path: root/include/asterisk/hashtab.h

/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2006, Digium, Inc.
 *
 * Steve Murphy <murf@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */
#ifndef _ASTERISK_HASHTAB_H_
#define _ASTERISK_HASHTAB_H_
#define __USE_UNIX98 1          /* to get the MUTEX_RECURSIVE stuff */

/* generic (perhaps overly so) hashtable implementation */

/* notes:

A hash table is a structure that allows for an exact-match search
in O(1) (or close to that) time.

The method: given: a set of {key,val} pairs. (at a minimum).
            given: a hash function, which, given a key,
            will return an integer. Ideally, each key in the
            set will have its own unique associated hash value.
			This hash number will index into an array. "buckets"
            are what the elements of this array are called. To
            handle possible collisions in hash values, buckets can form a list.

The key for a value must be contained in the value, or we won't
be able to find it in the bucket list.

This implementation is pretty generic, because:
 1. The value and key are expected to be in a structure
    (along with other data, perhaps) and it's address is a "void *".
 2. The pointer to a compare function must be passed in at the
    time of creation, and is stored in the hashtable.
 3. The pointer to a resize function, which returns 1 if the
    hash table is to be grown. A default routine is provided
    if the pointer is NULL, and uses the java hashtable metric
    of a 75% load factor.
 4. The pointer to a "new size" function, which returns a preferable
    new size for the hash table bucket array. By default, a function
    is supplied which roughly doubles the size of the array, is provided.
    This size should ideally be a prime number.
 5. The hashing function pointer must also be supplied. This function
    must be written by the user to access the keys in the objects being
    stored. Some helper functions that use a simple "mult by prime, add
    the next char", sort of string hash, or a simple modulus of the hash
    table size for ints, is provided; the user can use these simple
    algorithms to generate a hash, or implement any other algorithms they
    wish.
 6. Recently updated the hash routines to use Doubly-linked lists for buckets,
    and added a doubly-linked list that threads thru every bucket in the table.
    The list of all buckets is on the HashTab struct. The Traversal was modified
    to go thru this list instead of searching the bucket array for buckets.
    This also should make it safe to remove a bucket during the traversal.
    Removal and destruction routines will work faster.
*/

struct ast_hashtab_bucket
{
	const void *object;                    /* whatever it is we are storing in this table */
	struct ast_hashtab_bucket *next;       /* a DLL of buckets in hash collision */
	struct ast_hashtab_bucket *prev;       /* a DLL of buckets in hash collision */
	struct ast_hashtab_bucket *tnext;      /* a DLL of all the hash buckets for traversal */
	struct ast_hashtab_bucket *tprev;      /* a DLL of all the hash buckets for traversal */
};

struct ast_hashtab
{
	struct ast_hashtab_bucket **array;
	struct ast_hashtab_bucket *tlist; /* the head of a DLList of all the hashbuckets in the table (for traversal). */
	
	int (*compare) (const void *a, const void *b);            /* a ptr to func that returns int, and take two void* ptrs, compares them, 
													 rets -1 if a < b; rets 0 if a==b; rets 1 if a>b */
	int (*newsize) (struct ast_hashtab *tab);     /* a ptr to func that returns int, a new size for hash tab, based on curr_size */
	int (*resize) (struct ast_hashtab *tab);      /* a function to decide whether this hashtable should be resized now */
	unsigned int (*hash) (const void *obj);         /* a hash func ptr for this table. Given a raw ptr to an obj, 
													 it calcs a hash.*/
	int hash_tab_size;                            /* the size of the bucket array */
	int hash_tab_elements;                        /* the number of objects currently stored in the table */
	int largest_bucket_size;                      /* a stat on the health of the table */
	int resize_count;                             /* a count of the number of times this table has been
													 resized */
	int do_locking;                               /* if 1, use locks to guarantee safety of insertions/deletions */
	/* this spot reserved for the proper lock storage */
	ast_rwlock_t lock;                                /* is this as good as it sounds? */
};

struct ast_hashtab_iter              /* an iterator for traversing the buckets */
{
	struct ast_hashtab *tab;
	struct ast_hashtab_bucket *next;
};


/* some standard, default routines for general use */

int isPrime(int num); /* this one is handy for sizing the hash table, tells if num is prime or not */

int ast_hashtab_compare_strings(const void *a, const void *b); /* assumes a and b are char * and returns 0 if they match */


int ast_hashtab_compare_strings_nocase(const void *a, const void *b); /* assumes a & b are strings, returns 0 if they match (strcasecmp) */


int ast_hashtab_compare_ints(const void *a, const void *b);  /* assumes a & b are int *, returns a != b */


int ast_hashtab_compare_shorts(const void *a, const void *b);  /* assumes a & b are short *, returns a != b */


int ast_hashtab_resize_java(struct ast_hashtab *tab); /* returns 1 if the table is 75% full or more */


int ast_hashtab_resize_tight(struct ast_hashtab *tab); /* not yet specified; probably will return 1 if table is 100% full */


int ast_hashtab_resize_none(struct ast_hashtab *tab); /* no resizing; always return 0 */


int ast_hashtab_newsize_java(struct ast_hashtab *tab);  /* returns a prime number roughly 2x the current table size */


int ast_hashtab_newsize_tight(struct ast_hashtab *tab); /* not yet specified, probably will return 1.5x the current table size */


int ast_hashtab_newsize_none(struct ast_hashtab *tab); /* always return current size -- no resizing */


unsigned int ast_hashtab_hash_string(const void *obj); /* hashes a string to a number, mod is applied so it in the range 0 to mod-1 */


