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Differences Between: [Versions 310 and 401] [Versions 311 and 401] [Versions 39 and 401] [Versions 400 and 401] [Versions 401 and 402] [Versions 401 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 loaders
  19   *
  20   * This file is part of Moodle's cache API, affectionately called MUC.
  21   * It contains the components that are required 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 main cache class.
  33   *
  34   * This class if the first class that any end developer will interact with.
  35   * In order to create an instance of a cache that they can work with they must call one of the static make methods belonging
  36   * to this class.
  37   *
  38   * @package    core
  39   * @category   cache
  40   * @copyright  2012 Sam Hemelryk
  41   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  42   */
  43  class cache implements cache_loader {
  44  
  45      /**
  46       * @var int Constant for cache entries that do not have a version number
  47       */
  48      const VERSION_NONE = -1;
  49  
  50      /**
  51       * We need a timestamp to use within the cache API.
  52       * This stamp needs to be used for all ttl and time based operations to ensure that we don't end up with
  53       * timing issues.
  54       * @var int
  55       */
  56      protected static $now;
  57  
  58      /**
  59       * A purge token used to distinguish between multiple cache purges in the same second.
  60       * This is in the format <microtime>-<random string>.
  61       *
  62       * @var string
  63       */
  64      protected static $purgetoken;
  65  
  66      /**
  67       * The definition used when loading this cache if there was one.
  68       * @var cache_definition
  69       */
  70      private $definition = false;
  71  
  72      /**
  73       * The cache store that this loader will make use of.
  74       * @var cache_store
  75       */
  76      private $store;
  77  
  78      /**
  79       * The next cache loader in the chain if there is one.
  80       * If a cache request misses for the store belonging to this loader then the loader
  81       * stored here will be checked next.
  82       * If there is a loader here then $datasource must be false.
  83       * @var cache_loader|false
  84       */
  85      private $loader = false;
  86  
  87      /**
  88       * The data source to use if we need to load data (because if doesn't exist in the cache store).
  89       * If there is a data source here then $loader above must be false.
  90       * @var cache_data_source|false
  91       */
  92      private $datasource = false;
  93  
  94      /**
  95       * Used to quickly check if the store supports key awareness.
  96       * This is set when the cache is initialised and is used to speed up processing.
  97       * @var bool
  98       */
  99      private $supportskeyawareness = null;
 100  
 101      /**
 102       * Used to quickly check if the store supports ttl natively.
 103       * This is set when the cache is initialised and is used to speed up processing.
 104       * @var bool
 105       */
 106      private $supportsnativettl = null;
 107  
 108      /**
 109       * Gets set to true if the cache is going to be using a static array for acceleration.
 110       * The array statically caches items used during the lifetime of the request. This greatly speeds up interaction
 111       * with the cache in areas where it will be repetitively hit for the same information such as with strings.
 112       * There are several other variables to control how this static acceleration array works.
 113       * @var bool
 114       */
 115      private $staticacceleration = false;
 116  
 117      /**
 118       * The static acceleration array.
 119       * Items will be stored in this cache as they were provided. This ensure there is no unnecessary processing taking place.
 120       * @var array
 121       */
 122      private $staticaccelerationarray = array();
 123  
 124      /**
 125       * The number of items in the static acceleration array. Avoids count calls like you wouldn't believe.
 126       * @var int
 127       */
 128      private $staticaccelerationcount = 0;
 129  
 130      /**
 131       * An array containing just the keys being used in the static acceleration array.
 132       * This seems redundant perhaps but is used when managing the size of the static acceleration array.
 133       * Items are added to the end of the array and the when we need to reduce the size of the cache we use the
 134       * key that is first on this array.
 135       * @var array
 136       */
 137      private $staticaccelerationkeys = array();
 138  
 139      /**
 140       * The maximum size of the static acceleration array.
 141       *
 142       * If set to false there is no max size.
 143       * Caches that make use of static acceleration should seriously consider setting this to something reasonably small, but
 144       * still large enough to offset repetitive calls.
 145       *
 146       * @var int|false
 147       */
 148      private $staticaccelerationsize = false;
 149  
 150      /**
 151       * Gets set to true during initialisation if the definition is making use of a ttl.
 152       * Used to speed up processing.
 153       * @var bool
 154       */
 155      private $hasattl = false;
 156  
 157      /**
 158       * Gets set to the class name of the store during initialisation. This is used several times in the cache class internally
 159       * and having it here helps speed up processing.
 160       * @var strubg
 161       */
 162      protected $storetype = 'unknown';
 163  
 164      /**
 165       * Gets set to true if we want to collect performance information about the cache API.
 166       * @var bool
 167       */
 168      protected $perfdebug = false;
 169  
 170      /**
 171       * Determines if this loader is a sub loader, not the top of the chain.
 172       * @var bool
 173       */
 174      protected $subloader = false;
 175  
 176      /**
 177       * Creates a new cache instance for a pre-defined definition.
 178       *
 179       * @param string $component The component for the definition
 180       * @param string $area The area for the definition
 181       * @param array $identifiers Any additional identifiers that should be provided to the definition.
 182       * @param string $unused Used to be datasourceaggregate but that was removed and this is now unused.
 183       * @return cache_application|cache_session|cache_store
 184       */
 185      public static function make($component, $area, array $identifiers = array(), $unused = null) {
 186          $factory = cache_factory::instance();
 187          return $factory->create_cache_from_definition($component, $area, $identifiers);
 188      }
 189  
 190      /**
 191       * Creates a new cache instance based upon the given params.
 192       *
 193       * @param int $mode One of cache_store::MODE_*
 194       * @param string $component The component this cache relates to.
 195       * @param string $area The area this cache relates to.
 196       * @param array $identifiers Any additional identifiers that should be provided to the definition.
 197       * @param array $options An array of options, available options are:
 198       *   - simplekeys : Set to true if the keys you will use are a-zA-Z0-9_
 199       *   - simpledata : Set to true if the type of the data you are going to store is scalar, or an array of scalar vars
 200       *   - staticacceleration : If set to true the cache will hold onto data passing through it.
 201       *   - staticaccelerationsize : The max size for the static acceleration array.
 202       * @return cache_application|cache_session|cache_store
 203       */
 204      public static function make_from_params($mode, $component, $area, array $identifiers = array(), array $options = array()) {
 205          $factory = cache_factory::instance();
 206          return $factory->create_cache_from_params($mode, $component, $area, $identifiers, $options);
 207      }
 208  
 209      /**
 210       * Constructs a new cache instance.
 211       *
 212       * You should not call this method from your code, instead you should use the cache::make methods.
 213       *
 214       * This method is public so that the cache_factory is able to instantiate cache instances.
 215       * Ideally we would make this method protected and expose its construction to the factory method internally somehow.
 216       * The factory class is responsible for this in order to centralise the storage of instances once created. This way if needed
 217       * we can force a reset of the cache API (used during unit testing).
 218       *
 219       * @param cache_definition $definition The definition for the cache instance.
 220       * @param cache_store $store The store that cache should use.
 221       * @param cache_loader|cache_data_source $loader The next loader in the chain or the data source if there is one and there
 222       *      are no other cache_loaders in the chain.
 223       */
 224      public function __construct(cache_definition $definition, cache_store $store, $loader = null) {
 225          global $CFG;
 226          $this->definition = $definition;
 227          $this->store = $store;
 228          $this->storetype = get_class($store);
 229          $this->perfdebug = (!empty($CFG->perfdebug) and $CFG->perfdebug > 7);
 230          if ($loader instanceof cache_loader) {
 231              $this->set_loader($loader);
 232          } else if ($loader instanceof cache_data_source) {
 233              $this->set_data_source($loader);
 234          }
 235          $this->definition->generate_definition_hash();
 236          $this->staticacceleration = $this->definition->use_static_acceleration();
 237          if ($this->staticacceleration) {
 238              $this->staticaccelerationsize = $this->definition->get_static_acceleration_size();
 239          }
 240          $this->hasattl = ($this->definition->get_ttl() > 0);
 241      }
 242  
 243      /**
 244       * Set the loader for this cache.
 245       *
 246       * @param   cache_loader $loader
 247       */
 248      protected function set_loader(cache_loader $loader): void {
 249          $this->loader = $loader;
 250  
 251          // Mark the loader as a sub (chained) loader.
 252          $this->loader->set_is_sub_loader(true);
 253      }
 254  
 255      /**
 256       * Set the data source for this cache.
 257       *
 258       * @param   cache_data_source $datasource
 259       */
 260      protected function set_data_source(cache_data_source $datasource): void {
 261          $this->datasource = $datasource;
 262      }
 263  
 264      /**
 265       * Used to inform the loader of its state as a sub loader, or as the top of the chain.
 266       *
 267       * This is important as it ensures that we do not have more than one loader keeping static acceleration data.
 268       * Subloaders need to be "pure" loaders in the sense that they are used to store and retrieve information from stores or the
 269       * next loader/data source in the chain.
 270       * Nothing fancy, nothing flash.
 271       *
 272       * @param bool $setting
 273       */
 274      protected function set_is_sub_loader($setting = true) {
 275          if ($setting) {
 276              $this->subloader = true;
 277              // Subloaders should not keep static acceleration data.
 278              $this->staticacceleration = false;
 279              $this->staticaccelerationsize = false;
 280          } else {
 281              $this->subloader = true;
 282              $this->staticacceleration = $this->definition->use_static_acceleration();
 283              if ($this->staticacceleration) {
 284                  $this->staticaccelerationsize = $this->definition->get_static_acceleration_size();
 285              }
 286          }
 287      }
 288  
 289      /**
 290       * Alters the identifiers that have been provided to the definition.
 291       *
 292       * This is an advanced method and should not be used unless really needed.
 293       * It allows the developer to slightly alter the definition without having to re-establish the cache.
 294       * It will cause more processing as the definition will need to clear and reprepare some of its properties.
 295       *
 296       * @param array $identifiers
 297       */
 298      public function set_identifiers(array $identifiers) {
 299          if ($this->definition->set_identifiers($identifiers)) {
 300              // As static acceleration uses input keys and not parsed keys
 301              // it much be cleared when the identifier set is changed.
 302              $this->staticaccelerationarray = array();
 303              if ($this->staticaccelerationsize !== false) {
 304                  $this->staticaccelerationkeys = array();
 305                  $this->staticaccelerationcount = 0;
 306              }
 307          }
 308      }
 309  
 310      /**
 311       * Process any outstanding invalidation events for the cache we are registering,
 312       *
 313       * Identifiers and event invalidation are not compatible with each other at this time.
 314       * As a result the cache does not need to consider identifiers when working out what to invalidate.
 315       */
 316      protected function handle_invalidation_events() {
 317          if (!$this->definition->has_invalidation_events()) {
 318              return;
 319          }
 320  
 321          // Each cache stores the current 'lastinvalidation' value within the cache itself.
 322          $lastinvalidation = $this->get('lastinvalidation');
 323          if ($lastinvalidation === false) {
 324              // There is currently no  value for the lastinvalidation token, therefore the token is not set, and there
 325              // can be nothing to invalidate.
 326              // Set the lastinvalidation value to the current purge token and return early.
 327              $this->set('lastinvalidation', self::get_purge_token());
 328              return;
 329          } else if ($lastinvalidation == self::get_purge_token()) {
 330              // The current purge request has already been fully handled by this cache.
 331              return;
 332          }
 333  
 334          /*
 335           * Now that the whole cache check is complete, we check the meaning of any specific cache invalidation events.
 336           * These are stored in the core/eventinvalidation cache as an multi-dimensinoal array in the form:
 337           *  [
 338           *      eventname => [
 339           *          keyname => purgetoken,
 340           *      ]
 341           *  ]
 342           *
 343           * The 'keyname' value is used to delete a specific key in the cache.
 344           * If the keyname is set to the special value 'purged', then the whole cache is purged instead.
 345           *
 346           * The 'purgetoken' is the token that this key was last purged.
 347           * a) If the purgetoken matches the last invalidation, then the key/cache is not purged.
 348           * b) If the purgetoken is newer than the last invalidation, then the key/cache is not purged.
 349           * c) If the purge token is older than the last invalidation, or it has a different token component, then the
 350           *    cache is purged.
