Proyectos de Subversion Moodle

<?php

// This file is part of Moodle - http://moodle.org/

//

// Moodle is free software: you can redistribute it and/or modify

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation, either version 3 of the License, or

// (at your option) any later version.

//

// Moodle is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

//

// You should have received a copy of the GNU General Public License

// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**

 * Cache helper class

 *

 * This file is part of Moodle's cache API, affectionately called MUC.

 * It contains the components that are requried in order to use caching.

 *

 * @package    core

 * @category   cache

 * @copyright  2012 Sam Hemelryk

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

defined('MOODLE_INTERNAL') || die();

/**

 * The cache helper class.

 *

 * The cache helper class provides common functionality to the cache API and is useful to developers within to interact with

 * the cache API in a general way.

 *

 * @package    core

 * @category   cache

 * @copyright  2012 Sam Hemelryk

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

class cache_helper {

    /**

     * Statistics gathered by the cache API during its operation will be used here.

     * @static

     * @var array

     */

    protected static $stats = array();

    /**

     * The instance of the cache helper.

     * @var cache_helper

     */

    protected static $instance;

    /**

     * The site identifier used by the cache.

     * Set the first time get_site_identifier is called.

     * @var string

     */

    protected static $siteidentifier = null;

    /**

     * Returns true if the cache API can be initialised before Moodle has finished initialising itself.

     *

     * This check is essential when trying to cache the likes of configuration information. It checks to make sure that the cache

     * configuration file has been created which allows use to set up caching when ever is required.

     *

     * @return bool

     */

    public static function ready_for_early_init() {

        return cache_config::config_file_exists();

    }

    /**

     * Returns an instance of the cache_helper.

     *

     * This is designed for internal use only and acts as a static store.

     * @staticvar null $instance

     * @return cache_helper

     */

    protected static function instance() {

        if (is_null(self::$instance)) {

            self::$instance = new cache_helper();

        }

        return self::$instance;

    }

    /**

     * Constructs an instance of the cache_helper class. Again for internal use only.

     */

    protected function __construct() {

        // Nothing to do here, just making sure you can't get an instance of this.

    }

    /**

     * Used as a data store for initialised definitions.

     * @var array

     */

    protected $definitions = array();

    /**

     * Used as a data store for initialised cache stores

     * We use this because we want to avoid establishing multiple instances of a single store.

     * @var array

     */

    protected $stores = array();

    /**

     * Returns the class for use as a cache loader for the given mode.

     *

     * @param int $mode One of cache_store::MODE_

     * @return string

     * @throws coding_exception

     */

    public static function get_class_for_mode($mode) {

        switch ($mode) {

            case cache_store::MODE_APPLICATION :

                return 'cache_application';

            case cache_store::MODE_REQUEST :

                return 'cache_request';

            case cache_store::MODE_SESSION :

                return 'cache_session';

        }

        throw new coding_exception('Unknown cache mode passed. Must be one of cache_store::MODE_*');

    }

    /**

     * Returns the cache stores to be used with the given definition.

     * @param cache_definition $definition

     * @return array

     */

    public static function get_cache_stores(cache_definition $definition) {

        $instance = cache_config::instance();

        $stores = $instance->get_stores_for_definition($definition);

        $stores = self::initialise_cachestore_instances($stores, $definition);

        return $stores;

    }

    /**

     * Internal function for initialising an array of stores against a given cache definition.

     *

     * @param array $stores

     * @param cache_definition $definition

     * @return cache_store[]

     */

    protected static function initialise_cachestore_instances(array $stores, cache_definition $definition) {

        $return = array();

        $factory = cache_factory::instance();

        foreach ($stores as $name => $details) {

            $store = $factory->create_store_from_config($name, $details, $definition);

            if ($store !== false) {

                $return[] = $store;

            }

        }

        return $return;

    }

    /**

     * Returns a cache_lock instance suitable for use with the store.

     *

     * @param cache_store $store

     * @return cache_lock_interface

     */

    public static function get_cachelock_for_store(cache_store $store) {

        $instance = cache_config::instance();

        $lockconf = $instance->get_lock_for_store($store->my_name());

        $factory = cache_factory::instance();

        return $factory->create_lock_instance($lockconf);

    }

    /**

     * Returns an array of plugins without using core methods.