unsigned int ast_hashtab_hash_string_nocase(const void *obj);  /* upcases each char before using them for a hash */


unsigned int ast_hashtab_hash_string_sax(const void *obj); /* from Josh */


unsigned int ast_hashtab_hash_int(const int num);  /* right now, both these funcs are just result = num%modulus; */


unsigned int ast_hashtab_hash_short(const short num);


struct ast_hashtab * ast_hashtab_create(int initial_buckets,
					int (*compare)(const void *a, const void *b),        /* a func to compare two elements in the hash -- cannot be null  */
					int (*resize)(struct ast_hashtab *),     /* a func to decide if the table needs to be resized, 
										a NULL ptr here will cause a default to be used */
					int (*newsize)(struct ast_hashtab *tab), /* a ptr to func that returns a new size of the array. 
										A NULL will cause a default to be used */
					unsigned int (*hash)(const void *obj),     /* a func to do the hashing */
					int do_locking );                        /* use locks to guarantee safety of iterators/insertion/deletion */


	/* this func will free the hash table and all its memory. It
	   doesn't touch the objects stored in it */
void ast_hashtab_destroy( struct ast_hashtab *tab, void (*objdestroyfunc)(void *obj));


	/* normally, you'd insert "safely" by checking to see if the element is
	   already there; in this case, you must already have checked. If an element
	   is already in the hashtable, that matches this one, most likely this one
	   will be found first. */
	/* will force a resize if the resize func returns 1 */
	/* returns 1 on success, 0 if there's a problem */
int ast_hashtab_insert_immediate(struct ast_hashtab *tab, const void *obj);

	/* same as the above, but h is the hash index; won't hash to find the index */
int ast_hashtab_insert_immediate_bucket(struct ast_hashtab *tab, const void *obj, unsigned int h);


	/* check to see if the element is already there; insert only if
	   it is not there.*/
	/* will force a resize if the resize func returns 1 */
	/* returns 1 on success, 0 if there's a problem, or it's already there. */
int ast_hashtab_insert_safe(struct ast_hashtab *tab, const void *obj);


	/* lookup this object in the hash table. return a ptr if found, or NULL if not */
void * ast_hashtab_lookup(struct ast_hashtab *tab, const void *obj);

    /* if you know the hash val for the object, then use this and avoid the recalc
	   of the hash (the modulus (table_size) is not applied) */
void * ast_hashtab_lookup_with_hash(struct ast_hashtab *tab, const void *obj, unsigned int hashval);

	/* same as the above lookup, but sets h to the key hash value if the lookup fails -- this has the modulus 
       applied, and will not be useful for long term storage if the table is resizable */
void * ast_hashtab_lookup_bucket(struct ast_hashtab *tab, const void *obj, unsigned int *h);

	/* returns key stats for the table */
void ast_hashtab_get_stats( struct ast_hashtab *tab, int *biggest_bucket_size, int *resize_count, int *num_objects, int *num_buckets);

	/* this function returns the number of elements stored in the hashtab */
int  ast_hashtab_size( struct ast_hashtab *tab);

	/* this function returns the size of the bucket array in the hashtab */
int  ast_hashtab_capacity( struct ast_hashtab *tab);

    /* this function will return a copy of the table */
struct ast_hashtab *ast_hashtab_dup(struct ast_hashtab *tab, void *(*obj_dup_func)(const void *obj));

	/* returns an iterator */
struct ast_hashtab_iter *ast_hashtab_start_traversal(struct ast_hashtab *tab);

	/* end the traversal, free the iterator, unlock if necc. */
void ast_hashtab_end_traversal(struct ast_hashtab_iter *it);

	/* returns the next object in the list, advances iter one step, returns null on end of traversal */
void *ast_hashtab_next(struct ast_hashtab_iter *it);


	/* looks up the object; removes the corresponding bucket */
void *ast_hashtab_remove_object_via_lookup(struct ast_hashtab *tab, void *obj);


	/* looks up the object by hash and then comparing pts in bucket list instead of
	   calling the compare routine; removes the bucket */
void *ast_hashtab_remove_this_object(struct ast_hashtab *tab, void *obj);

/* ------------------ */
/* for lock-enabled traversals with ability to remove an object during the traversal*/
/* ------------------ */

	/* returns an iterator */
struct ast_hashtab_iter *ast_hashtab_start_write_traversal(struct ast_hashtab *tab);

	/* looks up the object; removes the corresponding bucket */
void *ast_hashtab_remove_object_via_lookup_nolock(struct ast_hashtab *tab, void *obj);


	/* looks up the object by hash and then comparing pts in bucket list instead of
	   calling the compare routine; removes the bucket */
void *ast_hashtab_remove_this_object_nolock(struct ast_hashtab *tab, void *obj);

/* ------------------ */
/* ------------------ */

/* user-controlled hashtab locking. Create a hashtab without locking, then call the
   following locking routines yourself to lock the table between threads. */

void ast_hashtab_initlock(struct ast_hashtab *tab); /* call this after you create the table to init the lock */
void ast_hashtab_wrlock(struct ast_hashtab *tab); /* request a write-lock on the  table. */
void ast_hashtab_rdlock(struct ast_hashtab *tab); /* request a read-lock on the table-- don't change anything! */
void ast_hashtab_unlock(struct ast_hashtab *tab);      /* release a read- or write- lock. */
void ast_hashtab_destroylock(struct ast_hashtab *tab); /* call this before you destroy the table. */


#endif