458 lines
14 KiB
C
458 lines
14 KiB
C
/* Implement a cached obstack.
|
||
Written by Fred Fish <fnf@cygnus.com>
|
||
Rewritten by Jim Blandy <jimb@cygnus.com>
|
||
|
||
Copyright (C) 1999, 2000, 2002, 2003, 2007, 2008, 2009, 2010
|
||
Free Software Foundation, Inc.
|
||
|
||
This file is part of GDB.
|
||
|
||
This program is free software; you can redistribute it and/or modify
|
||
it under the terms of the GNU General Public License as published by
|
||
the Free Software Foundation; either version 3 of the License, or
|
||
(at your option) any later version.
|
||
|
||
This program is distributed in the hope that it will be useful,
|
||
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
GNU General Public License for more details.
|
||
|
||
You should have received a copy of the GNU General Public License
|
||
along with this program. If not, see <http://www.gnu.org/licenses/>. */
|
||
|
||
#include "defs.h"
|
||
#include "gdb_obstack.h"
|
||
#include "bcache.h"
|
||
#include "gdb_string.h" /* For memcpy declaration */
|
||
#include "gdb_assert.h"
|
||
|
||
#include <stddef.h>
|
||
#include <stdlib.h>
|
||
|
||
/* The type used to hold a single bcache string. The user data is
|
||
stored in d.data. Since it can be any type, it needs to have the
|
||
same alignment as the most strict alignment of any type on the host
|
||
machine. I don't know of any really correct way to do this in
|
||
stock ANSI C, so just do it the same way obstack.h does. */
|
||
|
||
struct bstring
|
||
{
|
||
/* Hash chain. */
|
||
struct bstring *next;
|
||
/* Assume the data length is no more than 64k. */
|
||
unsigned short length;
|
||
/* The half hash hack. This contains the upper 16 bits of the hash
|
||
value and is used as a pre-check when comparing two strings and
|
||
avoids the need to do length or memcmp calls. It proves to be
|
||
roughly 100% effective. */
|
||
unsigned short half_hash;
|
||
|
||
union
|
||
{
|
||
char data[1];
|
||
double dummy;
|
||
}
|
||
d;
|
||
};
|
||
|
||
|
||
/* The structure for a bcache itself. The bcache is initialized, in
|
||
bcache_xmalloc(), by filling it with zeros and then setting the
|
||
corresponding obstack's malloc() and free() methods. */
|
||
|
||
struct bcache
|
||
{
|
||
/* All the bstrings are allocated here. */
|
||
struct obstack cache;
|
||
|
||
/* How many hash buckets we're using. */
|
||
unsigned int num_buckets;
|
||
|
||
/* Hash buckets. This table is allocated using malloc, so when we
|
||
grow the table we can return the old table to the system. */
|
||
struct bstring **bucket;
|
||
|
||
/* Statistics. */
|
||
unsigned long unique_count; /* number of unique strings */
|
||
long total_count; /* total number of strings cached, including dups */
|
||
long unique_size; /* size of unique strings, in bytes */
|
||
long total_size; /* total number of bytes cached, including dups */
|
||
long structure_size; /* total size of bcache, including infrastructure */
|
||
/* Number of times that the hash table is expanded and hence
|
||
re-built, and the corresponding number of times that a string is
|
||
[re]hashed as part of entering it into the expanded table. The
|
||
total number of hashes can be computed by adding TOTAL_COUNT to
|
||
expand_hash_count. */
|
||
unsigned long expand_count;
|
||
unsigned long expand_hash_count;
|
||
/* Number of times that the half-hash compare hit (compare the upper
|
||
16 bits of hash values) hit, but the corresponding combined
|
||
length/data compare missed. */
|
||
unsigned long half_hash_miss_count;
|
||
};
|
||
|
||
/* The old hash function was stolen from SDBM. This is what DB 3.0 uses now,
|
||
* and is better than the old one.
