00001 /* 00002 * astobj2 - replacement containers for asterisk data structures. 00003 * 00004 * Copyright (C) 2006 Marta Carbone, Luigi Rizzo - Univ. di Pisa, Italy 00005 * 00006 * See http://www.asterisk.org for more information about 00007 * the Asterisk project. Please do not directly contact 00008 * any of the maintainers of this project for assistance; 00009 * the project provides a web site, mailing lists and IRC 00010 * channels for your use. 00011 * 00012 * This program is free software, distributed under the terms of 00013 * the GNU General Public License Version 2. See the LICENSE file 00014 * at the top of the source tree. 00015 */ 00016 00017 #ifndef _ASTERISK_ASTOBJ2_H 00018 #define _ASTERISK_ASTOBJ2_H 00019 00020 /*! \file 00021 * 00022 * \brief Object Model implementing objects and containers. 00023 00024 These functions implement an abstraction for objects (with 00025 locks and reference counts) and containers for these user-defined objects, 00026 supporting locking, reference counting and callbacks. 00027 00028 The internal implementation of the container is opaque to the user, 00029 so we can use different data structures as needs arise. 00030 00031 At the moment, however, the only internal data structure is a hash 00032 table. When other structures will be implemented, the initialization 00033 function may change. 00034 00035 USAGE - OBJECTS 00036 00037 An object is a block of memory that must be allocated with the 00038 function ao2_alloc(), and for which the system keeps track (with 00039 abit of help from the programmer) of the number of references around. 00040 When an object has no more references, it is destroyed, by first 00041 invoking whatever 'destructor' function the programmer specifies 00042 (it can be NULL), and then freeing the memory. 00043 This way objects can be shared without worrying who is in charge 00044 of freeing them. 00045 00046 Basically, creating an object requires the size of the object and 00047 and a pointer to the destructor function: 00048 00049 struct foo *o; 00050 00051 o = ao2_alloc(sizeof(struct foo), my_destructor_fn); 00052 00053 The object returned has a refcount = 1. 00054 Note that the memory for the object is allocated and zeroed. 00055 - We cannot realloc() the object itself. 00056 - We cannot call free(o) to dispose of the object; rather we 00057 tell the system that we do not need the reference anymore: 00058 00059 ao2_ref(o, -1) 00060 00061 causing the destructor to be called (and then memory freed) when 00062 the refcount goes to 0. This is also available as ao2_unref(o), 00063 and returns NULL as a convenience, so you can do things like 00064 o = ao2_unref(o); 00065 and clean the original pointer to prevent errors. 00066 00067 - ao2_ref(o, +1) can be used to modify the refcount on the 00068 object in case we want to pass it around. 00069 00070 00071 - other calls on the object are ao2_lock(obj), ao2_unlock(), 00072 ao2_trylock(), to manipulate the lock. 00073 00074 00075 USAGE - CONTAINERS 00076 00077 A containers is an abstract data structure where we can store 00078 objects, search them (hopefully in an efficient way), and iterate 00079 or apply a callback function to them. A container is just an object 00080 itself. 00081 00082 A container must first be allocated, specifying the initial 00083 parameters. At the moment, this is done as follows: 00084 00085 <b>Sample Usage:</b> 00086 \code 00087 00088 struct ao2_container *c; 00089 00090 c = ao2_container_alloc(MAX_BUCKETS, my_hash_fn, my_cmp_fn); 00091 00092 where 00093 - MAX_BUCKETS is the number of buckets in the hash table, 00094 - my_hash_fn() is the (user-supplied) function that returns a 00095 hash key for the object (further reduced moduly MAX_BUCKETS 00096 by the container's code); 00097 - my_cmp_fn() is the default comparison function used when doing 00098 searches on the container, 00099 00100 A container knows little or nothing about the object itself, 00101 other than the fact that it has been created by ao2_alloc() 00102 All knowledge of the (user-defined) internals of the object 00103 is left to the (user-supplied) functions passed as arguments 00104 to ao2_container_alloc(). 