wcfsetup/install/files/lib/system/SingletonFactory.class.php

   1 <?php
   2
   3 namespace wcf\system;
   4
   5 use wcf\system\exception\SystemException;
   6
   7 /**
   8  * Base class for singleton factories.
   9  *
  10  * @author  Alexander Ebert
  11  * @copyright   2001-2019 WoltLab GmbH
  12  * @license GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
  13  */
  14 abstract class SingletonFactory
  15 {
  16     /**
  17      * list of singletons
  18      * @var SingletonFactory[]
  19      */
  20     protected static $__singletonObjects = [];
  21
  22     /**
  23      * Singletons do not support a public constructor. Override init() if
  24      * your class needs to initialize components on creation.
  25      */
  26     final protected function __construct()
  27     {
  28         $this->init();
  29     }
  30
  31     /**
  32      * Called within __construct(), override if necessary.
  33      */
  34     protected function init()
  35     {
  36     }
  37
  38     /**
  39      * Object cloning is disallowed.
  40      */
  41     final protected function __clone()
  42     {
  43     }
  44
  45     /**
  46      * Object serializing is disallowed.
  47      */
  48     final public function __sleep()
  49     {
  50         throw new SystemException('Serializing of Singletons is not allowed');
  51     }
  52
  53     /**
  54      * Returns an unique instance of current child class.
  55      *
  56      * @return  static
  57      * @throws  SystemException
  58      */
  59     final public static function getInstance()
  60     {
  61         $className = static::class;
  62         if (!isset(self::$__singletonObjects[$className])) {
  63             // The previously used `null` value forced us into using `array_key_exists()` which has a bad performance,
  64             // especially with the growing list of derived classes that are used today. Saves a few ms on every request.
  65             self::$__singletonObjects[$className] = false;
  66             self::$__singletonObjects[$className] = new $className();
  67         } elseif (self::$__singletonObjects[$className] === false) {
  68             throw new SystemException(
  69                 "Infinite loop detected while trying to retrieve object for '" . $className . "'"
  70             );
  71         }
  72
  73         return self::$__singletonObjects[$className];
  74     }
  75
  76     /**
  77      * Returns whether this singleton is already initialized.
  78      *
  79      * @return  bool
  80      */
  81     final public static function isInitialized()
  82     {
  83         $className = static::class;
  84
  85         return isset(self::$__singletonObjects[$className]);
  86     }
  87 }