|
||
*/
|
||
|
||
unsigned long
|
||
hash(const void *addr, int length)
|
||
{
|
||
const unsigned char *k, *e;
|
||
unsigned long h;
|
||
|
||
k = (const unsigned char *)addr;
|
||
e = k+length;
|
||
for (h=0; k< e;++k)
|
||
{
|
||
h *=16777619;
|
||
h ^= *k;
|
||
}
|
||
return (h);
|
||
}
|
||
|
||
/* Growing the bcache's hash table. */
|
||
|
||
/* If the average chain length grows beyond this, then we want to
|
||
resize our hash table. */
|
||
#define CHAIN_LENGTH_THRESHOLD (5)
|
||
|
||
static void
|
||
expand_hash_table (struct bcache *bcache)
|
||
{
|
||
/* A table of good hash table sizes. Whenever we grow, we pick the
|
||
next larger size from this table. sizes[i] is close to 1 << (i+10),
|
||
so we roughly double the table size each time. After we fall off
|
||
the end of this table, we just double. Don't laugh --- there have
|
||
been executables sighted with a gigabyte of debug info. */
|
||
static unsigned long sizes[] = {
|
||
1021, 2053, 4099, 8191, 16381, 32771,
|
||
65537, 131071, 262144, 524287, 1048573, 2097143,
|
||
4194301, 8388617, 16777213, 33554467, 67108859, 134217757,
|
||
268435459, 536870923, 1073741827, 2147483659UL
|
||
};
|
||
unsigned int new_num_buckets;
|
||
struct bstring **new_buckets;
|
||
unsigned int i;
|
||
|
||
/* Count the stats. Every unique item needs to be re-hashed and
|
||
re-entered. */
|
||
bcache->expand_count++;
|
||
bcache->expand_hash_count += bcache->unique_count;
|
||
|
||
/* Find the next size. */
|
||
new_num_buckets = bcache->num_buckets * 2;
|
||
for (i = 0; i < (sizeof (sizes) / sizeof (sizes[0])); i++)
|
||
if (sizes[i] > bcache->num_buckets)
|
||
{
|
||
new_num_buckets = sizes[i];
|
||
break;
|
||
}
|
||
|
||
/* Allocate the new table. */
|
||
{
|
||
size_t new_size = new_num_buckets * sizeof (new_buckets[0]);
|
||
new_buckets = (struct bstring **) xmalloc (new_size);
|
||
memset (new_buckets, 0, new_size);
|
||
|
||
bcache->structure_size -= (bcache->num_buckets
|
||
* sizeof (bcache->bucket[0]));
|
||
bcache->structure_size += new_size;
|
||
}
|
||
|
||
/* Rehash all existing strings. */
|
||
for (i = 0; i < bcache->num_buckets; i++)
|
||
{
|
||
struct bstring *s, *next;
|
||
|
||
for (s = bcache->bucket[i]; s; s = next)
|
||
{
|
||
struct bstring **new_bucket;
|
||
next = s->next;
|
||
|
||
new_bucket = &new_buckets[(hash (&s->d.data, s->length)
|
||
% new_num_buckets)];
|
||
s->next = *new_bucket;
|
||
*new_bucket = s;
|
||
}
|
||
}
|
||
|
||
/* Plug in the new table. */
|
||
if (bcache->bucket)
|
||
xfree (bcache->bucket);
|
||
bcache->bucket = new_buckets;
|
||
bcache->num_buckets = new_num_buckets;
|
||
}
|
||
|
||
|
||
/* Looking up things in the bcache. */
|
||
|
||
/* The number of bytes needed to allocate a struct bstring whose data
|
||
is N bytes long. */
|
||
#define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n))
|
||
|
||
/* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
|
||
never seen those bytes before, add a copy of them to BCACHE. In
|
||
either case, return a pointer to BCACHE's copy of that string. */
|
||
const void *
|
||
bcache (const void *addr, int length, struct bcache *bcache)
|
||
{
|
||
return bcache_full (addr, length, bcache, NULL);
|
||
}
|
||
|
||
/* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
|
||
never seen those bytes before, add a copy of them to BCACHE. In
|
||
either case, return a pointer to BCACHE's copy of that string. If
|
||
optional ADDED is not NULL, return 1 in case of new entry or 0 if
|
||
returning an old entry. */
|
||
|
||
const void *
|
||
bcache_full (const void *addr, int length, struct bcache *bcache, int *added)
|
||
{
|
||
unsigned long full_hash;
|
||
unsigned short half_hash;
|
||
int hash_index;
|
||
struct bstring *s;
|
||
|
||
if (added)
|
||
*added = 0;
|
||
|
||
/* Lazily initialize the obstack. This can save quite a bit of
|
||
memory in some cases. */
|
||
if (bcache->total_count == 0)
|
||
{
|
||
/* We could use obstack_specify_allocation here instead, but
|
||
gdb_obstack.h specifies the allocation/deallocation
|
||
functions. */
|
||
obstack_init (&bcache->cache);
|
||
}
|
||
|
||
/* If our average chain length is too high, expand the hash table. */
|
||
if (bcache->unique_count >= bcache->num_buckets * CHAIN_LENGTH_THRESHOLD)
|
||
expand_hash_table (bcache);
|
||
|
||
bcache->total_count++;
|
||
bcache->total_size += length;
|
||
|
||
full_hash = hash (addr, length);
|
||
half_hash = (full_hash >> 16);
|
||
hash_index = full_hash % bcache->num_buckets;
|
||
|
||
/* Search the hash bucket for a string identical to the caller's.
