1 /* Implement a cached obstack.
2 Written by Fred Fish <fnf@cygnus.com>
3 Rewritten by Jim Blandy <jimb@cygnus.com>
5 Copyright (C) 1999, 2000, 2002, 2003, 2007, 2008, 2009, 2010
6 Free Software Foundation, Inc.
8 This file is part of GDB.
10 This program is free software; you can redistribute it and/or modify
11 it under the terms of the GNU General Public License as published by
12 the Free Software Foundation; either version 3 of the License, or
13 (at your option) any later version.
15 This program is distributed in the hope that it will be useful,
16 but WITHOUT ANY WARRANTY; without even the implied warranty of
17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 GNU General Public License for more details.
20 You should have received a copy of the GNU General Public License
21 along with this program. If not, see <http://www.gnu.org/licenses/>. */
24 #include "gdb_obstack.h"
26 #include "gdb_string.h" /* For memcpy declaration */
27 #include "gdb_assert.h"
32 /* The type used to hold a single bcache string. The user data is
33 stored in d.data. Since it can be any type, it needs to have the
34 same alignment as the most strict alignment of any type on the host
35 machine. I don't know of any really correct way to do this in
36 stock ANSI C, so just do it the same way obstack.h does. */
42 /* Assume the data length is no more than 64k. */
43 unsigned short length
;
44 /* The half hash hack. This contains the upper 16 bits of the hash
45 value and is used as a pre-check when comparing two strings and
46 avoids the need to do length or memcmp calls. It proves to be
47 roughly 100% effective. */
48 unsigned short half_hash
;
59 /* The structure for a bcache itself. The bcache is initialized, in
60 bcache_xmalloc(), by filling it with zeros and then setting the
61 corresponding obstack's malloc() and free() methods. */
65 /* All the bstrings are allocated here. */
68 /* How many hash buckets we're using. */
69 unsigned int num_buckets
;
71 /* Hash buckets. This table is allocated using malloc, so when we
72 grow the table we can return the old table to the system. */
73 struct bstring
**bucket
;
76 unsigned long unique_count
; /* number of unique strings */
77 long total_count
; /* total number of strings cached, including dups */
78 long unique_size
; /* size of unique strings, in bytes */
79 long total_size
; /* total number of bytes cached, including dups */
80 long structure_size
; /* total size of bcache, including infrastructure */
81 /* Number of times that the hash table is expanded and hence
82 re-built, and the corresponding number of times that a string is
83 [re]hashed as part of entering it into the expanded table. The
84 total number of hashes can be computed by adding TOTAL_COUNT to
86 unsigned long expand_count
;
87 unsigned long expand_hash_count
;
88 /* Number of times that the half-hash compare hit (compare the upper
89 16 bits of hash values) hit, but the corresponding combined
90 length/data compare missed. */
91 unsigned long half_hash_miss_count
;
94 /* The old hash function was stolen from SDBM. This is what DB 3.0 uses now,
95 * and is better than the old one.
99 hash(const void *addr
, int length
)
101 const unsigned char *k
, *e
;
104 k
= (const unsigned char *)addr
;
114 /* Growing the bcache's hash table. */
116 /* If the average chain length grows beyond this, then we want to
117 resize our hash table. */
118 #define CHAIN_LENGTH_THRESHOLD (5)
121 expand_hash_table (struct bcache
*bcache
)
123 /* A table of good hash table sizes. Whenever we grow, we pick the
124 next larger size from this table. sizes[i] is close to 1 << (i+10),
125 so we roughly double the table size each time. After we fall off
126 the end of this table, we just double. Don't laugh --- there have
127 been executables sighted with a gigabyte of debug info. */
128 static unsigned long sizes
[] = {
129 1021, 2053, 4099, 8191, 16381, 32771,
130 65537, 131071, 262144, 524287, 1048573, 2097143,
131 4194301, 8388617, 16777213, 33554467, 67108859, 134217757,
132 268435459, 536870923, 1073741827, 2147483659UL
134 unsigned int new_num_buckets
;
135 struct bstring
**new_buckets
;
