forked from Mirror/frr
6f6f00107e
Adds the ability to name hash tables, and a new cli command that will show various summary statistics for named hash tables. Statistics computed are - load factor - full load factor (see comments) - stddev of full load factor Standard deviation is computed by storing the sum of squares of bucket lengths. This is somewhat susceptible to overflow. On platforms where a double is 32 bits, placing 65535 or more elements into a hash table opens up the potential for overflow, depending on how they are arranged in buckets (which depends on the hash function). For example, placing 65535 elements into one hash bucket would cause ssq overflow, but distributing 40000000 elements evenly among 400000 buckets (100 elements per bucket) would not. These cases are extremely degenerate, so the vague possibility of overflow in an informational command is deemed an acceptable tradeoff for constant time calculation of variance without locks or compromising efficiency of actual table operations. Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>
113 lines
2.8 KiB
C
113 lines
2.8 KiB
C
/* Hash routine.
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* Copyright (C) 1998 Kunihiro Ishiguro
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*
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* This file is part of GNU Zebra.
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*
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* GNU Zebra is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published
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* by the Free Software Foundation; either version 2, or (at your
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* option) any later version.
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*
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* GNU Zebra is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; see the file COPYING; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef _ZEBRA_HASH_H
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#define _ZEBRA_HASH_H
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#include "memory.h"
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#include "frratomic.h"
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DECLARE_MTYPE(HASH)
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DECLARE_MTYPE(HASH_BACKET)
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/* Default hash table size. */
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#define HASH_INITIAL_SIZE 256 /* initial number of backets. */
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#define HASH_THRESHOLD 10 /* expand when backet. */
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#define HASHWALK_CONTINUE 0
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#define HASHWALK_ABORT -1
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struct hash_backet
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{
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/* if this backet is the head of the linked listed, len denotes the number of
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* elements in the list */
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int len;
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/* Linked list. */
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struct hash_backet *next;
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/* Hash key. */
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unsigned int key;
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/* Data. */
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void *data;
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};
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struct hashstats
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{
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/* number of empty hash buckets */
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_Atomic int empty;
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/* sum of squares of bucket length */
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_Atomic uint64_t ssq;
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};
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struct hash
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{
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/* Hash backet. */
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struct hash_backet **index;
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/* Hash table size. Must be power of 2 */
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unsigned int size;
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/* If expansion failed. */
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int no_expand;
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/* Key make function. */
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unsigned int (*hash_key) (void *);
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/* Data compare function. */
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int (*hash_cmp) (const void *, const void *);
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/* Backet alloc. */
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unsigned long count;
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struct hashstats stats;
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/* hash name */
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char *name;
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};
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extern struct hash *hash_create (unsigned int (*) (void *),
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int (*) (const void *, const void *),
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const char *);
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extern struct hash *hash_create_size (unsigned int, unsigned int (*) (void *),
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int (*) (const void *, const void *),
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const char *);
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extern void *hash_get (struct hash *, void *, void * (*) (void *));
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extern void *hash_alloc_intern (void *);
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extern void *hash_lookup (struct hash *, void *);
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extern void *hash_release (struct hash *, void *);
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extern void hash_iterate (struct hash *,
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void (*) (struct hash_backet *, void *), void *);
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extern void hash_walk (struct hash *,
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int (*) (struct hash_backet *, void *), void *);
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extern void hash_clean (struct hash *, void (*) (void *));
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extern void hash_free (struct hash *);
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extern unsigned int string_hash_make (const char *);
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extern void hash_cmd_init (void);
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#endif /* _ZEBRA_HASH_H */
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