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Asterisk developer's documentation


hashtab.h

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00001 /*
00002  * Asterisk -- An open source telephony toolkit.
00003  *
00004  * Copyright (C) 2006, Digium, Inc.
00005  *
00006  * Steve Murphy <murf@digium.com>
00007  *
00008  * See http://www.asterisk.org for more information about
00009  * the Asterisk project. Please do not directly contact
00010  * any of the maintainers of this project for assistance;
00011  * the project provides a web site, mailing lists and IRC
00012  * channels for your use.
00013  *
00014  * This program is free software, distributed under the terms of
00015  * the GNU General Public License Version 2. See the LICENSE file
00016  * at the top of the source tree.
00017  */
00018 #ifndef _ASTERISK_HASHTAB_H_
00019 #define _ASTERISK_HASHTAB_H_
00020 #define __USE_UNIX98 1          /* to get the MUTEX_RECURSIVE stuff */
00021 
00022 /*! \file
00023  * \brief Generic (perhaps overly so) hashtable implementation
00024  * \ref AstHash
00025  */
00026 /*! \page AstHash Hash Table support in Asterisk
00027 
00028 A hash table is a structure that allows for an exact-match search
00029 in O(1) (or close to that) time.
00030 
00031 The method: given: a set of {key,val} pairs. (at a minimum).
00032             given: a hash function, which, given a key,
00033             will return an integer. Ideally, each key in the
00034             set will have its own unique associated hash value.
00035          This hash number will index into an array. "buckets"
00036             are what the elements of this array are called. To
00037             handle possible collisions in hash values, buckets can form a list.
00038 
00039 The key for a value must be contained in the value, or we won't
00040 be able to find it in the bucket list.
00041 
00042 This implementation is pretty generic, because:
00043 
00044  1. The value and key are expected to be in a structure
00045     (along with other data, perhaps) and it's address is a "void *".
00046  2. The pointer to a compare function must be passed in at the
00047     time of creation, and is stored in the hashtable.
00048  3. The pointer to a resize function, which returns 1 if the
00049     hash table is to be grown. A default routine is provided
00050     if the pointer is NULL, and uses the java hashtable metric
00051     of a 75% load factor.
00052  4. The pointer to a "new size" function, which returns a preferable
00053     new size for the hash table bucket array. By default, a function
00054     is supplied which roughly doubles the size of the array, is provided.
00055     This size should ideally be a prime number.
00056  5. The hashing function pointer must also be supplied. This function
00057     must be written by the user to access the keys in the objects being
00058     stored. Some helper functions that use a simple "mult by prime, add
00059     the next char", sort of string hash, or a simple modulus of the hash
00060     table size for ints, is provided; the user can use these simple
00061     algorithms to generate a hash, or implement any other algorithms they
00062     wish.
00063  6. Recently updated the hash routines to use Doubly-linked lists for buckets,
00064     and added a doubly-linked list that threads thru every bucket in the table.
00065     The list of all buckets is on the HashTab struct. The Traversal was modified
00066     to go thru this list instead of searching the bucket array for buckets.