     *

     * This function explicitly does NOT use core functions as it will in some circumstances be called before Moodle has

     * finished initialising. This happens when loading configuration for instance.

     *

     * @return array

     */

    public static function early_get_cache_plugins() {

        global $CFG;

        $result = array();

        $ignored = array('CVS', '_vti_cnf', 'simpletest', 'db', 'yui', 'tests');

        $fulldir = $CFG->dirroot.'/cache/stores';

        $items = new DirectoryIterator($fulldir);

        foreach ($items as $item) {

            if ($item->isDot() or !$item->isDir()) {

                continue;

            }

            $pluginname = $item->getFilename();

            if (in_array($pluginname, $ignored)) {

                continue;

            }

            if (!is_valid_plugin_name($pluginname)) {

                // Better ignore plugins with problematic names here.

                continue;

            }

            $result[$pluginname] = $fulldir.'/'.$pluginname;

            unset($item);

        }

        unset($items);

        return $result;

    }

    /**

     * Invalidates a given set of keys from a given definition.

     *

     * @todo Invalidating by definition should also add to the event cache so that sessions can be invalidated (when required).

     *

     * @param string $component

     * @param string $area

     * @param array $identifiers

     * @param array|string|int $keys

     * @return boolean

     * @throws coding_exception

     */

    public static function invalidate_by_definition($component, $area, array $identifiers = array(), $keys = array()) {

        $cache = cache::make($component, $area, $identifiers);

        if (is_array($keys)) {

            $cache->delete_many($keys);

        } else if (is_scalar($keys)) {

            $cache->delete($keys);

        } else {

            throw new coding_exception('cache_helper::invalidate_by_definition only accepts $keys as array, or scalar.');

        }

        return true;

    }

    /**

     * Invalidates a given set of keys by means of an event.

     *

     * Events cannot determine what identifiers might need to be cleared. Event based purge and invalidation

     * are only supported on caches without identifiers.

     *

     * @param string $event

     * @param array $keys

     */

    public static function invalidate_by_event($event, array $keys) {

        $instance = cache_config::instance();

        $invalidationeventset = false;

        $factory = cache_factory::instance();

        $inuse = $factory->get_caches_in_use();

        $purgetoken = null;

        foreach ($instance->get_definitions() as $name => $definitionarr) {

            $definition = cache_definition::load($name, $definitionarr);

            if ($definition->invalidates_on_event($event)) {

                // First up check if there is a cache loader for this definition already.

                // If there is we need to invalidate the keys from there.

                $definitionkey = $definition->get_component().'/'.$definition->get_area();

                if (isset($inuse[$definitionkey])) {

                    $inuse[$definitionkey]->delete_many($keys);

                }

                // We should only log events for application and session caches.

                // Request caches shouldn't have events as all data is lost at the end of the request.

                // Events should only be logged once of course and likely several definitions are watching so we

                // track its logging with $invalidationeventset.

                $logevent = ($invalidationeventset === false && $definition->get_mode() !== cache_store::MODE_REQUEST);

                if ($logevent) {

                    // Get the event invalidation cache.

                    $cache = cache::make('core', 'eventinvalidation');

                    // Get any existing invalidated keys for this cache.

                    $data = $cache->get($event);

                    if ($data === false) {

                        // There are none.

                        $data = array();

                    }

                    // Add our keys to them with the current cache timestamp.

                    if (null === $purgetoken) {

                        $purgetoken = cache::get_purge_token(true);

                    }

                    foreach ($keys as $key) {

                        $data[$key] = $purgetoken;

                    }

                    // Set that data back to the cache.

                    $cache->set($event, $data);

                    // This only needs to occur once.

                    $invalidationeventset = true;

                }

            }

        }

    }

    /**

     * Purges the cache for a specific definition.

     *

     * @param string $component

     * @param string $area

     * @param array $identifiers

     * @return bool

     */

    public static function purge_by_definition($component, $area, array $identifiers = array()) {

        // Create the cache.

