1 /* Implement a cached obstack.
2 Written by Fred Fish <fnf@cygnus.com>
3 Rewritten by Jim Blandy <jimb@cygnus.com>
5 Copyright (C) 1999-2017 Free Software Foundation, Inc.
7 This file is part of GDB.
9 This program is free software; you can redistribute it and/or modify
10 it under the terms of the GNU General Public License as published by
11 the Free Software Foundation; either version 3 of the License, or
12 (at your option) any later version.
14 This program is distributed in the hope that it will be useful,
15 but WITHOUT ANY WARRANTY; without even the implied warranty of
16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 GNU General Public License for more details.
19 You should have received a copy of the GNU General Public License
20 along with this program. If not, see <http://www.gnu.org/licenses/>. */
23 #include "gdb_obstack.h"
26 /* The type used to hold a single bcache string. The user data is
27 stored in d.data. Since it can be any type, it needs to have the
28 same alignment as the most strict alignment of any type on the host
29 machine. I don't know of any really correct way to do this in
30 stock ANSI C, so just do it the same way obstack.h does. */
36 /* Assume the data length is no more than 64k. */
37 unsigned short length
;
38 /* The half hash hack. This contains the upper 16 bits of the hash
39 value and is used as a pre-check when comparing two strings and
40 avoids the need to do length or memcmp calls. It proves to be
41 roughly 100% effective. */
42 unsigned short half_hash
;
53 /* The structure for a bcache itself. The bcache is initialized, in
54 bcache_xmalloc(), by filling it with zeros and then setting the
55 corresponding obstack's malloc() and free() methods. */
59 /* All the bstrings are allocated here. */
62 /* How many hash buckets we're using. */
63 unsigned int num_buckets
;
65 /* Hash buckets. This table is allocated using malloc, so when we
66 grow the table we can return the old table to the system. */
67 struct bstring
**bucket
;
70 unsigned long unique_count
; /* number of unique strings */
71 long total_count
; /* total number of strings cached, including dups */
72 long unique_size
; /* size of unique strings, in bytes */
73 long total_size
; /* total number of bytes cached, including dups */
74 long structure_size
; /* total size of bcache, including infrastructure */
75 /* Number of times that the hash table is expanded and hence
76 re-built, and the corresponding number of times that a string is
77 [re]hashed as part of entering it into the expanded table. The
78 total number of hashes can be computed by adding TOTAL_COUNT to
80 unsigned long expand_count
;
81 unsigned long expand_hash_count
;
82 /* Number of times that the half-hash compare hit (compare the upper
83 16 bits of hash values) hit, but the corresponding combined
84 length/data compare missed. */
85 unsigned long half_hash_miss_count
;
87 /* Hash function to be used for this bcache object. */
88 unsigned long (*hash_function
)(const void *addr
, int length
);
90 /* Compare function to be used for this bcache object. */
91 int (*compare_function
)(const void *, const void *, int length
);
94 /* The old hash function was stolen from SDBM. This is what DB 3.0
95 uses now, and is better than the old one. */
98 hash(const void *addr
, int length
)
100 return hash_continue (addr
, length
, 0);
103 /* Continue the calculation of the hash H at the given address. */
106 hash_continue (const void *addr
, int length
, unsigned long h
)
108 const unsigned char *k
, *e
;
110 k
= (const unsigned char *)addr
;
120 /* Growing the bcache's hash table. */
122 /* If the average chain length grows beyond this, then we want to
123 resize our hash table. */
124 #define CHAIN_LENGTH_THRESHOLD (5)
127 expand_hash_table (struct bcache
*bcache
)
129 /* A table of good hash table sizes. Whenever we grow, we pick the
130 next larger size from this table. sizes[i] is close to 1 << (i+10),
131 so we roughly double the table size each time. After we fall off
132 the end of this table, we just double. Don't laugh --- there have
133 been executables sighted with a gigabyte of debug info. */
134 static unsigned long sizes
[] = {
135 1021, 2053, 4099, 8191, 16381, 32771,
136 65537, 131071, 262144, 524287, 1048573, 2097143,
137 4194301, 8388617, 16777213, 33554467, 67108859, 134217757,