 351           *
 352           * Option b should not happen under normal operation, but may happen in race condition whereby a long-running
 353           * request's cache is cleared in another process during that request, and prior to that long-running request
 354           * creating the cache. In such a condition, it would be incorrect to clear that cache.
 355           */
 356          $cache = self::make('core', 'eventinvalidation');
 357          $events = $cache->get_many($this->definition->get_invalidation_events());
 358          $todelete = array();
 359          $purgeall = false;
 360  
 361          // Iterate the returned data for the events.
 362          foreach ($events as $event => $keys) {
 363              if ($keys === false) {
 364                  // No data to be invalidated yet.
 365                  continue;
 366              }
 367  
 368              // Look at each key and check the timestamp.
 369              foreach ($keys as $key => $purgetoken) {
 370                  // If the timestamp of the event is more than or equal to the last invalidation (happened between the last
 371                  // invalidation and now), then we need to invaliate the key.
 372                  if (self::compare_purge_tokens($purgetoken, $lastinvalidation) > 0) {
 373                      if ($key === 'purged') {
 374                          $purgeall = true;
 375                          break;
 376                      } else {
 377                          $todelete[] = $key;
 378                      }
 379                  }
 380              }
 381          }
 382          if ($purgeall) {
 383              $this->purge();
 384          } else if (!empty($todelete)) {
 385              $todelete = array_unique($todelete);
 386              $this->delete_many($todelete);
 387          }
 388          // Set the time of the last invalidation.
 389          if ($purgeall || !empty($todelete)) {
 390              $this->set('lastinvalidation', self::get_purge_token(true));
 391          }
 392      }
 393  
 394      /**
 395       * Retrieves the value for the given key from the cache.
 396       *
 397       * @param string|int $key The key for the data being requested.
 398       *      It can be any structure although using a scalar string or int is recommended in the interests of performance.
 399       *      In advanced cases an array may be useful such as in situations requiring the multi-key functionality.
 400       * @param int $strictness One of IGNORE_MISSING | MUST_EXIST
 401       * @return mixed|false The data from the cache or false if the key did not exist within the cache.
 402       * @throws coding_exception
 403       */
 404      public function get($key, $strictness = IGNORE_MISSING) {
 405          return $this->get_implementation($key, self::VERSION_NONE, $strictness);
 406      }
 407  
 408      /**
 409       * Retrieves the value and actual version for the given key, with at least the required version.
 410       *
 411       * If there is no value for the key, or there is a value but it doesn't have the required
 412       * version, then this function will return null (or throw an exception if you set strictness
 413       * to MUST_EXIST).
 414       *
 415       * This function can be used to make it easier to support localisable caches (where the cache
 416       * could be stored on a local server as well as a shared cache). Specifying the version means
 417       * that it will automatically retrieve the correct version if available, either from the local
 418       * server or [if that has an older version] from the shared server.
 419       *
 420       * If the cached version is newer than specified version, it will be returned regardless. For
 421       * example, if you request version 4, but the locally cached version is 5, it will be returned.
 422       * If you request version 6, and the locally cached version is 5, then the system will look in
 423       * higher-level caches (if any); if there still isn't a version 6 or greater, it will return
 424       * null.
 425       *
 426       * You must use this function if you use set_versioned.
 427       *
 428       * @param string|int $key The key for the data being requested.
 429       * @param int $requiredversion Minimum required version of the data
 430       * @param int $strictness One of IGNORE_MISSING or MUST_EXIST.
 431       * @param mixed $actualversion If specified, will be set to the actual version number retrieved
 432       * @return mixed Data from the cache, or false if the key did not exist or was too old
 433       * @throws \coding_exception If you call get_versioned on a non-versioned cache key
 434       */
 435      public function get_versioned($key, int $requiredversion, int $strictness = IGNORE_MISSING, &$actualversion = null) {
 436          return $this->get_implementation($key, $requiredversion, $strictness, $actualversion);
 437      }
 438  
 439      /**
 440       * Checks returned data to see if it matches the specified version number.
 441       *
 442       * For versioned data, this returns the version_wrapper object (or false). For other
 443       * data, it returns the actual data (or false).
 444       *
 445       * @param mixed $result Result data
 446       * @param int $requiredversion Required version number or VERSION_NONE if there must be no version
 447       * @return bool True if version is current, false if not (or if result is false)
 448       * @throws \coding_exception If unexpected type of data (versioned vs non-versioned) is found
 449       */
 450      protected static function check_version($result, int $requiredversion): bool {
 451          if ($requiredversion === self::VERSION_NONE) {
 452              if ($result instanceof \core_cache\version_wrapper) {
 453                  throw new \coding_exception('Unexpectedly found versioned cache entry');
 454              } else {
 455                  // No version checks, so version is always correct.
 456                  return true;
 457              }
 458          } else {
 459              // If there's no result, obviously it doesn't meet the required version.
 460              if (!cache_helper::result_found($result)) {
 461                  return false;
 462              }
 463              if (!($result instanceof \core_cache\version_wrapper)) {
 464                  throw new \coding_exception('Unexpectedly found non-versioned cache entry');
 465              }
 466              // If the result doesn't match the required version tag, return false.
 467              if ($result->version < $requiredversion) {
 468                  return false;
 469              }
 470              // The version meets the requirement.
 471              return true;
 472          }
 473      }
 474  
 475      /**
 476       * Retrieves the value for the given key from the cache.
 477       *
 478       * @param string|int $key The key for the data being requested.
 479       *      It can be any structure although using a scalar string or int is recommended in the interests of performance.
 480       *      In advanced cases an array may be useful such as in situations requiring the multi-key functionality.
 481       * @param int $requiredversion Minimum required version of the data or cache::VERSION_NONE
 482       * @param int $strictness One of IGNORE_MISSING | MUST_EXIST
 483       * @param mixed $actualversion If specified, will be set to the actual version number retrieved
 484       * @return mixed|false The data from the cache or false if the key did not exist within the cache.
 485       * @throws coding_exception
 486       */
 487      protected function get_implementation($key, int $requiredversion, int $strictness, &$actualversion = null) {
 488          // 1. Get it from the static acceleration array if we can (only when it is enabled and it has already been requested/set).
 489          $usesstaticacceleration = $this->use_static_acceleration();
 490  
 491          if ($usesstaticacceleration) {
 492              $result = $this->static_acceleration_get($key);
 493              if (cache_helper::result_found($result) && self::check_version($result, $requiredversion)) {
 494                  if ($requiredversion === self::VERSION_NONE) {
 495                      return $result;
 496                  } else {
 497                      $actualversion = $result->version;
 498                      return $result->data;
 499                  }
 500              }
 501          }
 502  
 503          // 2. Parse the key.
 504          $parsedkey = $this->parse_key($key);
 505  
 506          // 3. Get it from the store. Obviously wasn't in the static acceleration array.
 507          $result = $this->store->get($parsedkey);
 508          if (cache_helper::result_found($result)) {
 509              // Check the result has at least the required version.
 510              try {
 511                  $validversion = self::check_version($result, $requiredversion);
 512              } catch (\coding_exception $e) {
 513                  // In certain circumstances this could happen before users are taken to the upgrade
 514                  // screen when upgrading from an earlier Moodle version that didn't use a versioned
 515                  // cache for this item, so redirect instead of showing error if that's the case.
 516                  redirect_if_major_upgrade_required();
 517  
 518                  // If we still get an exception because there is incorrect data in the cache (not
 519                  // versioned when it ought to be), delete it so this exception goes away next time.
 520                  // The exception should only happen if there is a code bug (which is why we still
 521                  // throw it) but there are unusual scenarios in development where it might happen
 522                  // and that would be annoying if it doesn't fix itself.
 523                  $this->store->delete($parsedkey);
 524                  throw $e;
 525              }
 526  
 527              if (!$validversion) {
 528                  // If the result was too old, don't use it.
 529                  $result = false;
 530  
 531                  // Also delete it immediately. This improves performance in the
 532                  // case when the cache item is large and there may be multiple clients simultaneously
 533                  // requesting it - they won't all have to do a megabyte of IO just in order to find
 534                  // that it's out of date.
 535                  $this->store->delete($parsedkey);
 536              }
 537          }
 538          if (cache_helper::result_found($result)) {
 539              // Look to see if there's a TTL wrapper. It might be inside a version wrapper.
 540              if ($requiredversion !== self::VERSION_NONE) {
 541                  $ttlconsider = $result->data;
 542              } else {
 543                  $ttlconsider = $result;
 544              }
 545              if ($ttlconsider instanceof cache_ttl_wrapper) {
 546                  if ($ttlconsider->has_expired()) {
 547                      $this->store->delete($parsedkey);
 548                      $result = false;
 549                  } else if ($requiredversion === self::VERSION_NONE) {
 550                      // Use the data inside the TTL wrapper as the result.
 551                      $result = $ttlconsider->data;
 552                  } else {
 553                      // Put the data from the TTL wrapper directly inside the version wrapper.
 554                      $result->data = $ttlconsider->data;
 555                  }
 556              }
 557              if ($usesstaticacceleration) {
 558                  $this->static_acceleration_set($key, $result);
 559              }
 560              // Remove version wrapper if necessary.
 561              if ($requiredversion !== self::VERSION_NONE) {
 562                  $actualversion = $result->version;
 563                  $result = $result->data;
 564              }
 565              if ($result instanceof cache_cached_object) {
 566                  $result = $result->restore_object();
 567              }
 568          }
 569  
 570          // 4. Load if from the loader/datasource if we don't already have it.
 571          $setaftervalidation = false;
 572          if (!cache_helper::result_found($result)) {
 573              if ($this->perfdebug) {
 574                  cache_helper::record_cache_miss($this->store, $this->definition);
 575              }
 576              if ($this->loader !== false) {
 577                  // We must pass the original (unparsed) key to the next loader in the chain.
 578                  // The next loader will parse the key as it sees fit. It may be parsed differently
 579                  // depending upon the capabilities of the store associated with the loader.
 580                  if ($requiredversion === self::VERSION_NONE) {
 581                      $result = $this->loader->get($key);
 582                  } else {
 583                      $result = $this->loader->get_versioned($key, $requiredversion, IGNORE_MISSING, $actualversion);
 584                  }
 585              } else if ($this->datasource !== false) {
 586                  if ($requiredversion === self::VERSION_NONE) {
 587                      $result = $this->datasource->load_for_cache($key);
 588                  } else {
 589                      if (!$this->datasource instanceof cache_data_source_versionable) {
 590                          throw new \coding_exception('Data source is not versionable');
 591                      }
 592                      $result = $this->datasource->load_for_cache_versioned($key, $requiredversion, $actualversion);
 593                      if ($result && $actualversion < $requiredversion) {
 594                          throw new \coding_exception('Data source returned outdated version');
 595                      }
 596                  }
 597              }
 598              $setaftervalidation = (cache_helper::result_found($result));
 599          } else if ($this->perfdebug) {
 600              $readbytes = $this->store->get_last_io_bytes();
 601              cache_helper::record_cache_hit($this->store, $this->definition, 1, $readbytes);
 602          }
 603          // 5. Validate strictness.
 604          if ($strictness === MUST_EXIST && !cache_helper::result_found($result)) {
 605              throw new coding_exception('Requested key did not exist in any cache stores and could not be loaded.');
 606          }
 607          // 6. Set it to the store if we got it from the loader/datasource. Only set to this direct
 608          // store; parent method will have set it to all stores if needed.
 609          if ($setaftervalidation) {
 610              $lock = null;
 611              if (!empty($this->requirelockingbeforewrite)) {
 612                  $lock = $this->acquire_lock($key);
 613              }
 614              if ($requiredversion === self::VERSION_NONE) {
 615                  $this->set_implementation($key, self::VERSION_NONE, $result, false);
 616              } else {
 617                  $this->set_implementation($key, $actualversion, $result, false);
 618              }
 619              if ($lock) {
 620                  $this->release_lock($key);
 621              }
 622          }
 623          // 7. Make sure we don't pass back anything that could be a reference.
 624          //    We don't want people modifying the data in the cache.
