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See Release Notes
Long Term Support Release

  • Bug fixes for general core bugs in 3.9.x will end* 10 May 2021 (12 months).
  • Bug fixes for security issues in 3.9.x will end* 8 May 2023 (36 months).
  • PHP version: minimum PHP 7.2.0 Note: minimum PHP version has increased since Moodle 3.8. PHP 7.3.x and 7.4.x are supported too.

Differences Between: [Versions 39 and 310] [Versions 39 and 311] [Versions 39 and 400] [Versions 39 and 401] [Versions 39 and 402] [Versions 39 and 403]

   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 helper class
  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   * The cache helper class.
  33   *
  34   * The cache helper class provides common functionality to the cache API and is useful to developers within to interact with
  35   * the cache API in a general way.
  36   *
  37   * @package    core
  38   * @category   cache
  39   * @copyright  2012 Sam Hemelryk
  40   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  41   */
  42  class cache_helper {
  43  
  44      /**
  45       * Statistics gathered by the cache API during its operation will be used here.
  46       * @static
  47       * @var array
  48       */
  49      protected static $stats = array();
  50  
  51      /**
  52       * The instance of the cache helper.
  53       * @var cache_helper
  54       */
  55      protected static $instance;
  56  
  57      /**
  58       * The site identifier used by the cache.
  59       * Set the first time get_site_identifier is called.
  60       * @var string
  61       */
  62      protected static $siteidentifier = null;
  63  
  64      /**
  65       * Returns true if the cache API can be initialised before Moodle has finished initialising itself.
  66       *
  67       * This check is essential when trying to cache the likes of configuration information. It checks to make sure that the cache
  68       * configuration file has been created which allows use to set up caching when ever is required.
  69       *
  70       * @return bool
  71       */
  72      public static function ready_for_early_init() {
  73          return cache_config::config_file_exists();
  74      }
  75  
  76      /**
  77       * Returns an instance of the cache_helper.
  78       *
  79       * This is designed for internal use only and acts as a static store.
  80       * @staticvar null $instance
  81       * @return cache_helper
  82       */
  83      protected static function instance() {
  84          if (is_null(self::$instance)) {
  85              self::$instance = new cache_helper();
  86          }
  87          return self::$instance;
  88      }
  89  
  90      /**
  91       * Constructs an instance of the cache_helper class. Again for internal use only.
  92       */
  93      protected function __construct() {
  94          // Nothing to do here, just making sure you can't get an instance of this.
  95      }
  96  
  97      /**
  98       * Used as a data store for initialised definitions.
  99       * @var array
 100       */
 101      protected $definitions = array();
 102  
 103      /**
 104       * Used as a data store for initialised cache stores
 105       * We use this because we want to avoid establishing multiple instances of a single store.
 106       * @var array
 107       */
 108      protected $stores = array();
 109  
 110      /**
 111       * Returns the class for use as a cache loader for the given mode.
 112       *
 113       * @param int $mode One of cache_store::MODE_
 114       * @return string
 115       * @throws coding_exception
 116       */
 117      public static function get_class_for_mode($mode) {
 118          switch ($mode) {
 119              case cache_store::MODE_APPLICATION :
 120                  return 'cache_application';
 121              case cache_store::MODE_REQUEST :
 122                  return 'cache_request';
 123              case cache_store::MODE_SESSION :
 124                  return 'cache_session';
 125          }
 126          throw new coding_exception('Unknown cache mode passed. Must be one of cache_store::MODE_*');
 127      }
 128  
 129      /**
 130       * Returns the cache stores to be used with the given definition.
 131       * @param cache_definition $definition
 132       * @return array
 133       */
 134      public static function get_cache_stores(cache_definition $definition) {
 135          $instance = cache_config::instance();
 136          $stores = $instance->get_stores_for_definition($definition);
 137          $stores = self::initialise_cachestore_instances($stores, $definition);
 138          return $stores;
 139      }
 140  
 141      /**
 142       * Internal function for initialising an array of stores against a given cache definition.