138 268435459, 536870923, 1073741827, 2147483659UL
140 unsigned int new_num_buckets
;
141 struct bstring
**new_buckets
;
144 /* Count the stats. Every unique item needs to be re-hashed and
146 bcache
->expand_count
++;
147 bcache
->expand_hash_count
+= bcache
->unique_count
;
149 /* Find the next size. */
150 new_num_buckets
= bcache
->num_buckets
* 2;
151 for (i
= 0; i
< (sizeof (sizes
) / sizeof (sizes
[0])); i
++)
152 if (sizes
[i
] > bcache
->num_buckets
)
154 new_num_buckets
= sizes
[i
];
158 /* Allocate the new table. */
160 size_t new_size
= new_num_buckets
* sizeof (new_buckets
[0]);
162 new_buckets
= (struct bstring
**) xmalloc (new_size
);
163 memset (new_buckets
, 0, new_size
);
165 bcache
->structure_size
-= (bcache
->num_buckets
166 * sizeof (bcache
->bucket
[0]));
167 bcache
->structure_size
+= new_size
;
170 /* Rehash all existing strings. */
171 for (i
= 0; i
< bcache
->num_buckets
; i
++)
173 struct bstring
*s
, *next
;
175 for (s
= bcache
->bucket
[i
]; s
; s
= next
)
177 struct bstring
**new_bucket
;
180 new_bucket
= &new_buckets
[(bcache
->hash_function (&s
->d
.data
,
183 s
->next
= *new_bucket
;
188 /* Plug in the new table. */
190 xfree (bcache
->bucket
);
191 bcache
->bucket
= new_buckets
;
192 bcache
->num_buckets
= new_num_buckets
;
196 /* Looking up things in the bcache. */
198 /* The number of bytes needed to allocate a struct bstring whose data
200 #define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n))
202 /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
203 never seen those bytes before, add a copy of them to BCACHE. In
204 either case, return a pointer to BCACHE's copy of that string. */
206 bcache (const void *addr
, int length
, struct bcache
*cache
)
208 return bcache_full (addr
, length
, cache
, NULL
);
211 /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
212 never seen those bytes before, add a copy of them to BCACHE. In
213 either case, return a pointer to BCACHE's copy of that string. If
214 optional ADDED is not NULL, return 1 in case of new entry or 0 if
215 returning an old entry. */
218 bcache_full (const void *addr
, int length
, struct bcache
*bcache
, int *added
)
220 unsigned long full_hash
;
221 unsigned short half_hash
;
228 /* Lazily initialize the obstack. This can save quite a bit of
229 memory in some cases. */
230 if (bcache
->total_count
== 0)
232 /* We could use obstack_specify_allocation here instead, but
233 gdb_obstack.h specifies the allocation/deallocation
235 obstack_init (&bcache
->cache
);
238 /* If our average chain length is too high, expand the hash table. */
239 if (bcache
->unique_count
>= bcache
->num_buckets
* CHAIN_LENGTH_THRESHOLD
)
240 expand_hash_table (bcache
);
242 bcache
->total_count
++;
243 bcache
->total_size
+= length
;
245 full_hash
= bcache
->hash_function (addr
, length
);
247 half_hash
= (full_hash
>> 16);
248 hash_index
= full_hash
% bcache
->num_buckets
;
250 /* Search the hash bucket for a string identical to the caller's.
251 As a short-circuit first compare the upper part of each hash
253 for (s
= bcache
->bucket
[hash_index
]; s
; s
= s
->next
)
255 if (s
->half_hash
== half_hash
)
257 if (s
->length
== length
258 && bcache
->compare_function (&s
->d
.data
, addr
, length
))
261 bcache
->half_hash_miss_count
++;
265 /* The user's string isn't in the list. Insert it after *ps. */
267 struct bstring
*newobj
268 = (struct bstring
*) obstack_alloc (&bcache
->cache
,
269 BSTRING_SIZE (length
));
271 memcpy (&newobj
->d
.data
, addr
, length
);
272 newobj
->length
= length
;
273 newobj
->next
= bcache
->bucket
[hash_index
];
274 newobj
->half_hash
= half_hash
;
275 bcache
->bucket
[hash_index
] = newobj
;
277 bcache
->unique_count
++;
278 bcache
->unique_size
+= length
;
279 bcache
->structure_size
+= BSTRING_SIZE (length
);
284 return &newobj
->d
.data
;
289 /* Compare the byte string at ADDR1 of lenght LENGHT to the
290 string at ADDR2. Return 1 if they are equal. */
293 bcache_compare (const void *addr1
, const void *addr2
, int length
)
295 return memcmp (addr1
, addr2
, length
) == 0;
298 /* Allocating and freeing bcaches. */
300 /* Allocated a bcache. HASH_FUNCTION and COMPARE_FUNCTION can be used
301 to pass in custom hash, and compare functions to be used by this
302 bcache. If HASH_FUNCTION is NULL hash() is used and if
