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 #include "asterisk/compat.h" 00021 00022 /*! \file 00023 * 00024 * \brief Object Model implementing objects and containers. 00025 00026 These functions implement an abstraction for objects (with 00027 locks and reference counts) and containers for these user-defined objects, 00028 supporting locking, reference counting and callbacks. 00029 00030 The internal implementation of the container is opaque to the user, 00031 so we can use different data structures as needs arise. 00032 00033 At the moment, however, the only internal data structure is a hash 00034 table. When other structures will be implemented, the initialization 00035 function may change. 00036 00037 USAGE - OBJECTS 00038 00039 An object is a block of memory that must be allocated with the 00040 function ao2_alloc(), and for which the system keeps track (with 00041 abit of help from the programmer) of the number of references around. 00042 When an object has no more references, it is destroyed, by first 00043 invoking whatever 'destructor' function the programmer specifies 00044 (it can be NULL), and then freeing the memory. 00045 This way objects can be shared without worrying who is in charge 00046 of freeing them. 00047 00048 Basically, creating an object requires the size of the object and 00049 and a pointer to the destructor function: 00050 00051 struct foo *o; 00052 00053 o = ao2_alloc(sizeof(struct foo), my_destructor_fn); 00054 00055 The object returned has a refcount = 1. 00056 Note that the memory for the object is allocated and zeroed. 00057 - We cannot realloc() the object itself. 00058 - We cannot call free(o) to dispose of the object; rather we 00059 tell the system that we do not need the reference anymore: 00060 00061 ao2_ref(o, -1) 00062 00063 causing the destructor to be called (and then memory freed) when 00064 the refcount goes to 0. This is also available as ao2_unref(o), 00065 and returns NULL as a convenience, so you can do things like 00066 o = ao2_unref(o); 00067 and clean the original pointer to prevent errors. 00068 00069 - ao2_ref(o, +1) can be used to modify the refcount on the 00070 object in case we want to pass it around. 00071 00072 00073 - other calls on the object are ao2_lock(obj), ao2_unlock(), 00074 ao2_trylock(), to manipulate the lock. 00075 00076 00077 USAGE - CONTAINERS 00078 00079 A containers is an abstract data structure where we can store 00080 objects, search them (hopefully in an efficient way), and iterate 00081 or apply a callback function to them. A container is just an object 00082 itself. 00083 00084 A container must first be allocated, specifying the initial 00085 parameters. At the moment, this is done as follows: 00086 00087 <b>Sample Usage:</b> 00088 \code 00089 00090 struct ao2_container *c; 00091 00092 c = ao2_container_alloc(MAX_BUCKETS, my_hash_fn, my_cmp_fn); 00093 00094 where 00095 - MAX_BUCKETS is the number of buckets in the hash table, 00096 - my_hash_fn() is the (user-supplied) function that returns a 00097 hash key for the object (further reduced moduly MAX_BUCKETS 00098 by the container's code); 00099 - my_cmp_fn() is the default comparison function used when doing 00100 searches on the container, 00101 00102 A container knows little or nothing about the object itself, 00103 other than the fact that it has been created by ao2_alloc() 00104 All knowledge of the (user-defined) internals of the object 00105 is left to the (user-supplied) functions passed as arguments 00106 to ao2_container_alloc(). 00107 00108 If we want to insert the object in the container, we should 00109 initialize its fields -- especially, those used by my_hash_fn() -- 00110 to compute the bucket to use. 00111 Once done, we can link an object to a container with 00112 00113 ao2_link(c, o); 00114 00115 The function returns NULL in case of errors (and the object 00116 is not inserted in the container). Other values mean success 00117 (we are not supposed to use the value as a pointer to anything). 