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 * \ref AstObj2 00024 * 00025 * \page AstObj2 Object Model implementing objects and containers. 00026 00027 This module implements an abstraction for objects (with locks and 00028 reference counts), and containers for these user-defined objects, 00029 also supporting locking, reference counting and callbacks. 00030 00031 The internal implementation of objects and containers is opaque to the user, 00032 so we can use different data structures as needs arise. 00033 00034 \section AstObj2_UsageObjects USAGE - OBJECTS 00035 00036 An ao2 object is a block of memory that the user code can access, 00037 and for which the system keeps track (with a bit of help from the 00038 programmer) of the number of references around. When an object has 00039 no more references (refcount == 0), it is destroyed, by first 00040 invoking whatever 'destructor' function the programmer specifies 00041 (it can be NULL if none is necessary), and then freeing the memory. 00042 This way objects can be shared without worrying who is in charge 00043 of freeing them. 00044 As an additional feature, ao2 objects are associated to individual 00045 locks. 00046 00047 Creating an object requires the size of the object and 00048 and a pointer to the destructor function: 00049 00050 struct foo *o; 00051 00052 o = ao2_alloc(sizeof(struct foo), my_destructor_fn); 00053 00054 The value returned points to the user-visible portion of the objects 00055 (user-data), but is also used as an identifier for all object-related 00056 operations such as refcount and lock manipulations. 00057 00058 On return from ao2_alloc(): 00059 00060 - the object has a refcount = 1; 00061 - the memory for the object is allocated dynamically and zeroed; 00062 - we cannot realloc() the object itself; 00063 - we cannot call free(o) to dispose of the object. Rather, we 00064 tell the system that we do not need the reference anymore: 00065 00066 ao2_ref(o, -1) 00067 00068 causing the destructor to be called (and then memory freed) when 00069 the refcount goes to 0. This is also available as ao2_unref(o), 00070 and returns NULL as a convenience, so you can do things like 00071 00072 o = ao2_unref(o); 00073 00074 and clean the original pointer to prevent errors. 00075 00076 - ao2_ref(o, +1) can be used to modify the refcount on the 00077 object in case we want to pass it around. 00078 00079 - ao2_lock(obj), ao2_unlock(obj), ao2_trylock(obj) can be used 00080 to manipulate the lock associated with the object. 00081 00082 00083 \section AstObj2_UsageContainers USAGE - CONTAINERS 00084 00085 An ao2 container is an abstract data structure where we can store 00086 ao2 objects, search them (hopefully in an efficient way), and iterate 00087 or apply a callback function to them. A container is just an ao2 object 00088 itself. 00089 00090 A container must first be allocated, specifying the initial 00091 parameters. At the moment, this is done as follows: 00092 00093 <b>Sample Usage:</b> 00094 \code 00095 00096 struct ao2_container *c; 00097 00098 c = ao2_container_alloc(MAX_BUCKETS, my_hash_fn, my_cmp_fn); 00099 \endcode 00100 00101 where 00102 00103 - MAX_BUCKETS is the number of buckets in the hash table, 00104 - my_hash_fn() is the (user-supplied) function that returns a 00105 hash key for the object (further reduced modulo MAX_BUCKETS 00106 by the container's code); 00107 - my_cmp_fn() is the default comparison function used when doing 00108 searches on the container, 00109 00110 A container knows little or nothing about the objects it stores, 00111 other than the fact that they have been created by ao2_alloc(). 00112 All knowledge of the (user-defined) internals of the objects 00113 is left to the (user-supplied) functions passed as arguments 00114 to ao2_container_alloc(). 00115 00116 If we want to insert an object in a container, we should 00117 initialize its fields -- especially, those used by my_hash_fn() -- 00118 to compute the bucket to use. 00119 Once done, we can link an object to a container with 00120 00121 ao2_link(c, o); 00122 00123 The function returns NULL in case of errors (and the object 00124 is not inserted in the container). Other values mean success 00125 (we are not supposed to use the value as a pointer to anything). 00126 00127 \note While an object o is in a container, we expect that 00128 my_hash_fn(o) will always return the same value. The function 00129 does not lock the object to be computed, so modifications of 00130 those fields that affect the computation of the hash should 00131 be done by extracting the object from the container, and 00132 reinserting it after the change (this is not terribly expensive). 