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
;
93 /* Hash function to be used for this bcache object. */
94 unsigned long (*hash_function
)(const void *addr
, int length
);
96 /* Compare function to be used for this bcache object. */
97 int (*compare_function
)(const void *, const void *, int length
);
100 /* The old hash function was stolen from SDBM. This is what DB 3.0 uses now,
101 * and is better than the old one.
105 hash(const void *addr
, int length
)
107 return hash_continue (addr
, length
, 0);
110 /* Continue the calculation of the hash H at the given address. */
113 hash_continue (const void *addr
, int length
, unsigned long h
)
115 const unsigned char *k
, *e
;
117 k
= (const unsigned char *)addr
;
127 /* Growing the bcache's hash table. */
129 /* If the average chain length grows beyond this, then we want to
130 resize our hash table. */
131 #define CHAIN_LENGTH_THRESHOLD (5)
134 expand_hash_table (struct bcache
*bcache
)
136 /* A table of good hash table sizes. Whenever we grow, we pick the
137 next larger size from this table. sizes[i] is close to 1 << (i+10),
138 so we roughly double the table size each time. After we fall off
139 the end of this table, we just double. Don't laugh --- there have
140 been executables sighted with a gigabyte of debug info. */
141 static unsigned long sizes
[] = {
142 1021, 2053, 4099, 8191, 16381, 32771,
143 65537, 131071, 262144, 524287, 1048573, 2097143,
144 4194301, 8388617, 16777213, 33554467, 67108859, 134217757,
145 268435459, 536870923, 1073741827, 2147483659UL
147 unsigned int new_num_buckets
;
148 struct bstring
**new_buckets
;
151 /* Count the stats. Every unique item needs to be re-hashed and
153 bcache
->expand_count
++;
154 bcache
->expand_hash_count
+= bcache
->unique_count
;
156 /* Find the next size. */
157 new_num_buckets
= bcache
->num_buckets
* 2;
158 for (i
= 0; i
< (sizeof (sizes
) / sizeof (sizes
[0])); i
++)
159 if (sizes
[i
] > bcache
->num_buckets
)
161 new_num_buckets
= sizes
[i
];
165 /* Allocate the new table. */
167 size_t new_size
= new_num_buckets
* sizeof (new_buckets
[0]);
169 new_buckets
= (struct bstring
**) xmalloc (new_size
);
170 memset (new_buckets
, 0, new_size
);
172 bcache
->structure_size
-= (bcache
->num_buckets
173 * sizeof (bcache
->bucket
[0]));
174 bcache
->structure_size
+= new_size
;
177 /* Rehash all existing strings. */
178 for (i
= 0; i
< bcache
->num_buckets
; i
++)
180 struct bstring
*s
, *next
;
182 for (s
= bcache
->bucket
[i
]; s
; s
= next
)
184 struct bstring
**new_bucket
;
187 new_bucket
= &new_buckets
[(hash (&s
->d
.data
, s
->length
)
189 s
->next
= *new_bucket
;
194 /* Plug in the new table. */
196 xfree (bcache
->bucket
);
197 bcache
->bucket
= new_buckets
;
198 bcache
->num_buckets
= new_num_buckets
;
202 /* Looking up things in the bcache. */
204 /* The number of bytes needed to allocate a struct bstring whose data
206 #define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n))
208 /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
209 never seen those bytes before, add a copy of them to BCACHE. In
210 either case, return a pointer to BCACHE's copy of that string. */
212 bcache (const void *addr
, int length
, struct bcache
*bcache
)
214 return bcache_full (addr
, length
, bcache
, NULL
);
217 /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
218 never seen those bytes before, add a copy of them to BCACHE. In
219 either case, return a pointer to BCACHE's copy of that string. If
220 optional ADDED is not NULL, return 1 in case of new entry or 0 if
221 returning an old entry. */
224 bcache_full (const void *addr
, int length
, struct bcache
*bcache
, int *added
)
226 unsigned long full_hash
;
227 unsigned short half_hash
;
234 /* Lazily initialize the obstack. This can save quite a bit of
235 memory in some cases. */
236 if (bcache
->total_count
== 0)
238 /* We could use obstack_specify_allocation here instead, but
239 gdb_obstack.h specifies the allocation/deallocation
241 obstack_init (&bcache
->cache
);
244 /* If our average chain length is too high, expand the hash table. */
245 if (bcache
->unique_count
>= bcache
->num_buckets
* CHAIN_LENGTH_THRESHOLD
)
246 expand_hash_table (bcache
);
248 bcache
->total_count
++;
249 bcache
->total_size
+= length
;
251 full_hash
= bcache
->hash_function (addr
, length
);
253 half_hash
= (full_hash
>> 16);
254 hash_index
= full_hash
% bcache
->num_buckets
;
256 /* Search the hash bucket for a string identical to the caller's.
