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 the value and actual version for the given key, with at least the required version.
  53      *
  54      * If there is no value for the key, or there is a value but it doesn't have the required
  55      * version, then this function will return false (or throw an exception if you set strictness
  56      * to MUST_EXIST).
  57      *
  58      * This function can be used to make it easier to support localisable caches (where the cache
  59      * could be stored on a local server as well as a shared cache). Specifying the version means
  60      * that it will automatically retrieve the correct version if available, either from the local
  61      * server or [if that has an older version] from the shared server.
  62      *
  63      * If the cached version is newer than specified version, it will be returned regardless. For
  64      * example, if you request version 4, but the locally cached version is 5, it will be returned.
  65      * If you request version 6, and the locally cached version is 5, then the system will look in
  66      * higher-level caches (if any); if there still isn't a version 6 or greater, it will return
  67      * null.
  68      *
  69      * You must use this function if you use set_versioned.
  70      *
  71      * @param string|int $key The key for the data being requested.
  72      * @param int $requiredversion Minimum required version of the data
  73      * @param int $strictness One of IGNORE_MISSING or MUST_EXIST.
  74      * @param mixed $actualversion If specified, will be set to the actual version number retrieved
  75      * @return mixed Data from the cache, or false if the key did not exist or was too old
  76      */
  77     public function get_versioned($key, int $requiredversion, int $strictness = IGNORE_MISSING, &$actualversion = null);
  78
  79     /**
  80      * Retrieves an array of values for an array of keys.
  81      *
  82      * Using this function comes with potential performance implications.
  83      * Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
  84      * the equivalent singular method for each item provided.
  85      * This should not deter you from using this function as there is a performance benefit in situations where the cache
  86      * store does support it, but you should be aware of this fact.
  87      *
  88      * @param array $keys The keys of the data being requested.
  89      * @param int $strictness One of IGNORE_MISSING or MUST_EXIST.
  90      * @return array An array of key value pairs for the items that could be retrieved from the cache.
  91      *      If MUST_EXIST was used and not all keys existed within the cache then an exception will be thrown.
  92      *      Otherwise any key that did not exist will have a data value of false within the results.
  93      */
  94     public function get_many(array $keys, $strictness = IGNORE_MISSING);
  95
  96     /**
  97      * Sends a key => value pair to the cache.
  98      *
  99      * <code>
 100      * // This code will add four entries to the cache, one for each url.
 101      * $cache->set('main', 'http://moodle.org');
 102      * $cache->set('docs', 'http://docs.moodle.org');
 103      * $cache->set('tracker', 'http://tracker.moodle.org');
 104      * $cache->set('qa', 'http://qa.moodle.net');
 105      * </code>
 106      *
 107      * @param string|int $key The key for the data being requested.
 108      * @param mixed $data The data to set against the key.
 109      * @return bool True on success, false otherwise.
 110      */
 111     public function set($key, $data);
 112
 113     /**
 114      * Sets the value for the given key with the given version.
 115      *
 116      * The cache does not store multiple versions - any existing version will be overwritten with
 117      * this one. This function should only be used if there is a known 'current version' (e.g.
 118      * stored in a database table). It only ensures that the cache does not return outdated data.
 119      *
 120      * This function can be used to help implement localisable caches (where the cache could be
 121      * stored on a local server as well as a shared cache). The version will be recorded alongside
 122      * the item and get_versioned will always return the correct version.
 123      *
 124      * The version number must be an integer that always increases. This could be based on the
 125      * current time, or a stored value that increases by 1 each time it changes, etc.
 126      *
 127      * If you use this function you must use get_versioned to retrieve the data.
 128      *
 129      * @param string|int $key The key for the data being set.
 130      * @param int $version Integer for the version of the data
 131      * @param mixed $data The data to set against the key.
 132      * @return bool True on success, false otherwise.
 133      */
 134     public function set_versioned($key, int $version, $data): bool;
 135
 136     /**
 137      * Sends several key => value pairs to the cache.
 138      *
 139      * Using this function comes with potential performance implications.
 140      * Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
 141      * the equivalent singular method for each item provided.
 142      * This should not deter you from using this function as there is a performance benefit in situations where the cache store
 143      * does support it, but you should be aware of this fact.
