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   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  namespace core_cache;
  18  
  19  /**
  20   * Create and keep an instance of this class to allow temporary caches when caches are disabled.
  21   *
  22   * This class works together with code in {@see cache_factory_disabled}.
  23   *
  24   * The intention is that temporary cache should be short-lived (not for the entire install process),
  25   * which avoids two problems: first, that we might run out of memory for the caches, and second,
  26   * that some code e.g. install.php/upgrade.php files, is entitled to assume that caching is not
  27   * used and make direct database changes.
  28   *
  29   * @package core_cache
  30   * @copyright 2022 The Open University
  31   * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  32   */
  33  class allow_temporary_caches {
  34      /** @var int Number of references of this class; if more than 0, temporary caches are allowed */
  35      protected static $references = 0;
  36  
  37      /**
  38       * Constructs an instance of this class.
  39       *
  40       * Temporary caches will be allowed until this instance goes out of scope. Store this token
  41       * in a local variable, so that the caches have a limited life; do not save it outside your
  42       * function.
  43       *
  44       * If cache is not disabled then normal (non-temporary) caches will be used, and this class
  45       * does nothing.
  46       *
  47       * If an object of this class already exists then creating (or destroying) another one will
  48       * have no effect.
  49       */
  50      public function __construct() {
  51          self::$references++;
  52      }
  53  
  54      /**
  55       * Destroys an instance of this class.
  56       *
  57       * You do not need to call this manually; PHP will call it automatically when your variable
  58       * goes out of scope. If you do need to remove your token at other times, use unset($token);
  59       *
  60       * If there are no other instances of this object, then all temporary caches will be discarded.
  61       */
  62      public function __destruct() {
  63          global $CFG;
  64          require_once($CFG->dirroot . '/cache/disabledlib.php');
  65  
  66          self::$references--;
  67          if (self::$references === 0) {
  68              \cache_factory_disabled::clear_temporary_caches();
  69          }
  70      }
  71  
  72      /**
  73       * Checks if temp caches are currently allowed.
  74       *
  75       * @return bool True if allowed
  76       */
  77      public static function is_allowed(): bool {
  78          return self::$references > 0;
  79      }
  80  }