/* Implement a cached obstack. Written by Fred Fish Rewritten by Jim Blandy Copyright 1999, 2000 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 #include #include "defs.h" #include "obstack.h" #include "bcache.h" #include "gdb_string.h" /* For memcpy declaration */ /* 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(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 (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"); }