00118 00119 \note While an object o is in a container, we expect that 00120 my_hash_fn(o) will always return the same value. The function 00121 does not lock the object to be computed, so modifications of 00122 those fields that affect the computation of the hash should 00123 be done by extractiong the object from the container, and 00124 reinserting it after the change (this is not terribly expensive). 00125 00126 \note A container with a single buckets is effectively a linked 00127 list. However there is no ordering among elements. 00128 00129 Objects implement a reference counter keeping the count 00130 of the number of references that reference an object. 00131 00132 When this number becomes zero the destructor will be 00133 called and the object will be free'd. 00134 */ 00135 00136 /*! 00137 * Invoked just before freeing the memory for the object. 00138 * It is passed a pointer to user data. 00139 */ 00140 typedef void (*ao2_destructor_fn)(void *); 00141 00142 void ao2_bt(void); /* backtrace */ 00143 /*! 00144 * Allocate and initialize an object. 00145 * 00146 * \param data_size The sizeof() of user-defined structure. 00147 * \param destructor_fn The function destructor (can be NULL) 00148 * \return A pointer to user data. 00149 * 00150 * Allocates a struct astobj2 with sufficient space for the 00151 * user-defined structure. 00152 * \notes: 00153 * - storage is zeroed; XXX maybe we want a flag to enable/disable this. 00154 * - the refcount of the object just created is 1 00155 * - the returned pointer cannot be free()'d or realloc()'ed; 00156 * rather, we just call ao2_ref(o, -1); 00157 */ 00158 void *ao2_alloc(const size_t data_size, ao2_destructor_fn destructor_fn); 00159 00160 /*! 00161 * Reference/unreference an object and return the old refcount. 00162 * 00163 * \param o A pointer to the object 00164 * \param delta Value to add to the reference counter. 00165 * \return The value of the reference counter before the operation. 00166 * 00167 * Increase/decrease the reference counter according 00168 * the value of delta. 00169 * 00170 * If the refcount goes to zero, the object is destroyed. 00171 * 00172 * \note The object must not be locked by the caller of this function, as 00173 * it is invalid to try to unlock it after releasing the reference. 00174 * 00175 * \note if we know the pointer to an object, it is because we 00176 * have a reference count to it, so the only case when the object 00177 * can go away is when we release our reference, and it is 00178 * the last one in existence. 00179 */ 00180 int ao2_ref(void *o, int delta); 00181 00182 /*! 00183 * Lock an object. 00184 * 00185 * \param a A pointer to the object we want lock. 00186 * \return 0 on success, other values on error. 00187 */ 00188 int ao2_lock(void *a); 00189 00190 /*! 00191 * Unlock an object. 00192 * 00193 * \param a A pointer to the object we want unlock. 00194 * \return 0 on success, other values on error. 00195 */ 00196 int ao2_unlock(void *a); 00197 00198 /*! 00199 * 00200 * Containers 00201 00202 containers are data structures meant to store several objects, 00203 and perform various operations on them. 00204 Internally, objects are stored in lists, hash tables or other 00205 data structures depending on the needs. 00206 00207 NOTA BENE: at the moment the only container we support is the 00208 hash table and its degenerate form, the list. 00209 00210 Operations on container include: 00211 00212 c = ao2_container_alloc(size, cmp_fn, hash_fn) 00213 allocate a container with desired size and default compare 00214 and hash function 00215 00216 ao2_find(c, arg, flags) 00217 returns zero or more element matching a given criteria 00218 (specified as arg). Flags indicate how many results we 00219 want (only one or all matching entries), and whether we 00220 should unlink the object from the container. 00221 00222 ao2_callback(c, flags, fn, arg) 00223 apply fn(obj, arg) to all objects in the container. 00224 Similar to find. fn() can tell when to stop, and 00225 do anything with the object including unlinking it. 00226 Note that the entire operation is run with the container 00227 locked, so noone else can change its content while we work on it. 00228 However, we pay this with the fact that doing 00229 anything blocking in the callback keeps the container 00230 blocked. 