 625          if (!$this->store->supports_dereferencing_objects() && !is_scalar($result)) {
 626              // If data is an object it will be a reference.
 627              // If data is an array if may contain references.
 628              // We want to break references so that the cache cannot be modified outside of itself.
 629              // Call the function to unreference it (in the best way possible).
 630              $result = $this->unref($result);
 631          }
 632          return $result;
 633      }
 634  
 635      /**
 636       * Retrieves an array of values for an array of keys.
 637       *
 638       * Using this function comes with potential performance implications.
 639       * Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
 640       * the equivalent singular method for each item provided.
 641       * This should not deter you from using this function as there is a performance benefit in situations where the cache store
 642       * does support it, but you should be aware of this fact.
 643       *
 644       * @param array $keys The keys of the data being requested.
 645       *      Each key can be any structure although using a scalar string or int is recommended in the interests of performance.
 646       *      In advanced cases an array may be useful such as in situations requiring the multi-key functionality.
 647       * @param int $strictness One of IGNORE_MISSING or MUST_EXIST.
 648       * @return array An array of key value pairs for the items that could be retrieved from the cache.
 649       *      If MUST_EXIST was used and not all keys existed within the cache then an exception will be thrown.
 650       *      Otherwise any key that did not exist will have a data value of false within the results.
 651       * @throws coding_exception
 652       */
 653      public function get_many(array $keys, $strictness = IGNORE_MISSING) {
 654  
 655          $keysparsed = array();
 656          $parsedkeys = array();
 657          $resultpersist = array();
 658          $resultstore = array();
 659          $keystofind = array();
 660          $readbytes = cache_store::IO_BYTES_NOT_SUPPORTED;
 661  
 662          // First up check the persist cache for each key.
 663          $isusingpersist = $this->use_static_acceleration();
 664          foreach ($keys as $key) {
 665              $pkey = $this->parse_key($key);
 666              if (is_array($pkey)) {
 667                  $pkey = $pkey['key'];
 668              }
 669              $keysparsed[$key] = $pkey;
 670              $parsedkeys[$pkey] = $key;
 671              $keystofind[$pkey] = $key;
 672              if ($isusingpersist) {
 673                  $value = $this->static_acceleration_get($key);
 674                  if ($value !== false) {
 675                      $resultpersist[$pkey] = $value;
 676                      unset($keystofind[$pkey]);
 677                  }
 678              }
 679          }
 680  
 681          // Next assuming we didn't find all of the keys in the persist cache try loading them from the store.
 682          if (count($keystofind)) {
 683              $resultstore = $this->store->get_many(array_keys($keystofind));
 684              if ($this->perfdebug) {
 685                  $readbytes = $this->store->get_last_io_bytes();
 686              }
 687              // Process each item in the result to "unwrap" it.
 688              foreach ($resultstore as $key => $value) {
 689                  if ($value instanceof cache_ttl_wrapper) {
 690                      if ($value->has_expired()) {
 691                          $value = false;
 692                      } else {
 693                          $value = $value->data;
 694                      }
 695                  }
 696                  if ($value !== false && $this->use_static_acceleration()) {
 697                      $this->static_acceleration_set($keystofind[$key], $value);
 698                  }
 699                  if ($value instanceof cache_cached_object) {
 700                      $value = $value->restore_object();
 701                  }
 702                  $resultstore[$key] = $value;
 703              }
 704          }
 705  
 706          // Merge the result from the persis cache with the results from the store load.
 707          $result = $resultpersist + $resultstore;
 708          unset($resultpersist);
 709          unset($resultstore);
 710  
 711          // Next we need to find any missing values and load them from the loader/datasource next in the chain.
 712          $usingloader = ($this->loader !== false);
 713          $usingsource = (!$usingloader && ($this->datasource !== false));
 714          if ($usingloader || $usingsource) {
 715              $missingkeys = array();
 716              foreach ($result as $key => $value) {
 717                  if ($value === false) {
 718                      $missingkeys[] = $parsedkeys[$key];
 719                  }
 720              }
 721              if (!empty($missingkeys)) {
 722                  if ($usingloader) {
 723                      $resultmissing = $this->loader->get_many($missingkeys);
 724                  } else {
 725                      $resultmissing = $this->datasource->load_many_for_cache($missingkeys);
 726                  }
 727                  foreach ($resultmissing as $key => $value) {
 728                      $result[$keysparsed[$key]] = $value;
 729                      $lock = null;
 730                      if (!empty($this->requirelockingbeforewrite)) {
 731                          $lock = $this->acquire_lock($key);
 732                      }
 733                      if ($value !== false) {
 734                          $this->set($key, $value);
 735                      }
 736                      if ($lock) {
 737                          $this->release_lock($key);
 738                      }
 739                  }
 740                  unset($resultmissing);
 741              }
 742              unset($missingkeys);
 743          }
 744  
 745          // Create an array with the original keys and the found values. This will be what we return.
 746          $fullresult = array();
 747          foreach ($result as $key => $value) {
 748              if (!is_scalar($value)) {
 749                  // If data is an object it will be a reference.
 750                  // If data is an array if may contain references.
 751                  // We want to break references so that the cache cannot be modified outside of itself.
 752                  // Call the function to unreference it (in the best way possible).
 753                  $value = $this->unref($value);
 754              }
 755              $fullresult[$parsedkeys[$key]] = $value;
 756          }
 757          unset($result);
 758  
 759          // Final step is to check strictness.
 760          if ($strictness === MUST_EXIST) {
 761              foreach ($keys as $key) {
 762                  if (!array_key_exists($key, $fullresult)) {
 763                      throw new coding_exception('Not all the requested keys existed within the cache stores.');
 764                  }
 765              }
 766          }
 767  
 768          if ($this->perfdebug) {
 769              $hits = 0;
 770              $misses = 0;
 771              foreach ($fullresult as $value) {
 772                  if ($value === false) {
 773                      $misses++;
 774                  } else {
 775                      $hits++;
 776                  }
 777              }
 778              cache_helper::record_cache_hit($this->store, $this->definition, $hits, $readbytes);
 779              cache_helper::record_cache_miss($this->store, $this->definition, $misses);
 780          }
 781  
 782          // Return the result. Phew!
 783          return $fullresult;
 784      }
 785  
 786      /**
 787       * Sends a key => value pair to the cache.
 788       *
 789       * <code>
 790       * // This code will add four entries to the cache, one for each url.
 791       * $cache->set('main', 'http://moodle.org');
 792       * $cache->set('docs', 'http://docs.moodle.org');
 793       * $cache->set('tracker', 'http://tracker.moodle.org');
 794       * $cache->set('qa', 'http://qa.moodle.net');
 795       * </code>
 796       *
 797       * @param string|int $key The key for the data being requested.
 798       *      It can be any structure although using a scalar string or int is recommended in the interests of performance.
 799       *      In advanced cases an array may be useful such as in situations requiring the multi-key functionality.
 800       * @param mixed $data The data to set against the key.
 801       * @return bool True on success, false otherwise.
 802       */
 803      public function set($key, $data) {
 804          return $this->set_implementation($key, self::VERSION_NONE, $data);
 805      }
 806  
 807      /**
 808       * Sets the value for the given key with the given version.
 809       *
 810       * The cache does not store multiple versions - any existing version will be overwritten with
 811       * this one. This function should only be used if there is a known 'current version' (e.g.
 812       * stored in a database table). It only ensures that the cache does not return outdated data.
 813       *
 814       * This function can be used to help implement localisable caches (where the cache could be
 815       * stored on a local server as well as a shared cache). The version will be recorded alongside
 816       * the item and get_versioned will always return the correct version.
 817       *
 818       * The version number must be an integer that always increases. This could be based on the
 819       * current time, or a stored value that increases by 1 each time it changes, etc.
 820       *
 821       * If you use this function you must use get_versioned to retrieve the data.
 822       *
 823       * @param string|int $key The key for the data being set.
 824       * @param int $version Integer for the version of the data
 825       * @param mixed $data The data to set against the key.
 826       * @return bool True on success, false otherwise.
 827       */
 828      public function set_versioned($key, int $version, $data): bool {
 829          return $this->set_implementation($key, $version, $data);
 830      }
 831  
 832      /**
 833       * Sets the value for the given key, optionally with a version tag.
 834       *
 835       * @param string|int $key The key for the data being set.
 836       * @param int $version Version number for the data or cache::VERSION_NONE if none
 837       * @param mixed $data The data to set against the key.
 838       * @param bool $setparents If true, sets all parent loaders, otherwise only this one
 839       * @return bool True on success, false otherwise.
 840       */
 841      protected function set_implementation($key, int $version, $data, bool $setparents = true): bool {
 842          if ($this->loader !== false && $setparents) {
 843              // We have a loader available set it there as well.
 844              // We have to let the loader do its own parsing of data as it may be unique.
 845              if ($version === self::VERSION_NONE) {
 846                  $this->loader->set($key, $data);
 847              } else {
 848                  $this->loader->set_versioned($key, $version, $data);
 849              }
 850          }
 851          $usestaticacceleration = $this->use_static_acceleration();
 852  
 853          if (is_object($data) && $data instanceof cacheable_object) {
 854              $data = new cache_cached_object($data);
 855          } else if (!$this->store->supports_dereferencing_objects() && !is_scalar($data)) {
 856              // If data is an object it will be a reference.
 857              // If data is an array if may contain references.
 858              // We want to break references so that the cache cannot be modified outside of itself.
 859              // Call the function to unreference it (in the best way possible).
 860              $data = $this->unref($data);
 861          }
 862  
 863          if ($usestaticacceleration) {
 864              // Static acceleration cache should include the cache version wrapper, but not TTL.
 865              if ($version === self::VERSION_NONE) {
 866                  $this->static_acceleration_set($key, $data);
 867              } else {
 868                  $this->static_acceleration_set($key, new \core_cache\version_wrapper($data, $version));
 869              }
 870          }
 871  
 872          if ($this->has_a_ttl() && !$this->store_supports_native_ttl()) {
 873              $data = new cache_ttl_wrapper($data, $this->definition->get_ttl());
 874          }
 875          $parsedkey = $this->parse_key($key);
 876  
 877          if ($version !== self::VERSION_NONE) {
 878              $data = new \core_cache\version_wrapper($data, $version);
 879          }
 880  
 881          $success = $this->store->set($parsedkey, $data);
 882          if ($this->perfdebug) {
 883              cache_helper::record_cache_set($this->store, $this->definition, 1,
 884                      $this->store->get_last_io_bytes());
 885          }
 886          return $success;
 887      }
 888  
 889      /**
 890       * Removes references where required.
 891       *
 892       * @param stdClass|array $data
 893       * @return mixed What ever was put in but without any references.
 894       */
 895      protected function unref($data) {
 896          if ($this->definition->uses_simple_data()) {
 897              return $data;
 898          }
 899          // Check if it requires serialisation in order to produce a reference free copy.
 900          if ($this->requires_serialisation($data)) {
 901              // Damn, its going to have to be serialise.
 902              $data = serialize($data);
 903              // We unserialise immediately so that we don't have to do it every time on get.
 904              $data = unserialize($data);
 905          } else if (!is_scalar($data)) {
 906              // Its safe to clone, lets do it, its going to beat the pants of serialisation.
 907              $data = $this->deep_clone($data);
 908          }
 909          return $data;
 910      }
 911  
 912      /**
 913       * Checks to see if a var requires serialisation.
 914       *
 915       * @param mixed $value The value to check.
 916       * @param int $depth Used to ensure we don't enter an endless loop (think recursion).
 917       * @return bool Returns true if the value is going to require serialisation in order to ensure a reference free copy
 918       *      or false if its safe to clone.
 919       */
 920      protected function requires_serialisation($value, $depth = 1) {
 921          if (is_scalar($value)) {
 922              return false;
 923          } else if (is_array($value) || $value instanceof stdClass || $value instanceof Traversable) {
 924              if ($depth > 5) {
 925                  // Skrew it, mega-deep object, developer you suck, we're just going to serialise.
 926                  return true;
 927              }
 928              foreach ($value as $key => $subvalue) {
 929                  if ($this->requires_serialisation($subvalue, $depth++)) {
 930                      return true;
 931                  }
 932              }
 933          }
 934          // Its not scalar, array, or stdClass so we'll need to serialise.