 143       *
 144       * @param array $stores
 145       * @param cache_definition $definition
 146       * @return cache_store[]
 147       */
 148      protected static function initialise_cachestore_instances(array $stores, cache_definition $definition) {
 149          $return = array();
 150          $factory = cache_factory::instance();
 151          foreach ($stores as $name => $details) {
 152              $store = $factory->create_store_from_config($name, $details, $definition);
 153              if ($store !== false) {
 154                  $return[] = $store;
 155              }
 156          }
 157          return $return;
 158      }
 159  
 160      /**
 161       * Returns a cache_lock instance suitable for use with the store.
 162       *
 163       * @param cache_store $store
 164       * @return cache_lock_interface
 165       */
 166      public static function get_cachelock_for_store(cache_store $store) {
 167          $instance = cache_config::instance();
 168          $lockconf = $instance->get_lock_for_store($store->my_name());
 169          $factory = cache_factory::instance();
 170          return $factory->create_lock_instance($lockconf);
 171      }
 172  
 173      /**
 174       * Returns an array of plugins without using core methods.
 175       *
 176       * This function explicitly does NOT use core functions as it will in some circumstances be called before Moodle has
 177       * finished initialising. This happens when loading configuration for instance.
 178       *
 179       * @return string
 180       */
 181      public static function early_get_cache_plugins() {
 182          global $CFG;
 183          $result = array();
 184          $ignored = array('CVS', '_vti_cnf', 'simpletest', 'db', 'yui', 'tests');
 185          $fulldir = $CFG->dirroot.'/cache/stores';
 186          $items = new DirectoryIterator($fulldir);
 187          foreach ($items as $item) {
 188              if ($item->isDot() or !$item->isDir()) {
 189                  continue;
 190              }
 191              $pluginname = $item->getFilename();
 192              if (in_array($pluginname, $ignored)) {
 193                  continue;
 194              }
 195              if (!is_valid_plugin_name($pluginname)) {
 196                  // Better ignore plugins with problematic names here.
 197                  continue;
 198              }
 199              $result[$pluginname] = $fulldir.'/'.$pluginname;
 200              unset($item);
 201          }
 202          unset($items);
 203          return $result;
 204      }
 205  
 206      /**
 207       * Invalidates a given set of keys from a given definition.
 208       *
 209       * @todo Invalidating by definition should also add to the event cache so that sessions can be invalidated (when required).
 210       *
 211       * @param string $component
 212       * @param string $area
 213       * @param array $identifiers
 214       * @param array $keys
 215       * @return boolean
 216       */
 217      public static function invalidate_by_definition($component, $area, array $identifiers = array(), $keys = array()) {
 218          $cache = cache::make($component, $area, $identifiers);
 219          if (is_array($keys)) {
 220              $cache->delete_many($keys);
 221          } else if (is_scalar($keys)) {
 222              $cache->delete($keys);
 223          } else {
 224              throw new coding_exception('cache_helper::invalidate_by_definition only accepts $keys as array, or scalar.');
 225          }
 226          return true;
 227      }
 228  
 229      /**
 230       * Invalidates a given set of keys by means of an event.
 231       *
 232       * Events cannot determine what identifiers might need to be cleared. Event based purge and invalidation
 233       * are only supported on caches without identifiers.
 234       *
 235       * @param string $event
 236       * @param array $keys
 237       */
 238      public static function invalidate_by_event($event, array $keys) {
 239          $instance = cache_config::instance();
 240          $invalidationeventset = false;
 241          $factory = cache_factory::instance();
 242          $inuse = $factory->get_caches_in_use();
 243          $purgetoken = null;
 244          foreach ($instance->get_definitions() as $name => $definitionarr) {
 245              $definition = cache_definition::load($name, $definitionarr);
 246              if ($definition->invalidates_on_event($event)) {
 247                  // First up check if there is a cache loader for this definition already.
