem_pool_new (size, FALSE);
354 while (i < N_ITERATIONS)
356 to_free[j] = _dbus_mem_pool_alloc (pool);
357 _dbus_assert (to_free[j] != NULL); /* in a real app of course this is wrong */
361 if (j == FREE_ARRAY_SIZE)
364 while (j < FREE_ARRAY_SIZE)
366 _dbus_mem_pool_dealloc (pool, to_free[j]);
376 _dbus_mem_pool_free (pool);
380 _dbus_verbose (" created/destroyed %d elements in %g seconds\n",
381 N_ITERATIONS, (end - start) / (double) CLOCKS_PER_SEC);
383 _dbus_verbose (" zeroed malloc\n");
389 while (i < N_ITERATIONS)
391 to_free[j] = dbus_malloc0 (size);
392 _dbus_assert (to_free[j] != NULL); /* in a real app of course this is wrong */
396 if (j == FREE_ARRAY_SIZE)
399 while (j < FREE_ARRAY_SIZE)
401 dbus_free (to_free[j]);
413 _dbus_verbose (" created/destroyed %d elements in %g seconds\n",
414 N_ITERATIONS, (end - start) / (double) CLOCKS_PER_SEC);
416 _dbus_verbose (" zeroed mempools\n");
420 pool = _dbus_mem_pool_new (size, TRUE);
424 while (i < N_ITERATIONS)
426 to_free[j] = _dbus_mem_pool_alloc (pool);
427 _dbus_assert (to_free[j] != NULL); /* in a real app of course this is wrong */
431 if (j == FREE_ARRAY_SIZE)
434 while (j < FREE_ARRAY_SIZE)
436 _dbus_mem_pool_dealloc (pool, to_free[j]);
446 _dbus_mem_pool_free (pool);
450 _dbus_verbose (" created/destroyed %d elements in %g seconds\n",
451 N_ITERATIONS, (end - start) / (double) CLOCKS_PER_SEC);
455 * @ingroup DBusMemPoolInternals
456 * Unit test for DBusMemPool
457 * @returns #TRUE on success.
460 _dbus_mem_pool_test (void)
463 int element_sizes[] = { 4, 8, 16, 50, 124 };
466 while (i < _DBUS_N_ELEMENTS (element_sizes))
468 time_for_size (element_sizes[i]);
475 #endif /* DBUS_BUILD_TESTS */