cache/classes/interfaces.php

   1 <?php
   2 // This file is part of Moodle - http://moodle.org/
   3 //
   4 // Moodle is free software: you can redistribute it and/or modify
   5 // it under the terms of the GNU General Public License as published by
   6 // the Free Software Foundation, either version 3 of the License, or
   7 // (at your option) any later version.
   8 //
   9 // Moodle is distributed in the hope that it will be useful,
  10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 // GNU General Public License for more details.
  13 //
  14 // You should have received a copy of the GNU General Public License
  15 // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
  16
  17 /**
  18  * Cache API interfaces
  19  *
  20  * This file is part of Moodle's cache API, affectionately called MUC.
  21  * It contains the components that are requried in order to use caching.
  22  *
  23  * @package    core
  24  * @category   cache
  25  * @copyright  2012 Sam Hemelryk
  26  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  27  */
  28
  29 defined('MOODLE_INTERNAL') || die();
  30
  31 /**
  32  * Cache Loader.
  33  *
  34  * This cache loader interface provides the required structure for classes that wish to be interacted with as a
  35  * means of accessing and interacting with a cache.
  36  *
  37  * Can be implemented by any class wishing to be a cache loader.
  38  */
  39 interface cache_loader {
  40
  41     /**
  42      * Retrieves the value for the given key from the cache.
  43      *
  44      * @param string|int $key The key for the data being requested.
  45      * @param int $strictness One of IGNORE_MISSING or MUST_EXIST.
  46      * @return mixed The data retrieved from the cache, or false if the key did not exist within the cache.
  47      *      If MUST_EXIST was used then an exception will be thrown if the key does not exist within the cache.
  48      */
  49     public function get($key, $strictness = IGNORE_MISSING);
  50
  51     /**
  52      * Retrieves an array of values for an array of keys.
  53      *
  54      * Using this function comes with potential performance implications.
  55      * Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
  56      * the equivalent singular method for each item provided.
  57      * This should not deter you from using this function as there is a performance benefit in situations where the cache
  58      * store does support it, but you should be aware of this fact.
  59      *
  60      * @param array $keys The keys of the data being requested.
  61      * @param int $strictness One of IGNORE_MISSING or MUST_EXIST.
  62      * @return array An array of key value pairs for the items that could be retrieved from the cache.
  63      *      If MUST_EXIST was used and not all keys existed within the cache then an exception will be thrown.
  64      *      Otherwise any key that did not exist will have a data value of false within the results.
  65      */
  66     public function get_many(array $keys, $strictness = IGNORE_MISSING);
  67
  68     /**
  69      * Sends a key => value pair to the cache.
  70      *
  71      * <code>
  72      * // This code will add four entries to the cache, one for each url.
  73      * $cache->set('main', 'http://moodle.org');
  74      * $cache->set('docs', 'http://docs.moodle.org');
  75      * $cache->set('tracker', 'http://tracker.moodle.org');
  76      * $cache->set('qa', 'http://qa.moodle.net');
  77      * </code>
  78      *
  79      * @param string|int $key The key for the data being requested.
  80      * @param mixed $data The data to set against the key.
  81      * @return bool True on success, false otherwise.
  82      */
  83     public function set($key, $data);
  84
  85     /**
  86      * Sends several key => value pairs to the cache.
  87      *
  88      * Using this function comes with potential performance implications.
  89      * Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
  90      * the equivalent singular method for each item provided.
  91      * This should not deter you from using this function as there is a performance benefit in situations where the cache store
  92      * does support it, but you should be aware of this fact.
  93      *
  94      * <code>
  95      * // This code will add four entries to the cache, one for each url.
  96      * $cache->set_many(array(
  97      *     'main' => 'http://moodle.org',
  98      *     'docs' => 'http://docs.moodle.org',
  99      *     'tracker' => 'http://tracker.moodle.org',
 100      *     'qa' => ''http://qa.moodle.net'
 101      * ));
 102      * </code>
 103      *
 104      * @param array $keyvaluearray An array of key => value pairs to send to the cache.
 105      * @return int The number of items successfully set. It is up to the developer to check this matches the number of items.
 106      *      ... if they care that is.
 107      */
 108     public function set_many(array $keyvaluearray);
 109
 110     /**
 111      * Test is a cache has a key.
 112      *
 113      * The use of the has methods is strongly discouraged. In a high load environment the cache may well change between the
 114      * test and any subsequent action (get, set, delete etc).
 115      * Instead it is recommended to write your code in such a way they it performs the following steps:
 116      * <ol>
 117      * <li>Attempt to retrieve the information.</li>
 118      * <li>Generate the information.</li>
 119      * <li>Attempt to set the information</li>
 120      * </ol>
 121      *
 122      * Its also worth mentioning that not all stores support key tests.