00067     This also should make it safe to remove a bucket during the traversal.
00068     Removal and destruction routines will work faster.
00069 */
00070 
00071 struct ast_hashtab_bucket
00072 {
00073    const void *object;                    /*!< whatever it is we are storing in this table */
00074    struct ast_hashtab_bucket *next;       /*!< a DLL of buckets in hash collision */
00075    struct ast_hashtab_bucket *prev;       /*!< a DLL of buckets in hash collision */
00076    struct ast_hashtab_bucket *tnext;      /*!< a DLL of all the hash buckets for traversal */
00077    struct ast_hashtab_bucket *tprev;      /*!< a DLL of all the hash buckets for traversal */
00078 };
00079 
00080 struct ast_hashtab
00081 {
00082    struct ast_hashtab_bucket **array;
00083    struct ast_hashtab_bucket *tlist;      /*!< the head of a DLList of all the hashbuckets in the table (for traversal). */
00084 
00085    int (*compare) (const void *a, const void *b);  /*!< a ptr to func that returns int, and take two void* ptrs, compares them,
00086                                         rets -1 if a < b; rets 0 if a==b; rets 1 if a>b */
00087    int (*newsize) (struct ast_hashtab *tab); /*!< a ptr to func that returns int, a new size for hash tab, based on curr_size */
00088    int (*resize) (struct ast_hashtab *tab);  /*!< a function to decide whether this hashtable should be resized now */
00089    unsigned int (*hash) (const void *obj);         /*!< a hash func ptr for this table. Given a raw ptr to an obj,
00090                                         it calcs a hash.*/
00091    int hash_tab_size;                            /*!< the size of the bucket array */
00092    int hash_tab_elements;                        /*!< the number of objects currently stored in the table */
00093    int largest_bucket_size;                      /*!< a stat on the health of the table */
00094    int resize_count;                             /*!< a count of the number of times this table has been
00095                                         resized */
00096    int do_locking;                               /*!< if 1 use locks to guarantee safety of insertions/deletions */
00097    /* this spot reserved for the proper lock storage */
00098    ast_rwlock_t lock;                                /* is this as good as it sounds? */
00099 };
00100 
00101 /*! \brief an iterator for traversing the buckets */
00102 struct ast_hashtab_iter
00103 {
00104    struct ast_hashtab *tab;
00105    struct ast_hashtab_bucket *next;
00106 };
00107 
00108 
00109 /* some standard, default routines for general use */
00110 
00111 /*!
00112  * \brief Determines if the specified number is prime.
00113  *
00114  * \param num the number to test
00115  * \retval 0 if the number is not prime
00116  * \retval 1 if the number is prime
00117  */
00118 int ast_is_prime(int num);
00119 
00120 /*!
00121  * \brief Compares two strings for equality.
00122  *
00123  * \param a a character string
00124  * \param b a character string
00125  * \retval 0 if the strings match
00126  * \retval <0 if string a is less than string b
00127  * \retval >0 if string a is greather than string b
00128  */
00129 int ast_hashtab_compare_strings(const void *a, const void *b);
00130 
00131 /*!
00132  * \brief Compares two strings for equality, ignoring case.
00133  *
00134  * \param a a character string
00135  * \param b a character string
00136  * \retval 0 if the strings match
00137  * \retval <0 if string a is less than string b
00138  * \retval >0 if string a is greather than string b
00139  */
00140 int ast_hashtab_compare_strings_nocase(const void *a, const void *b);
00141 
00142 /*!
00143  * \brief Compares two integers for equality.
00144  *
00145  * \param a an integer pointer (int *)
00146  * \param b an integer pointer (int *)
00147  * \retval 0 if the integers pointed to are equal
00148  * \retval 1 if a is greater than b
00149  * \retval -1 if a is less than b
00150  */
00151 int ast_hashtab_compare_ints(const void *a, const void *b);
00152 
00153 /*!
00154  * \brief Compares two shorts for equality.
00155  *
00156  * \param a a short pointer (short *)
00157  * \param b a short pointer (short *)
00158  * \retval 0 if the shorts pointed to are equal
00159  * \retval 1 if a is greater than b
00160  * \retval -1 if a is less than b
00161  */
00162 int ast_hashtab_compare_shorts(const void *a, const void *b);
00163 
00164 /*!
00165  * \brief Determines if a table resize should occur using the Java algorithm
00166  *        (if the table load factor is 75% or higher).
00167  *
00168  * \param tab the hash table to operate on
00169  * \retval 0 if the table load factor is less than or equal to 75%
00170  * \retval 1 if the table load factor is greater than 75%
00171  */
00172 int ast_hashtab_resize_java(struct ast_hashtab *tab);
00173 
00174 /*! \brief Causes a resize whenever the number of elements stored in the table
00175  *         exceeds the number of buckets in the table.
00176  *
00177  * \param tab the hash table to operate on
00178  * \retval 0 if the number of elements in the table is less than or equal to
00179  *           the number of buckets
00180  * \retval 1 if the number of elements in the table exceeds the number of
00181  *           buckets
00182  */
00183 int ast_hashtab_resize_tight(struct ast_hashtab *tab);
00184 
00185 /*!
00186  * \brief Effectively disables resizing by always returning 0, regardless of
00187  *        of load factor.