 248                  // If there is we need to invalidate the keys from there.
 249                  $definitionkey = $definition->get_component().'/'.$definition->get_area();
 250                  if (isset($inuse[$definitionkey])) {
 251                      $inuse[$definitionkey]->delete_many($keys);
 252                  }
 253  
 254                  // We should only log events for application and session caches.
 255                  // Request caches shouldn't have events as all data is lost at the end of the request.
 256                  // Events should only be logged once of course and likely several definitions are watching so we
 257                  // track its logging with $invalidationeventset.
 258                  $logevent = ($invalidationeventset === false && $definition->get_mode() !== cache_store::MODE_REQUEST);
 259  
 260                  if ($logevent) {
 261                      // Get the event invalidation cache.
 262                      $cache = cache::make('core', 'eventinvalidation');
 263                      // Get any existing invalidated keys for this cache.
 264                      $data = $cache->get($event);
 265                      if ($data === false) {
 266                          // There are none.
 267                          $data = array();
 268                      }
 269                      // Add our keys to them with the current cache timestamp.
 270                      if (null === $purgetoken) {
 271                          $purgetoken = cache::get_purge_token(true);
 272                      }
 273                      foreach ($keys as $key) {
 274                          $data[$key] = $purgetoken;
 275                      }
 276                      // Set that data back to the cache.
 277                      $cache->set($event, $data);
 278                      // This only needs to occur once.
 279                      $invalidationeventset = true;
 280                  }
 281              }
 282          }
 283      }
 284  
 285      /**
 286       * Purges the cache for a specific definition.
 287       *
 288       * @param string $component
 289       * @param string $area
 290       * @param array $identifiers
 291       * @return bool
 292       */
 293      public static function purge_by_definition($component, $area, array $identifiers = array()) {
 294          // Create the cache.
 295          $cache = cache::make($component, $area, $identifiers);
 296          // Initialise, in case of a store.
 297          if ($cache instanceof cache_store) {
 298              $factory = cache_factory::instance();
 299              $definition = $factory->create_definition($component, $area, null);
 300              $cacheddefinition = clone $definition;
 301              $cacheddefinition->set_identifiers($identifiers);
 302              $cache->initialise($cacheddefinition);
 303          }
 304          // Purge baby, purge.
 305          $cache->purge();
 306          return true;
 307      }
 308  
 309      /**
 310       * Purges a cache of all information on a given event.
 311       *
 312       * Events cannot determine what identifiers might need to be cleared. Event based purge and invalidation
 313       * are only supported on caches without identifiers.
 314       *
 315       * @param string $event
 316       */
 317      public static function purge_by_event($event) {
 318          $instance = cache_config::instance();
 319          $invalidationeventset = false;
 320          $factory = cache_factory::instance();
 321          $inuse = $factory->get_caches_in_use();
 322          $purgetoken = null;
 323          foreach ($instance->get_definitions() as $name => $definitionarr) {
 324              $definition = cache_definition::load($name, $definitionarr);
 325              if ($definition->invalidates_on_event($event)) {
 326                  // First up check if there is a cache loader for this definition already.
 327                  // If there is we need to invalidate the keys from there.
 328                  $definitionkey = $definition->get_component().'/'.$definition->get_area();
 329                  if (isset($inuse[$definitionkey])) {
 330                      $inuse[$definitionkey]->purge();
 331                  } else {
 332                      cache::make($definition->get_component(), $definition->get_area())->purge();
 333                  }
 334  
 335                  // We should only log events for application and session caches.
 336                  // Request caches shouldn't have events as all data is lost at the end of the request.
 337                  // Events should only be logged once of course and likely several definitions are watching so we
 338                  // track its logging with $invalidationeventset.
 339                  $logevent = ($invalidationeventset === false && $definition->get_mode() !== cache_store::MODE_REQUEST);
 340  
 341                  // We need to flag the event in the "Event invalidation" cache if it hasn't already happened.