 123      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 124      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 125      *
 126      * @param string|int $key
 127      * @return bool True if the cache has the requested key, false otherwise.
 128      */
 129     public function has($key);
 130
 131     /**
 132      * Test if a cache has at least one of the given keys.
 133      *
 134      * It is strongly recommended to avoid the use of this function if not absolutely required.
 135      * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
 136      *
 137      * Its also worth mentioning that not all stores support key tests.
 138      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 139      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 140      *
 141      * @param array $keys
 142      * @return bool True if the cache has at least one of the given keys
 143      */
 144     public function has_any(array $keys);
 145
 146     /**
 147      * Test is a cache has all of the given keys.
 148      *
 149      * It is strongly recommended to avoid the use of this function if not absolutely required.
 150      * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
 151      *
 152      * Its also worth mentioning that not all stores support key tests.
 153      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 154      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 155      *
 156      * @param array $keys
 157      * @return bool True if the cache has all of the given keys, false otherwise.
 158      */
 159     public function has_all(array $keys);
 160
 161     /**
 162      * Delete the given key from the cache.
 163      *
 164      * @param string|int $key The key to delete.
 165      * @param bool $recurse When set to true the key will also be deleted from all stacked cache loaders and their stores.
 166      *     This happens by default and ensure that all the caches are consistent. It is NOT recommended to change this.
 167      * @return bool True of success, false otherwise.
 168      */
 169     public function delete($key, $recurse = true);
 170
 171     /**
 172      * Delete all of the given keys from the cache.
 173      *
 174      * @param array $keys The key to delete.
 175      * @param bool $recurse When set to true the key will also be deleted from all stacked cache loaders and their stores.
 176      *     This happens by default and ensure that all the caches are consistent. It is NOT recommended to change this.
 177      * @return int The number of items successfully deleted.
 178      */
 179     public function delete_many(array $keys, $recurse = true);
 180 }
 181
 182 /**
 183  * Cache Loader supporting locking.
 184  *
 185  * This interface should be given to classes already implementing cache_loader that also wish to support locking.
 186  * It outlines the required structure for utilising locking functionality when using a cache.
 187  *
 188  * Can be implemented by any class already implementing the cache_loader interface.
 189  */
 190 interface cache_loader_with_locking {
 191
 192     /**
 193      * Acquires a lock for the given key.
 194      *
 195      * Please note that this happens automatically if the cache definition requires locking.
 196      * it is still made a public method so that adhoc caches can use it if they choose.
 197      * However this doesn't guarantee consistent access. It will become the responsibility of the calling code to ensure
 198      * locks are acquired, checked, and released.
 199      *
 200      * @param string|int $key
 201      * @return bool True if the lock could be acquired, false otherwise.
 202      */
 203     public function acquire_lock($key);
 204
 205     /**
 206      * Checks if the cache loader owns the lock for the given key.
 207      *
 208      * Please note that this happens automatically if the cache definition requires locking.
 209      * it is still made a public method so that adhoc caches can use it if they choose.
 210      * However this doesn't guarantee consistent access. It will become the responsibility of the calling code to ensure
 211      * locks are acquired, checked, and released.
 212      *
 213      * @param string|int $key
 214      * @return bool True if this code has the lock, false if there is a lock but this code doesn't have it,
 215      *      null if there is no lock.
 216      */
 217     public function check_lock_state($key);
 218
 219     /**
 220      * Releases the lock for the given key.
 221      *
 222      * Please note that this happens automatically if the cache definition requires locking.
 223      * it is still made a public method so that adhoc caches can use it if they choose.
 224      * However this doesn't guarantee consistent access. It will become the responsibility of the calling code to ensure
 225      * locks are acquired, checked, and released.
 226      *
 227      * @param string|int $key
 228      * @return bool True if the lock has been released, false if there was a problem releasing the lock.
 229      */
 230     public function release_lock($key);
 231 }
 232
 233 /**
 234  * Cache store feature: locking
 235  *
 236  * This is a feature that cache stores can implement if they wish to support locking themselves rather
 237  * than having the cache loader handle it for them.
 238  *
 239  * Can be implemented by classes already implementing cache_store.
 240  */
 241 interface cache_is_lockable {
 242
 243     /**
 244      * Acquires a lock on the given key for the given identifier.
 245      *
 246      * @param string $key The key we are locking.
 247      * @param string $ownerid The identifier so we can check if we have the lock or if it is someone else.
 248      *      The use of this property is entirely optional and implementations can act as they like upon it.
 249      * @return bool True if the lock could be acquired, false otherwise.
 250      */
 251     public function acquire_lock($key, $ownerid);
 252
 253     /**
 254      * Test if there is already a lock for the given key and if there is whether it belongs to the calling code.