00188  *
00189  * \param tab the hash table to operate on
00190  * \return 0 is always returned
00191  */
00192 int ast_hashtab_resize_none(struct ast_hashtab *tab);
00193 
00194 /*! \brief Create a prime number roughly 2x the current table size */
00195 int ast_hashtab_newsize_java(struct ast_hashtab *tab);
00196 
00197 /* not yet specified, probably will return 1.5x the current table size */
00198 int ast_hashtab_newsize_tight(struct ast_hashtab *tab);
00199 
00200 /*! \brief always return current size -- no resizing */
00201 int ast_hashtab_newsize_none(struct ast_hashtab *tab);
00202 
00203 /*!
00204  * \brief Hashes a string to a number
00205  *
00206  * \param obj the string to hash
00207  * \return Integer hash of the specified string
00208  * \sa ast_hashtable_hash_string_nocase
00209  * \sa ast_hashtab_hash_string_sax
00210  * \note A modulus will be applied to the return value of this function
00211  */
00212 unsigned int ast_hashtab_hash_string(const void *obj);
00213 
00214 /*!
00215  * \brief Hashes a string to a number ignoring case
00216  *
00217  * \param obj the string to hash
00218  * \return Integer hash of the specified string
00219  * \sa ast_hashtable_hash_string
00220  * \sa ast_hashtab_hash_string_sax
00221  * \note A modulus will be applied to the return value of this function
00222  */
00223 unsigned int ast_hashtab_hash_string_nocase(const void *obj);
00224 
00225 /*!
00226  * \brief Hashes a string to a number using a modified Shift-And-XOR algorithm
00227  *
00228  * \param obj the string to hash
00229  * \return Integer has of the specified string
00230  * \sa ast_hastable_hash_string
00231  * \sa ast_hastable_hash_string_nocase
00232  */
00233 unsigned int ast_hashtab_hash_string_sax(const void *obj);
00234 
00235 
00236 unsigned int ast_hashtab_hash_int(const int num);  /* right now, both these funcs are just result = num%modulus; */
00237 
00238 
00239 unsigned int ast_hashtab_hash_short(const short num);
00240 
00241 
00242 /*!
00243  * \brief Create the hashtable list
00244  * \param initial_buckets starting number of buckets
00245  * \param compare a func ptr to compare two elements in the hash -- cannot be null
00246  * \param resize a func ptr to decide if the table needs to be resized, a NULL ptr here will cause a default to be used
00247  * \param newsize a func ptr that returns a new size of the array. A NULL will cause a default to be used
00248  * \param hash a func ptr to do the hashing
00249  * \param do_locking use locks to guarantee safety of iterators/insertion/deletion -- real simpleminded right now
00250 */
00251 #if (defined(MALLOC_DEBUG) && !defined(STANDALONE))
00252 struct ast_hashtab * _ast_hashtab_create(int initial_buckets,
00253                int (*compare)(const void *a, const void *b),
00254                int (*resize)(struct ast_hashtab *),
00255                int (*newsize)(struct ast_hashtab *tab),
00256                unsigned int (*hash)(const void *obj),
00257                int do_locking, const char *file, int lineno, const char *function);
00258 #define ast_hashtab_create(a,b,c,d,e,f)   _ast_hashtab_create(a,b,c,d,e,f,__FILE__,__LINE__,__PRETTY_FUNCTION__)
00259 #else
00260 struct ast_hashtab * ast_hashtab_create(int initial_buckets,
00261                int (*compare)(const void *a, const void *b),
00262                int (*resize)(struct ast_hashtab *),
00263                int (*newsize)(struct ast_hashtab *tab),
00264                unsigned int (*hash)(const void *obj),
00265                int do_locking );
00266 #endif
00267 
00268 /*!
00269  * \brief This func will free the hash table and all its memory.
00270  * \note It doesn't touch the objects stored in it, unless you
00271  *       specify a destroy func; it will call that func for each
00272  *       object in the hashtab, remove all the objects, and then
00273  *       free the hashtab itself. If no destroyfunc is specified
00274  *       then the routine will assume you will free it yourself.
00275  * \param tab
00276  * \param objdestroyfunc
00277 */
00278 void ast_hashtab_destroy( struct ast_hashtab *tab, void (*objdestroyfunc)(void *obj));
00279 
00280 
00281 /*!