 342                  if ($logevent && $invalidationeventset === false) {
 343                      // Get the event invalidation cache.
 344                      $cache = cache::make('core', 'eventinvalidation');
 345                      // Create a key to invalidate all.
 346                      if (null === $purgetoken) {
 347                          $purgetoken = cache::get_purge_token(true);
 348                      }
 349                      $data = array(
 350                          'purged' => $purgetoken,
 351                      );
 352                      // Set that data back to the cache.
 353                      $cache->set($event, $data);
 354                      // This only needs to occur once.
 355                      $invalidationeventset = true;
 356                  }
 357              }
 358          }
 359      }
 360  
 361      /**
 362       * Ensure that the stats array is ready to collect information for the given store and definition.
 363       * @param string $store
 364       * @param string $storeclass
 365       * @param string $definition A string that identifies the definition.
 366       * @param int $mode One of cache_store::MODE_*. Since 2.9.
 367       */
 368      protected static function ensure_ready_for_stats($store, $storeclass, $definition, $mode = cache_store::MODE_APPLICATION) {
 369          // This function is performance-sensitive, so exit as quickly as possible
 370          // if we do not need to do anything.
 371          if (isset(self::$stats[$definition]['stores'][$store])) {
 372              return;
 373          }
 374  
 375          if (!array_key_exists($definition, self::$stats)) {
 376              self::$stats[$definition] = array(
 377                  'mode' => $mode,
 378                  'stores' => array(
 379                      $store => array(
 380                          'class' => $storeclass,
 381                          'hits' => 0,
 382                          'misses' => 0,
 383                          'sets' => 0,
 384                      )
 385                  )
 386              );
 387          } else if (!array_key_exists($store, self::$stats[$definition]['stores'])) {
 388              self::$stats[$definition]['stores'][$store] = array(
 389                  'class' => $storeclass,
 390                  'hits' => 0,
 391                  'misses' => 0,
 392                  'sets' => 0,
 393              );
 394          }
 395      }
 396  
 397      /**
 398       * Returns a string to describe the definition.
 399       *
 400       * This method supports the definition as a string due to legacy requirements.
 401       * It is backwards compatible when a string is passed but is not accurate.
 402       *
 403       * @since 2.9
 404       * @param cache_definition|string $definition
 405       * @return string
 406       */
 407      protected static function get_definition_stat_id_and_mode($definition) {
 408          if (!($definition instanceof cache_definition)) {
 409              // All core calls to this method have been updated, this is the legacy state.
 410              // We'll use application as the default as that is the most common, really this is not accurate of course but
 411              // at this point we can only guess and as it only affects calls to cache stat outside of core (of which there should
 412              // be none) I think that is fine.
 413              debugging('Please update you cache stat calls to pass the definition rather than just its ID.', DEBUG_DEVELOPER);
 414              return array((string)$definition, cache_store::MODE_APPLICATION);
 415          }
 416          return array($definition->get_id(), $definition->get_mode());
 417      }
 418  
 419      /**
 420       * Record a cache hit in the stats for the given store and definition.
 421       *
 422       * In Moodle 2.9 the $definition argument changed from accepting only a string to accepting a string or a
 423       * cache_definition instance. It is preferable to pass a cache definition instance.
 424       *
 425       * In Moodle 3.9 the first argument changed to also accept a cache_store.
 426       *
 427       * @internal
 428       * @param string|cache_store $store
 429       * @param cache_definition $definition You used to be able to pass a string here, however that is deprecated please pass the
 430       *      actual cache_definition object now.