 255      *
 256      * @param string $key The key we are locking.
 257      * @param string $ownerid The identifier so we can check if we have the lock or if it is someone else.
 258      * @return bool True if this code has the lock, false if there is a lock but this code doesn't have it, null if there
 259      *      is no lock.
 260      */
 261     public function check_lock_state($key, $ownerid);
 262
 263     /**
 264      * Releases the lock on the given key.
 265      *
 266      * @param string $key The key we are locking.
 267      * @param string $ownerid The identifier so we can check if we have the lock or if it is someone else.
 268      *      The use of this property is entirely optional and implementations can act as they like upon it.
 269      * @return bool True if the lock has been released, false if there was a problem releasing the lock.
 270      */
 271     public function release_lock($key, $ownerid);
 272 }
 273
 274 /**
 275  * Cache store feature: key awareness.
 276  *
 277  * This is a feature that cache stores and cache loaders can both choose to implement.
 278  * If a cache store implements this then it will be made responsible for tests for items within the cache.
 279  * If the cache store being used doesn't implement this then it will be the responsibility of the cache loader to use the
 280  * equivalent get methods to mimick the functionality of these tests.
 281  *
 282  * Cache stores should only override these methods if they natively support such features or if they have a better performing
 283  * means of performing these tests than the handling that would otherwise take place in the cache_loader.
 284  *
 285  * Can be implemented by classes already implementing cache_store.
 286  */
 287 interface cache_is_key_aware {
 288
 289     /**
 290      * Test is a cache has a key.
 291      *
 292      * The use of the has methods is strongly discouraged. In a high load environment the cache may well change between the
 293      * test and any subsequent action (get, set, delete etc).
 294      * Instead it is recommended to write your code in such a way they it performs the following steps:
 295      * <ol>
 296      * <li>Attempt to retrieve the information.</li>
 297      * <li>Generate the information.</li>
 298      * <li>Attempt to set the information</li>
 299      * </ol>
 300      *
 301      * Its also worth mentioning that not all stores support key tests.
 302      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 303      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 304      *
 305      * @param string|int $key
 306      * @return bool True if the cache has the requested key, false otherwise.
 307      */
 308     public function has($key);
 309
 310     /**
 311      * Test if a cache has at least one of the given keys.
 312      *
 313      * It is strongly recommended to avoid the use of this function if not absolutely required.
 314      * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
 315      *
 316      * Its also worth mentioning that not all stores support key tests.
 317      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 318      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 319      *
 320      * @param array $keys
 321      * @return bool True if the cache has at least one of the given keys
 322      */
 323     public function has_any(array $keys);
 324
 325     /**
 326      * Test is a cache has all of the given keys.
 327      *
 328      * It is strongly recommended to avoid the use of this function if not absolutely required.
 329      * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
 330      *
 331      * Its also worth mentioning that not all stores support key tests.
 332      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 333      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 334      *
 335      * @param array $keys
 336      * @return bool True if the cache has all of the given keys, false otherwise.
 337      */
 338     public function has_all(array $keys);
 339 }
 340
 341 /**
 342  * Cache store feature: keys are searchable.
 343  *
 344  * Cache stores can choose to implement this interface.
 345  * In order for a store to be usable as a session cache it must implement this interface.
 346  *
 347  * @since 2.4.4
 348  */
 349 interface cache_is_searchable {
 350     /**
 351      * Finds all of the keys being used by the cache store.
 352      *
 353      * @return array.
 354      */
 355     public function find_all();
 356
 357     /**
 358      * Finds all of the keys whose keys start with the given prefix.
 359      *
 360      * @param string $prefix
 361      */
 362     public function find_by_prefix($prefix);
 363 }
 364
 365 /**
 366  * Cache store feature: configurable.
 367  *
 368  * This feature should be implemented by all cache stores that are configurable when adding an instance.
 369  * It requires the implementation of methods required to convert form data into the a configuration array for the
 370  * store instance, and then the reverse converting configuration data into an array that can be used to set the
 371  * data for the edit form.
 372  *
 373  * Can be implemented by classes already implementing cache_store.
 374  */
 375 interface cache_is_configurable {
 376
 377     /**
 378      * Given the data from the add instance form this function creates a configuration array.
 379      *
 380      * @param stdClass $data
 381      * @return array
 382      */
 383     public static function config_get_configuration_array($data);
 384
 385     /**
 386      * Allows the cache store to set its data against the edit form before it is shown to the user.
 387      *
 388      * @param moodleform $editform
 389      * @param array $config
 390      */
 391     public static function config_set_edit_form_data(moodleform $editform, array $config);
 392 }
 393
 394 /**
 395  * Cache Data Source.
 396  *
 397  * The cache data source interface can be implemented by any class within Moodle.
