294 lines
8.3 KiB
C
294 lines
8.3 KiB
C
/* Implement a cached obstack.
|
||
Written by Fred Fish <fnf@cygnus.com>
|
||
Rewritten by Jim Blandy <jimb@cygnus.com>
|
||
|
||
Copyright 1999, 2000, 2002 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 2 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, write to the Free Software
|
||
Foundation, Inc., 59 Temple Place - Suite 330,
|
||
Boston, MA 02111-1307, USA. */
|
||
|
||
#include "defs.h"
|
||
#include "obstack.h"
|
||
#include "bcache.h"
|
||
#include "gdb_string.h" /* For memcpy declaration */
|
||
|
||
#include <stddef.h>
|
||
#include <stdlib.h>
|
||
|
||
/* 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;
|
||
|
||
/* 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. */
|
||
void *
|
||
bcache (const void *addr, int length, struct bcache *bcache)
|
||
{
|
||
int hash_index;
|
||
struct bstring *s;
|
||
|
||
/* 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;
|
||
|
||
hash_index = hash (addr, length) % bcache->num_buckets;
|
||
|
||
/* Search the hash bucket for a string identical to the caller's. */
|
||
for (s = bcache->bucket[hash_index]; s; s = s->next)
|
||
if (s->length == length
|
||
&& ! memcmp (&s->d.data, addr, length))
|
||
return &s->d.data;
|
||
|
||
/* 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];
|
||
bcache->bucket[hash_index] = new;
|
||
|
||
bcache->unique_count++;
|
||
bcache->unique_size += length;
|
||
bcache->structure_size += BSTRING_SIZE (length);
|
||
|
||
return &new->d.data;
|
||
}
|
||
}
|
||
|
||
|
||
/* Freeing bcaches. */
|
||
|
||
/* Free all the storage associated with BCACHE. */
|
||
void
|
||
free_bcache (struct bcache *bcache)
|
||
{
|
||
obstack_free (&bcache->cache, 0);
|
||
if (bcache->bucket)
|
||
xfree (bcache->bucket);
|
||
|
||
/* This isn't necessary, but at least the bcache is always in a
|
||
consistent state. */
|
||
memset (bcache, 0, sizeof (*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)
|
||
printf_filtered ("(not applicable)\n");
|
||
else
|
||
printf_filtered ("%3d%%\n", portion * 100 / 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;
|
||
|
||
/* Count the number of occupied buckets, and measure chain lengths. */
|
||
{
|
||
unsigned int b;
|
||
int *chain_length
|
||
= (int *) alloca (c->num_buckets * sizeof (*chain_length));
|
||
|
||
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)
|
||
{
|
||
chain_length[b]++;
|
||
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);
|
||
|
||
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;
|
||
}
|
||
}
|
||
|
||
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 (" 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 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
|
||
printf_filtered ("(not applicable)\n");
|
||
printf_filtered (" Maximum hash chain length: %3d\n", max_chain_length);
|
||
printf_filtered ("\n");
|
||
}
|