00105 00106 If we want to insert the object in the container, we should 00107 initialize its fields -- especially, those used by my_hash_fn() -- 00108 to compute the bucket to use. 00109 Once done, we can link an object to a container with 00110 00111 ao2_link(c, o); 00112 00113 The function returns NULL in case of errors (and the object 00114 is not inserted in the container). Other values mean success 00115 (we are not supposed to use the value as a pointer to anything). 00116 00117 \note While an object o is in a container, we expect that 00118 my_hash_fn(o) will always return the same value. The function 00119 does not lock the object to be computed, so modifications of 00120 those fields that affect the computation of the hash should 00121 be done by extractiong the object from the container, and 00122 reinserting it after the change (this is not terribly expensive). 00123 00124 \note A container with a single buckets is effectively a linked 00125 list. However there is no ordering among elements. 00126 00127 Objects implement a reference counter keeping the count 00128 of the number of references that reference an object. 00129 00130 When this number becomes zero the destructor will be 00131 called and the object will be free'd. 00132 */ 00133 00134 /*! 00135 * Invoked just before freeing the memory for the object. 00136 * It is passed a pointer to user data. 00137 */ 00138 typedef void (*ao2_destructor_fn)(void *); 00139 00140 void ao2_bt(void); /* backtrace */ 00141 /*! 00142 * Allocate and initialize an object. 00143 * 00144 * \param data_size The sizeof() of user-defined structure. 00145 * \param destructor_fn The function destructor (can be NULL) 00146 * \return A pointer to user data. 00147 * 00148 * Allocates a struct astobj2 with sufficient space for the 00149 * user-defined structure. 00150 * \notes: 00151 * - storage is zeroed; XXX maybe we want a flag to enable/disable this. 00152 * - the refcount of the object just created is 1 00153 * - the returned pointer cannot be free()'d or realloc()'ed; 00154 * rather, we just call ao2_ref(o, -1); 00155 */ 00156 void *ao2_alloc(const size_t data_size, ao2_destructor_fn destructor_fn); 00157 00158 /*! 00159 * Reference/unreference an object and return the old refcount. 00160 * 00161 * \param o A pointer to the object 00162 * \param delta Value to add to the reference counter. 00163 * \return The value of the reference counter before the operation. 00164 * 00165 * Increase/decrease the reference counter according 00166 * the value of delta. 00167 * 00168 * If the refcount goes to zero, the object is destroyed. 00169 * 00170 * \note The object must not be locked by the caller of this function, as 00171 * it is invalid to try to unlock it after releasing the reference. 00172 * 00173 * \note if we know the pointer to an object, it is because we 00174 * have a reference count to it, so the only case when the object 00175 * can go away is when we release our reference, and it is 00176 * the last one in existence. 00177 */ 00178 int ao2_ref(void *o, int delta); 00179 00180 /*! 00181 * Lock an object. 00182 * 00183 * \param a A pointer to the object we want lock. 00184 * \return 0 on success, other values on error. 00185 */ 00186 int ao2_lock(void *a); 00187 00188 /*! 00189 * Unlock an object. 00190 * 00191 * \param a A pointer to the object we want unlock. 00192 * \return 0 on success, other values on error. 00193 */ 00194 int ao2_unlock(void *a); 00195 00196 /*! 00197 * 00198 * Containers 00199 00200 containers are data structures meant to store several objects, 00201 and perform various operations on them. 00202 Internally, objects are stored in lists, hash tables or other 00203 data structures depending on the needs. 00204 00205 NOTA BENE: at the moment the only container we support is the 00206 hash table and its degenerate form, the list. 00207 00208 Operations on container include: 00209 00210 c = ao2_container_alloc(size, cmp_fn, hash_fn) 00211 allocate a container with desired size and default compare 00212 and hash function 00213 00214 ao2_find(c, arg, flags) 00215 returns zero or more element matching a given criteria 00216 (specified as arg). Flags indicate how many results we 00217 want (only one or all matching entries), and whether we 00218 should unlink the object from the container. 