 398  * If implemented then the class can be reference in a cache definition and will be used to load information that cannot be
 399  * retrieved from the cache. As part of its retrieval that information will also be loaded into the cache.
 400  *
 401  * This allows developers to created a complete cache solution that can be used through code ensuring consistent cache
 402  * interaction and loading. Allowing them in turn to centralise code and help keeps things more easily maintainable.
 403  *
 404  * Can be implemented by any class.
 405  *
 406  * @package    core
 407  * @category   cache
 408  * @copyright  2012 Sam Hemelryk
 409  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 410  */
 411 interface cache_data_source {
 412
 413     /**
 414      * Returns an instance of the data source class that the cache can use for loading data using the other methods
 415      * specified by this interface.
 416      *
 417      * @param cache_definition $definition
 418      * @return object
 419      */
 420     public static function get_instance_for_cache(cache_definition $definition);
 421
 422     /**
 423      * Loads the data for the key provided ready formatted for caching.
 424      *
 425      * @param string|int $key The key to load.
 426      * @return mixed What ever data should be returned, or false if it can't be loaded.
 427      */
 428     public function load_for_cache($key);
 429
 430     /**
 431      * Loads several keys for the cache.
 432      *
 433      * @param array $keys An array of keys each of which will be string|int.
 434      * @return array An array of matching data items.
 435      */
 436     public function load_many_for_cache(array $keys);
 437 }
 438
 439 /**
 440  * Cacheable object.
 441  *
 442  * This interface can be implemented by any class that is going to be passed into a cache and allows it to take control of the
 443  * structure and the information about to be cached, as well as how to deal with it when it is retrieved from a cache.
 444  * Think of it like serialisation and the __sleep and __wakeup methods.
 445  * This is used because cache stores are responsible for how they interact with data and what they do when storing it. This
 446  * interface ensures there is always a guaranteed action.
 447  */
 448 interface cacheable_object {
 449
 450     /**
 451      * Prepares the object for caching. Works like the __sleep method.
 452      *
 453      * @return mixed The data to cache, can be anything except a class that implements the cacheable_object... that would
 454      *      be dumb.
 455      */
 456     public function prepare_to_cache();
 457
 458     /**
 459      * Takes the data provided by prepare_to_cache and reinitialises an instance of the associated from it.
 460      *
 461      * @param mixed $data
 462      * @return object The instance for the given data.
 463      */
 464     public static function wake_from_cache($data);
 465 }
 466
 467 /**
 468  * Cache lock interface
 469  *
 470  * This interface needs to be inherited by all cache lock plugins.
 471  */
 472 interface cache_lock_interface {
 473     /**
 474      * Constructs an instance of the cache lock given its name and its configuration data
 475      *
 476      * @param string $name The unique name of the lock instance
 477      * @param array $configuration
 478      */
 479     public function __construct($name, array $configuration = array());
 480
 481     /**
 482      * Acquires a lock on a given key.
 483      *
 484      * @param string $key The key to acquire a lock for.
 485      * @param string $ownerid An unique identifier for the owner of this lock. It is entirely optional for the cache lock plugin
 486      *      to use this. Each implementation can decide for themselves.
 487      * @param bool $block If set to true the application will wait until a lock can be acquired
 488      * @return bool True if the lock can be acquired false otherwise.
 489      */
 490     public function lock($key, $ownerid, $block = false);
 491
 492     /**
 493      * Releases the lock held on a certain key.
 494      *
 495      * @param string $key The key to release the lock for.
 496      * @param string $ownerid An unique identifier for the owner of this lock. It is entirely optional for the cache lock plugin
 497      *      to use this. Each implementation can decide for themselves.
 498      * @param bool $forceunlock If set to true the lock will be removed if it exists regardless of whether or not we own it.
 499      */
 500     public function unlock($key, $ownerid, $forceunlock = false);
 501
 502     /**
 503      * Checks the state of the given key.
 504      *
 505      * Returns true if the key is locked and belongs to the ownerid.
 506      * Returns false if the key is locked but does not belong to the ownerid.
 507      * Returns null if there is no lock
 508      *
 509      * @param string $key The key we are checking for.
 510      * @param string $ownerid The identifier so we can check if we have the lock or if it is someone else.
 511      * @return bool True if this code has the lock, false if there is a lock but this code doesn't have it, null if there
 512      *      is no lock.
 513      */
 514     public function check_state($key, $ownerid);
 515
 516     /**
 517      * Cleans up any left over locks.
 518      *
 519      * This function MUST clean up any locks that have been acquired and not released during processing.
 520      * Although the situation of acquiring a lock and not releasing it should be insanely rare we need to deal with it.
 521      * Things such as unfortunate timeouts etc could cause this situation.
 522      */
 523     public function __destruct();
 524 }