00133 00134 \note A container with a single buckets is effectively a linked 00135 list. However there is no ordering among elements. 00136 00137 - \ref AstObj2_Containers 00138 - \ref astobj2.h All documentation for functions and data structures 00139 00140 */ 00141 00142 /*! \brief 00143 * Typedef for an object destructor. This is called just before freeing 00144 * the memory for the object. It is passed a pointer to the user-defined 00145 * data of the object. 00146 */ 00147 typedef void (*ao2_destructor_fn)(void *); 00148 00149 00150 /*! \brief 00151 * Allocate and initialize an object. 00152 * 00153 * \param data_size The sizeof() of the user-defined structure. 00154 * \param destructor_fn The destructor function (can be NULL) 00155 * \return A pointer to user-data. 00156 * 00157 * Allocates a struct astobj2 with sufficient space for the 00158 * user-defined structure. 00159 * \note 00160 * - storage is zeroed; XXX maybe we want a flag to enable/disable this. 00161 * - the refcount of the object just created is 1 00162 * - the returned pointer cannot be free()'d or realloc()'ed; 00163 * rather, we just call ao2_ref(o, -1); 00164 */ 00165 void *ao2_alloc(const size_t data_size, ao2_destructor_fn destructor_fn); 00166 00167 /*! \brief 00168 * Reference/unreference an object and return the old refcount. 00169 * 00170 * \param o A pointer to the object 00171 * \param delta Value to add to the reference counter. 00172 * \return The value of the reference counter before the operation. 00173 * 00174 * Increase/decrease the reference counter according 00175 * the value of delta. 00176 * 00177 * If the refcount goes to zero, the object is destroyed. 00178 * 00179 * \note The object must not be locked by the caller of this function, as 00180 * it is invalid to try to unlock it after releasing the reference. 00181 * 00182 * \note if we know the pointer to an object, it is because we 00183 * have a reference count to it, so the only case when the object 00184 * can go away is when we release our reference, and it is 00185 * the last one in existence. 00186 */ 00187 int ao2_ref(void *o, int delta); 00188 00189 /*! \brief 00190 * Lock an object. 00191 * 00192 * \param a A pointer to the object we want lock. 00193 * \return 0 on success, other values on error. 00194 */ 00195 #ifndef DEBUG_THREADS 00196 int ao2_lock(void *a); 00197 #else 00198 #define ao2_lock(a) _ao2_lock(a, __FILE__, __PRETTY_FUNCTION__, __LINE__, #a) 00199 int _ao2_lock(void *a, const char *file, const char *func, int line, const char *var); 00200 #endif 00201 00202 /*! \brief 00203 * Unlock an object. 00204 * 00205 * \param a A pointer to the object we want unlock. 00206 * \return 0 on success, other values on error. 00207 */ 00208 #ifndef DEBUG_THREADS 00209 int ao2_unlock(void *a); 00210 #else 00211 #define ao2_unlock(a) _ao2_unlock(a, __FILE__, __PRETTY_FUNCTION__, __LINE__, #a) 00212 int _ao2_unlock(void *a, const char *file, const char *func, int line, const char *var); 00213 #endif 00214 00215 /*! \brief 00216 * Try locking-- (don't block if fail) 00217 * 00218 * \param a A pointer to the object we want to lock. 00219 * \return 0 on success, other values on error. 00220 */ 00221 #ifndef DEBUG_THREADS 00222 int ao2_trylock(void *a); 00223 #else 00224 #define ao2_trylock(a) _ao2_trylock(a, __FILE__, __PRETTY_FUNCTION__, __LINE__, #a) 00225 int _ao2_trylock(void *a, const char *file, const char *func, int line, const char *var); 00226 #endif 00227 00228 /*! 00229 * 00230 \page AstObj2_Containers AstObj2 Containers 00231 00232 Containers are data structures meant to store several objects, 00233 and perform various operations on them. 00234 Internally, objects are stored in lists, hash tables or other 00235 data structures depending on the needs. 00236 00237 \note NOTA BENE: at the moment the only container we support is the 00238 hash table and its degenerate form, the list. 00239 00240 Operations on container include: 00241 00242 - c = \b ao2_container_alloc(size, cmp_fn, hash_fn) 00243 allocate a container with desired size and default compare 00244 and hash function 00245 00246 - \b ao2_find(c, arg, flags) 00247 returns zero or more element matching a given criteria 00248 (specified as arg). Flags indicate how many results we 00249 want (only one or all matching entries), and whether we 00250 should unlink the object from the container. 