00219 00220 ao2_callback(c, flags, fn, arg) 00221 apply fn(obj, arg) to all objects in the container. 00222 Similar to find. fn() can tell when to stop, and 00223 do anything with the object including unlinking it. 00224 Note that the entire operation is run with the container 00225 locked, so noone else can change its content while we work on it. 00226 However, we pay this with the fact that doing 00227 anything blocking in the callback keeps the container 00228 blocked. 00229 The mechanism is very flexible because the callback function fn() 00230 can do basically anything e.g. counting, deleting records, etc. 00231 possibly using arg to store the results. 00232 00233 iterate on a container 00234 this is done with the following sequence 00235 00236 struct ao2_container *c = ... // our container 00237 struct ao2_iterator i; 00238 void *o; 00239 00240 i = ao2_iterator_init(c, flags); 00241 00242 while ( (o = ao2_iterator_next(&i)) ) { 00243 ... do something on o ... 00244 ao2_ref(o, -1); 00245 } 00246 00247 The difference with the callback is that the control 00248 on how to iterate is left to us. 00249 00250 ao2_ref(c, -1) 00251 dropping a reference to a container destroys it, very simple! 00252 00253 Containers are astobj2 object themselves, and this is why their 00254 implementation is simple too. 00255 00256 */ 00257 00258 /*! 00259 * We can perform different operation on an object. We do this 00260 * according the following flags. 00261 */ 00262 enum search_flags { 00263 /*! unlink the object found */ 00264 OBJ_UNLINK = (1 << 0), 00265 /*! on match, don't return the object or increase its reference count. */ 00266 OBJ_NODATA = (1 << 1), 00267 /*! don't stop at the first match 00268 * \note This is not fully implemented. */ 00269 OBJ_MULTIPLE = (1 << 2), 00270 /*! obj is an object of the same type as the one being searched for. 00271 * This implies that it can be passed to the object's hash function 00272 * for optimized searching. */ 00273 OBJ_POINTER = (1 << 3), 00274 }; 00275 00276 /*! 00277 * Type of a generic function to generate a hash value from an object. 00278 * 00279 */ 00280 typedef int (*ao2_hash_fn)(const void *obj, const int flags); 00281 00282 /*! 00283 * valid callback results: 00284 * We return a combination of 00285 * CMP_MATCH when the object matches the request, 00286 * and CMP_STOP when we should not continue the search further. 00287 */ 00288 enum _cb_results { 00289 CMP_MATCH = 0x1, 00290 CMP_STOP = 0x2, 00291 }; 00292 00293 /*! 00294 * generic function to compare objects. 00295 * This, as other callbacks, should return a combination of 00296 * _cb_results as described above. 00297 * 00298 * \param o object from container 00299 * \param arg search parameters (directly from ao2_find) 00300 * \param flags passed directly from ao2_find 00301 * XXX explain. 00302 */ 00303 00304 /*! 00305 * Type of a generic callback function 00306 * \param obj pointer to the (user-defined part) of an object. 00307 * \param arg callback argument from ao2_callback() 00308 * \param flags flags from ao2_callback() 00309 * The return values are the same as a compare function. 00310 * In fact, they are the same thing. 00311 */ 00312 typedef int (*ao2_callback_fn)(void *obj, void *arg, int flags); 00313 00314 /*! 00315 * Here start declarations of containers. 00316 */ 00317 struct ao2_container; 00318 00319 /*! 00320 * Allocate and initialize a container 00321 * with the desired number of buckets. 00322 * 00323 * We allocate space for a struct astobj_container, struct container 00324 * and the buckets[] array. 00325 * 00326 * \param my_hash_fn Pointer to a function computing a hash value. 00327 * \param my_cmp_fn Pointer to a function comparating key-value 00328 * with a string. (can be NULL) 00329 * \return A pointer to a struct container. 00330 * 00331 * destructor is set implicitly. 00332 */ 00333 struct ao2_container *ao2_container_alloc(const uint n_buckets, 00334 ao2_hash_fn hash_fn, ao2_callback_fn cmp_fn); 00335 00336 /*! 00337 * Returns the number of elements in a container. 00338 */ 00339 int ao2_container_count(struct ao2_container *c); 00340 00341 /* 00342 * Here we have functions to manage objects. 