00231 The mechanism is very flexible because the callback function fn() 00232 can do basically anything e.g. counting, deleting records, etc. 00233 possibly using arg to store the results. 00234 00235 iterate on a container 00236 this is done with the following sequence 00237 00238 struct ao2_container *c = ... // our container 00239 struct ao2_iterator i; 00240 void *o; 00241 00242 i = ao2_iterator_init(c, flags); 00243 00244 while ( (o = ao2_iterator_next(&i)) ) { 00245 ... do something on o ... 00246 ao2_ref(o, -1); 00247 } 00248 00249 The difference with the callback is that the control 00250 on how to iterate is left to us. 00251 00252 ao2_ref(c, -1) 00253 dropping a reference to a container destroys it, very simple! 00254 00255 Containers are astobj2 object themselves, and this is why their 00256 implementation is simple too. 00257 00258 */ 00259 00260 /*! 00261 * We can perform different operation on an object. We do this 00262 * according the following flags. 00263 */ 00264 enum search_flags { 00265 /*! unlink the object found */ 00266 OBJ_UNLINK = (1 << 0), 00267 /*! on match, don't return the object or increase its reference count. */ 00268 OBJ_NODATA = (1 << 1), 00269 /*! don't stop at the first match 00270 * \note This is not fully implemented. */ 00271 OBJ_MULTIPLE = (1 << 2), 00272 /*! obj is an object of the same type as the one being searched for. 00273 * This implies that it can be passed to the object's hash function 00274 * for optimized searching. */ 00275 OBJ_POINTER = (1 << 3), 00276 }; 00277 00278 /*! 00279 * Type of a generic function to generate a hash value from an object. 00280 * 00281 */ 00282 typedef int (*ao2_hash_fn)(const void *obj, const int flags); 00283 00284 /*! 00285 * valid callback results: 00286 * We return a combination of 00287 * CMP_MATCH when the object matches the request, 00288 * and CMP_STOP when we should not continue the search further. 00289 */ 00290 enum _cb_results { 00291 CMP_MATCH = 0x1, 00292 CMP_STOP = 0x2, 00293 }; 00294 00295 /*! 00296 * generic function to compare objects. 00297 * This, as other callbacks, should return a combination of 00298 * _cb_results as described above. 00299 * 00300 * \param o object from container 00301 * \param arg search parameters (directly from ao2_find) 00302 * \param flags passed directly from ao2_find 00303 * XXX explain. 00304 */ 00305 00306 /*! 00307 * Type of a generic callback function 00308 * \param obj pointer to the (user-defined part) of an object. 00309 * \param arg callback argument from ao2_callback() 00310 * \param flags flags from ao2_callback() 00311 * The return values are the same as a compare function. 00312 * In fact, they are the same thing. 00313 */ 00314 typedef int (*ao2_callback_fn)(void *obj, void *arg, int flags); 00315 00316 /*! 00317 * Here start declarations of containers. 00318 */ 00319 struct ao2_container; 00320 00321 /*! 00322 * Allocate and initialize a container 00323 * with the desired number of buckets. 00324 * 00325 * We allocate space for a struct astobj_container, struct container 00326 * and the buckets[] array. 00327 * 00328 * \param my_hash_fn Pointer to a function computing a hash value. 00329 * \param my_cmp_fn Pointer to a function comparating key-value 00330 * with a string. (can be NULL) 00331 * \return A pointer to a struct container. 00332 * 00333 * destructor is set implicitly. 00334 */ 00335 struct ao2_container *ao2_container_alloc(const uint n_buckets, 00336 ao2_hash_fn hash_fn, ao2_callback_fn cmp_fn); 00337 00338 /*! 00339 * Returns the number of elements in a container. 00340 */ 00341 int ao2_container_count(struct ao2_container *c); 00342 00343 /* 00344 * Here we have functions to manage objects. 00345 * 00346 * We can use the functions below on any kind of 00347 * object defined by the user. 00348 */ 00349 00350 /*! 00351 * \brief Add an object to a container. 00352 * 00353 * \param c the container to operate on. 00354 * \param newobj the object to be added. 