 935          return true;
 936      }
 937  
 938      /**
 939       * Creates a reference free clone of the given value.
 940       *
 941       * @param mixed $value
 942       * @return mixed
 943       */
 944      protected function deep_clone($value) {
 945          if (is_object($value)) {
 946              // Objects must be cloned to begin with.
 947              $value = clone $value;
 948          }
 949          if (is_array($value) || is_object($value)) {
 950              foreach ($value as $key => $subvalue) {
 951                  $value[$key] = $this->deep_clone($subvalue);
 952              }
 953          }
 954          return $value;
 955      }
 956  
 957      /**
 958       * Sends several key => value pairs to the cache.
 959       *
 960       * Using this function comes with potential performance implications.
 961       * Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
 962       * the equivalent singular method for each item provided.
 963       * This should not deter you from using this function as there is a performance benefit in situations where the cache store
 964       * does support it, but you should be aware of this fact.
 965       *
 966       * <code>
 967       * // This code will add four entries to the cache, one for each url.
 968       * $cache->set_many(array(
 969       *     'main' => 'http://moodle.org',
 970       *     'docs' => 'http://docs.moodle.org',
 971       *     'tracker' => 'http://tracker.moodle.org',
 972       *     'qa' => ''http://qa.moodle.net'
 973       * ));
 974       * </code>
 975       *
 976       * @param array $keyvaluearray An array of key => value pairs to send to the cache.
 977       * @return int The number of items successfully set. It is up to the developer to check this matches the number of items.
 978       *      ... if they care that is.
 979       */
 980      public function set_many(array $keyvaluearray) {
 981          if ($this->loader !== false) {
 982              // We have a loader available set it there as well.
 983              // We have to let the loader do its own parsing of data as it may be unique.
 984              $this->loader->set_many($keyvaluearray);
 985          }
 986          $data = array();
 987          $simulatettl = $this->has_a_ttl() && !$this->store_supports_native_ttl();
 988          $usestaticaccelerationarray = $this->use_static_acceleration();
 989          $needsdereferencing = !$this->store->supports_dereferencing_objects();
 990          foreach ($keyvaluearray as $key => $value) {
 991              if (is_object($value) && $value instanceof cacheable_object) {
 992                  $value = new cache_cached_object($value);
 993              } else if ($needsdereferencing && !is_scalar($value)) {
 994                  // If data is an object it will be a reference.
 995                  // If data is an array if may contain references.
 996                  // We want to break references so that the cache cannot be modified outside of itself.
 997                  // Call the function to unreference it (in the best way possible).
 998                  $value = $this->unref($value);
 999              }
1000              if ($usestaticaccelerationarray) {
1001                  $this->static_acceleration_set($key, $value);
1002              }
1003              if ($simulatettl) {
1004                  $value = new cache_ttl_wrapper($value, $this->definition->get_ttl());
1005              }
1006              $data[$key] = array(
1007                  'key' => $this->parse_key($key),
1008                  'value' => $value
1009              );
1010          }
1011          $successfullyset = $this->store->set_many($data);
1012          if ($this->perfdebug && $successfullyset) {
1013              cache_helper::record_cache_set($this->store, $this->definition, $successfullyset,
1014                      $this->store->get_last_io_bytes());
1015          }
1016          return $successfullyset;
1017      }
1018  
1019      /**
1020       * Test is a cache has a key.
1021       *
1022       * The use of the has methods is strongly discouraged. In a high load environment the cache may well change between the
1023       * test and any subsequent action (get, set, delete etc).
1024       * Instead it is recommended to write your code in such a way they it performs the following steps:
1025       * <ol>
1026       * <li>Attempt to retrieve the information.</li>
1027       * <li>Generate the information.</li>
1028       * <li>Attempt to set the information</li>
1029       * </ol>
1030       *
1031       * Its also worth mentioning that not all stores support key tests.
1032       * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
1033       * Just one more reason you should not use these methods unless you have a very good reason to do so.
1034       *
1035       * @param string|int $key
1036       * @param bool $tryloadifpossible If set to true, the cache doesn't contain the key, and there is another cache loader or
1037       *      data source then the code will try load the key value from the next item in the chain.
1038       * @return bool True if the cache has the requested key, false otherwise.
1039       */
1040      public function has($key, $tryloadifpossible = false) {
1041          if ($this->static_acceleration_has($key)) {
1042              // Hoorah, that was easy. It exists in the static acceleration array so we definitely have it.
1043              return true;
1044          }
1045          $parsedkey = $this->parse_key($key);
1046  
1047          if ($this->has_a_ttl() && !$this->store_supports_native_ttl()) {
1048              // The data has a TTL and the store doesn't support it natively.
1049              // We must fetch the data and expect a ttl wrapper.
1050              $data = $this->store->get($parsedkey);
1051              $has = ($data instanceof cache_ttl_wrapper && !$data->has_expired());
1052          } else if (!$this->store_supports_key_awareness()) {
1053              // The store doesn't support key awareness, get the data and check it manually... puke.
1054              // Either no TTL is set of the store supports its handling natively.
1055              $data = $this->store->get($parsedkey);
1056              $has = ($data !== false);
1057          } else {
1058              // The store supports key awareness, this is easy!
1059              // Either no TTL is set of the store supports its handling natively.
1060              $has = $this->store->has($parsedkey);
1061          }
1062          if (!$has && $tryloadifpossible) {
1063              if ($this->loader !== false) {
1064                  $result = $this->loader->get($parsedkey);
1065              } else if ($this->datasource !== null) {
1066                  $result = $this->datasource->load_for_cache($key);
1067              }
1068              $has = ($result !== null);
1069              if ($has) {
1070                  $this->set($key, $result);
1071              }
1072          }
1073          return $has;
1074      }
1075  
1076      /**
1077       * Test is a cache has all of the given keys.
1078       *
1079       * It is strongly recommended to avoid the use of this function if not absolutely required.
1080       * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
1081       *
1082       * Its also worth mentioning that not all stores support key tests.
1083       * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
1084       * Just one more reason you should not use these methods unless you have a very good reason to do so.
1085       *
1086       * @param array $keys
1087       * @return bool True if the cache has all of the given keys, false otherwise.
1088       */
1089      public function has_all(array $keys) {
1090          if (($this->has_a_ttl() && !$this->store_supports_native_ttl()) || !$this->store_supports_key_awareness()) {
1091              foreach ($keys as $key) {
1092                  if (!$this->has($key)) {
1093                      return false;
1094                  }
1095              }
1096              return true;
1097          }
1098          $parsedkeys = array_map(array($this, 'parse_key'), $keys);
1099          return $this->store->has_all($parsedkeys);
1100      }
1101  
1102      /**
1103       * Test if a cache has at least one of the given keys.
1104       *
1105       * It is strongly recommended to avoid the use of this function if not absolutely required.
1106       * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
1107       *
1108       * Its also worth mentioning that not all stores support key tests.
1109       * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
1110       * Just one more reason you should not use these methods unless you have a very good reason to do so.
1111       *
1112       * @param array $keys
1113       * @return bool True if the cache has at least one of the given keys
1114       */
1115      public function has_any(array $keys) {
1116          if (($this->has_a_ttl() && !$this->store_supports_native_ttl()) || !$this->store_supports_key_awareness()) {
1117              foreach ($keys as $key) {
1118                  if ($this->has($key)) {
1119                      return true;
1120                  }
1121              }
1122              return false;
1123          }
1124  
1125          if ($this->use_static_acceleration()) {
1126              foreach ($keys as $id => $key) {
1127                  if ($this->static_acceleration_has($key)) {
1128                      return true;
1129                  }
1130              }
1131          }
1132          $parsedkeys = array_map(array($this, 'parse_key'), $keys);
1133          return $this->store->has_any($parsedkeys);
1134      }
1135  
1136      /**
1137       * Delete the given key from the cache.
1138       *
1139       * @param string|int $key The key to delete.
1140       * @param bool $recurse When set to true the key will also be deleted from all stacked cache loaders and their stores.
1141       *     This happens by default and ensure that all the caches are consistent. It is NOT recommended to change this.
1142       * @return bool True of success, false otherwise.
1143       */
1144      public function delete($key, $recurse = true) {
1145          $this->static_acceleration_delete($key);
1146          if ($recurse && $this->loader !== false) {
1147              // Delete from the bottom of the stack first.
1148              $this->loader->delete($key, $recurse);
1149          }
1150          $parsedkey = $this->parse_key($key);
1151          return $this->store->delete($parsedkey);
1152      }
1153  
1154      /**
1155       * Delete all of the given keys from the cache.
1156       *
1157       * @param array $keys The key to delete.
1158       * @param bool $recurse When set to true the key will also be deleted from all stacked cache loaders and their stores.
1159       *     This happens by default and ensure that all the caches are consistent. It is NOT recommended to change this.
1160       * @return int The number of items successfully deleted.
1161       */
1162      public function delete_many(array $keys, $recurse = true) {
1163          if ($this->use_static_acceleration()) {
1164              foreach ($keys as $key) {
1165                  $this->static_acceleration_delete($key);
1166              }
1167          }
1168          if ($recurse && $this->loader !== false) {
1169              // Delete from the bottom of the stack first.
1170              $this->loader->delete_many($keys, $recurse);
1171          }
1172          $parsedkeys = array_map(array($this, 'parse_key'), $keys);
1173          return $this->store->delete_many($parsedkeys);
1174      }
1175  
1176      /**
1177       * Purges the cache store, and loader if there is one.
1178       *
1179       * @return bool True on success, false otherwise
1180       */
1181      public function purge() {
1182          // 1. Purge the static acceleration array.
1183          $this->static_acceleration_purge();
1184          // 2. Purge the store.
1185          $this->store->purge();
1186          // 3. Optionally pruge any stacked loaders.
1187          if ($this->loader) {
1188              $this->loader->purge();
1189          }
1190          return true;
1191      }
1192  
1193      /**
1194       * Parses the key turning it into a string (or array is required) suitable to be passed to the cache store.
1195       *
1196       * @param string|int $key As passed to get|set|delete etc.
1197       * @return string|array String unless the store supports multi-identifiers in which case an array if returned.
1198       */
1199      protected function parse_key($key) {
1200          // First up if the store supports multiple keys we'll go with that.
1201          if ($this->store->supports_multiple_identifiers()) {
1202              $result = $this->definition->generate_multi_key_parts();
1203              $result['key'] = $key;
1204              return $result;
1205          }
1206          // If not we need to generate a hash and to for that we use the cache_helper.
1207          return cache_helper::hash_key($key, $this->definition);
1208      }
1209  
1210      /**
1211       * Returns true if the cache is making use of a ttl.
1212       * @return bool
1213       */
1214      protected function has_a_ttl() {
1215          return $this->hasattl;
1216      }
1217  
1218      /**
1219       * Returns true if the cache store supports native ttl.
1220       * @return bool
1221       */
1222      protected function store_supports_native_ttl() {
1223          if ($this->supportsnativettl === null) {
1224              $this->supportsnativettl = ($this->store->supports_native_ttl());
1225          }
1226          return $this->supportsnativettl;
1227      }
1228  
1229      /**
1230       * Returns the cache definition.
1231       *
1232       * @return cache_definition
1233       */
1234      protected function get_definition() {
1235          return $this->definition;
1236      }
1237  
1238      /**
1239       * Returns the cache store
1240       *
1241       * @return cache_store
1242       */
1243      protected function get_store() {
1244          return $this->store;
1245      }
1246  
1247      /**
1248       * Returns the loader associated with this instance.
1249       *
1250       * @since Moodle 2.4.4
1251       * @return cache|false
1252       */
1253      protected function get_loader() {
1254          return $this->loader;
1255      }
1256  
1257      /**
1258       * Returns the data source associated with this cache.
1259       *
1260       * @since Moodle 2.4.4
1261       * @return cache_data_source|false
1262       */
1263      protected function get_datasource() {
1264          return $this->datasource;
1265      }
1266  
1267      /**
1268       * Returns true if the store supports key awareness.