00343 * 00344 * We can use the functions below on any kind of 00345 * object defined by the user. 00346 */ 00347 00348 /*! 00349 * \brief Add an object to a container. 00350 * 00351 * \param c the container to operate on. 00352 * \param newobj the object to be added. 00353 * 00354 * \return NULL on errors, other values on success. 00355 * 00356 * This function inserts an object in a container according its key. 00357 * 00358 * \note Remember to set the key before calling this function. 00359 * 00360 * \note This function automatically increases the reference count to 00361 * account for the reference to the object that the container now holds. 00362 * 00363 * For Asterisk 1.4 only, there is a dirty hack here to ensure that chan_iax2 00364 * can have objects linked in to the container at the head instead of tail 00365 * when it is just a linked list. This is to maintain some existing behavior 00366 * where the order must be maintained as it was before this conversion so that 00367 * matching behavior doesn't change. 00368 */ 00369 #define ao2_link(c, o) __ao2_link(c, o, 0) 00370 void *__ao2_link(struct ao2_container *c, void *newobj, int iax2_hack); 00371 00372 /*! 00373 * \brief Remove an object from the container 00374 * 00375 * \arg c the container 00376 * \arg obj the object to unlink 00377 * 00378 * \retval NULL, always 00379 * 00380 * \note The object requested to be unlinked must be valid. However, if it turns 00381 * out that it is not in the container, this function is still safe to 00382 * be called. 00383 * 00384 * \note If the object gets unlinked from the container, the container's 00385 * reference to the object will be automatically released. 00386 */ 00387 void *ao2_unlink(struct ao2_container *c, void *obj); 00388 00389 /*! \struct Used as return value if the flag OBJ_MULTIPLE is set */ 00390 struct ao2_list { 00391 struct ao2_list *next; 00392 void *obj; /* pointer to the user portion of the object */ 00393 }; 00394 00395 /*! 00396 * ao2_callback() and astob2_find() are the same thing with only one difference: 00397 * the latter uses as a callback the function passed as my_cmp_f() at 00398 * the time of the creation of the container. 00399 * 00400 * \param c A pointer to the container to operate on. 00401 * \param arg passed to the callback. 00402 * \param flags A set of flags specifying the operation to perform, 00403 partially used by the container code, but also passed to 00404 the callback. 00405 * \return A pointer to the object found/marked, 00406 * a pointer to a list of objects matching comparison function, 00407 * NULL if not found. 00408 * If the function returns any objects, their refcount is incremented, 00409 * and the caller is in charge of decrementing them once done. 00410 * Also, in case of multiple values returned, the list used 00411 * to store the objects must be freed by the caller. 00412 * 00413 * This function searches through a container and performs operations 00414 * on objects according on flags passed. 00415 * XXX describe better 00416 * The comparison is done calling the compare function set implicitly. 00417 * The p pointer can be a pointer to an object or to a key, 00418 * we can say this looking at flags value. 00419 * If p points to an object we will search for the object pointed 00420 * by this value, otherwise we serch for a key value. 00421 * If the key is not uniq we only find the first matching valued. 00422 * If we use the OBJ_MARK flags, we mark all the objects matching 00423 * the condition. 00424 * 00425 * The use of flags argument is the follow: 00426 * 00427 * OBJ_UNLINK unlinks the object found 00428 * OBJ_NODATA on match, do return an object 00429 * Callbacks use OBJ_NODATA as a default 00430 * functions such as find() do 00431 * OBJ_MULTIPLE return multiple matches 00432 * Default for _find() is no. 00433 * to a key (not yet supported) 00434 * OBJ_POINTER the pointer is an object pointer 00435 * 00436 * In case we return a list, the callee must take care to destroy 00437 * that list when no longer used. 00438 * 00439 * \note When the returned object is no longer in use, ao2_ref() should 00440 * be used to free the additional reference possibly created by this function. 