00251 00252 - \b ao2_callback(c, flags, fn, arg) 00253 apply fn(obj, arg) to all objects in the container. 00254 Similar to find. fn() can tell when to stop, and 00255 do anything with the object including unlinking it. 00256 Note that the entire operation is run with the container 00257 locked, so noone else can change its content while we work on it. 00258 However, we pay this with the fact that doing 00259 anything blocking in the callback keeps the container 00260 blocked. 00261 The mechanism is very flexible because the callback function fn() 00262 can do basically anything e.g. counting, deleting records, etc. 00263 possibly using arg to store the results. 00264 00265 - \b iterate on a container 00266 this is done with the following sequence 00267 00268 \code 00269 00270 struct ao2_container *c = ... // our container 00271 struct ao2_iterator i; 00272 void *o; 00273 00274 i = ao2_iterator_init(c, flags); 00275 00276 while ( (o = ao2_iterator_next(&i)) ) { 00277 ... do something on o ... 00278 ao2_ref(o, -1); 00279 } 00280 \endcode 00281 00282 The difference with the callback is that the control 00283 on how to iterate is left to us. 00284 00285 - \b ao2_ref(c, -1) 00286 dropping a reference to a container destroys it, very simple! 00287 00288 Containers are ao2 objects themselves, and this is why their 00289 implementation is simple too. 00290 00291 Before declaring containers, we need to declare the types of the 00292 arguments passed to the constructor - in turn, this requires 00293 to define callback and hash functions and their arguments. 00294 00295 - \ref AstObj2 00296 - \ref astobj2.h 00297 */ 00298 00299 /*! \brief 00300 * Type of a generic callback function 00301 * \param obj pointer to the (user-defined part) of an object. 00302 * \param arg callback argument from ao2_callback() 00303 * \param flags flags from ao2_callback() 00304 * 00305 * The return values are a combination of enum _cb_results. 00306 * Callback functions are used to search or manipulate objects in a container, 00307 */ 00308 typedef int (ao2_callback_fn)(void *obj, void *arg, int flags); 00309 00310 /*! \brief a very common callback is one that matches by address. */ 00311 ao2_callback_fn ao2_match_by_addr; 00312 00313 /*! \brief 00314 * A callback function will return a combination of CMP_MATCH and CMP_STOP. 00315 * The latter will terminate the search in a container. 00316 */ 00317 enum _cb_results { 00318 CMP_MATCH = 0x1, /*!< the object matches the request */ 00319 CMP_STOP = 0x2, /*!< stop the search now */ 00320 }; 00321 00322 /*! \brief 00323 * Flags passed to ao2_callback() and ao2_hash_fn() to modify its behaviour. 00324 */ 00325 enum search_flags { 00326 /*! Unlink the object for which the callback function 00327 * returned CMP_MATCH . This is the only way to extract 00328 * objects from a container. */ 00329 OBJ_UNLINK = (1 << 0), 00330 /*! On match, don't return the object hence do not increase 00331 * its refcount. */ 00332 OBJ_NODATA = (1 << 1), 00333 /*! Don't stop at the first match in ao2_callback() 00334 * \note This is not fully implemented. */ 00335 OBJ_MULTIPLE = (1 << 2), 00336 /*! obj is an object of the same type as the one being searched for, 00337 * so use the object's hash function for optimized searching. 00338 * The search function is unaffected (i.e. use the one passed as 00339 * argument, or match_by_addr if none specified). */ 00340 OBJ_POINTER = (1 << 3), 00341 }; 00342 00343 /*! 00344 * Type of a generic function to generate a hash value from an object. 00345 * flags is ignored at the moment. Eventually, it will include the 00346 * value of OBJ_POINTER passed to ao2_callback(). 00347 */ 00348 typedef int (ao2_hash_fn)(const void *obj, const int flags); 00349 00350 /*! \name Object Containers 00351 * Here start declarations of containers. 00352 */ 00353 /*@{ */ 00354 struct ao2_container; 00355 00356 /*! \brief 00357 * Allocate and initialize a container 00358 * with the desired number of buckets. 00359 * 00360 * We allocate space for a struct astobj_container, struct container 00361 * and the buckets[] array. 00362 * 00363 * \param n_buckets Number of buckets for hash 00364 * \param hash_fn Pointer to a function computing a hash value. 00365 * \param cmp_fn Pointer to a function comparating key-value 00366 * with a string. (can be NULL) 00367 * \return A pointer to a struct container. 00368 * 00369 * destructor is set implicitly. 