 144      *
 145      * <code>
 146      * // This code will add four entries to the cache, one for each url.
 147      * $cache->set_many(array(
 148      *     'main' => 'http://moodle.org',
 149      *     'docs' => 'http://docs.moodle.org',
 150      *     'tracker' => 'http://tracker.moodle.org',
 151      *     'qa' => ''http://qa.moodle.net'
 152      * ));
 153      * </code>
 154      *
 155      * @param array $keyvaluearray An array of key => value pairs to send to the cache.
 156      * @return int The number of items successfully set. It is up to the developer to check this matches the number of items.
 157      *      ... if they care that is.
 158      */
 159     public function set_many(array $keyvaluearray);
 160
 161     /**
 162      * Test is a cache has a key.
 163      *
 164      * The use of the has methods is strongly discouraged. In a high load environment the cache may well change between the
 165      * test and any subsequent action (get, set, delete etc).
 166      * Instead it is recommended to write your code in such a way they it performs the following steps:
 167      * <ol>
 168      * <li>Attempt to retrieve the information.</li>
 169      * <li>Generate the information.</li>
 170      * <li>Attempt to set the information</li>
 171      * </ol>
 172      *
 173      * Its also worth mentioning that not all stores support key tests.
 174      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 175      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 176      *
 177      * @param string|int $key
 178      * @return bool True if the cache has the requested key, false otherwise.
 179      */
 180     public function has($key);
 181
 182     /**
 183      * Test if a cache has at least one of the given keys.
 184      *
 185      * It is strongly recommended to avoid the use of this function if not absolutely required.
 186      * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
 187      *
 188      * Its also worth mentioning that not all stores support key tests.
 189      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 190      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 191      *
 192      * @param array $keys
 193      * @return bool True if the cache has at least one of the given keys
 194      */
 195     public function has_any(array $keys);
 196
 197     /**
 198      * Test is a cache has all of the given keys.
 199      *
 200      * It is strongly recommended to avoid the use of this function if not absolutely required.
 201      * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
 202      *
 203      * Its also worth mentioning that not all stores support key tests.
 204      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 205      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 206      *
 207      * @param array $keys
 208      * @return bool True if the cache has all of the given keys, false otherwise.
 209      */
 210     public function has_all(array $keys);
 211
 212     /**
 213      * Delete the given key from the cache.
 214      *
 215      * @param string|int $key The key to delete.
 216      * @param bool $recurse When set to true the key will also be deleted from all stacked cache loaders and their stores.
 217      *     This happens by default and ensure that all the caches are consistent. It is NOT recommended to change this.
 218      * @return bool True of success, false otherwise.
 219      */
 220     public function delete($key, $recurse = true);
 221
 222     /**
 223      * Delete all of the given keys from the cache.
 224      *
 225      * @param array $keys The key to delete.
 226      * @param bool $recurse When set to true the key will also be deleted from all stacked cache loaders and their stores.
 227      *     This happens by default and ensure that all the caches are consistent. It is NOT recommended to change this.
 228      * @return int The number of items successfully deleted.
 229      */
 230     public function delete_many(array $keys, $recurse = true);
 231 }
 232
 233 /**
 234  * Cache Loader supporting locking.
 235  *
 236  * This interface should be given to classes already implementing cache_loader that also wish to support locking.
 237  * It outlines the required structure for utilising locking functionality when using a cache.
 238  *
 239  * Can be implemented by any class already implementing the cache_loader interface.
 240  */
 241 interface cache_loader_with_locking {
 242
 243     /**
 244      * Acquires a lock for the given key.
 245      *
 246      * Please note that this happens automatically if the cache definition requires locking.
 247      * it is still made a public method so that adhoc caches can use it if they choose.
 248      * However this doesn't guarantee consistent access. It will become the responsibility of the calling code to ensure
 249      * locks are acquired, checked, and released.
 250      *
 251      * Prior to Moodle 4,3 this function used to return false if the lock cannot be obtained. It
 252      * now always returns true, and throws an exception if the lock cannot be obtained.