1269       *
1270       * @return bool
1271       */
1272      protected function store_supports_key_awareness() {
1273          if ($this->supportskeyawareness === null) {
1274              $this->supportskeyawareness = ($this->store instanceof cache_is_key_aware);
1275          }
1276          return $this->supportskeyawareness;
1277      }
1278  
1279      /**
1280       * Returns true if the store natively supports locking.
1281       *
1282       * @return bool
1283       */
1284      protected function store_supports_native_locking() {
1285          if ($this->nativelocking === null) {
1286              $this->nativelocking = ($this->store instanceof cache_is_lockable);
1287          }
1288          return $this->nativelocking;
1289      }
1290  
1291      /**
1292       * @deprecated since 2.6
1293       * @see cache::use_static_acceleration()
1294       */
1295      protected function is_using_persist_cache() {
1296          throw new coding_exception('cache::is_using_persist_cache() can not be used anymore.' .
1297              ' Please use cache::use_static_acceleration() instead.');
1298      }
1299  
1300      /**
1301       * Returns true if this cache is making use of the static acceleration array.
1302       *
1303       * @return bool
1304       */
1305      protected function use_static_acceleration() {
1306          return $this->staticacceleration;
1307      }
1308  
1309      /**
1310       * @see cache::static_acceleration_has
1311       * @deprecated since 2.6
1312       */
1313      protected function is_in_persist_cache() {
1314          throw new coding_exception('cache::is_in_persist_cache() can not be used anymore.' .
1315              ' Please use cache::static_acceleration_has() instead.');
1316      }
1317  
1318      /**
1319       * Returns true if the requested key exists within the static acceleration array.
1320       *
1321       * @param string $key The parsed key
1322       * @return bool
1323       */
1324      protected function static_acceleration_has($key) {
1325          // This could be written as a single line, however it has been split because the ttl check is faster than the instanceof
1326          // and has_expired calls.
1327          if (!$this->staticacceleration || !isset($this->staticaccelerationarray[$key])) {
1328              return false;
1329          }
1330          return true;
1331      }
1332  
1333      /**
1334       * @deprecated since 2.6
1335       * @see cache::static_acceleration_get
1336       */
1337      protected function get_from_persist_cache() {
1338          throw new coding_exception('cache::get_from_persist_cache() can not be used anymore.' .
1339              ' Please use cache::static_acceleration_get() instead.');
1340      }
1341  
1342      /**
1343       * Returns the item from the static acceleration array if it exists there.
1344       *
1345       * @param string $key The parsed key
1346       * @return mixed|false Dereferenced data from the static acceleration array or false if it wasn't there.
1347       */
1348      protected function static_acceleration_get($key) {
1349          if (!$this->staticacceleration || !isset($this->staticaccelerationarray[$key])) {
1350              $result = false;
1351          } else {
1352              $data = $this->staticaccelerationarray[$key]['data'];
1353  
1354              if ($data instanceof cache_cached_object) {
1355                  $result = $data->restore_object();
1356              } else if ($this->staticaccelerationarray[$key]['serialized']) {
1357                  $result = unserialize($data);
1358              } else {
1359                  $result = $data;
1360              }
1361          }
1362          if (cache_helper::result_found($result)) {
1363              if ($this->perfdebug) {
1364                  cache_helper::record_cache_hit(cache_store::STATIC_ACCEL, $this->definition);
1365              }
1366              if ($this->staticaccelerationsize > 1 && $this->staticaccelerationcount > 1) {
1367                  // Check to see if this is the last item on the static acceleration keys array.
1368                  if (end($this->staticaccelerationkeys) !== $key) {
1369                      // It isn't the last item.
1370                      // Move the item to the end of the array so that it is last to be removed.
1371                      unset($this->staticaccelerationkeys[$key]);
1372                      $this->staticaccelerationkeys[$key] = $key;
1373                  }
1374              }
1375              return $result;
1376          } else {
1377              if ($this->perfdebug) {
1378                  cache_helper::record_cache_miss(cache_store::STATIC_ACCEL, $this->definition);
1379              }
1380              return false;
1381          }
1382      }
1383  
1384      /**
1385       * @deprecated since 2.6
1386       * @see cache::static_acceleration_set
1387       */
1388      protected function set_in_persist_cache() {
1389          throw new coding_exception('cache::set_in_persist_cache() can not be used anymore.' .
1390              ' Please use cache::static_acceleration_set() instead.');
1391      }
1392  
1393      /**
1394       * Sets a key value pair into the static acceleration array.
1395       *
1396       * @param string $key The parsed key
1397       * @param mixed $data
1398       * @return bool
1399       */
1400      protected function static_acceleration_set($key, $data) {
1401          if ($this->staticaccelerationsize !== false && isset($this->staticaccelerationkeys[$key])) {
1402              $this->staticaccelerationcount--;
1403              unset($this->staticaccelerationkeys[$key]);
1404          }
1405  
1406          // We serialize anything that's not;
1407          // 1. A known scalar safe value.
1408          // 2. A definition that says it's simpledata.  We trust it that it doesn't contain dangerous references.
1409          // 3. An object that handles dereferencing by itself.
1410          if (is_scalar($data) || $this->definition->uses_simple_data()
1411                  || $data instanceof cache_cached_object) {
1412              $this->staticaccelerationarray[$key]['data'] = $data;
1413              $this->staticaccelerationarray[$key]['serialized'] = false;
1414          } else {
1415              $this->staticaccelerationarray[$key]['data'] = serialize($data);
1416              $this->staticaccelerationarray[$key]['serialized'] = true;
1417          }
1418          if ($this->staticaccelerationsize !== false) {
1419              $this->staticaccelerationcount++;
1420              $this->staticaccelerationkeys[$key] = $key;
1421              if ($this->staticaccelerationcount > $this->staticaccelerationsize) {
1422                  $dropkey = array_shift($this->staticaccelerationkeys);
1423                  unset($this->staticaccelerationarray[$dropkey]);
1424                  $this->staticaccelerationcount--;
1425              }
1426          }
1427          return true;
1428      }
1429  
1430      /**
1431       * @deprecated since 2.6
1432       * @see cache::static_acceleration_delete()
1433       */
1434      protected function delete_from_persist_cache() {
1435          throw new coding_exception('cache::delete_from_persist_cache() can not be used anymore.' .
1436              ' Please use cache::static_acceleration_delete() instead.');
1437      }
1438  
1439      /**
1440       * Deletes an item from the static acceleration array.
1441       *
1442       * @param string|int $key As given to get|set|delete
1443       * @return bool True on success, false otherwise.
1444       */
1445      protected function static_acceleration_delete($key) {
1446          unset($this->staticaccelerationarray[$key]);
1447          if ($this->staticaccelerationsize !== false && isset($this->staticaccelerationkeys[$key])) {
1448              unset($this->staticaccelerationkeys[$key]);
1449              $this->staticaccelerationcount--;
1450          }
1451          return true;
1452      }
1453  
1454      /**
1455       * Purge the static acceleration cache.
1456       */
1457      protected function static_acceleration_purge() {
1458          $this->staticaccelerationarray = array();
1459          if ($this->staticaccelerationsize !== false) {
1460              $this->staticaccelerationkeys = array();
1461              $this->staticaccelerationcount = 0;
1462          }
1463      }
1464  
1465      /**
1466       * Returns the timestamp from the first request for the time from the cache API.
1467       *
1468       * This stamp needs to be used for all ttl and time based operations to ensure that we don't end up with
1469       * timing issues.
1470       *
1471       * @param   bool    $float Whether to use floating precision accuracy.
1472       * @return  int|float
1473       */
1474      public static function now($float = false) {
1475          if (self::$now === null) {
1476              self::$now = microtime(true);
1477          }
1478  
1479          if ($float) {
1480              return self::$now;
1481          } else {
1482              return (int) self::$now;
1483          }
1484      }
1485  
1486      /**
1487       * Get a 'purge' token used for cache invalidation handling.
1488       *
1489       * Note: This function is intended for use from within the Cache API only and not by plugins, or cache stores.
1490       *
1491       * @param   bool    $reset  Whether to reset the token and generate a new one.
1492       * @return  string
1493       */
1494      public static function get_purge_token($reset = false) {
1495          if (self::$purgetoken === null || $reset) {
1496              self::$now = null;
1497              self::$purgetoken = self::now(true) . '-' . uniqid('', true);
1498          }
1499  
1500          return self::$purgetoken;
1501      }
1502  
1503      /**
1504       * Compare a pair of purge tokens.
1505       *
1506       * If the two tokens are identical, then the return value is 0.
1507       * If the time component of token A is newer than token B, then a positive value is returned.
1508       * If the time component of token B is newer than token A, then a negative value is returned.
1509       *
1510       * Note: This function is intended for use from within the Cache API only and not by plugins, or cache stores.
1511       *
1512       * @param   string  $tokena
1513       * @param   string  $tokenb
1514       * @return  int
1515       */
1516      public static function compare_purge_tokens($tokena, $tokenb) {
1517          if ($tokena === $tokenb) {
1518              // There is an exact match.
1519              return 0;
1520          }
1521  
1522          // The token for when the cache was last invalidated.
1523          list($atime) = explode('-', "{$tokena}-", 2);
1524  
1525          // The token for this cache.
1526          list($btime) = explode('-', "{$tokenb}-", 2);
1527  
1528          if ($atime >= $btime) {
1529              // Token A is newer.
1530              return 1;
1531          } else {
1532              // Token A is older.
1533              return -1;
1534          }
1535      }
1536  
1537      /**
1538       * Subclasses may support purging cache of all data belonging to the
1539       * current user.
1540       */
1541      public function purge_current_user() {
1542      }
1543  }
1544  
1545  /**
1546   * An application cache.
1547   *
1548   * This class is used for application caches returned by the cache::make methods.
1549   * On top of the standard functionality it also allows locking to be required and or manually operated.
1550   *
1551   * This cache class should never be interacted with directly. Instead you should always use the cache::make methods.
1552   * It is technically possible to call those methods through this class however there is no guarantee that you will get an
1553   * instance of this class back again.
1554   *
1555   * @internal don't use me directly.
1556   *
1557   * @package    core
1558   * @category   cache
1559   * @copyright  2012 Sam Hemelryk
1560   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
1561   */
1562  class cache_application extends cache implements cache_loader_with_locking {
1563  
1564      /**
1565       * Lock identifier.
1566       * This is used to ensure the lock belongs to the cache instance + definition + user.
1567       * @var string
1568       */
1569      protected $lockidentifier;
1570  
1571      /**
1572       * Gets set to true if the cache's primary store natively supports locking.
1573       * If it does then we use that, otherwise we need to instantiate a second store to use for locking.
1574       * @var cache_store
1575       */
1576      protected $nativelocking = null;
1577  
1578      /**
1579       * Gets set to true if the cache is going to be using locking.
1580       * This isn't a requirement, it doesn't need to use locking (most won't) and this bool is used to quickly check things.
1581       * If required then locking will be forced for the get|set|delete operation.
1582       * @var bool
1583       */
1584      protected $requirelocking = false;
1585  
1586      /**
1587       * Gets set to true if the cache must use read locking (get|has).
1588       * @var bool
1589       */
1590      protected $requirelockingread = false;
1591  
1592      /**
1593       * Gets set to true if the cache must use write locking (set|delete)
1594       * @var bool
1595       */
1596      protected $requirelockingwrite = false;
1597  
1598      /**
1599       * Gets set to true if the cache writes (set|delete) must have a manual lock created first
1600       * @var bool
1601       */
1602      protected $requirelockingbeforewrite = false;
1603  
1604      /**
1605       * Gets set to a cache_store to use for locking if the caches primary store doesn't support locking natively.
1606       * @var cache_lock_interface
1607       */
1608      protected $cachelockinstance;
1609  
1610      /**
1611       * Store a list of locks acquired by this process.
1612       * @var array
1613       */
1614      protected $locks;
1615  
1616      /**
1617       * Overrides the cache construct method.
1618       *
1619       * You should not call this method from your code, instead you should use the cache::make methods.