 431       * @param int $hits The number of hits to record (by default 1)
 432       */
 433      public static function record_cache_hit($store, $definition, $hits = 1) {
 434          $storeclass = '';
 435          if ($store instanceof cache_store) {
 436              $storeclass = get_class($store);
 437              $store = $store->my_name();
 438          }
 439          list($definitionstr, $mode) = self::get_definition_stat_id_and_mode($definition);
 440          self::ensure_ready_for_stats($store, $storeclass, $definitionstr, $mode);
 441          self::$stats[$definitionstr]['stores'][$store]['hits'] += $hits;
 442      }
 443  
 444      /**
 445       * Record a cache miss in the stats for the given store and definition.
 446       *
 447       * In Moodle 2.9 the $definition argument changed from accepting only a string to accepting a string or a
 448       * cache_definition instance. It is preferable to pass a cache definition instance.
 449       *
 450       * In Moodle 3.9 the first argument changed to also accept a cache_store.
 451       *
 452       * @internal
 453       * @param string|cache_store $store
 454       * @param cache_definition $definition You used to be able to pass a string here, however that is deprecated please pass the
 455       *      actual cache_definition object now.
 456       * @param int $misses The number of misses to record (by default 1)
 457       */
 458      public static function record_cache_miss($store, $definition, $misses = 1) {
 459          $storeclass = '';
 460          if ($store instanceof cache_store) {
 461              $storeclass = get_class($store);
 462              $store = $store->my_name();
 463          }
 464          list($definitionstr, $mode) = self::get_definition_stat_id_and_mode($definition);
 465          self::ensure_ready_for_stats($store, $storeclass, $definitionstr, $mode);
 466          self::$stats[$definitionstr]['stores'][$store]['misses'] += $misses;
 467      }
 468  
 469      /**
 470       * Record a cache set in the stats for the given store and definition.
 471       *
 472       * In Moodle 2.9 the $definition argument changed from accepting only a string to accepting a string or a
 473       * cache_definition instance. It is preferable to pass a cache definition instance.
 474       *
 475       * In Moodle 3.9 the first argument changed to also accept a cache_store.
 476       *
 477       * @internal
 478       * @param string|cache_store $store
 479       * @param cache_definition $definition You used to be able to pass a string here, however that is deprecated please pass the
 480       *      actual cache_definition object now.
 481       * @param int $sets The number of sets to record (by default 1)
 482       */
 483      public static function record_cache_set($store, $definition, $sets = 1) {
 484          $storeclass = '';
 485          if ($store instanceof cache_store) {
 486              $storeclass = get_class($store);
 487              $store = $store->my_name();
 488          }
 489          list($definitionstr, $mode) = self::get_definition_stat_id_and_mode($definition);
 490          self::ensure_ready_for_stats($store, $storeclass, $definitionstr, $mode);
 491          self::$stats[$definitionstr]['stores'][$store]['sets'] += $sets;
 492      }
 493  
 494      /**
 495       * Return the stats collected so far.
 496       * @return array
 497       */
 498      public static function get_stats() {
 499          return self::$stats;
 500      }
 501  
 502      /**
 503       * Purge all of the cache stores of all of their data.
 504       *
 505       * Think twice before calling this method. It will purge **ALL** caches regardless of whether they have been used recently or
 506       * anything. This will involve full setup of the cache + the purge operation. On a site using caching heavily this WILL be
 507       * painful.
 508       *
 509       * @param bool $usewriter If set to true the cache_config_writer class is used. This class is special as it avoids
 510       *      it is still usable when caches have been disabled.
 511       *      Please use this option only if you really must. It's purpose is to allow the cache to be purged when it would be
 512       *      otherwise impossible.
 513       */
 514      public static function purge_all($usewriter = false) {
 515          $factory = cache_factory::instance();
 516          $config = $factory->create_config_instance($usewriter);
 517          foreach ($config->get_all_stores() as $store) {
 518              self::purge_store($store['name'], $config);
 519          }
 520          foreach ($factory->get_adhoc_caches_in_use() as $cache) {
 521              $cache->purge();
 522          }
 523      }
 524  
 525      /**
 526       * Purges a store given its name.