        $cache = cache::make($component, $area, $identifiers);

        // Initialise, in case of a store.

        if ($cache instanceof cache_store) {

            $factory = cache_factory::instance();

            $definition = $factory->create_definition($component, $area, null);

            $cacheddefinition = clone $definition;

            $cacheddefinition->set_identifiers($identifiers);

            $cache->initialise($cacheddefinition);

        }

        // Purge baby, purge.

        $cache->purge();

        return true;

    }

    /**

     * Purges a cache of all information on a given event.

     *

     * Events cannot determine what identifiers might need to be cleared. Event based purge and invalidation

     * are only supported on caches without identifiers.

     *

     * @param string $event

     */

    public static function purge_by_event($event) {

        $instance = cache_config::instance();

        $invalidationeventset = false;

        $factory = cache_factory::instance();

        $inuse = $factory->get_caches_in_use();

        $purgetoken = null;

        foreach ($instance->get_definitions() as $name => $definitionarr) {

            $definition = cache_definition::load($name, $definitionarr);

            if ($definition->invalidates_on_event($event)) {

                // First up check if there is a cache loader for this definition already.

                // If there is we need to invalidate the keys from there.

                $definitionkey = $definition->get_component().'/'.$definition->get_area();

                if (isset($inuse[$definitionkey])) {

                    $inuse[$definitionkey]->purge();

                } else {

                    cache::make($definition->get_component(), $definition->get_area())->purge();

                }

                // We should only log events for application and session caches.

                // Request caches shouldn't have events as all data is lost at the end of the request.

                // Events should only be logged once of course and likely several definitions are watching so we

                // track its logging with $invalidationeventset.

                $logevent = ($invalidationeventset === false && $definition->get_mode() !== cache_store::MODE_REQUEST);

                // We need to flag the event in the "Event invalidation" cache if it hasn't already happened.

                if ($logevent && $invalidationeventset === false) {

                    // Get the event invalidation cache.

                    $cache = cache::make('core', 'eventinvalidation');

                    // Create a key to invalidate all.

                    if (null === $purgetoken) {

                        $purgetoken = cache::get_purge_token(true);

                    }

                    $data = array(

                        'purged' => $purgetoken,

                    );

                    // Set that data back to the cache.

                    $cache->set($event, $data);

                    // This only needs to occur once.

                    $invalidationeventset = true;

                }

            }

        }

    }

    /**

     * Ensure that the stats array is ready to collect information for the given store and definition.

     * @param string $store

     * @param string $storeclass

     * @param string $definition A string that identifies the definition.

     * @param int $mode One of cache_store::MODE_*. Since 2.9.

     */

    protected static function ensure_ready_for_stats($store, $storeclass, $definition, $mode = cache_store::MODE_APPLICATION) {

        // This function is performance-sensitive, so exit as quickly as possible

        // if we do not need to do anything.

        if (isset(self::$stats[$definition]['stores'][$store])) {

            return;

        }

        if (!array_key_exists($definition, self::$stats)) {

            self::$stats[$definition] = array(

                'mode' => $mode,

                'stores' => array(

                    $store => array(

                        'class' => $storeclass,

                        'hits' => 0,

                        'misses' => 0,

                        'sets' => 0,

                        'iobytes' => cache_store::IO_BYTES_NOT_SUPPORTED,

                        'locks' => 0,

                    )

                )

            );

        } else if (!array_key_exists($store, self::$stats[$definition]['stores'])) {

            self::$stats[$definition]['stores'][$store] = array(

                'class' => $storeclass,

                'hits' => 0,

                'misses' => 0,

                'sets' => 0,

                'iobytes' => cache_store::IO_BYTES_NOT_SUPPORTED,

                'locks' => 0,

            );

        }

    }

    /**

     * Returns a string to describe the definition.

     *

     * This method supports the definition as a string due to legacy requirements.

     * It is backwards compatible when a string is passed but is not accurate.

     *

     * @since 2.9

     * @param cache_definition|string $definition

     * @return string

     */

    protected static function get_definition_stat_id_and_mode($definition) {

        if (!($definition instanceof cache_definition)) {

            // All core calls to this method have been updated, this is the legacy state.