138 /* Count the stats. Every unique item needs to be re-hashed and
140 bcache
->expand_count
++;
141 bcache
->expand_hash_count
+= bcache
->unique_count
;
143 /* Find the next size. */
144 new_num_buckets
= bcache
->num_buckets
* 2;
145 for (i
= 0; i
< (sizeof (sizes
) / sizeof (sizes
[0])); i
++)
146 if (sizes
[i
] > bcache
->num_buckets
)
148 new_num_buckets
= sizes
[i
];
152 /* Allocate the new table. */
154 size_t new_size
= new_num_buckets
* sizeof (new_buckets
[0]);
156 new_buckets
= (struct bstring
**) xmalloc (new_size
);
157 memset (new_buckets
, 0, new_size
);
159 bcache
->structure_size
-= (bcache
->num_buckets
160 * sizeof (bcache
->bucket
[0]));
161 bcache
->structure_size
+= new_size
;
164 /* Rehash all existing strings. */
165 for (i
= 0; i
< bcache
->num_buckets
; i
++)
167 struct bstring
*s
, *next
;
169 for (s
= bcache
->bucket
[i
]; s
; s
= next
)
171 struct bstring
**new_bucket
;
174 new_bucket
= &new_buckets
[(hash (&s
->d
.data
, s
->length
)
176 s
->next
= *new_bucket
;
181 /* Plug in the new table. */
183 xfree (bcache
->bucket
);
184 bcache
->bucket
= new_buckets
;
185 bcache
->num_buckets
= new_num_buckets
;
189 /* Looking up things in the bcache. */
191 /* The number of bytes needed to allocate a struct bstring whose data
193 #define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n))
195 /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
196 never seen those bytes before, add a copy of them to BCACHE. In
197 either case, return a pointer to BCACHE's copy of that string. */
199 bcache (const void *addr
, int length
, struct bcache
*bcache
)
201 return bcache_full (addr
, length
, bcache
, NULL
);
204 /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
205 never seen those bytes before, add a copy of them to BCACHE. In
206 either case, return a pointer to BCACHE's copy of that string. If
207 optional ADDED is not NULL, return 1 in case of new entry or 0 if
208 returning an old entry. */
211 bcache_full (const void *addr
, int length
, struct bcache
*bcache
, int *added
)
213 unsigned long full_hash
;
214 unsigned short half_hash
;
221 /* Lazily initialize the obstack. This can save quite a bit of
222 memory in some cases. */
223 if (bcache
->total_count
== 0)
225 /* We could use obstack_specify_allocation here instead, but
226 gdb_obstack.h specifies the allocation/deallocation
228 obstack_init (&bcache
->cache
);
231 /* If our average chain length is too high, expand the hash table. */
232 if (bcache
->unique_count
>= bcache
->num_buckets
* CHAIN_LENGTH_THRESHOLD
)
233 expand_hash_table (bcache
);
235 bcache
->total_count
++;
236 bcache
->total_size
+= length
;
238 full_hash
= hash (addr
, length
);
239 half_hash
= (full_hash
>> 16);
240 hash_index
= full_hash
% bcache
->num_buckets
;
242 /* Search the hash bucket for a string identical to the caller's.
243 As a short-circuit first compare the upper part of each hash
245 for (s
= bcache
->bucket
[hash_index
]; s
; s
= s
->next
)
247 if (s
->half_hash
== half_hash
)
249 if (s
->length
== length
250 && ! memcmp (&s
->d
.data
, addr
, length
))
253 bcache
->half_hash_miss_count
++;
257 /* The user's string isn't in the list. Insert it after *ps. */
260 = obstack_alloc (&bcache
->cache
, BSTRING_SIZE (length
));
262 memcpy (&new->d
.data
, addr
, length
);
263 new->length
= length
;
264 new->next
= bcache
->bucket
[hash_index
];
265 new->half_hash
= half_hash
;
266 bcache
->bucket
[hash_index
] = new;
268 bcache
->unique_count
++;
269 bcache
->unique_size
+= length
;
270 bcache
->structure_size
+= BSTRING_SIZE (length
);
279 /* Allocating and freeing bcaches. */
282 bcache_xmalloc (void)
284 /* Allocate the bcache pre-zeroed. */
285 struct bcache
*b
= XCALLOC (1, struct bcache
);
290 /* Free all the storage associated with BCACHE. */
292 bcache_xfree (struct bcache
*bcache
)
296 /* Only free the obstack if we actually initialized it. */
297 if (bcache
->total_count
> 0)
298 obstack_free (&bcache
->cache
, 0);
299 xfree (bcache
->bucket
);
305 /* Printing statistics. */
308 print_percentage (int portion
, int total
)
311 /* i18n: Like "Percentage of duplicates, by count: (not applicable)" */
312 printf_filtered (_("(not applicable)\n"));