|
||
As a short-circuit first compare the upper part of each hash
|
||
values. */
|
||
for (s = bcache->bucket[hash_index]; s; s = s->next)
|
||
{
|
||
if (s->half_hash == half_hash)
|
||
{
|
||
if (s->length == length
|
||
&& ! memcmp (&s->d.data, addr, length))
|
||
return &s->d.data;
|
||
else
|
||
bcache->half_hash_miss_count++;
|
||
}
|
||
}
|
||
|
||
/* The user's string isn't in the list. Insert it after *ps. */
|
||
{
|
||
struct bstring *new
|
||
= obstack_alloc (&bcache->cache, BSTRING_SIZE (length));
|
||
memcpy (&new->d.data, addr, length);
|
||
new->length = length;
|
||
new->next = bcache->bucket[hash_index];
|
||
new->half_hash = half_hash;
|
||
bcache->bucket[hash_index] = new;
|
||
|
||
bcache->unique_count++;
|
||
bcache->unique_size += length;
|
||
bcache->structure_size += BSTRING_SIZE (length);
|
||
|
||
if (added)
|
||
*added = 1;
|
||
|
||
return &new->d.data;
|
||
}
|
||
}
|
||
|
||
/* Allocating and freeing bcaches. */
|
||
|
||
struct bcache *
|
||
bcache_xmalloc (void)
|
||
{
|
||
/* Allocate the bcache pre-zeroed. */
|
||
struct bcache *b = XCALLOC (1, struct bcache);
|
||
return b;
|
||
}
|
||
|
||
/* Free all the storage associated with BCACHE. */
|
||
void
|
||
bcache_xfree (struct bcache *bcache)
|
||
{
|
||
if (bcache == NULL)
|
||
return;
|
||
/* Only free the obstack if we actually initialized it. */
|
||
if (bcache->total_count > 0)
|
||
obstack_free (&bcache->cache, 0);
|
||
xfree (bcache->bucket);
|
||
xfree (bcache);
|
||
}
|
||
|
||
|
||
|
||
/* Printing statistics. */
|
||
|
||
static int
|
||
compare_ints (const void *ap, const void *bp)
|
||
{
|
||
/* Because we know we're comparing two ints which are positive,
|
||
there's no danger of overflow here. */
|
||
return * (int *) ap - * (int *) bp;
|
||
}
|
||
|
||
|
||
static void
|
||
print_percentage (int portion, int total)
|
||
{
|
||
if (total == 0)
|
||
/* i18n: Like "Percentage of duplicates, by count: (not applicable)" */
|
||
printf_filtered (_("(not applicable)\n"));
|
||
else
|
||
printf_filtered ("%3d%%\n", (int) (portion * 100.0 / total));
|
||
}
|
||
|
||
|
||
/* Print statistics on BCACHE's memory usage and efficacity at
|
||
eliminating duplication. NAME should describe the kind of data
|
||
BCACHE holds. Statistics are printed using `printf_filtered' and
|
||
its ilk. */
|
||
void
|
||
print_bcache_statistics (struct bcache *c, char *type)
|
||
{
|
||
int occupied_buckets;
|
||
int max_chain_length;
|
||
int median_chain_length;
|
||
int max_entry_size;
|
||
int median_entry_size;
|
||
|
||
/* Count the number of occupied buckets, tally the various string
|
||
lengths, and measure chain lengths. */
|
||
{
|
||
unsigned int b;
|
||
int *chain_length = XCALLOC (c->num_buckets + 1, int);
|
||
int *entry_size = XCALLOC (c->unique_count + 1, int);
|
||
int stringi = 0;
|
||
|
||
occupied_buckets = 0;
|
||
|
||
for (b = 0; b < c->num_buckets; b++)
|
||
{
|
||
struct bstring *s = c->bucket[b];
|
||
|
||
chain_length[b] = 0;
|
||
|
||
if (s)
|
||
{
|
||
occupied_buckets++;
|
||
|
||
while (s)
|
||
{
|
||
gdb_assert (b < c->num_buckets);
|
||
chain_length[b]++;
|
||
gdb_assert (stringi < c->unique_count);
|
||
entry_size[stringi++] = s->length;
|
||
s = s->next;
|
||
}
|
||
}
|
||
}
|
||
|
||
/* To compute the median, we need the set of chain lengths sorted. */
|
||