1620       *
1621       * @param cache_definition $definition
1622       * @param cache_store $store
1623       * @param cache_loader|cache_data_source $loader
1624       */
1625      public function __construct(cache_definition $definition, cache_store $store, $loader = null) {
1626          parent::__construct($definition, $store, $loader);
1627          $this->nativelocking = $this->store_supports_native_locking();
1628          if ($definition->require_locking()) {
1629              $this->requirelocking = true;
1630              $this->requirelockingread = $definition->require_locking_read();
1631              $this->requirelockingwrite = $definition->require_locking_write();
1632              $this->requirelockingbeforewrite = $definition->require_locking_before_write();
1633          }
1634  
1635          $this->handle_invalidation_events();
1636      }
1637  
1638      /**
1639       * Returns the identifier to use
1640       *
1641       * @staticvar int $instances Counts the number of instances. Used as part of the lock identifier.
1642       * @return string
1643       */
1644      public function get_identifier() {
1645          static $instances = 0;
1646          if ($this->lockidentifier === null) {
1647              $this->lockidentifier = md5(
1648                  $this->get_definition()->generate_definition_hash() .
1649                  sesskey() .
1650                  $instances++ .
1651                  'cache_application'
1652              );
1653          }
1654          return $this->lockidentifier;
1655      }
1656  
1657      /**
1658       * Fixes the instance up after a clone.
1659       */
1660      public function __clone() {
1661          // Force a new idenfitier.
1662          $this->lockidentifier = null;
1663      }
1664  
1665      /**
1666       * Acquires a lock on the given key.
1667       *
1668       * This is done automatically if the definition requires it.
1669       * It is recommended to use a definition if you want to have locking although it is possible to do locking without having
1670       * it required by the definition.
1671       * The problem with such an approach is that you cannot ensure that code will consistently use locking. You will need to
1672       * rely on the integrators review skills.
1673       *
1674       * @param string|int $key The key as given to get|set|delete
1675       * @return bool Returns true if the lock could be acquired, false otherwise.
1676       */
1677      public function acquire_lock($key) {
1678          $releaseparent = false;
1679          if ($this->get_loader() !== false) {
1680              if (!$this->get_loader()->acquire_lock($key)) {
1681                  return false;
1682              }
1683              // We need to release this lock later if the lock is not successful.
1684              $releaseparent = true;
1685          }
1686          $hashedkey = cache_helper::hash_key($key, $this->get_definition());
1687          $before = microtime(true);
1688          if ($this->nativelocking) {
1689              $lock = $this->get_store()->acquire_lock($hashedkey, $this->get_identifier());
1690          } else {
1691              $this->ensure_cachelock_available();
1692              $lock = $this->cachelockinstance->lock($hashedkey, $this->get_identifier());
1693          }
1694          $after = microtime(true);
1695          if ($lock) {
1696              $this->locks[$hashedkey] = $lock;
1697              if ((defined('MDL_PERF') && MDL_PERF) || $this->perfdebug) {
1698                  \core\lock\timing_wrapper_lock_factory::record_lock_data($after, $before,
1699                          $this->get_definition()->get_id(), $hashedkey, $lock, $this->get_identifier() . $hashedkey);
1700              }
1701          } else {
1702              // If we successfully got the parent lock, but are now failing to get this lock, then we should release
1703              // the parent one.
1704              if ($releaseparent) {
1705                  $this->get_loader()->release_lock($key);
1706              }
1707          }
1708          return $lock;
1709      }
1710  
1711      /**
1712       * Checks if this cache has a lock on the given key.
1713       *
1714       * @param string|int $key The key as given to get|set|delete
1715       * @return bool|null Returns true if there is a lock and this cache has it, null if no one has a lock on that key, false if
1716       *      someone else has the lock.
1717       */
1718      public function check_lock_state($key) {
1719          $key = cache_helper::hash_key($key, $this->get_definition());
1720          if (!empty($this->locks[$key])) {
1721              return true; // Shortcut to save having to make a call to the cache store if the lock is held by this process.
1722          }
1723          if ($this->nativelocking) {
1724              return $this->get_store()->check_lock_state($key, $this->get_identifier());
1725          } else {
1726              $this->ensure_cachelock_available();
1727              return $this->cachelockinstance->check_state($key, $this->get_identifier());
1728          }
1729      }
1730  
1731      /**
1732       * Releases the lock this cache has on the given key
1733       *
1734       * @param string|int $key
1735       * @return bool True if the operation succeeded, false otherwise.
1736       */
1737      public function release_lock($key) {
1738          $loaderkey = $key;
1739          $key = cache_helper::hash_key($key, $this->get_definition());
1740          if ($this->nativelocking) {
1741              $released = $this->get_store()->release_lock($key, $this->get_identifier());
1742          } else {
1743              $this->ensure_cachelock_available();
1744              $released = $this->cachelockinstance->unlock($key, $this->get_identifier());
1745          }
1746          if ($released && array_key_exists($key, $this->locks)) {
1747              unset($this->locks[$key]);
1748              if ((defined('MDL_PERF') && MDL_PERF) || $this->perfdebug) {
1749                  \core\lock\timing_wrapper_lock_factory::record_lock_released_data($this->get_identifier() . $key);
1750              }
1751          }
1752          if ($this->get_loader() !== false) {
1753              $this->get_loader()->release_lock($loaderkey);
1754          }
1755          return $released;
1756      }
1757  
1758      /**
1759       * Ensure that the dedicated lock store is ready to go.
1760       *
1761       * This should only happen if the cache store doesn't natively support it.
1762       */
1763      protected function ensure_cachelock_available() {
1764          if ($this->cachelockinstance === null) {
1765              $this->cachelockinstance = cache_helper::get_cachelock_for_store($this->get_store());
1766          }
1767      }
1768  
1769      /**
1770       * Sends a key => value pair to the cache.
1771       *
1772       * <code>
1773       * // This code will add four entries to the cache, one for each url.
1774       * $cache->set('main', 'http://moodle.org');
1775       * $cache->set('docs', 'http://docs.moodle.org');
1776       * $cache->set('tracker', 'http://tracker.moodle.org');
1777       * $cache->set('qa', 'http://qa.moodle.net');
1778       * </code>
1779       *
1780       * @param string|int $key The key for the data being requested.
1781       * @param int $version Version number
1782       * @param mixed $data The data to set against the key.
1783       * @param bool $setparents If true, sets all parent loaders, otherwise only this one
1784       * @return bool True on success, false otherwise.
1785       */
1786      protected function set_implementation($key, int $version, $data, bool $setparents = true): bool {
1787          if ($this->requirelockingbeforewrite && !$this->check_lock_state($key)) {
1788              throw new coding_exception('Attempted to set cache key "' . $key . '" without a lock. '
1789                  . 'Locking before writes is required for ' . $this->get_definition()->get_id());
1790          }
1791          if ($this->requirelockingwrite && !$this->acquire_lock($key)) {
1792              return false;
1793          }
1794          $result = parent::set_implementation($key, $version, $data, $setparents);
1795          if ($this->requirelockingwrite && !$this->release_lock($key)) {
1796              debugging('Failed to release cache lock on set operation... this should not happen.', DEBUG_DEVELOPER);
1797          }
1798          return $result;
1799      }
1800  
1801      /**
1802       * Sends several key => value pairs to the cache.
1803       *
1804       * Using this function comes with potential performance implications.
1805       * Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
1806       * the equivalent singular method for each item provided.
1807       * This should not deter you from using this function as there is a performance benefit in situations where the cache store
1808       * does support it, but you should be aware of this fact.
1809       *
1810       * <code>
1811       * // This code will add four entries to the cache, one for each url.
1812       * $cache->set_many(array(
1813       *     'main' => 'http://moodle.org',
1814       *     'docs' => 'http://docs.moodle.org',
1815       *     'tracker' => 'http://tracker.moodle.org',
1816       *     'qa' => ''http://qa.moodle.net'
1817       * ));
1818       * </code>
1819       *
1820       * @param array $keyvaluearray An array of key => value pairs to send to the cache.
1821       * @return int The number of items successfully set. It is up to the developer to check this matches the number of items.
1822       *      ... if they care that is.
1823       */
1824      public function set_many(array $keyvaluearray) {
1825          if ($this->requirelockingbeforewrite) {
1826              foreach ($keyvaluearray as $key => $value) {
1827                  if (!$this->check_lock_state($key)) {
1828                      debugging('Attempted to set cache key "' . $key . '" without a lock. '
1829                              . 'Locking before writes is required for ' . $this->get_definition()->get_name(), DEBUG_DEVELOPER);
1830                      unset($keyvaluearray[$key]);
1831                  }
1832              }
1833          }
1834          if ($this->requirelockingwrite) {
1835              $locks = array();
1836              foreach ($keyvaluearray as $id => $pair) {
1837                  $key = $pair['key'];
1838                  if ($this->acquire_lock($key)) {
1839                      $locks[] = $key;
1840                  } else {
1841                      unset($keyvaluearray[$id]);
1842                  }
1843              }
1844          }
1845          $result = parent::set_many($keyvaluearray);
1846          if ($this->requirelockingwrite) {
1847              foreach ($locks as $key) {
1848                  if ($this->release_lock($key)) {
1849                      debugging('Failed to release cache lock on set_many operation... this should not happen.', DEBUG_DEVELOPER);
1850                  }
1851              }
1852          }
1853          return $result;
1854      }
1855  
1856      /**
1857       * Retrieves the value for the given key from the cache.
1858       *
1859       * @param string|int $key The key for the data being requested.
1860       * @param int $requiredversion Minimum required version of the data or cache::VERSION_NONE
1861       * @param int $strictness One of IGNORE_MISSING | MUST_EXIST
1862       * @param mixed &$actualversion If specified, will be set to the actual version number retrieved
1863       * @return mixed|false The data from the cache or false if the key did not exist within the cache.
1864       */
1865      protected function get_implementation($key, int $requiredversion, int $strictness, &$actualversion = null) {
1866          if ($this->requirelockingread && $this->check_lock_state($key) === false) {
1867              // Read locking required and someone else has the read lock.
1868              return false;
1869          }
1870          return parent::get_implementation($key, $requiredversion, $strictness, $actualversion);
1871      }
1872  
1873      /**
1874       * Retrieves an array of values for an array of keys.
1875       *
1876       * Using this function comes with potential performance implications.
1877       * Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
1878       * the equivalent singular method for each item provided.
1879       * This should not deter you from using this function as there is a performance benefit in situations where the cache store
1880       * does support it, but you should be aware of this fact.
1881       *
1882       * @param array $keys The keys of the data being requested.
1883       * @param int $strictness One of IGNORE_MISSING or MUST_EXIST.
1884       * @return array An array of key value pairs for the items that could be retrieved from the cache.
1885       *      If MUST_EXIST was used and not all keys existed within the cache then an exception will be thrown.
1886       *      Otherwise any key that did not exist will have a data value of false within the results.
1887       * @throws coding_exception
1888       */
1889      public function get_many(array $keys, $strictness = IGNORE_MISSING) {
1890          $locks = [];
1891          if ($this->requirelockingread) {
1892              foreach ($keys as $id => $key) {
1893                  $locks[$key] = $this->acquire_lock($key);
1894                  if (!$locks[$key]) {
1895                      if ($strictness === MUST_EXIST) {
1896                          throw new coding_exception('Could not acquire read locks for all of the items being requested.');
1897                      } else {
1898                          // Can't return this as we couldn't get a read lock.
1899                          unset($keys[$id]);
1900                      }
1901                  }
1902  
1903              }
1904          }
1905          $result = parent::get_many($keys, $strictness);
1906          if ($this->requirelockingread) {
1907              foreach ($locks as $key => $lock) {
1908                  $this->release_lock($key);
1909              }
1910          }
1911          return $result;
1912      }
1913  
1914      /**
1915       * Delete the given key from the cache.
1916       *
1917       * @param string|int $key The key to delete.
1918       * @param bool $recurse When set to true the key will also be deleted from all stacked cache loaders and their stores.
1919       *     This happens by default and ensure that all the caches are consistent. It is NOT recommended to change this.
1920       * @return bool True of success, false otherwise.