            // We'll use application as the default as that is the most common, really this is not accurate of course but

            // at this point we can only guess and as it only affects calls to cache stat outside of core (of which there should

            // be none) I think that is fine.

            debugging('Please update you cache stat calls to pass the definition rather than just its ID.', DEBUG_DEVELOPER);

            return array((string)$definition, cache_store::MODE_APPLICATION);

        }

        return array($definition->get_id(), $definition->get_mode());

    }

    /**

     * Record a cache hit in the stats for the given store and definition.

     *

     * In Moodle 2.9 the $definition argument changed from accepting only a string to accepting a string or a

     * cache_definition instance. It is preferable to pass a cache definition instance.

     *

     * In Moodle 3.9 the first argument changed to also accept a cache_store.

     *

     * @internal

     * @param string|cache_store $store

     * @param cache_definition $definition You used to be able to pass a string here, however that is deprecated please pass the

     *      actual cache_definition object now.

     * @param int $hits The number of hits to record (by default 1)

     * @param int $readbytes Number of bytes read from the cache or cache_store::IO_BYTES_NOT_SUPPORTED

     */

    public static function record_cache_hit($store, $definition, int $hits = 1, int $readbytes = cache_store::IO_BYTES_NOT_SUPPORTED): void {

        $storeclass = '';

        if ($store instanceof cache_store) {

            $storeclass = get_class($store);

            $store = $store->my_name();

        }

        list($definitionstr, $mode) = self::get_definition_stat_id_and_mode($definition);

        self::ensure_ready_for_stats($store, $storeclass, $definitionstr, $mode);

        self::$stats[$definitionstr]['stores'][$store]['hits'] += $hits;

        if ($readbytes !== cache_store::IO_BYTES_NOT_SUPPORTED) {

            if (self::$stats[$definitionstr]['stores'][$store]['iobytes'] === cache_store::IO_BYTES_NOT_SUPPORTED) {

                self::$stats[$definitionstr]['stores'][$store]['iobytes'] = $readbytes;

            } else {

                self::$stats[$definitionstr]['stores'][$store]['iobytes'] += $readbytes;

            }

        }

    }

    /**

     * Record a cache miss in the stats for the given store and definition.

     *

     * In Moodle 2.9 the $definition argument changed from accepting only a string to accepting a string or a

     * cache_definition instance. It is preferable to pass a cache definition instance.

     *

     * In Moodle 3.9 the first argument changed to also accept a cache_store.

     *

     * @internal

     * @param string|cache_store $store

     * @param cache_definition $definition You used to be able to pass a string here, however that is deprecated please pass the

     *      actual cache_definition object now.

     * @param int $misses The number of misses to record (by default 1)

     */

    public static function record_cache_miss($store, $definition, $misses = 1) {

        $storeclass = '';

        if ($store instanceof cache_store) {

            $storeclass = get_class($store);

            $store = $store->my_name();

        }

        list($definitionstr, $mode) = self::get_definition_stat_id_and_mode($definition);

        self::ensure_ready_for_stats($store, $storeclass, $definitionstr, $mode);

        self::$stats[$definitionstr]['stores'][$store]['misses'] += $misses;

    }

    /**

     * Record a cache set in the stats for the given store and definition.

     *

     * In Moodle 2.9 the $definition argument changed from accepting only a string to accepting a string or a

     * cache_definition instance. It is preferable to pass a cache definition instance.

     *

     * In Moodle 3.9 the first argument changed to also accept a cache_store.

     *

     * @internal

     * @param string|cache_store $store

     * @param cache_definition $definition You used to be able to pass a string here, however that is deprecated please pass the

     *      actual cache_definition object now.