 253      *
 254      * @param string|int $key
 255      * @return bool Always returns true (for backwards compatibility)
 256      * @throws moodle_exception If the lock cannot be obtained after a timeout
 257      */
 258     public function acquire_lock($key);
 259
 260     /**
 261      * Checks if the cache loader owns the lock for the given key.
 262      *
 263      * Please note that this happens automatically if the cache definition requires locking.
 264      * it is still made a public method so that adhoc caches can use it if they choose.
 265      * However this doesn't guarantee consistent access. It will become the responsibility of the calling code to ensure
 266      * locks are acquired, checked, and released.
 267      *
 268      * @param string|int $key
 269      * @return bool True if this code has the lock, false if there is a lock but this code doesn't have it,
 270      *      null if there is no lock.
 271      */
 272     public function check_lock_state($key);
 273
 274     /**
 275      * Releases the lock for the given key.
 276      *
 277      * Please note that this happens automatically if the cache definition requires locking.
 278      * it is still made a public method so that adhoc caches can use it if they choose.
 279      * However this doesn't guarantee consistent access. It will become the responsibility of the calling code to ensure
 280      * locks are acquired, checked, and released.
 281      *
 282      * @param string|int $key
 283      * @return bool True if the lock has been released, false if there was a problem releasing the lock.
 284      */
 285     public function release_lock($key);
 286 }
 287
 288 /**
 289  * Cache store feature: locking
 290  *
 291  * This is a feature that cache stores can implement if they wish to support locking themselves rather
 292  * than having the cache loader handle it for them.
 293  *
 294  * Can be implemented by classes already implementing cache_store.
 295  */
 296 interface cache_is_lockable {
 297
 298     /**
 299      * Acquires a lock on the given key for the given identifier.
 300      *
 301      * @param string $key The key we are locking.
 302      * @param string $ownerid The identifier so we can check if we have the lock or if it is someone else.
 303      *      The use of this property is entirely optional and implementations can act as they like upon it.
 304      * @return bool True if the lock could be acquired, false otherwise.
 305      */
 306     public function acquire_lock($key, $ownerid);
 307
 308     /**
 309      * Test if there is already a lock for the given key and if there is whether it belongs to the calling code.
 310      *
 311      * @param string $key The key we are locking.
 312      * @param string $ownerid The identifier so we can check if we have the lock or if it is someone else.
 313      * @return bool True if this code has the lock, false if there is a lock but this code doesn't have it, null if there
 314      *      is no lock.
 315      */
 316     public function check_lock_state($key, $ownerid);
 317
 318     /**
 319      * Releases the lock on the given key.
 320      *
 321      * @param string $key The key we are locking.
 322      * @param string $ownerid The identifier so we can check if we have the lock or if it is someone else.
 323      *      The use of this property is entirely optional and implementations can act as they like upon it.
 324      * @return bool True if the lock has been released, false if there was a problem releasing the lock.
 325      */
 326     public function release_lock($key, $ownerid);
 327 }
 328
 329 /**
 330  * Cache store feature: key awareness.
 331  *
 332  * This is a feature that cache stores and cache loaders can both choose to implement.
 333  * If a cache store implements this then it will be made responsible for tests for items within the cache.
 334  * If the cache store being used doesn't implement this then it will be the responsibility of the cache loader to use the
 335  * equivalent get methods to mimick the functionality of these tests.
 336  *
 337  * Cache stores should only override these methods if they natively support such features or if they have a better performing
 338  * means of performing these tests than the handling that would otherwise take place in the cache_loader.
 339  *
 340  * Can be implemented by classes already implementing cache_store.
 341  */
 342 interface cache_is_key_aware {
 343
 344     /**
 345      * Test is a cache has a key.
 346      *
 347      * The use of the has methods is strongly discouraged. In a high load environment the cache may well change between the
 348      * test and any subsequent action (get, set, delete etc).
 349      * Instead it is recommended to write your code in such a way they it performs the following steps:
 350      * <ol>
 351      * <li>Attempt to retrieve the information.</li>
 352      * <li>Generate the information.</li>
 353      * <li>Attempt to set the information</li>
 354      * </ol>
 355      *
 356      * Its also worth mentioning that not all stores support key tests.
 357      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 358      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 359      *
 360      * @param string|int $key
 361      * @return bool True if the cache has the requested key, false otherwise.