00370 */ 00371 struct ao2_container *ao2_container_alloc(const unsigned int n_buckets, 00372 ao2_hash_fn *hash_fn, ao2_callback_fn *cmp_fn); 00373 00374 /*! \brief 00375 * Returns the number of elements in a container. 00376 */ 00377 int ao2_container_count(struct ao2_container *c); 00378 /*@} */ 00379 00380 /*! \name Object Management 00381 * Here we have functions to manage objects. 00382 * 00383 * We can use the functions below on any kind of 00384 * object defined by the user. 00385 */ 00386 /*@{ */ 00387 00388 /*! 00389 * \brief Add an object to a container. 00390 * 00391 * \param c the container to operate on. 00392 * \param newobj the object to be added. 00393 * 00394 * \retval NULL on errors 00395 * \retval newobj on success. 00396 * 00397 * This function inserts an object in a container according its key. 00398 * 00399 * \note Remember to set the key before calling this function. 00400 * 00401 * \note This function automatically increases the reference count to account 00402 * for the reference that the container now holds to the object. 00403 */ 00404 void *ao2_link(struct ao2_container *c, void *newobj); 00405 00406 /*! 00407 * \brief Remove an object from the container 00408 * 00409 * \arg c the container 00410 * \arg obj the object to unlink 00411 * 00412 * \retval NULL, always 00413 * 00414 * \note The object requested to be unlinked must be valid. However, if it turns 00415 * out that it is not in the container, this function is still safe to 00416 * be called. 00417 * 00418 * \note If the object gets unlinked from the container, the container's 00419 * reference to the object will be automatically released. 00420 */ 00421 void *ao2_unlink(struct ao2_container *c, void *obj); 00422 00423 /*! \brief Used as return value if the flag OBJ_MULTIPLE is set */ 00424 struct ao2_list { 00425 struct ao2_list *next; 00426 void *obj; /* pointer to the user portion of the object */ 00427 }; 00428 /*@} */ 00429 00430 /*! \brief 00431 * ao2_callback() is a generic function that applies cb_fn() to all objects 00432 * in a container, as described below. 00433 * 00434 * \param c A pointer to the container to operate on. 00435 * \param arg passed to the callback. 00436 * \param flags A set of flags specifying the operation to perform, 00437 partially used by the container code, but also passed to 00438 the callback. 00439 * \return A pointer to the object found/marked, 00440 * a pointer to a list of objects matching comparison function, 00441 * NULL if not found. 00442 * 00443 * If the function returns any objects, their refcount is incremented, 00444 * and the caller is in charge of decrementing them once done. 00445 * Also, in case of multiple values returned, the list used 00446 * to store the objects must be freed by the caller. 00447 * 00448 * Typically, ao2_callback() is used for two purposes: 00449 * - to perform some action (including removal from the container) on one 00450 * or more objects; in this case, cb_fn() can modify the object itself, 00451 * and to perform deletion should set CMP_MATCH on the matching objects, 00452 * and have OBJ_UNLINK set in flags. 00453 * - to look for a specific object in a container; in this case, cb_fn() 00454 * should not modify the object, but just return a combination of 00455 * CMP_MATCH and CMP_STOP on the desired object. 00456 * Other usages are also possible, of course. 00457 00458 * This function searches through a container and performs operations 00459 * on objects according on flags passed. 00460 * XXX describe better 00461 * The comparison is done calling the compare function set implicitly. 00462 * The p pointer can be a pointer to an object or to a key, 00463 * we can say this looking at flags value. 00464 * If p points to an object we will search for the object pointed 00465 * by this value, otherwise we serch for a key value. 00466 * If the key is not uniq we only find the first matching valued. 00467 * If we use the OBJ_MARK flags, we mark all the objects matching 00468 * the condition. 00469 * 00470 * The use of flags argument is the follow: 00471 * 00472 * OBJ_UNLINK unlinks the object found 00473 * OBJ_NODATA on match, do return an object 00474 * Callbacks use OBJ_NODATA as a default 00475 * functions such as find() do 00476 * OBJ_MULTIPLE return multiple matches 00477 * Default for _find() is no. 00478 * to a key (not yet supported) 00479 * OBJ_POINTER the pointer is an object pointer 00480 * 00481 * In case we return a list, the callee must take care to destroy 00482 * that list when no longer used. 00483 * 00484 * \note When the returned object is no longer in use, ao2_ref() should 00485 * be used to free the additional reference possibly created by this function. 