     * @param int $sets The number of sets to record (by default 1)

     * @param int $writebytes Number of bytes written to the cache or cache_store::IO_BYTES_NOT_SUPPORTED

     */

    public static function record_cache_set($store, $definition, int $sets = 1,

            int $writebytes = cache_store::IO_BYTES_NOT_SUPPORTED) {

        $storeclass = '';

        if ($store instanceof cache_store) {

            $storeclass = get_class($store);

            $store = $store->my_name();

        }

        list($definitionstr, $mode) = self::get_definition_stat_id_and_mode($definition);

        self::ensure_ready_for_stats($store, $storeclass, $definitionstr, $mode);

        self::$stats[$definitionstr]['stores'][$store]['sets'] += $sets;

        if ($writebytes !== cache_store::IO_BYTES_NOT_SUPPORTED) {

            if (self::$stats[$definitionstr]['stores'][$store]['iobytes'] === cache_store::IO_BYTES_NOT_SUPPORTED) {

                self::$stats[$definitionstr]['stores'][$store]['iobytes'] = $writebytes;

            } else {

                self::$stats[$definitionstr]['stores'][$store]['iobytes'] += $writebytes;

            }

        }

    }

    /**

     * Return the stats collected so far.

     * @return array

     */

    public static function get_stats() {

        return self::$stats;

    }

    /**

     * Purge all of the cache stores of all of their data.

     *

     * Think twice before calling this method. It will purge **ALL** caches regardless of whether they have been used recently or

     * anything. This will involve full setup of the cache + the purge operation. On a site using caching heavily this WILL be

     * painful.

     *

     * @param bool $usewriter If set to true the cache_config_writer class is used. This class is special as it avoids

     *      it is still usable when caches have been disabled.

     *      Please use this option only if you really must. It's purpose is to allow the cache to be purged when it would be

     *      otherwise impossible.

     */

    public static function purge_all($usewriter = false) {

        $factory = cache_factory::instance();

        $config = $factory->create_config_instance($usewriter);

        foreach ($config->get_all_stores() as $store) {

            self::purge_store($store['name'], $config);

        }

        foreach ($factory->get_adhoc_caches_in_use() as $cache) {

            $cache->purge();

        }

    }

    /**

     * Purges a store given its name.

     *

     * @param string $storename

     * @param cache_config $config

     * @return bool

     */

    public static function purge_store($storename, cache_config $config = null) {

        if ($config === null) {

            $config = cache_config::instance();

        }

        $stores = $config->get_all_stores();

        if (!array_key_exists($storename, $stores)) {

            // The store does not exist.

            return false;

        }

        $store = $stores[$storename];

        $class = $store['class'];

        // We check are_requirements_met although we expect is_ready is going to check as well.

        if (!$class::are_requirements_met()) {

            return false;

        }

        // Found the store: is it ready?

        /* @var cache_store $instance */

        $instance = new $class($store['name'], $store['configuration']);

        if (!$instance->is_ready()) {

            unset($instance);

            return false;

        }

        foreach ($config->get_definitions_by_store($storename) as $id => $definition) {

            $definition = cache_definition::load($id, $definition);

            $definitioninstance = clone($instance);

            $definitioninstance->initialise($definition);

            $definitioninstance->purge();

            unset($definitioninstance);

        }

        return true;

    }

    /**

     * Purges all of the stores used by a definition.

     *

     * Unlike cache_helper::purge_by_definition this purges all of the data from the stores not

     * just the data relating to the definition.

     * This function is useful when you must purge a definition that requires setup but you don't

     * want to set it up.

     *

     * @param string $component

     * @param string $area

     */

    public static function purge_stores_used_by_definition($component, $area) {

        $factory = cache_factory::instance();

        $config = $factory->create_config_instance();

        $definition = $factory->create_definition($component, $area);

        $stores = $config->get_stores_for_definition($definition);

        foreach ($stores as $store) {

            self::purge_store($store['name']);

        }

    }

    /**

     * Returns the translated name of the definition.

     *

     * @param cache_definition $definition

     * @return lang_string

     */

    public static function get_definition_name($definition) {

        if ($definition instanceof cache_definition) {

            return $definition->get_name();

        }

        $identifier = 'cachedef_'.clean_param($definition['area'], PARAM_STRINGID);

        $component = $definition['component'];

        if ($component === 'core') {

            $component = 'cache';

        }

        return new lang_string($identifier, $component);

    }

    /**

     * Hashes a descriptive key to make it shorter and still unique.