1921       */
1922      public function delete($key, $recurse = true) {
1923          if ($this->requirelockingwrite && !$this->acquire_lock($key)) {
1924              return false;
1925          }
1926          $result = parent::delete($key, $recurse);
1927          if ($this->requirelockingwrite && !$this->release_lock($key)) {
1928              debugging('Failed to release cache lock on delete operation... this should not happen.', DEBUG_DEVELOPER);
1929          }
1930          return $result;
1931      }
1932  
1933      /**
1934       * Delete all of the given keys from the cache.
1935       *
1936       * @param array $keys The key to delete.
1937       * @param bool $recurse When set to true the key will also be deleted from all stacked cache loaders and their stores.
1938       *     This happens by default and ensure that all the caches are consistent. It is NOT recommended to change this.
1939       * @return int The number of items successfully deleted.
1940       */
1941      public function delete_many(array $keys, $recurse = true) {
1942          if ($this->requirelockingwrite) {
1943              $locks = array();
1944              foreach ($keys as $id => $key) {
1945                  if ($this->acquire_lock($key)) {
1946                      $locks[] = $key;
1947                  } else {
1948                      unset($keys[$id]);
1949                  }
1950              }
1951          }
1952          $result = parent::delete_many($keys, $recurse);
1953          if ($this->requirelockingwrite) {
1954              foreach ($locks as $key) {
1955                  if ($this->release_lock($key)) {
1956                      debugging('Failed to release cache lock on delete_many operation... this should not happen.', DEBUG_DEVELOPER);
1957                  }
1958              }
1959          }
1960          return $result;
1961      }
1962  }
1963  
1964  /**
1965   * A session cache.
1966   *
1967   * This class is used for session caches returned by the cache::make methods.
1968   *
1969   * It differs from the application loader in a couple of noteable ways:
1970   *    1. Sessions are always expected to exist.
1971   *       Because of this we don't ever use the static acceleration array.
1972   *    2. Session data for a loader instance (store + definition) is consolidate into a
1973   *       single array for storage within the store.
1974   *       Along with this we embed a lastaccessed time with the data. This way we can
1975   *       check sessions for a last access time.
1976   *    3. Session stores are required to support key searching and must
1977   *       implement cache_is_searchable. This ensures stores used for the cache can be
1978   *       targetted for garbage collection of session data.
1979   *
1980   * This cache class should never be interacted with directly. Instead you should always use the cache::make methods.
1981   * It is technically possible to call those methods through this class however there is no guarantee that you will get an
1982   * instance of this class back again.
1983   *
1984   * @todo we should support locking in the session as well. Should be pretty simple to set up.
1985   *
1986   * @internal don't use me directly.
1987   * @method cache_store|cache_is_searchable get_store() Returns the cache store which must implement both cache_is_searchable.
1988   *
1989   * @package    core
1990   * @category   cache
1991   * @copyright  2012 Sam Hemelryk
1992   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
1993   */
1994  class cache_session extends cache {
1995      /**
1996       * The user the session has been established for.
1997       * @var int
1998       */
1999      protected static $loadeduserid = null;
2000  
2001      /**
2002       * The userid this cache is currently using.
2003       * @var int
2004       */
2005      protected $currentuserid = null;
2006  
2007      /**
2008       * The session id we are currently using.
2009       * @var array
2010       */
2011      protected $sessionid = null;
2012  
2013      /**
2014       * The session data for the above session id.
2015       * @var array
2016       */
2017      protected $session = null;
2018  
2019      /**
2020       * Constant used to prefix keys.
2021       */
2022      const KEY_PREFIX = 'sess_';
2023  
2024      /**
2025       * This is the key used to track last access.
2026       */
2027      const LASTACCESS = '__lastaccess__';
2028  
2029      /**
2030       * Override the cache::construct method.
2031       *
2032       * This function gets overriden so that we can process any invalidation events if need be.
2033       * If the definition doesn't have any invalidation events then this occurs exactly as it would for the cache class.
2034       * Otherwise we look at the last invalidation time and then check the invalidation data for events that have occured
2035       * between then now.
2036       *
2037       * You should not call this method from your code, instead you should use the cache::make methods.
2038       *
2039       * @param cache_definition $definition
2040       * @param cache_store $store
2041       * @param cache_loader|cache_data_source $loader
2042       */
2043      public function __construct(cache_definition $definition, cache_store $store, $loader = null) {
2044          // First up copy the loadeduserid to the current user id.
2045          $this->currentuserid = self::$loadeduserid;
2046          $this->set_session_id();
2047          parent::__construct($definition, $store, $loader);
2048  
2049          // This will trigger check tracked user. If this gets removed a call to that will need to be added here in its place.
2050          $this->set(self::LASTACCESS, cache::now());
2051  
2052          $this->handle_invalidation_events();
2053      }
2054  
2055      /**
2056       * Sets the session id for the loader.
2057       */
2058      protected function set_session_id() {
2059          $this->sessionid = preg_replace('#[^a-zA-Z0-9_]#', '_', session_id());
2060      }
2061  
2062      /**
2063       * Returns the prefix used for all keys.
2064       * @return string
2065       */
2066      protected function get_key_prefix() {
2067          return 'u'.$this->currentuserid.'_'.$this->sessionid;
2068      }
2069  
2070      /**
2071       * Parses the key turning it into a string (or array is required) suitable to be passed to the cache store.
2072       *
2073       * This function is called for every operation that uses keys. For this reason we use this function to also check
2074       * that the current user is the same as the user who last used this cache.
2075       *
2076       * On top of that if prepends the string 'sess_' to the start of all keys. The _ ensures things are easily identifiable.
2077       *
2078       * @param string|int $key As passed to get|set|delete etc.
2079       * @return string|array String unless the store supports multi-identifiers in which case an array if returned.
2080       */
2081      protected function parse_key($key) {
2082          $prefix = $this->get_key_prefix();
2083          if ($key === self::LASTACCESS) {
2084              return $key.$prefix;
2085          }
2086          return $prefix.'_'.parent::parse_key($key);
2087      }
2088  
2089      /**
2090       * Check that this cache instance is tracking the current user.
2091       */
2092      protected function check_tracked_user() {
2093          if (isset($_SESSION['USER']->id) && $_SESSION['USER']->id !== null) {
2094              // Get the id of the current user.
2095              $new = $_SESSION['USER']->id;
2096          } else {
2097              // No user set up yet.
2098              $new = 0;
2099          }
2100          if ($new !== self::$loadeduserid) {
2101              // The current user doesn't match the tracked userid for this request.
2102              if (!is_null(self::$loadeduserid)) {
2103                  // Purge the data we have for the old user.
2104                  // This way we don't bloat the session.
2105                  $this->purge();
2106              }
2107              self::$loadeduserid = $new;
2108              $this->currentuserid = $new;
2109          } else if ($new !== $this->currentuserid) {
2110              // The current user matches the loaded user but not the user last used by this cache.
2111              $this->purge_current_user();
2112              $this->currentuserid = $new;
2113          }
2114      }
2115  
2116      /**
2117       * Purges the session cache of all data belonging to the current user.
2118       */
2119      public function purge_current_user() {
2120          $keys = $this->get_store()->find_by_prefix($this->get_key_prefix());
2121          $this->get_store()->delete_many($keys);
2122      }
2123  
2124      /**
2125       * Retrieves the value for the given key from the cache.
2126       *
2127       * @param string|int $key The key for the data being requested.
2128       *      It can be any structure although using a scalar string or int is recommended in the interests of performance.
2129       *      In advanced cases an array may be useful such as in situations requiring the multi-key functionality.
2130       * @param int $requiredversion Minimum required version of the data or cache::VERSION_NONE
2131       * @param int $strictness One of IGNORE_MISSING | MUST_EXIST
2132       * @param mixed &$actualversion If specified, will be set to the actual version number retrieved
2133       * @return mixed|false The data from the cache or false if the key did not exist within the cache.
2134       * @throws coding_exception
2135       */
2136      protected function get_implementation($key, int $requiredversion, int $strictness, &$actualversion = null) {
2137          // Check the tracked user.
2138          $this->check_tracked_user();
2139  
2140          // Use parent code.
2141          return parent::get_implementation($key, $requiredversion, $strictness, $actualversion);
2142      }
2143  
2144      /**
2145       * Sends a key => value pair to the cache.
2146       *
2147       * <code>
2148       * // This code will add four entries to the cache, one for each url.
2149       * $cache->set('main', 'http://moodle.org');
2150       * $cache->set('docs', 'http://docs.moodle.org');
2151       * $cache->set('tracker', 'http://tracker.moodle.org');
2152       * $cache->set('qa', 'http://qa.moodle.net');
2153       * </code>
2154       *
2155       * @param string|int $key The key for the data being requested.
2156       *      It can be any structure although using a scalar string or int is recommended in the interests of performance.
2157       *      In advanced cases an array may be useful such as in situations requiring the multi-key functionality.
2158       * @param mixed $data The data to set against the key.
2159       * @return bool True on success, false otherwise.
2160       */
2161      public function set($key, $data) {
2162          $this->check_tracked_user();
2163          $loader = $this->get_loader();
2164          if ($loader !== false) {
2165              // We have a loader available set it there as well.
2166              // We have to let the loader do its own parsing of data as it may be unique.
2167              $loader->set($key, $data);
2168          }
2169          if (is_object($data) && $data instanceof cacheable_object) {
2170              $data = new cache_cached_object($data);
2171          } else if (!$this->get_store()->supports_dereferencing_objects() && !is_scalar($data)) {
2172              // If data is an object it will be a reference.
2173              // If data is an array if may contain references.
2174              // We want to break references so that the cache cannot be modified outside of itself.
2175              // Call the function to unreference it (in the best way possible).
2176              $data = $this->unref($data);
2177          }
2178          // We dont' support native TTL here as we consolidate data for sessions.
2179          if ($this->has_a_ttl() && !$this->store_supports_native_ttl()) {
2180              $data = new cache_ttl_wrapper($data, $this->get_definition()->get_ttl());
2181          }
2182          $success = $this->get_store()->set($this->parse_key($key), $data);
2183          if ($this->perfdebug) {
2184              cache_helper::record_cache_set($this->get_store(), $this->get_definition(), 1,
2185                      $this->get_store()->get_last_io_bytes());
2186          }
2187          return $success;
2188      }
2189  
2190      /**
2191       * Delete the given key from the cache.
2192       *
2193       * @param string|int $key The key to delete.
2194       * @param bool $recurse When set to true the key will also be deleted from all stacked cache loaders and their stores.
2195       *     This happens by default and ensure that all the caches are consistent. It is NOT recommended to change this.
2196       * @return bool True of success, false otherwise.
2197       */
2198      public function delete($key, $recurse = true) {
2199          $parsedkey = $this->parse_key($key);
2200          if ($recurse && $this->get_loader() !== false) {
2201              // Delete from the bottom of the stack first.
2202              $this->get_loader()->delete($key, $recurse);
2203          }
2204          return $this->get_store()->delete($parsedkey);
2205      }
2206  
2207      /**
2208       * Retrieves an array of values for an array of keys.
2209       *
2210       * Using this function comes with potential performance implications.
2211       * Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
2212       * the equivalent singular method for each item provided.
2213       * This should not deter you from using this function as there is a performance benefit in situations where the cache store
2214       * does support it, but you should be aware of this fact.
2215       *
2216       * @param array $keys The keys of the data being requested.
2217       *      Each key can be any structure although using a scalar string or int is recommended in the interests of performance.
2218       *      In advanced cases an array may be useful such as in situations requiring the multi-key functionality.
2219       * @param int $strictness One of IGNORE_MISSING or MUST_EXIST.
2220       * @return array An array of key value pairs for the items that could be retrieved from the cache.
2221       *      If MUST_EXIST was used and not all keys existed within the cache then an exception will be thrown.
2222       *      Otherwise any key that did not exist will have a data value of false within the results.