257 As a short-circuit first compare the upper part of each hash
259 for (s
= bcache
->bucket
[hash_index
]; s
; s
= s
->next
)
261 if (s
->half_hash
== half_hash
)
263 if (s
->length
== length
264 && bcache
->compare_function (&s
->d
.data
, addr
, length
))
267 bcache
->half_hash_miss_count
++;
271 /* The user's string isn't in the list. Insert it after *ps. */
274 = obstack_alloc (&bcache
->cache
, BSTRING_SIZE (length
));
276 memcpy (&new->d
.data
, addr
, length
);
277 new->length
= length
;
278 new->next
= bcache
->bucket
[hash_index
];
279 new->half_hash
= half_hash
;
280 bcache
->bucket
[hash_index
] = new;
282 bcache
->unique_count
++;
283 bcache
->unique_size
+= length
;
284 bcache
->structure_size
+= BSTRING_SIZE (length
);
294 /* Compare the byte string at ADDR1 of lenght LENGHT to the
295 string at ADDR2. Return 1 if they are equal. */
298 bcache_compare (const void *addr1
, const void *addr2
, int length
)
300 return memcmp (addr1
, addr2
, length
) == 0;
303 /* Allocating and freeing bcaches. */
305 /* Allocated a bcache. HASH_FUNCTION and COMPARE_FUNCTION can be used
306 to pass in custom hash, and compare functions to be used by this
307 bcache. If HASH_FUNCTION is NULL hash() is used and if COMPARE_FUNCTION
308 is NULL memcmp() is used. */
311 bcache_xmalloc (unsigned long (*hash_function
)(const void *, int length
),
312 int (*compare_function
)(const void *, const void *, int length
))
314 /* Allocate the bcache pre-zeroed. */
315 struct bcache
*b
= XCALLOC (1, struct bcache
);
318 b
->hash_function
= hash_function
;
320 b
->hash_function
= hash
;
322 if (compare_function
)
323 b
->compare_function
= compare_function
;
325 b
->compare_function
= bcache_compare
;
329 /* Free all the storage associated with BCACHE. */
331 bcache_xfree (struct bcache
*bcache
)
335 /* Only free the obstack if we actually initialized it. */
336 if (bcache
->total_count
> 0)
337 obstack_free (&bcache
->cache
, 0);
338 xfree (bcache
->bucket
);
344 /* Printing statistics. */
347 print_percentage (int portion
, int total
)
350 /* i18n: Like "Percentage of duplicates, by count: (not applicable)" */
351 printf_filtered (_("(not applicable)\n"));
353 printf_filtered ("%3d%%\n", (int) (portion
* 100.0 / total
));
357 /* Print statistics on BCACHE's memory usage and efficacity at
358 eliminating duplication. NAME should describe the kind of data
359 BCACHE holds. Statistics are printed using `printf_filtered' and
362 print_bcache_statistics (struct bcache
*c
, char *type
)
364 int occupied_buckets
;
365 int max_chain_length
;
366 int median_chain_length
;
368 int median_entry_size
;
370 /* Count the number of occupied buckets, tally the various string
371 lengths, and measure chain lengths. */
374 int *chain_length
= XCALLOC (c
->num_buckets
+ 1, int);
375 int *entry_size
= XCALLOC (c
->unique_count
+ 1, int);
378 occupied_buckets
= 0;
380 for (b
= 0; b
< c
->num_buckets
; b
++)
382 struct bstring
*s
= c
->bucket
[b
];
392 gdb_assert (b
< c
->num_buckets
);
394 gdb_assert (stringi
< c
->unique_count
);
395 entry_size
[stringi
++] = s
->length
;
401 /* To compute the median, we need the set of chain lengths sorted. */