 362      */
 363     public function has($key);
 364
 365     /**
 366      * Test if a cache has at least one of the given keys.
 367      *
 368      * It is strongly recommended to avoid the use of this function if not absolutely required.
 369      * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
 370      *
 371      * Its also worth mentioning that not all stores support key tests.
 372      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 373      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 374      *
 375      * @param array $keys
 376      * @return bool True if the cache has at least one of the given keys
 377      */
 378     public function has_any(array $keys);
 379
 380     /**
 381      * Test is a cache has all of the given keys.
 382      *
 383      * It is strongly recommended to avoid the use of this function if not absolutely required.
 384      * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
 385      *
 386      * Its also worth mentioning that not all stores support key tests.
 387      * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
 388      * Just one more reason you should not use these methods unless you have a very good reason to do so.
 389      *
 390      * @param array $keys
 391      * @return bool True if the cache has all of the given keys, false otherwise.
 392      */
 393     public function has_all(array $keys);
 394 }
 395
 396 /**
 397  * Cache store feature: keys are searchable.
 398  *
 399  * Cache stores can choose to implement this interface.
 400  * In order for a store to be usable as a session cache it must implement this interface.
 401  *
 402  * @since Moodle 2.4.4
 403  */
 404 interface cache_is_searchable {
 405     /**
 406      * Finds all of the keys being used by the cache store.
 407      *
 408      * @return array.
 409      */
 410     public function find_all();
 411
 412     /**
 413      * Finds all of the keys whose keys start with the given prefix.
 414      *
 415      * @param string $prefix
 416      */
 417     public function find_by_prefix($prefix);
 418 }
 419
 420 /**
 421  * Cache store feature: configurable.
 422  *
 423  * This feature should be implemented by all cache stores that are configurable when adding an instance.
 424  * It requires the implementation of methods required to convert form data into the a configuration array for the
 425  * store instance, and then the reverse converting configuration data into an array that can be used to set the
 426  * data for the edit form.
 427  *
 428  * Can be implemented by classes already implementing cache_store.
 429  */
 430 interface cache_is_configurable {
 431
 432     /**
 433      * Given the data from the add instance form this function creates a configuration array.
 434      *
 435      * @param stdClass $data
 436      * @return array
 437      */
 438     public static function config_get_configuration_array($data);
 439
 440     /**
 441      * Allows the cache store to set its data against the edit form before it is shown to the user.
 442      *
 443      * @param moodleform $editform
 444      * @param array $config
 445      */
 446     public static function config_set_edit_form_data(moodleform $editform, array $config);
 447 }
 448
 449 /**
 450  * Cache Data Source.
 451  *
 452  * The cache data source interface can be implemented by any class within Moodle.
 453  * If implemented then the class can be reference in a cache definition and will be used to load information that cannot be
 454  * retrieved from the cache. As part of its retrieval that information will also be loaded into the cache.
 455  *
 456  * This allows developers to created a complete cache solution that can be used through code ensuring consistent cache
 457  * interaction and loading. Allowing them in turn to centralise code and help keeps things more easily maintainable.
 458  *
 459  * Can be implemented by any class.
 460  *
 461  * @package    core
 462  * @category   cache
 463  * @copyright  2012 Sam Hemelryk
 464  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 465  */
 466 interface cache_data_source {
 467
 468     /**
 469      * Returns an instance of the data source class that the cache can use for loading data using the other methods
 470      * specified by this interface.
 471      *
 472      * @param cache_definition $definition
 473      * @return object
 474      */
 475     public static function get_instance_for_cache(cache_definition $definition);
 476
 477     /**
 478      * Loads the data for the key provided ready formatted for caching.
 479      *
 480      * @param string|int $key The key to load.
 481      * @return mixed What ever data should be returned, or false if it can't be loaded.
 482      */
 483     public function load_for_cache($key);
 484
 485     /**
 486      * Loads several keys for the cache.
 487      *
 488      * @param array $keys An array of keys each of which will be string|int.
 489      * @return array An array of matching data items.
 490      */
 491     public function load_many_for_cache(array $keys);
 492 }
 493
 494 /**
 495  * Versionable cache data source.
 496  *
 497  * This interface extends the main cache data source interface to add an extra required method if
 498  * the data source is to be used for a versioned cache.