303 COMPARE_FUNCTION is NULL memcmp() is used. */
306 bcache_xmalloc (unsigned long (*hash_function
)(const void *, int length
),
307 int (*compare_function
)(const void *,
311 /* Allocate the bcache pre-zeroed. */
312 struct bcache
*b
= XCNEW (struct bcache
);
315 b
->hash_function
= hash_function
;
317 b
->hash_function
= hash
;
319 if (compare_function
)
320 b
->compare_function
= compare_function
;
322 b
->compare_function
= bcache_compare
;
326 /* Free all the storage associated with BCACHE. */
328 bcache_xfree (struct bcache
*bcache
)
332 /* Only free the obstack if we actually initialized it. */
333 if (bcache
->total_count
> 0)
334 obstack_free (&bcache
->cache
, 0);
335 xfree (bcache
->bucket
);
341 /* Printing statistics. */
344 print_percentage (int portion
, int total
)
347 /* i18n: Like "Percentage of duplicates, by count: (not applicable)". */
348 printf_filtered (_("(not applicable)\n"));
350 printf_filtered ("%3d%%\n", (int) (portion
* 100.0 / total
));
354 /* Print statistics on BCACHE's memory usage and efficacity at
355 eliminating duplication. NAME should describe the kind of data
356 BCACHE holds. Statistics are printed using `printf_filtered' and
359 print_bcache_statistics (struct bcache
*c
, const char *type
)
361 int occupied_buckets
;
362 int max_chain_length
;
363 int median_chain_length
;
365 int median_entry_size
;
367 /* Count the number of occupied buckets, tally the various string
368 lengths, and measure chain lengths. */
371 int *chain_length
= XCNEWVEC (int, c
->num_buckets
+ 1);
372 int *entry_size
= XCNEWVEC (int, c
->unique_count
+ 1);
375 occupied_buckets
= 0;
377 for (b
= 0; b
< c
->num_buckets
; b
++)
379 struct bstring
*s
= c
->bucket
[b
];
389 gdb_assert (b
< c
->num_buckets
);
391 gdb_assert (stringi
< c
->unique_count
);
392 entry_size
[stringi
++] = s
->length
;
398 /* To compute the median, we need the set of chain lengths
400 qsort (chain_length
, c
->num_buckets
, sizeof (chain_length
[0]),
401 compare_positive_ints
);
402 qsort (entry_size
, c
->unique_count
, sizeof (entry_size
[0]),
403 compare_positive_ints
);
405 if (c
->num_buckets
> 0)
407 max_chain_length
= chain_length
[c
->num_buckets
- 1];
408 median_chain_length
= chain_length
[c
->num_buckets
/ 2];
412 max_chain_length
= 0;
413 median_chain_length
= 0;
415 if (c
->unique_count
> 0)
417 max_entry_size
= entry_size
[c
->unique_count
- 1];
418 median_entry_size
= entry_size
[c
->unique_count
/ 2];
423 median_entry_size
= 0;
426 xfree (chain_length
);
430 printf_filtered (_(" Cached '%s' statistics:\n"), type
);
431 printf_filtered (_(" Total object count: %ld\n"), c
->total_count
);
432 printf_filtered (_(" Unique object count: %lu\n"), c
->unique_count
);
433 printf_filtered (_(" Percentage of duplicates, by count: "));
434 print_percentage (c
->total_count
- c
->unique_count
, c
->total_count
);
435 printf_filtered ("\n");
437 printf_filtered (_(" Total object size: %ld\n"), c
->total_size
);
438 printf_filtered (_(" Unique object size: %ld\n"), c
->unique_size
);
439 printf_filtered (_(" Percentage of duplicates, by size: "));
440 print_percentage (c
->total_size
- c
->unique_size
, c
->total_size
);
441 printf_filtered ("\n");
443 printf_filtered (_(" Max entry size: %d\n"), max_entry_size
);
444 printf_filtered (_(" Average entry size: "));
445 if (c
->unique_count
> 0)
446 printf_filtered ("%ld\n", c
->unique_size
/ c
->unique_count
);
448 /* i18n: "Average entry size: (not applicable)". */
449 printf_filtered (_("(not applicable)\n"));
450 printf_filtered (_(" Median entry size: %d\n"), median_entry_size
);
451 printf_filtered ("\n");
453 printf_filtered (_(" \
454 Total memory used by bcache, including overhead: %ld\n"),
456 printf_filtered (_(" Percentage memory overhead: "));
457 print_percentage (c
->structure_size
- c
->unique_size
, c
->unique_size
);
458 printf_filtered (_(" Net memory savings: "));
459 print_percentage (c
->total_size
- c
->structure_size
, c
->total_size
);
460 printf_filtered ("\n");
462 printf_filtered (_(" Hash table size: %3d\n"),
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"),
482 printf_filtered ("\n");
486 bcache_memory_used (struct bcache
*bcache
)
488 if (bcache
->total_count
== 0)
490 return obstack_memory_used (&bcache
->cache
);
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