 527       *
 528       * @param string $storename
 529       * @param cache_config $config
 530       * @return bool
 531       */
 532      public static function purge_store($storename, cache_config $config = null) {
 533          if ($config === null) {
 534              $config = cache_config::instance();
 535          }
 536  
 537          $stores = $config->get_all_stores();
 538          if (!array_key_exists($storename, $stores)) {
 539              // The store does not exist.
 540              return false;
 541          }
 542  
 543          $store = $stores[$storename];
 544          $class = $store['class'];
 545  
 546  
 547          // We check are_requirements_met although we expect is_ready is going to check as well.
 548          if (!$class::are_requirements_met()) {
 549              return false;
 550          }
 551          // Found the store: is it ready?
 552          /* @var cache_store $instance */
 553          $instance = new $class($store['name'], $store['configuration']);
 554          if (!$instance->is_ready()) {
 555              unset($instance);
 556              return false;
 557          }
 558          foreach ($config->get_definitions_by_store($storename) as $id => $definition) {
 559              $definition = cache_definition::load($id, $definition);
 560              $definitioninstance = clone($instance);
 561              $definitioninstance->initialise($definition);
 562              $definitioninstance->purge();
 563              unset($definitioninstance);
 564          }
 565  
 566          return true;
 567      }
 568  
 569      /**
 570       * Purges all of the stores used by a definition.
 571       *
 572       * Unlike cache_helper::purge_by_definition this purges all of the data from the stores not
 573       * just the data relating to the definition.
 574       * This function is useful when you must purge a definition that requires setup but you don't
 575       * want to set it up.
 576       *
 577       * @param string $component
 578       * @param string $area
 579       */
 580      public static function purge_stores_used_by_definition($component, $area) {
 581          $factory = cache_factory::instance();
 582          $config = $factory->create_config_instance();
 583          $definition = $factory->create_definition($component, $area);
 584          $stores = $config->get_stores_for_definition($definition);
 585          foreach ($stores as $store) {
 586              self::purge_store($store['name']);
 587          }
 588      }
 589  
 590      /**
 591       * Returns the translated name of the definition.
 592       *
 593       * @param cache_definition $definition
 594       * @return lang_string
 595       */
 596      public static function get_definition_name($definition) {
 597          if ($definition instanceof cache_definition) {
 598              return $definition->get_name();
 599          }
 600          $identifier = 'cachedef_'.clean_param($definition['area'], PARAM_STRINGID);
 601          $component = $definition['component'];
 602          if ($component === 'core') {
 603              $component = 'cache';
 604          }
 605          return new lang_string($identifier, $component);
 606      }
 607  
 608      /**
 609       * Hashes a descriptive key to make it shorter and still unique.
 610       * @param string|int $key
 611       * @param cache_definition $definition
 612       * @return string
 613       */
 614      public static function hash_key($key, cache_definition $definition) {
 615          if ($definition->uses_simple_keys()) {
 616              if (debugging() && preg_match('#[^a-zA-Z0-9_]#', $key)) {
 617                  throw new coding_exception('Cache definition '.$definition->get_id().' requires simple keys. Invalid key provided.', $key);
 618              }
 619              // We put the key first so that we can be sure the start of the key changes.
 620              return (string)$key . '-' . $definition->generate_single_key_prefix();
 621          }
 622          $key = $definition->generate_single_key_prefix() . '-' . $key;
 623          return sha1($key);
 624      }
 625  
 626      /**
 627       * Finds all definitions and updates them within the cache config file.
 628       *
 629       * @param bool $coreonly If set to true only core definitions will be updated.
 630       */
 631      public static function update_definitions($coreonly = false) {
 632          global $CFG;
 633          // Include locallib.
 634          require_once($CFG->dirroot.'/cache/locallib.php');
 635          // First update definitions
 636          cache_config_writer::update_definitions($coreonly);
 637          // Second reset anything we have already initialised to ensure we're all up to date.
 638          cache_factory::reset();
 639      }
 640  
 641      /**
 642       * Update the site identifier stored by the cache API.