00486 */ 00487 void *ao2_callback(struct ao2_container *c, 00488 enum search_flags flags, 00489 ao2_callback_fn *cb_fn, void *arg); 00490 00491 /*! ao2_find() is a short hand for ao2_callback(c, flags, c->cmp_fn, arg) 00492 * XXX possibly change order of arguments ? 00493 */ 00494 void *ao2_find(struct ao2_container *c, void *arg, enum search_flags flags); 00495 00496 /*! \brief 00497 * 00498 * 00499 * When we need to walk through a container, we use 00500 * ao2_iterator to keep track of the current position. 00501 * 00502 * Because the navigation is typically done without holding the 00503 * lock on the container across the loop, 00504 * objects can be inserted or deleted or moved 00505 * while we work. As a consequence, there is no guarantee that 00506 * the we manage to touch all the elements on the list, or it 00507 * is possible that we touch the same object multiple times. 00508 * However, within the current hash table container, the following is true: 00509 * - It is not possible to miss an object in the container while iterating 00510 * unless it gets added after the iteration begins and is added to a bucket 00511 * that is before the one the current object is in. In this case, even if 00512 * you locked the container around the entire iteration loop, you still would 00513 * not see this object, because it would still be waiting on the container 00514 * lock so that it can be added. 00515 * - It would be extremely rare to see an object twice. The only way this can 00516 * happen is if an object got unlinked from the container and added again 00517 * during the same iteration. Furthermore, when the object gets added back, 00518 * it has to be in the current or later bucket for it to be seen again. 00519 * 00520 * An iterator must be first initialized with ao2_iterator_init(), 00521 * then we can use o = ao2_iterator_next() to move from one 00522 * element to the next. Remember that the object returned by 00523 * ao2_iterator_next() has its refcount incremented, 00524 * and the reference must be explicitly released when done with it. 00525 * 00526 * Example: 00527 * 00528 * \code 00529 * 00530 * struct ao2_container *c = ... // the container we want to iterate on 00531 * struct ao2_iterator i; 00532 * struct my_obj *o; 00533 * 00534 * i = ao2_iterator_init(c, flags); 00535 * 00536 * while ( (o = ao2_iterator_next(&i)) ) { 00537 * ... do something on o ... 00538 * ao2_ref(o, -1); 00539 * } 00540 * 00541 * \endcode 00542 * 00543 */ 00544 00545 /*! \brief 00546 * The Astobj2 iterator 00547 * 00548 * \note You are not supposed to know the internals of an iterator! 00549 * We would like the iterator to be opaque, unfortunately 00550 * its size needs to be known if we want to store it around 00551 * without too much trouble. 00552 * Anyways... 00553 * The iterator has a pointer to the container, and a flags 00554 * field specifying various things e.g. whether the container 00555 * should be locked or not while navigating on it. 00556 * The iterator "points" to the current object, which is identified 00557 * by three values: 00558 * 00559 * - a bucket number; 00560 * - the object_id, which is also the container version number 00561 * when the object was inserted. This identifies the object 00562 * univoquely, however reaching the desired object requires 00563 * scanning a list. 00564 * - a pointer, and a container version when we saved the pointer. 00565 * If the container has not changed its version number, then we 00566 * can safely follow the pointer to reach the object in constant time. 00567 * 00568 * Details are in the implementation of ao2_iterator_next() 00569 * A freshly-initialized iterator has bucket=0, version = 0. 00570 */ 00571 struct ao2_iterator { 00572 /*! the container */ 00573 struct ao2_container *c; 00574 /*! operation flags */ 00575 int flags; 00576 #define F_AO2I_DONTLOCK 1 /*!< don't lock when iterating */ 00577 /*! current bucket */ 00578 int bucket; 00579 /*! container version */ 00580 unsigned int c_version; 00581 /*! pointer to the current object */ 00582 void *obj; 00583 /*! container version when the object was created */ 00584 unsigned int version; 00585 }; 00586 00587 struct ao2_iterator ao2_iterator_init(struct ao2_container *c, int flags); 00588 00589 void *ao2_iterator_next(struct ao2_iterator *a); 00590 00591 /* extra functions */ 00592 void ao2_bt(void); /* backtrace */ 00593 #endif /* _ASTERISK_ASTOBJ2_H */