     * @param string|int $key

     * @param cache_definition $definition

     * @return string

     */

    public static function hash_key($key, cache_definition $definition) {

        if ($definition->uses_simple_keys()) {

            if (debugging() && preg_match('#[^a-zA-Z0-9_]#', $key ?? '')) {

                throw new coding_exception('Cache definition '.$definition->get_id().' requires simple keys. Invalid key provided.', $key);

            }

            // We put the key first so that we can be sure the start of the key changes.

            return (string)$key . '-' . $definition->generate_single_key_prefix();

        }

        $key = $definition->generate_single_key_prefix() . '-' . $key;

        return sha1($key);

    }

    /**

     * Finds all definitions and updates them within the cache config file.

     *

     * @param bool $coreonly If set to true only core definitions will be updated.

     */

    public static function update_definitions($coreonly = false) {

        global $CFG;

        // Include locallib.

        require_once($CFG->dirroot.'/cache/locallib.php');

        // First update definitions

        cache_config_writer::update_definitions($coreonly);

        // Second reset anything we have already initialised to ensure we're all up to date.

        cache_factory::reset();

    }

    /**

     * Update the site identifier stored by the cache API.

     *

     * @param string $siteidentifier

     * @return string The new site identifier.

     */

    public static function update_site_identifier($siteidentifier) {

        global $CFG;

        // Include locallib.

        require_once($CFG->dirroot.'/cache/locallib.php');

        $factory = cache_factory::instance();

        $factory->updating_started();

        $config = $factory->create_config_instance(true);

        $siteidentifier = $config->update_site_identifier($siteidentifier);

        $factory->updating_finished();

        cache_factory::reset();

        return $siteidentifier;

    }

    /**

     * Returns the site identifier.

     *

     * @return string

     */

    public static function get_site_identifier() {

        global $CFG;

        if (!is_null(self::$siteidentifier)) {

            return self::$siteidentifier;

        }

        // If site identifier hasn't been collected yet attempt to get it from the cache config.

        $factory = cache_factory::instance();

        // If the factory is initialising then we don't want to try to get it from the config or we risk

        // causing the cache to enter an infinite initialisation loop.

        if (!$factory->is_initialising()) {

            $config = $factory->create_config_instance();

            self::$siteidentifier = $config->get_site_identifier();

        }

        if (is_null(self::$siteidentifier)) {

            // If the site identifier is still null then config isn't aware of it yet.

            // We'll see if the CFG is loaded, and if not we will just use unknown.

            // It's very important here that we don't use get_config. We don't want an endless cache loop!

            if (!empty($CFG->siteidentifier)) {

                self::$siteidentifier = self::update_site_identifier($CFG->siteidentifier);

            } else {

                // It's not being recorded in MUC's config and the config data hasn't been loaded yet.

                // Likely we are initialising.

                return 'unknown';

            }

        }

        return self::$siteidentifier;

    }

    /**

     * Returns the site version.

     *

     * @return string

     */

    public static function get_site_version() {

        global $CFG;

        return (string)$CFG->version;

    }

    /**

     * Runs cron routines for MUC.

     */

    public static function cron() {

        self::clean_old_session_data(true);

    }

    /**

     * Cleans old session data from cache stores used for session based definitions.

     *

     * @param bool $output If set to true output will be given.

     */

    public static function clean_old_session_data($output = false) {

        global $CFG;

        if ($output) {

            mtrace('Cleaning up stale session data from cache stores.');

        }

        $factory = cache_factory::instance();

        $config = $factory->create_config_instance();

        $definitions = $config->get_definitions();

        $purgetime = time() - $CFG->sessiontimeout;

        foreach ($definitions as $definitionarray) {

            // We are only interested in session caches.

            if (!($definitionarray['mode'] & cache_store::MODE_SESSION)) {

                continue;

            }

            $definition = $factory->create_definition($definitionarray['component'], $definitionarray['area']);

            $stores = $config->get_stores_for_definition($definition);

            // Turn them into store instances.

            $stores = self::initialise_cachestore_instances($stores, $definition);

            // Initialise all of the stores used for that definition.

            foreach ($stores as $store) {

                // If the store doesn't support searching we can skip it.

                if (!($store instanceof cache_is_searchable)) {

                    debugging('Cache stores used for session definitions should ideally be searchable.', DEBUG_DEVELOPER);

                    continue;

                }

                // Get all of the keys.