2223       * @throws coding_exception
2224       */
2225      public function get_many(array $keys, $strictness = IGNORE_MISSING) {
2226          $this->check_tracked_user();
2227          $parsedkeys = array();
2228          $keymap = array();
2229          foreach ($keys as $key) {
2230              $parsedkey = $this->parse_key($key);
2231              $parsedkeys[$key] = $parsedkey;
2232              $keymap[$parsedkey] = $key;
2233          }
2234          $result = $this->get_store()->get_many($parsedkeys);
2235          if ($this->perfdebug) {
2236              $readbytes = $this->get_store()->get_last_io_bytes();
2237          }
2238          $return = array();
2239          $missingkeys = array();
2240          $hasmissingkeys = false;
2241          foreach ($result as $parsedkey => $value) {
2242              $key = $keymap[$parsedkey];
2243              if ($value instanceof cache_ttl_wrapper) {
2244                  /* @var cache_ttl_wrapper $value */
2245                  if ($value->has_expired()) {
2246                      $this->delete($keymap[$parsedkey]);
2247                      $value = false;
2248                  } else {
2249                      $value = $value->data;
2250                  }
2251              }
2252              if ($value instanceof cache_cached_object) {
2253                  /* @var cache_cached_object $value */
2254                  $value = $value->restore_object();
2255              } else if (!$this->get_store()->supports_dereferencing_objects() && !is_scalar($value)) {
2256                  // If data is an object it will be a reference.
2257                  // If data is an array if may contain references.
2258                  // We want to break references so that the cache cannot be modified outside of itself.
2259                  // Call the function to unreference it (in the best way possible).
2260                  $value = $this->unref($value);
2261              }
2262              $return[$key] = $value;
2263              if ($value === false) {
2264                  $hasmissingkeys = true;
2265                  $missingkeys[$parsedkey] = $key;
2266              }
2267          }
2268          if ($hasmissingkeys) {
2269              // We've got missing keys - we've got to check any loaders or data sources.
2270              $loader = $this->get_loader();
2271              $datasource = $this->get_datasource();
2272              if ($loader !== false) {
2273                  foreach ($loader->get_many($missingkeys) as $key => $value) {
2274                      if ($value !== false) {
2275                          $return[$key] = $value;
2276                          unset($missingkeys[$parsedkeys[$key]]);
2277                      }
2278                  }
2279              }
2280              $hasmissingkeys = count($missingkeys) > 0;
2281              if ($datasource !== false && $hasmissingkeys) {
2282                  // We're still missing keys but we've got a datasource.
2283                  foreach ($datasource->load_many_for_cache($missingkeys) as $key => $value) {
2284                      if ($value !== false) {
2285                          $return[$key] = $value;
2286                          unset($missingkeys[$parsedkeys[$key]]);
2287                      }
2288                  }
2289                  $hasmissingkeys = count($missingkeys) > 0;
2290              }
2291          }
2292          if ($hasmissingkeys && $strictness === MUST_EXIST) {
2293              throw new coding_exception('Requested key did not exist in any cache stores and could not be loaded.');
2294          }
2295          if ($this->perfdebug) {
2296              $hits = 0;
2297              $misses = 0;
2298              foreach ($return as $value) {
2299                  if ($value === false) {
2300                      $misses++;
2301                  } else {
2302                      $hits++;
2303                  }
2304              }
2305              cache_helper::record_cache_hit($this->get_store(), $this->get_definition(), $hits, $readbytes);
2306              cache_helper::record_cache_miss($this->get_store(), $this->get_definition(), $misses);
2307          }
2308          return $return;
2309  
2310      }
2311  
2312      /**
2313       * Delete all of the given keys from the cache.
2314       *
2315       * @param array $keys The key to delete.
2316       * @param bool $recurse When set to true the key will also be deleted from all stacked cache loaders and their stores.
2317       *     This happens by default and ensure that all the caches are consistent. It is NOT recommended to change this.
2318       * @return int The number of items successfully deleted.
2319       */
2320      public function delete_many(array $keys, $recurse = true) {
2321          $parsedkeys = array_map(array($this, 'parse_key'), $keys);
2322          if ($recurse && $this->get_loader() !== false) {
2323              // Delete from the bottom of the stack first.
2324              $this->get_loader()->delete_many($keys, $recurse);
2325          }
2326          return $this->get_store()->delete_many($parsedkeys);
2327      }
2328  
2329      /**
2330       * Sends several key => value pairs to the cache.
2331       *
2332       * Using this function comes with potential performance implications.
2333       * Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
2334       * the equivalent singular method for each item provided.
2335       * This should not deter you from using this function as there is a performance benefit in situations where the cache store
2336       * does support it, but you should be aware of this fact.
2337       *
2338       * <code>
2339       * // This code will add four entries to the cache, one for each url.
2340       * $cache->set_many(array(
2341       *     'main' => 'http://moodle.org',
2342       *     'docs' => 'http://docs.moodle.org',
2343       *     'tracker' => 'http://tracker.moodle.org',
2344       *     'qa' => ''http://qa.moodle.net'
2345       * ));
2346       * </code>
2347       *
2348       * @param array $keyvaluearray An array of key => value pairs to send to the cache.
2349       * @return int The number of items successfully set. It is up to the developer to check this matches the number of items.
2350       *      ... if they care that is.
2351       */
2352      public function set_many(array $keyvaluearray) {
2353          $this->check_tracked_user();
2354          $loader = $this->get_loader();
2355          if ($loader !== false) {
2356              // We have a loader available set it there as well.
2357              // We have to let the loader do its own parsing of data as it may be unique.
2358              $loader->set_many($keyvaluearray);
2359          }
2360          $data = array();
2361          $definitionid = $this->get_definition()->get_ttl();
2362          $simulatettl = $this->has_a_ttl() && !$this->store_supports_native_ttl();
2363          foreach ($keyvaluearray as $key => $value) {
2364              if (is_object($value) && $value instanceof cacheable_object) {
2365                  $value = new cache_cached_object($value);
2366              } else if (!$this->get_store()->supports_dereferencing_objects() && !is_scalar($value)) {
2367                  // If data is an object it will be a reference.
2368                  // If data is an array if may contain references.
2369                  // We want to break references so that the cache cannot be modified outside of itself.
2370                  // Call the function to unreference it (in the best way possible).
2371                  $value = $this->unref($value);
2372              }
2373              if ($simulatettl) {
2374                  $value = new cache_ttl_wrapper($value, $definitionid);
2375              }
2376              $data[$key] = array(
2377                  'key' => $this->parse_key($key),
2378                  'value' => $value
2379              );
2380          }
2381          $successfullyset = $this->get_store()->set_many($data);
2382          if ($this->perfdebug && $successfullyset) {
2383              cache_helper::record_cache_set($this->get_store(), $this->get_definition(), $successfullyset,
2384                      $this->get_store()->get_last_io_bytes());
2385          }
2386          return $successfullyset;
2387      }
2388  
2389      /**
2390       * Purges the cache store, and loader if there is one.
2391       *
2392       * @return bool True on success, false otherwise
2393       */
2394      public function purge() {
2395          $this->get_store()->purge();
2396          if ($this->get_loader()) {
2397              $this->get_loader()->purge();
2398          }
2399          return true;
2400      }
2401  
2402      /**
2403       * Test is a cache has a key.
2404       *
2405       * The use of the has methods is strongly discouraged. In a high load environment the cache may well change between the
2406       * test and any subsequent action (get, set, delete etc).
2407       * Instead it is recommended to write your code in such a way they it performs the following steps:
2408       * <ol>
2409       * <li>Attempt to retrieve the information.</li>
2410       * <li>Generate the information.</li>
2411       * <li>Attempt to set the information</li>
2412       * </ol>
2413       *
2414       * Its also worth mentioning that not all stores support key tests.
2415       * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
2416       * Just one more reason you should not use these methods unless you have a very good reason to do so.
2417       *
2418       * @param string|int $key
2419       * @param bool $tryloadifpossible If set to true, the cache doesn't contain the key, and there is another cache loader or
2420       *      data source then the code will try load the key value from the next item in the chain.
2421       * @return bool True if the cache has the requested key, false otherwise.
2422       */
2423      public function has($key, $tryloadifpossible = false) {
2424          $this->check_tracked_user();
2425          $parsedkey = $this->parse_key($key);
2426          $store = $this->get_store();
2427          if ($this->has_a_ttl() && !$this->store_supports_native_ttl()) {
2428              // The data has a TTL and the store doesn't support it natively.
2429              // We must fetch the data and expect a ttl wrapper.
2430              $data = $store->get($parsedkey);
2431              $has = ($data instanceof cache_ttl_wrapper && !$data->has_expired());
2432          } else if (!$this->store_supports_key_awareness()) {
2433              // The store doesn't support key awareness, get the data and check it manually... puke.
2434              // Either no TTL is set of the store supports its handling natively.
2435              $data = $store->get($parsedkey);
2436              $has = ($data !== false);
2437          } else {
2438              // The store supports key awareness, this is easy!
2439              // Either no TTL is set of the store supports its handling natively.
2440              /* @var cache_store|cache_is_key_aware $store */
2441              $has = $store->has($parsedkey);
2442          }
2443          if (!$has && $tryloadifpossible) {
2444              $result = null;
2445              if ($this->get_loader() !== false) {
2446                  $result = $this->get_loader()->get($parsedkey);
2447              } else if ($this->get_datasource() !== null) {
2448                  $result = $this->get_datasource()->load_for_cache($key);
2449              }
2450              $has = ($result !== null);
2451              if ($has) {
2452                  $this->set($key, $result);
2453              }
2454          }
2455          return $has;
2456      }
2457  
2458      /**
2459       * Test is a cache has all of the given keys.
2460       *
2461       * It is strongly recommended to avoid the use of this function if not absolutely required.
2462       * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
2463       *
2464       * Its also worth mentioning that not all stores support key tests.
2465       * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
2466       * Just one more reason you should not use these methods unless you have a very good reason to do so.
2467       *
2468       * @param array $keys
2469       * @return bool True if the cache has all of the given keys, false otherwise.
2470       */
2471      public function has_all(array $keys) {
2472          $this->check_tracked_user();
2473          if (($this->has_a_ttl() && !$this->store_supports_native_ttl()) || !$this->store_supports_key_awareness()) {
2474              foreach ($keys as $key) {
2475                  if (!$this->has($key)) {
2476                      return false;
2477                  }
2478              }
2479              return true;
2480          }
2481          // The cache must be key aware and if support native ttl if it a ttl is set.
2482          /* @var cache_store|cache_is_key_aware $store */
2483          $store = $this->get_store();
2484          return $store->has_all(array_map(array($this, 'parse_key'), $keys));
2485      }
2486  
2487      /**
2488       * Test if a cache has at least one of the given keys.
2489       *
2490       * It is strongly recommended to avoid the use of this function if not absolutely required.
2491       * In a high load environment the cache may well change between the test and any subsequent action (get, set, delete etc).
2492       *
2493       * Its also worth mentioning that not all stores support key tests.
2494       * For stores that don't support key tests this functionality is mimicked by using the equivalent get method.
2495       * Just one more reason you should not use these methods unless you have a very good reason to do so.
2496       *
2497       * @param array $keys
2498       * @return bool True if the cache has at least one of the given keys
2499       */
2500      public function has_any(array $keys) {
2501          if (($this->has_a_ttl() && !$this->store_supports_native_ttl()) || !$this->store_supports_key_awareness()) {
2502              foreach ($keys as $key) {
2503                  if ($this->has($key)) {
2504                      return true;
2505                  }
2506              }
2507              return false;
2508          }
2509          /* @var cache_store|cache_is_key_aware $store */
2510          $store = $this->get_store();
2511          return $store->has_any(array_map(array($this, 'parse_key'), $keys));
2512      }
2513  
2514      /**
2515       * The session loader never uses static acceleration.
2516       * Instead it stores things in the static $session variable. Shared between all session loaders.
2517       *
2518       * @return bool
2519       */
2520      protected function use_static_acceleration() {
2521          return false;
2522      }
2523  }
2524  
2525  /**
2526   * An request cache.
2527   *
2528   * This class is used for request caches returned by the cache::make methods.
2529   *
2530   * This cache class should never be interacted with directly. Instead you should always use the cache::make methods.
2531   * It is technically possible to call those methods through this class however there is no guarantee that you will get an
2532   * instance of this class back again.
2533   *
2534   * @internal don't use me directly.
2535   *
2536   * @package    core
2537   * @category   cache
2538   * @copyright  2012 Sam Hemelryk
2539   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
2540   */
2541  class cache_request extends cache {
2542      // This comment appeases code pre-checker ;) !
2543  }