| /* 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 "gdb_obstack.h" |
| #include "bcache.h" |
| #include "gdb_string.h" /* For memcpy declaration */ |
| |
| #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 |
| { |
| struct bstring *next; |
| size_t length; |
| |
| 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 */ |
| }; |
| |
| /* 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; |
| } |
| } |
| |
| |
| /* Allocating and freeing bcaches. */ |
| |
| struct bcache * |
| bcache_xmalloc (void) |
| { |
| /* Allocate the bcache pre-zeroed. */ |
| struct bcache *b = XCALLOC (1, struct bcache); |
| obstack_specify_allocation (&b->cache, 0, 0, xmalloc, xfree); |
| return b; |
| } |
| |
| /* Free all the storage associated with BCACHE. */ |
| void |
| bcache_xfree (struct bcache *bcache) |
| { |
| if (bcache == NULL) |
| return; |
| 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) |
| 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"); |
| } |
| |
| int |
| bcache_memory_used (struct bcache *bcache) |
| { |
| return obstack_memory_used (&bcache->cache); |
| } |