<?php

/**

 * @file

 * Provides a stub cache implementation to be used during installation.

 */

/**

 * Defines a stub cache implementation to be used during installation.

 *

 * The stub implementation is needed when database access is not yet available.

 * Because Drupal's caching system never requires that cached data be present,

 * these stub functions can short-circuit the process and sidestep the need for

 * any persistent storage. Obviously, using this cache implementation during

 * normal operations would have a negative impact on performance.

 */

class DrupalFakeCache extends DrupalDatabaseCache implements DrupalCacheInterface {

  /**

   * Overrides DrupalDatabaseCache::get().

   */

  function get($cid) {

    return FALSE;

  }

  /**

   * Overrides DrupalDatabaseCache::getMultiple().

   */

  function getMultiple(&$cids) {

    return array();

  }

  /**

   * Overrides DrupalDatabaseCache::set().

   */

  function set($cid, $data, $expire = CACHE_PERMANENT) {

  }

  /**

   * Overrides DrupalDatabaseCache::clear().

   */

  function clear($cid = NULL, $wildcard = FALSE) {

    // If there is a database cache, attempt to clear it whenever possible. The

    // reason for doing this is that the database cache can accumulate data

    // during installation due to any full bootstraps that may occur at the

    // same time (for example, Ajax requests triggered by the installer). If we

    // didn't try to clear it whenever this function is called, the data in the

    // cache would become stale; for example, the installer sometimes calls

    // variable_set(), which updates the {variable} table and then clears the

    // cache to make sure that the next page request picks up the new value.

    // Not actually clearing the cache here therefore leads old variables to be

    // loaded on the first page requests after installation, which can cause

    // subtle bugs, some of which would not be fixed unless the site

    // administrator cleared the cache manually.

    try {

      if (class_exists('Database')) {

        parent::clear($cid, $wildcard);

      }

    }

    // If the attempt at clearing the cache causes an error, that means that

    // either the database connection is not set up yet or the relevant cache

    // table in the database has not yet been created, so we can safely do

    // nothing here.

    catch (Exception $e) {

    }

  }

  /**

   * Overrides DrupalDatabaseCache::isEmpty().

   */

  function isEmpty() {

    return TRUE;

  }

}