00355 * 00356 * \return NULL on errors, other values on success. 00357 * 00358 * This function inserts an object in a container according its key. 00359 * 00360 * \note Remember to set the key before calling this function. 00361 * 00362 * \note This function automatically increases the reference count to 00363 * account for the reference to the object that the container now holds. 00364 * 00365 * For Asterisk 1.4 only, there is a dirty hack here to ensure that chan_iax2 00366 * can have objects linked in to the container at the head instead of tail 00367 * when it is just a linked list. This is to maintain some existing behavior 00368 * where the order must be maintained as it was before this conversion so that 00369 * matching behavior doesn't change. 00370 */ 00371 #define ao2_link(c, o) __ao2_link(c, o, 0) 00372 void *__ao2_link(struct ao2_container *c, void *newobj, int iax2_hack); 00373 00374 /*! 00375 * \brief Remove an object from the container 00376 * 00377 * \arg c the container 00378 * \arg obj the object to unlink 00379 * 00380 * \retval NULL, always 00381 * 00382 * \note The object requested to be unlinked must be valid. However, if it turns 00383 * out that it is not in the container, this function is still safe to 00384 * be called. 00385 * 00386 * \note If the object gets unlinked from the container, the container's 00387 * reference to the object will be automatically released. 00388 */ 00389 void *ao2_unlink(struct ao2_container *c, void *obj); 00390 00391 /*! \struct Used as return value if the flag OBJ_MULTIPLE is set */ 00392 struct ao2_list { 00393 struct ao2_list *next; 00394 void *obj; /* pointer to the user portion of the object */ 00395 }; 00396 00397 /*! 00398 * ao2_callback() and astob2_find() are the same thing with only one difference: 00399 * the latter uses as a callback the function passed as my_cmp_f() at 00400 * the time of the creation of the container. 00401 * 00402 * \param c A pointer to the container to operate on. 00403 * \param arg passed to the callback. 00404 * \param flags A set of flags specifying the operation to perform, 00405 partially used by the container code, but also passed to 00406 the callback. 00407 * \return A pointer to the object found/marked, 00408 * a pointer to a list of objects matching comparison function, 00409 * NULL if not found. 00410 * If the function returns any objects, their refcount is incremented, 00411 * and the caller is in charge of decrementing them once done. 00412 * Also, in case of multiple values returned, the list used 00413 * to store the objects must be freed by the caller. 00414 * 00415 * This function searches through a container and performs operations 00416 * on objects according on flags passed. 00417 * XXX describe better 00418 * The comparison is done calling the compare function set implicitly. 00419 * The p pointer can be a pointer to an object or to a key, 00420 * we can say this looking at flags value. 00421 * If p points to an object we will search for the object pointed 00422 * by this value, otherwise we serch for a key value. 00423 * If the key is not uniq we only find the first matching valued. 00424 * If we use the OBJ_MARK flags, we mark all the objects matching 00425 * the condition. 00426 * 00427 * The use of flags argument is the follow: 00428 * 00429 * OBJ_UNLINK unlinks the object found 00430 * OBJ_NODATA on match, do return an object 00431 * Callbacks use OBJ_NODATA as a default 00432 * functions such as find() do 00433 * OBJ_MULTIPLE return multiple matches 00434 * Default for _find() is no. 00435 * to a key (not yet supported) 00436 * OBJ_POINTER the pointer is an object pointer 00437 * 00438 * In case we return a list, the callee must take care to destroy 00439 * that list when no longer used. 00440 * 00441 * \note When the returned object is no longer in use, ao2_ref() should 00442 * be used to free the additional reference possibly created by this function. 