qsort (chain_length, c->num_buckets, sizeof (chain_length[0]),
|
||
compare_ints);
|
||
qsort (entry_size, c->unique_count, sizeof (entry_size[0]),
|
||
compare_ints);
|
||
|
||
if (c->num_buckets > 0)
|
||
{
|
||
max_chain_length = chain_length[c->num_buckets - 1];
|
||
median_chain_length = chain_length[c->num_buckets / 2];
|
||
}
|
||
else
|
||
{
|
||
max_chain_length = 0;
|
||
median_chain_length = 0;
|
||
}
|
||
if (c->unique_count > 0)
|
||
{
|
||
max_entry_size = entry_size[c->unique_count - 1];
|
||
median_entry_size = entry_size[c->unique_count / 2];
|
||
}
|
||
else
|
||
{
|
||
max_entry_size = 0;
|
||
median_entry_size = 0;
|
||
}
|
||
|
||
xfree (chain_length);
|
||
xfree (entry_size);
|
||
}
|
||
|
||
printf_filtered (_(" Cached '%s' statistics:\n"), type);
|
||
printf_filtered (_(" Total object count: %ld\n"), c->total_count);
|
||
printf_filtered (_(" Unique object count: %lu\n"), c->unique_count);
|
||
printf_filtered (_(" Percentage of duplicates, by count: "));
|
||
print_percentage (c->total_count - c->unique_count, c->total_count);
|
||
printf_filtered ("\n");
|
||
|
||
printf_filtered (_(" Total object size: %ld\n"), c->total_size);
|
||
printf_filtered (_(" Unique object size: %ld\n"), c->unique_size);
|
||
printf_filtered (_(" Percentage of duplicates, by size: "));
|
||
print_percentage (c->total_size - c->unique_size, c->total_size);
|
||
printf_filtered ("\n");
|
||
|
||
printf_filtered (_(" Max entry size: %d\n"), max_entry_size);
|
||
printf_filtered (_(" Average entry size: "));
|
||
if (c->unique_count > 0)
|
||
printf_filtered ("%ld\n", c->unique_size / c->unique_count);
|
||
else
|
||
/* i18n: "Average entry size: (not applicable)" */
|
||
printf_filtered (_("(not applicable)\n"));
|
||
printf_filtered (_(" Median entry size: %d\n"), median_entry_size);
|
||
printf_filtered ("\n");
|
||
|
||
printf_filtered (_(" Total memory used by bcache, including overhead: %ld\n"),
|
||
c->structure_size);
|
||
printf_filtered (_(" Percentage memory overhead: "));
|
||
print_percentage (c->structure_size - c->unique_size, c->unique_size);
|
||
printf_filtered (_(" Net memory savings: "));
|
||
print_percentage (c->total_size - c->structure_size, c->total_size);
|
||
printf_filtered ("\n");
|
||
|
||
printf_filtered (_(" Hash table size: %3d\n"), c->num_buckets);
|
||
printf_filtered (_(" Hash table expands: %lu\n"),
|
||
c->expand_count);
|
||
printf_filtered (_(" Hash table hashes: %lu\n"),
|
||
c->total_count + c->expand_hash_count);
|
||
printf_filtered (_(" Half hash misses: %lu\n"),
|
||
c->half_hash_miss_count);
|
||
printf_filtered (_(" Hash table population: "));
|
||
print_percentage (occupied_buckets, c->num_buckets);
|
||
printf_filtered (_(" Median hash chain length: %3d\n"),
|
||
median_chain_length);
|
||
printf_filtered (_(" Average hash chain length: "));
|
||
if (c->num_buckets > 0)
|
||
printf_filtered ("%3lu\n", c->unique_count / c->num_buckets);
|
||
else
|
||
/* i18n: "Average hash chain length: (not applicable)" */
|
||
printf_filtered (_("(not applicable)\n"));
|
||
printf_filtered (_(" Maximum hash chain length: %3d\n"), max_chain_length);
|
||
printf_filtered ("\n");
|
||
}
|
||
|
||
int
|
||
bcache_memory_used (struct bcache *bcache)
|
||
{
|
||
if (bcache->total_count == 0)
|
||
return 0;
|
||
return obstack_memory_used (&bcache->cache);
|
||
}
|