 643       *
 644       * @param string $siteidentifier
 645       * @return string The new site identifier.
 646       */
 647      public static function update_site_identifier($siteidentifier) {
 648          global $CFG;
 649          // Include locallib.
 650          require_once($CFG->dirroot.'/cache/locallib.php');
 651          $factory = cache_factory::instance();
 652          $factory->updating_started();
 653          $config = $factory->create_config_instance(true);
 654          $siteidentifier = $config->update_site_identifier($siteidentifier);
 655          $factory->updating_finished();
 656          cache_factory::reset();
 657          return $siteidentifier;
 658      }
 659  
 660      /**
 661       * Returns the site identifier.
 662       *
 663       * @return string
 664       */
 665      public static function get_site_identifier() {
 666          global $CFG;
 667          if (!is_null(self::$siteidentifier)) {
 668              return self::$siteidentifier;
 669          }
 670          // If site identifier hasn't been collected yet attempt to get it from the cache config.
 671          $factory = cache_factory::instance();
 672          // If the factory is initialising then we don't want to try to get it from the config or we risk
 673          // causing the cache to enter an infinite initialisation loop.
 674          if (!$factory->is_initialising()) {
 675              $config = $factory->create_config_instance();
 676              self::$siteidentifier = $config->get_site_identifier();
 677          }
 678          if (is_null(self::$siteidentifier)) {
 679              // If the site identifier is still null then config isn't aware of it yet.
 680              // We'll see if the CFG is loaded, and if not we will just use unknown.
 681              // It's very important here that we don't use get_config. We don't want an endless cache loop!
 682              if (!empty($CFG->siteidentifier)) {
 683                  self::$siteidentifier = self::update_site_identifier($CFG->siteidentifier);
 684              } else {
 685                  // It's not being recorded in MUC's config and the config data hasn't been loaded yet.
 686                  // Likely we are initialising.
 687                  return 'unknown';
 688              }
 689          }
 690          return self::$siteidentifier;
 691      }
 692  
 693      /**
 694       * Returns the site version.
 695       *
 696       * @return string
 697       */
 698      public static function get_site_version() {
 699          global $CFG;
 700          return (string)$CFG->version;
 701      }
 702  
 703      /**
 704       * Runs cron routines for MUC.
 705       */
 706      public static function cron() {
 707          self::clean_old_session_data(true);
 708      }
 709  
 710      /**
 711       * Cleans old session data from cache stores used for session based definitions.
 712       *
 713       * @param bool $output If set to true output will be given.
 714       */
 715      public static function clean_old_session_data($output = false) {
 716          global $CFG;
 717          if ($output) {
 718              mtrace('Cleaning up stale session data from cache stores.');
 719          }
 720          $factory = cache_factory::instance();
 721          $config = $factory->create_config_instance();
 722          $definitions = $config->get_definitions();
 723          $purgetime = time() - $CFG->sessiontimeout;
 724          foreach ($definitions as $definitionarray) {
 725              // We are only interested in session caches.
 726              if (!($definitionarray['mode'] & cache_store::MODE_SESSION)) {
 727                  continue;
 728              }
 729              $definition = $factory->create_definition($definitionarray['component'], $definitionarray['area']);
 730              $stores = $config->get_stores_for_definition($definition);
 731              // Turn them into store instances.
 732              $stores = self::initialise_cachestore_instances($stores, $definition);
 733              // Initialise all of the stores used for that definition.
 734              foreach ($stores as $store) {
 735                  // If the store doesn't support searching we can skip it.
 736                  if (!($store instanceof cache_is_searchable)) {
 737                      debugging('Cache stores used for session definitions should ideally be searchable.', DEBUG_DEVELOPER);
 738                      continue;
 739                  }
 740                  // Get all of the keys.