00443 */ 00444 /* XXX order of arguments to find */ 00445 void *ao2_find(struct ao2_container *c, void *arg, enum search_flags flags); 00446 void *ao2_callback(struct ao2_container *c, 00447 enum search_flags flags, 00448 ao2_callback_fn cb_fn, void *arg); 00449 00450 int ao2_match_by_addr(void *user_data, void *arg, int flags); 00451 /*! 00452 * 00453 * 00454 * When we need to walk through a container, we use 00455 * ao2_iterator to keep track of the current position. 00456 * 00457 * Because the navigation is typically done without holding the 00458 * lock on the container across the loop, 00459 * objects can be inserted or deleted or moved 00460 * while we work. As a consequence, there is no guarantee that 00461 * the we manage to touch all the elements on the list, or it 00462 * is possible that we touch the same object multiple times. 00463 * However, within the current hash table container, the following is true: 00464 * - It is not possible to miss an object in the container while iterating 00465 * unless it gets added after the iteration begins and is added to a bucket 00466 * that is before the one the current object is in. In this case, even if 00467 * you locked the container around the entire iteration loop, you still would 00468 * not see this object, because it would still be waiting on the container 00469 * lock so that it can be added. 00470 * - It would be extremely rare to see an object twice. The only way this can 00471 * happen is if an object got unlinked from the container and added again 00472 * during the same iteration. Furthermore, when the object gets added back, 00473 * it has to be in the current or later bucket for it to be seen again. 00474 * 00475 * An iterator must be first initialized with ao2_iterator_init(), 00476 * then we can use o = ao2_iterator_next() to move from one 00477 * element to the next. Remember that the object returned by 00478 * ao2_iterator_next() has its refcount incremented, 00479 * and the reference must be explicitly released when done with it. 00480 * 00481 * Example: 00482 * 00483 * \code 00484 * 00485 * struct ao2_container *c = ... // the container we want to iterate on 00486 * struct ao2_iterator i; 00487 * struct my_obj *o; 00488 * 00489 * i = ao2_iterator_init(c, flags); 00490 * 00491 * while ( (o = ao2_iterator_next(&i)) ) { 00492 * ... do something on o ... 00493 * ao2_ref(o, -1); 00494 * } 00495 * 00496 * \endcode 00497 * 00498 */ 00499 00500 /*! 00501 * You are not supposed to know the internals of an iterator! 00502 * We would like the iterator to be opaque, unfortunately 00503 * its size needs to be known if we want to store it around 00504 * without too much trouble. 00505 * Anyways... 00506 * The iterator has a pointer to the container, and a flags 00507 * field specifying various things e.g. whether the container 00508 * should be locked or not while navigating on it. 00509 * The iterator "points" to the current object, which is identified 00510 * by three values: 00511 * - a bucket number; 00512 * - the object_id, which is also the container version number 00513 * when the object was inserted. This identifies the object 00514 * univoquely, however reaching the desired object requires 00515 * scanning a list. 00516 * - a pointer, and a container version when we saved the pointer. 00517 * If the container has not changed its version number, then we 00518 * can safely follow the pointer to reach the object in constant time. 00519 * Details are in the implementation of ao2_iterator_next() 00520 * A freshly-initialized iterator has bucket=0, version = 0. 00521 */ 00522 00523 struct ao2_iterator { 00524 /*! the container */ 00525 struct ao2_container *c; 00526 /*! operation flags */ 00527 int flags; 00528 #define F_AO2I_DONTLOCK 1 /*!< don't lock when iterating */ 00529 /*! current bucket */ 00530 int bucket; 00531 /*! container version */ 00532 uint c_version; 00533 /*! pointer to the current object */ 00534 void *obj; 00535 /*! container version when the object was created */ 00536 uint version; 00537 }; 00538 00539 struct ao2_iterator ao2_iterator_init(struct ao2_container *c, int flags); 00540 00541 void *ao2_iterator_next(struct ao2_iterator *a); 00542 00543 #endif /* _ASTERISK_ASTOBJ2_H */