314 printf_filtered ("%3d%%\n", (int) (portion
* 100.0 / total
));
318 /* Print statistics on BCACHE's memory usage and efficacity at
319 eliminating duplication. NAME should describe the kind of data
320 BCACHE holds. Statistics are printed using `printf_filtered' and
323 print_bcache_statistics (struct bcache
*c
, char *type
)
325 int occupied_buckets
;
326 int max_chain_length
;
327 int median_chain_length
;
329 int median_entry_size
;
331 /* Count the number of occupied buckets, tally the various string
332 lengths, and measure chain lengths. */
335 int *chain_length
= XCALLOC (c
->num_buckets
+ 1, int);
336 int *entry_size
= XCALLOC (c
->unique_count
+ 1, int);
339 occupied_buckets
= 0;
341 for (b
= 0; b
< c
->num_buckets
; b
++)
343 struct bstring
*s
= c
->bucket
[b
];
353 gdb_assert (b
< c
->num_buckets
);
355 gdb_assert (stringi
< c
->unique_count
);
356 entry_size
[stringi
++] = s
->length
;
362 /* To compute the median, we need the set of chain lengths sorted. */
363 qsort (chain_length
, c
->num_buckets
, sizeof (chain_length
[0]),
364 compare_positive_ints
);
365 qsort (entry_size
, c
->unique_count
, sizeof (entry_size
[0]),
366 compare_positive_ints
);
368 if (c
->num_buckets
> 0)
370 max_chain_length
= chain_length
[c
->num_buckets
- 1];
371 median_chain_length
= chain_length
[c
->num_buckets
/ 2];
375 max_chain_length
= 0;
376 median_chain_length
= 0;
378 if (c
->unique_count
> 0)
380 max_entry_size
= entry_size
[c
->unique_count
- 1];
381 median_entry_size
= entry_size
[c
->unique_count
/ 2];
386 median_entry_size
= 0;
389 xfree (chain_length
);
393 printf_filtered (_(" Cached '%s' statistics:\n"), type
);
394 printf_filtered (_(" Total object count: %ld\n"), c
->total_count
);
395 printf_filtered (_(" Unique object count: %lu\n"), c
->unique_count
);
396 printf_filtered (_(" Percentage of duplicates, by count: "));
397 print_percentage (c
->total_count
- c
->unique_count
, c
->total_count
);
398 printf_filtered ("\n");
400 printf_filtered (_(" Total object size: %ld\n"), c
->total_size
);
401 printf_filtered (_(" Unique object size: %ld\n"), c
->unique_size
);
402 printf_filtered (_(" Percentage of duplicates, by size: "));
403 print_percentage (c
->total_size
- c
->unique_size
, c
->total_size
);
404 printf_filtered ("\n");
406 printf_filtered (_(" Max entry size: %d\n"), max_entry_size
);
407 printf_filtered (_(" Average entry size: "));
408 if (c
->unique_count
> 0)
409 printf_filtered ("%ld\n", c
->unique_size
/ c
->unique_count
);
411 /* i18n: "Average entry size: (not applicable)" */
412 printf_filtered (_("(not applicable)\n"));
413 printf_filtered (_(" Median entry size: %d\n"), median_entry_size
);
414 printf_filtered ("\n");
416 printf_filtered (_(" Total memory used by bcache, including overhead: %ld\n"),
418 printf_filtered (_(" Percentage memory overhead: "));
419 print_percentage (c
->structure_size
- c
->unique_size
, c
->unique_size
);
420 printf_filtered (_(" Net memory savings: "));
421 print_percentage (c
->total_size
- c
->structure_size
, c
->total_size
);
422 printf_filtered ("\n");
424 printf_filtered (_(" Hash table size: %3d\n"), c
->num_buckets
);
425 printf_filtered (_(" Hash table expands: %lu\n"),
427 printf_filtered (_(" Hash table hashes: %lu\n"),
428 c
->total_count
+ c
->expand_hash_count
);
429 printf_filtered (_(" Half hash misses: %lu\n"),
430 c
->half_hash_miss_count
);
431 printf_filtered (_(" Hash table population: "));
432 print_percentage (occupied_buckets
, c
->num_buckets
);
433 printf_filtered (_(" Median hash chain length: %3d\n"),
434 median_chain_length
);
435 printf_filtered (_(" Average hash chain length: "));
436 if (c
->num_buckets
> 0)
437 printf_filtered ("%3lu\n", c
->unique_count
/ c
->num_buckets
);
439 /* i18n: "Average hash chain length: (not applicable)" */
440 printf_filtered (_("(not applicable)\n"));
441 printf_filtered (_(" Maximum hash chain length: %3d\n"), max_chain_length
);
442 printf_filtered ("\n");
446 bcache_memory_used (struct bcache
*bcache
)
448 if (bcache
->total_count
== 0)
450 return obstack_memory_used (&bcache
->cache
);
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