402 qsort (chain_length
, c
->num_buckets
, sizeof (chain_length
[0]),
403 compare_positive_ints
);
404 qsort (entry_size
, c
->unique_count
, sizeof (entry_size
[0]),
405 compare_positive_ints
);
407 if (c
->num_buckets
> 0)
409 max_chain_length
= chain_length
[c
->num_buckets
- 1];
410 median_chain_length
= chain_length
[c
->num_buckets
/ 2];
414 max_chain_length
= 0;
415 median_chain_length
= 0;
417 if (c
->unique_count
> 0)
419 max_entry_size
= entry_size
[c
->unique_count
- 1];
420 median_entry_size
= entry_size
[c
->unique_count
/ 2];
425 median_entry_size
= 0;
428 xfree (chain_length
);
432 printf_filtered (_(" Cached '%s' statistics:\n"), type
);
433 printf_filtered (_(" Total object count: %ld\n"), c
->total_count
);
434 printf_filtered (_(" Unique object count: %lu\n"), c
->unique_count
);
435 printf_filtered (_(" Percentage of duplicates, by count: "));
436 print_percentage (c
->total_count
- c
->unique_count
, c
->total_count
);
437 printf_filtered ("\n");
439 printf_filtered (_(" Total object size: %ld\n"), c
->total_size
);
440 printf_filtered (_(" Unique object size: %ld\n"), c
->unique_size
);
441 printf_filtered (_(" Percentage of duplicates, by size: "));
442 print_percentage (c
->total_size
- c
->unique_size
, c
->total_size
);
443 printf_filtered ("\n");
445 printf_filtered (_(" Max entry size: %d\n"), max_entry_size
);
446 printf_filtered (_(" Average entry size: "));
447 if (c
->unique_count
> 0)
448 printf_filtered ("%ld\n", c
->unique_size
/ c
->unique_count
);
450 /* i18n: "Average entry size: (not applicable)" */
451 printf_filtered (_("(not applicable)\n"));
452 printf_filtered (_(" Median entry size: %d\n"), median_entry_size
);
453 printf_filtered ("\n");
455 printf_filtered (_(" Total memory used by bcache, including overhead: %ld\n"),
457 printf_filtered (_(" Percentage memory overhead: "));
458 print_percentage (c
->structure_size
- c
->unique_size
, c
->unique_size
);
459 printf_filtered (_(" Net memory savings: "));
460 print_percentage (c
->total_size
- c
->structure_size
, c
->total_size
);
461 printf_filtered ("\n");
463 printf_filtered (_(" Hash table size: %3d\n"), c
->num_buckets
);
464 printf_filtered (_(" Hash table expands: %lu\n"),
466 printf_filtered (_(" Hash table hashes: %lu\n"),
467 c
->total_count
+ c
->expand_hash_count
);
468 printf_filtered (_(" Half hash misses: %lu\n"),
469 c
->half_hash_miss_count
);
470 printf_filtered (_(" Hash table population: "));
471 print_percentage (occupied_buckets
, c
->num_buckets
);
472 printf_filtered (_(" Median hash chain length: %3d\n"),
473 median_chain_length
);
474 printf_filtered (_(" Average hash chain length: "));
475 if (c
->num_buckets
> 0)
476 printf_filtered ("%3lu\n", c
->unique_count
/ c
->num_buckets
);
478 /* i18n: "Average hash chain length: (not applicable)" */
479 printf_filtered (_("(not applicable)\n"));
480 printf_filtered (_(" Maximum hash chain length: %3d\n"), max_chain_length
);
481 printf_filtered ("\n");
485 bcache_memory_used (struct bcache
*bcache
)
487 if (bcache
->total_count
== 0)
489 return obstack_memory_used (&bcache
->cache
);
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