00441 */ 00442 /* XXX order of arguments to find */ 00443 void *ao2_find(struct ao2_container *c, void *arg, enum search_flags flags); 00444 void *ao2_callback(struct ao2_container *c, 00445 enum search_flags flags, 00446 ao2_callback_fn cb_fn, void *arg); 00447 00448 int ao2_match_by_addr(void *user_data, void *arg, int flags); 00449 /*! 00450 * 00451 * 00452 * When we need to walk through a container, we use 00453 * ao2_iterator to keep track of the current position. 00454 * 00455 * Because the navigation is typically done without holding the 00456 * lock on the container across the loop, 00457 * objects can be inserted or deleted or moved 00458 * while we work. As a consequence, there is no guarantee that 00459 * the we manage to touch all the elements on the list, or it 00460 * is possible that we touch the same object multiple times. 00461 * However, within the current hash table container, the following is true: 00462 * - It is not possible to miss an object in the container while iterating 00463 * unless it gets added after the iteration begins and is added to a bucket 00464 * that is before the one the current object is in. In this case, even if 00465 * you locked the container around the entire iteration loop, you still would 00466 * not see this object, because it would still be waiting on the container 00467 * lock so that it can be added. 00468 * - It would be extremely rare to see an object twice. The only way this can 00469 * happen is if an object got unlinked from the container and added again 00470 * during the same iteration. Furthermore, when the object gets added back, 00471 * it has to be in the current or later bucket for it to be seen again. 00472 * 00473 * An iterator must be first initialized with ao2_iterator_init(), 00474 * then we can use o = ao2_iterator_next() to move from one 00475 * element to the next. Remember that the object returned by 00476 * ao2_iterator_next() has its refcount incremented, 00477 * and the reference must be explicitly released when done with it. 00478 * 00479 * Example: 00480 * 00481 * \code 00482 * 00483 * struct ao2_container *c = ... // the container we want to iterate on 00484 * struct ao2_iterator i; 00485 * struct my_obj *o; 00486 * 00487 * i = ao2_iterator_init(c, flags); 00488 * 00489 * while ( (o = ao2_iterator_next(&i)) ) { 00490 * ... do something on o ... 00491 * ao2_ref(o, -1); 00492 * } 00493 * 00494 * \endcode 00495 * 00496 */ 00497 00498 /*! 00499 * You are not supposed to know the internals of an iterator! 00500 * We would like the iterator to be opaque, unfortunately 00501 * its size needs to be known if we want to store it around 00502 * without too much trouble. 00503 * Anyways... 00504 * The iterator has a pointer to the container, and a flags 00505 * field specifying various things e.g. whether the container 00506 * should be locked or not while navigating on it. 00507 * The iterator "points" to the current object, which is identified 00508 * by three values: 00509 * - a bucket number; 00510 * - the object_id, which is also the container version number 00511 * when the object was inserted. This identifies the object 00512 * univoquely, however reaching the desired object requires 00513 * scanning a list. 00514 * - a pointer, and a container version when we saved the pointer. 00515 * If the container has not changed its version number, then we 00516 * can safely follow the pointer to reach the object in constant time. 00517 * Details are in the implementation of ao2_iterator_next() 00518 * A freshly-initialized iterator has bucket=0, version = 0. 00519 */ 00520 00521 struct ao2_iterator { 00522 /*! the container */ 00523 struct ao2_container *c; 00524 /*! operation flags */ 00525 int flags; 00526 #define F_AO2I_DONTLOCK 1 /*!< don't lock when iterating */ 00527 /*! current bucket */ 00528 int bucket; 00529 /*! container version */ 00530 uint c_version; 00531 /*! pointer to the current object */ 00532 void *obj; 00533 /*! container version when the object was created */ 00534 uint version; 00535 }; 00536 00537 struct ao2_iterator ao2_iterator_init(struct ao2_container *c, int flags); 00538 00539 void *ao2_iterator_next(struct ao2_iterator *a); 00540 00541 #endif /* _ASTERISK_ASTOBJ2_H */