00282  * \brief Insert without checking
00283  * \param tab
00284  * \param obj
00285  *
00286  * Normally, you'd insert "safely" by checking to see if the element is
00287  * already there; in this case, you must already have checked. If an element
00288  * is already in the hashtable, that matches this one, most likely this one
00289  * will be found first.
00290  * \note will force a resize if the resize func returns 1
00291  * \retval 1 on success
00292  * \retval 0 if there's a problem
00293 */
00294 #if (defined(MALLOC_DEBUG) && !defined(STANDALONE))
00295 int _ast_hashtab_insert_immediate(struct ast_hashtab *tab, const void *obj, const char *file, int lineno, const char *func);
00296 #define  ast_hashtab_insert_immediate(a,b)   _ast_hashtab_insert_immediate(a, b, __FILE__, __LINE__, __PRETTY_FUNCTION__)
00297 #else
00298 int ast_hashtab_insert_immediate(struct ast_hashtab *tab, const void *obj);
00299 #endif
00300 
00301 /*!
00302  * \brief Insert without checking, hashing or locking
00303  * \param tab
00304  * \param obj
00305  * \param h hashed index value
00306  *
00307  * \note Will force a resize if the resize func returns 1
00308  * \retval 1 on success
00309  * \retval 0 if there's a problem
00310 */
00311 #if (defined(MALLOC_DEBUG) && !defined(STANDALONE))
00312 int _ast_hashtab_insert_immediate_bucket(struct ast_hashtab *tab, const void *obj, unsigned int h, const char *file, int lineno, const char *func);
00313 #define  ast_hashtab_insert_immediate_bucket(a,b,c)   _ast_hashtab_insert_immediate_bucket(a, b, c, __FILE__, __LINE__, __PRETTY_FUNCTION__)
00314 #else
00315 int ast_hashtab_insert_immediate_bucket(struct ast_hashtab *tab, const void *obj, unsigned int h);
00316 #endif
00317 
00318 /*!
00319  * \brief Check and insert new object only if it is not there.
00320  * \note Will force a resize if the resize func returns 1
00321  * \retval 1 on success
00322  * \retval  0 if there's a problem, or it's already there.
00323 */
00324 #if (defined(MALLOC_DEBUG) && !defined(STANDALONE))
00325 int _ast_hashtab_insert_safe(struct ast_hashtab *tab, const void *obj, const char *file, int lineno, const char *func);
00326 #define  ast_hashtab_insert_safe(a,b)  _ast_hashtab_insert_safe(a,b,__FILE__, __LINE__, __PRETTY_FUNCTION__)
00327 #else
00328 int ast_hashtab_insert_safe(struct ast_hashtab *tab, const void *obj);
00329 #endif
00330 
00331 /*!
00332  * \brief Lookup this object in the hash table.
00333  * \param tab
00334  * \param obj
00335  * \retval a ptr if found
00336  * \retval NULL if not found
00337 */
00338 void * ast_hashtab_lookup(struct ast_hashtab *tab, const void *obj);
00339 
00340 /*!
00341  * \brief  Use this if have the hash val for the object
00342  * \note This and avoid the recalc of the hash (the modulus (table_size) is not applied)
00343 */
00344 void * ast_hashtab_lookup_with_hash(struct ast_hashtab *tab, const void *obj, unsigned int hashval);
00345 
00346 /*!
00347  * \brief Similar to ast_hashtab_lookup but sets h to the key hash value if the lookup fails.
00348  * \note This has the modulus applied, and will not be useful for long term storage if the table is resizable.