                $keys = $store->find_by_prefix(cache_session::KEY_PREFIX);

                $todelete = array();

                foreach ($store->get_many($keys) as $key => $value) {

                    if (strpos($key, cache_session::KEY_PREFIX) !== 0 || !is_array($value) || !isset($value['lastaccess'])) {

                        continue;

                    }

                    if ((int)$value['lastaccess'] < $purgetime || true) {

                        $todelete[] = $key;

                    }

                }

                if (count($todelete)) {

                    $outcome = (int)$store->delete_many($todelete);

                    if ($output) {

                        $strdef = s($definition->get_id());

                        $strstore = s($store->my_name());

                        mtrace("- Removed {$outcome} old {$strdef} sessions from the '{$strstore}' cache store.");

                    }

                }

            }

        }

    }

    /**

     * Returns an array of stores that would meet the requirements for every definition.

     *

     * These stores would be 100% suitable to map as defaults for cache modes.

     *

     * @return array[] An array of stores, keys are the store names.

     */

    public static function get_stores_suitable_for_mode_default() {

        $factory = cache_factory::instance();

        $config = $factory->create_config_instance();

        $requirements = 0;

        foreach ($config->get_definitions() as $definition) {

            $definition = cache_definition::load($definition['component'].'/'.$definition['area'], $definition);

            $requirements = $requirements | $definition->get_requirements_bin();

        }

        $stores = array();

        foreach ($config->get_all_stores() as $name => $store) {

            if (!empty($store['features']) && ($store['features'] & $requirements)) {

                $stores[$name] = $store;

            }

        }

        return $stores;

    }

    /**

     * Returns stores suitable for use with a given definition.

     *

     * @param cache_definition $definition

     * @return cache_store[]

     */

    public static function get_stores_suitable_for_definition(cache_definition $definition) {

        $factory = cache_factory::instance();

        $stores = array();

        if ($factory->is_initialising() || $factory->stores_disabled()) {

            // No suitable stores here.

            return $stores;

        } else {

            $stores = self::get_cache_stores($definition);

            // If mappingsonly is set, having 0 stores is ok.

            if ((count($stores) === 0) && (!$definition->is_for_mappings_only())) {

                // No suitable stores we found for the definition. We need to come up with a sensible default.

                // If this has happened we can be sure that the user has mapped custom stores to either the

                // mode of the definition. The first alternative to try is the system default for the mode.

                // e.g. the default file store instance for application definitions.

                $config = $factory->create_config_instance();

                foreach ($config->get_stores($definition->get_mode()) as $name => $details) {

                    if (!empty($details['default'])) {

                        $stores[] = $factory->create_store_from_config($name, $details, $definition);

                        break;

                    }

                }

            }

        }

        return $stores;

    }

    /**

     * Returns an array of warnings from the cache API.

     *

     * The warning returned here are for things like conflicting store instance configurations etc.

     * These get shown on the admin notifications page for example.

     *

     * @param array|null $stores An array of stores to get warnings for, or null for all.

     * @return string[]

     */

    public static function warnings(array $stores = null) {

        global $CFG;

        if ($stores === null) {

            require_once($CFG->dirroot.'/cache/locallib.php');

            $stores = core_cache\administration_helper::get_store_instance_summaries();

        }

        $warnings = array();

        foreach ($stores as $store) {

            if (!empty($store['warnings'])) {

                $warnings = array_merge($warnings, $store['warnings']);

            }

        }

        return $warnings;

    }

    /**

     * A helper to determine whether a result was found.

     *

     * This has been deemed required after people have been confused by the fact that [] == false.

     *

     * @param mixed $value

     * @return bool

     */

    public static function result_found($value): bool {

        return $value !== false;

    }

    /**

     * Checks whether the cluster mode is available in PHP.

     *

     * @return bool Return true if the PHP supports redis cluster, otherwise false.

     */

    public static function is_cluster_available(): bool {

        return class_exists('RedisCluster');

    }

}