 499  *
 500  * @package core_cache
 501  */
 502 interface cache_data_source_versionable extends cache_data_source {
 503     /**
 504      * Loads the data for the key provided ready formatted for caching.
 505      *
 506      * If there is no data for that key, or if the data for the required key has an older version
 507      * than the specified $requiredversion, then this returns null.
 508      *
 509      * If there is data then $actualversion should be set to the actual version number retrieved
 510      * (may be the same as $requiredversion or newer).
 511      *
 512      * @param string|int $key The key to load.
 513      * @param int $requiredversion Minimum required version
 514      * @param mixed $actualversion Should be set to the actual version number retrieved
 515      * @return mixed What ever data should be returned, or false if it can't be loaded.
 516      */
 517     public function load_for_cache_versioned($key, int $requiredversion, &$actualversion);
 518 }
 519
 520 /**
 521  * Cacheable object.
 522  *
 523  * 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
 524  * structure and the information about to be cached, as well as how to deal with it when it is retrieved from a cache.
 525  * Think of it like serialisation and the __sleep and __wakeup methods.
 526  * This is used because cache stores are responsible for how they interact with data and what they do when storing it. This
 527  * interface ensures there is always a guaranteed action.
 528  */
 529 interface cacheable_object {
 530
 531     /**
 532      * Prepares the object for caching. Works like the __sleep method.
 533      *
 534      * @return mixed The data to cache, can be anything except a class that implements the cacheable_object... that would
 535      *      be dumb.
 536      */
 537     public function prepare_to_cache();
 538
 539     /**
 540      * Takes the data provided by prepare_to_cache and reinitialises an instance of the associated from it.
 541      *
 542      * @param mixed $data
 543      * @return object The instance for the given data.
 544      */
 545     public static function wake_from_cache($data);
 546 }
 547
 548 /**
 549  * Cache lock interface
 550  *
 551  * This interface needs to be inherited by all cache lock plugins.
 552  */
 553 interface cache_lock_interface {
 554     /**
 555      * Constructs an instance of the cache lock given its name and its configuration data
 556      *
 557      * @param string $name The unique name of the lock instance
 558      * @param array $configuration
 559      */
 560     public function __construct($name, array $configuration = array());
 561
 562     /**
 563      * Acquires a lock on a given key.
 564      *
 565      * @param string $key The key to acquire a lock for.
 566      * @param string $ownerid An unique identifier for the owner of this lock. It is entirely optional for the cache lock plugin
 567      *      to use this. Each implementation can decide for themselves.
 568      * @param bool $block If set to true the application will wait until a lock can be acquired
 569      * @return bool True if the lock can be acquired false otherwise.
 570      */
 571     public function lock($key, $ownerid, $block = false);
 572
 573     /**
 574      * Releases the lock held on a certain key.
 575      *
 576      * @param string $key The key to release the lock for.
 577      * @param string $ownerid An unique identifier for the owner of this lock. It is entirely optional for the cache lock plugin
 578      *      to use this. Each implementation can decide for themselves.
 579      * @param bool $forceunlock If set to true the lock will be removed if it exists regardless of whether or not we own it.
 580      */
 581     public function unlock($key, $ownerid, $forceunlock = false);
 582
 583     /**
 584      * Checks the state of the given key.
 585      *
 586      * Returns true if the key is locked and belongs to the ownerid.
 587      * Returns false if the key is locked but does not belong to the ownerid.
 588      * Returns null if there is no lock
 589      *
 590      * @param string $key The key we are checking for.
 591      * @param string $ownerid The identifier so we can check if we have the lock or if it is someone else.
 592      * @return bool True if this code has the lock, false if there is a lock but this code doesn't have it, null if there
 593      *      is no lock.
 594      */
 595     public function check_state($key, $ownerid);
 596
 597     /**
 598      * Cleans up any left over locks.
 599      *
 600      * This function MUST clean up any locks that have been acquired and not released during processing.
 601      * Although the situation of acquiring a lock and not releasing it should be insanely rare we need to deal with it.
 602      * Things such as unfortunate timeouts etc could cause this situation.
 603      */
 604     public function __destruct();
 605 }