00349 */
00350 void * ast_hashtab_lookup_bucket(struct ast_hashtab *tab, const void *obj, unsigned int *h);
00351 
00352 /*! \brief Returns key stats for the table */
00353 void ast_hashtab_get_stats( struct ast_hashtab *tab, int *biggest_bucket_size, int *resize_count, int *num_objects, int *num_buckets);
00354 
00355 /*! \brief Returns the number of elements stored in the hashtab */
00356 int ast_hashtab_size( struct ast_hashtab *tab);
00357 
00358 /*! \brief Returns the size of the bucket array in the hashtab */
00359 int ast_hashtab_capacity( struct ast_hashtab *tab);
00360 
00361 /*! \brief Return a copy of the hash table */
00362 #if (defined(MALLOC_DEBUG) && !defined(STANDALONE))
00363 struct ast_hashtab *_ast_hashtab_dup(struct ast_hashtab *tab, void *(*obj_dup_func)(const void *obj), const char *file, int lineno, const char *func);
00364 #define  ast_hashtab_dup(a,b) _ast_hashtab_dup(a,b,__FILE__,__LINE__,__PRETTY_FUNCTION__)
00365 #else
00366 struct ast_hashtab *ast_hashtab_dup(struct ast_hashtab *tab, void *(*obj_dup_func)(const void *obj));
00367 #endif
00368 
00369 /*! \brief Gives an iterator to hastable */
00370 #if (defined(MALLOC_DEBUG) && !defined(STANDALONE))
00371 struct ast_hashtab_iter *_ast_hashtab_start_traversal(struct ast_hashtab *tab, const char *file, int lineno, const char *func);
00372 #define  ast_hashtab_start_traversal(a)   _ast_hashtab_start_traversal(a,__FILE__,__LINE__,__PRETTY_FUNCTION__)
00373 #else
00374 struct ast_hashtab_iter *ast_hashtab_start_traversal(struct ast_hashtab *tab);
00375 #endif
00376 
00377 /*! \brief end the traversal, free the iterator, unlock if necc. */
00378 void ast_hashtab_end_traversal(struct ast_hashtab_iter *it);
00379 
00380 /*! \brief Gets the next object in the list, advances iter one step returns null on end of traversal */
00381 void *ast_hashtab_next(struct ast_hashtab_iter *it);
00382 
00383 /*! \brief Looks up the object, removes the corresponding bucket */
00384 void *ast_hashtab_remove_object_via_lookup(struct ast_hashtab *tab, void *obj);
00385 
00386 /*! \brief Hash the object and then compare ptrs in bucket list instead of
00387       calling the compare routine, will remove the bucket */
00388 void *ast_hashtab_remove_this_object(struct ast_hashtab *tab, void *obj);
00389 
00390 /* ------------------ */
00391 /* for lock-enabled traversals with ability to remove an object during the traversal*/
00392 /* ------------------ */
00393 
00394 /*! \brief Gives an iterator to hastable */
00395 #if (defined(MALLOC_DEBUG) && !defined(STANDALONE))
00396 struct ast_hashtab_iter *_ast_hashtab_start_write_traversal(struct ast_hashtab *tab, const char *file, int lineno, const char *func);
00397 #define  ast_hashtab_start_write_traversal(a)   _ast_hashtab_start_write_traversal(a,__FILE__,__LINE__,__PRETTY_FUNCTION__)
00398 #else
00399 struct ast_hashtab_iter *ast_hashtab_start_write_traversal(struct ast_hashtab *tab);
00400 #endif
00401 
00402 /*! \brief Looks up the object, removes the corresponding bucket */
00403 void *ast_hashtab_remove_object_via_lookup_nolock(struct ast_hashtab *tab, void *obj);
00404 
00405 /*! \brief Hash the object and then compare ptrs in bucket list instead of
00406       calling the compare routine, will remove the bucket */
00407 void *ast_hashtab_remove_this_object_nolock(struct ast_hashtab *tab, void *obj);
00408 
00409 /* ------------------ */
00410 /* ------------------ */
00411 
00412 /* user-controlled hashtab locking. Create a hashtab without locking, then call the
00413    following locking routines yourself to lock the table between threads. */
00414 
00415 /*! \brief Call this after you create the table to init the lock */
00416 void ast_hashtab_initlock(struct ast_hashtab *tab);
00417 /*! \brief Request a write-lock on the table. */
00418 void ast_hashtab_wrlock(struct ast_hashtab *tab);
00419 /*! \brief Request a read-lock on the table -- don't change anything! */
00420 void ast_hashtab_rdlock(struct ast_hashtab *tab);
00421 /*! \brief release a read- or write- lock. */
00422 void ast_hashtab_unlock(struct ast_hashtab *tab);
00423 /*! \brief Call this before you destroy the table. */
00424 void ast_hashtab_destroylock(struct ast_hashtab *tab);
00425 
00426 
00427 #endif

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