 741                  $keys = $store->find_by_prefix(cache_session::KEY_PREFIX);
 742                  $todelete = array();
 743                  foreach ($store->get_many($keys) as $key => $value) {
 744                      if (strpos($key, cache_session::KEY_PREFIX) !== 0 || !is_array($value) || !isset($value['lastaccess'])) {
 745                          continue;
 746                      }
 747                      if ((int)$value['lastaccess'] < $purgetime || true) {
 748                          $todelete[] = $key;
 749                      }
 750                  }
 751                  if (count($todelete)) {
 752                      $outcome = (int)$store->delete_many($todelete);
 753                      if ($output) {
 754                          $strdef = s($definition->get_id());
 755                          $strstore = s($store->my_name());
 756                          mtrace("- Removed {$outcome} old {$strdef} sessions from the '{$strstore}' cache store.");
 757                      }
 758                  }
 759              }
 760          }
 761      }
 762  
 763      /**
 764       * Returns an array of stores that would meet the requirements for every definition.
 765       *
 766       * These stores would be 100% suitable to map as defaults for cache modes.
 767       *
 768       * @return array[] An array of stores, keys are the store names.
 769       */
 770      public static function get_stores_suitable_for_mode_default() {
 771          $factory = cache_factory::instance();
 772          $config = $factory->create_config_instance();
 773          $requirements = 0;
 774          foreach ($config->get_definitions() as $definition) {
 775              $definition = cache_definition::load($definition['component'].'/'.$definition['area'], $definition);
 776              $requirements = $requirements | $definition->get_requirements_bin();
 777          }
 778          $stores = array();
 779          foreach ($config->get_all_stores() as $name => $store) {
 780              if (!empty($store['features']) && ($store['features'] & $requirements)) {
 781                  $stores[$name] = $store;
 782              }
 783          }
 784          return $stores;
 785      }
 786  
 787      /**
 788       * Returns stores suitable for use with a given definition.
 789       *
 790       * @param cache_definition $definition
 791       * @return cache_store[]
 792       */
 793      public static function get_stores_suitable_for_definition(cache_definition $definition) {
 794          $factory = cache_factory::instance();
 795          $stores = array();
 796          if ($factory->is_initialising() || $factory->stores_disabled()) {
 797              // No suitable stores here.
 798              return $stores;
 799          } else {
 800              $stores = self::get_cache_stores($definition);
 801              // If mappingsonly is set, having 0 stores is ok.
 802              if ((count($stores) === 0) && (!$definition->is_for_mappings_only())) {
 803                  // No suitable stores we found for the definition. We need to come up with a sensible default.
 804                  // If this has happened we can be sure that the user has mapped custom stores to either the
 805                  // mode of the definition. The first alternative to try is the system default for the mode.
 806                  // e.g. the default file store instance for application definitions.
 807                  $config = $factory->create_config_instance();
 808                  foreach ($config->get_stores($definition->get_mode()) as $name => $details) {
 809                      if (!empty($details['default'])) {
 810                          $stores[] = $factory->create_store_from_config($name, $details, $definition);
 811                          break;
 812                      }
 813                  }
 814              }
 815          }
 816          return $stores;
 817      }
 818  
 819      /**
 820       * Returns an array of warnings from the cache API.
 821       *
 822       * The warning returned here are for things like conflicting store instance configurations etc.
 823       * These get shown on the admin notifications page for example.
 824       *
 825       * @param array|null $stores An array of stores to get warnings for, or null for all.
 826       * @return string[]
 827       */
 828      public static function warnings(array $stores = null) {
 829          global $CFG;
 830          if ($stores === null) {
 831              require_once($CFG->dirroot.'/cache/locallib.php');
 832              $stores = cache_administration_helper::get_store_instance_summaries();
 833          }
 834          $warnings = array();
 835          foreach ($stores as $store) {
 836              if (!empty($store['warnings'])) {
 837                  $warnings = array_merge($warnings, $store['warnings']);
 838              }
 839          }
 840          return $warnings;
 841      }
 842  }