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Drupal example source code file (cache.inc)

This example Drupal source code file (cache.inc) is included in the DevDaily.com "Drupal Source Code Warehouse" project. The intent of this project is to help you "Learn Drupal by Example".

PHP - Drupal tags/keywords

array, bin, cache, cache_flush, cid, cids, data, execute, expire, function, if, php, request_time, return

The cache.inc Drupal example source code

<?php
// $Id: cache.inc,v 1.51 2010/12/01 00:26:03 webchick Exp $

/**
 * Get the cache object for a cache bin.
 *
 * By default, this returns an instance of the DrupalDatabaseCache class.
 * Classes implementing DrupalCacheInterface can register themselves both as a
 * default implementation and for specific bins.
 *
 * @see DrupalCacheInterface
 *
 * @param $bin
 *   The cache bin for which the cache object should be returned.
 * @return DrupalCacheInterface
 *   The cache object associated with the specified bin.
 */
function _cache_get_object($bin) {
  // We do not use drupal_static() here because we do not want to change the
  // storage of a cache bin mid-request.
  static $cache_objects;
  if (!isset($cache_objects[$bin])) {
    $class = variable_get('cache_class_' . $bin);
    if (!isset($class)) {
      $class = variable_get('cache_default_class', 'DrupalDatabaseCache');
    }
    $cache_objects[$bin] = new $class($bin);
  }
  return $cache_objects[$bin];
}

/**
 * Return data from the persistent cache
 *
 * Data may be stored as either plain text or as serialized data. cache_get
 * will automatically return unserialized objects and arrays.
 *
 * @param $cid
 *   The cache ID of the data to retrieve.
 * @param $bin
 *   The cache bin to store the data in. Valid core values are 'cache_block',
 *   'cache_bootstrap', 'cache_field', 'cache_filter', 'cache_form',
 *   'cache_menu', 'cache_page', 'cache_path', 'cache_update' or 'cache' for
 *   the default cache.
 *
 * @return
 *   The cache or FALSE on failure.
 */
function cache_get($cid, $bin = 'cache') {
  return _cache_get_object($bin)->get($cid);
}

/**
 * Return data from the persistent cache when given an array of cache IDs.
 *
 * @param $cids
 *   An array of cache IDs for the data to retrieve. This is passed by
 *   reference, and will have the IDs successfully returned from cache removed.
 * @param $bin
 *   The cache bin where the data is stored.
 * @return
 *   An array of the items successfully returned from cache indexed by cid.
 */
function cache_get_multiple(array &$cids, $bin = 'cache') {
  return _cache_get_object($bin)->getMultiple($cids);
}

/**
 * Store data in the persistent cache.
 *
 * The persistent cache is split up into several cache bins. In the default
 * cache implementation, each cache bin corresponds to a database table by the
 * same name. Other implementations might want to store several bins in data
 * structures that get flushed together. While it is not a problem for most
 * cache bins if the entries in them are flushed before their expire time, some
 * might break functionality or are extremely expensive to recalculate. These
 * will be marked with a (*). The other bins expired automatically by core.
 * Contributed modules can add additional bins and get them expired
 * automatically by implementing hook_flush_caches().
 *
 *  - cache: Generic cache storage bin (used for variables, theme registry,
 *  locale date, list of simpletest tests etc).
 *
 *  - cache_block: Stores the content of various blocks.
 *
 *  - cache field: Stores the field data belonging to a given object.
 *
 *  - cache_filter: Stores filtered pieces of content.
 *
 *  - cache_form(*): Stores multistep forms. Flushing this bin means that some
 *  forms displayed to users lose their state and the data already submitted
 *  to them.
 *
 *  - cache_menu: Stores the structure of visible navigation menus per page.
 *
 *  - cache_page: Stores generated pages for anonymous users. It is flushed
 *  very often, whenever a page changes, at least for every ode and comment
 *  submission. This is the only bin affected by the page cache setting on
 *  the administrator panel.
 *
 *  - cache path: Stores the system paths that have an alias.
 *
 *  - cache update(*): Stores available releases. The update server (for
 *  example, drupal.org) needs to produce the relevant XML for every project
 *  installed on the current site. As this is different for (almost) every
 *  site, it's very expensive to recalculate for the update server.
 *
 * The reasons for having several bins are as follows:
 *
 * - smaller bins mean smaller database tables and allow for faster selects and
 *   inserts
 * - we try to put fast changing cache items and rather static ones into
 *   different bins. The effect is that only the fast changing bins will need a
 *   lot of writes to disk. The more static bins will also be better cacheable
 *   with MySQL's query cache.
 *
 * @param $cid
 *   The cache ID of the data to store.
 * @param $data
 *   The data to store in the cache. Complex data types will be automatically
 *   serialized before insertion.
 *   Strings will be stored as plain text and not serialized.
 * @param $bin
 *   The cache bin to store the data in. Valid core values are 'cache_block',
 *   'cache_bootstrap', 'cache_field', 'cache_filter', 'cache_form',
 *   'cache_menu', 'cache_page', 'cache_update' or 'cache' for the default
 *   cache.
 * @param $expire
 *   One of the following values:
 *   - CACHE_PERMANENT: Indicates that the item should never be removed unless
 *     explicitly told to using cache_clear_all() with a cache ID.
 *   - CACHE_TEMPORARY: Indicates that the item should be removed at the next
 *     general cache wipe.
 *   - A Unix timestamp: Indicates that the item should be kept at least until
 *     the given time, after which it behaves like CACHE_TEMPORARY.
 */
function cache_set($cid, $data, $bin = 'cache', $expire = CACHE_PERMANENT) {
  return _cache_get_object($bin)->set($cid, $data, $expire);
}

/**
 * Expire data from the cache.
 *
 * If called without arguments, expirable entries will be cleared from the
 * cache_page and cache_block bins.
 *
 * @param $cid
 *   If set, the cache ID to delete. Otherwise, all cache entries that can
 *   expire are deleted.
 *
 * @param $bin
 *   If set, the bin $bin to delete from. Mandatory
 *   argument if $cid is set.
 *
 * @param $wildcard
 *   If $wildcard is TRUE, cache IDs starting with $cid are deleted in
 *   addition to the exact cache ID specified by $cid.  If $wildcard is
 *   TRUE and $cid is '*' then the entire bin $bin is emptied.
 */
function cache_clear_all($cid = NULL, $bin = NULL, $wildcard = FALSE) {
  if (!isset($cid) && !isset($bin)) {
    // Clear the block cache first, so stale data will
    // not end up in the page cache.
    if (module_exists('block')) {
      cache_clear_all(NULL, 'cache_block');
    }
    cache_clear_all(NULL, 'cache_page');
    return;
  }
  return _cache_get_object($bin)->clear($cid, $wildcard);
}

/**
 * Check if a cache bin is empty.
 *
 * A cache bin is considered empty if it does not contain any valid data for any
 * cache ID.
 *
 * @param $bin
 *   The cache bin to check.
 * @return
 *   TRUE if the cache bin specified is empty.
 */
function cache_is_empty($bin) {
  return _cache_get_object($bin)->isEmpty();
}

/**
 * Interface for cache implementations.
 *
 * All cache implementations have to implement this interface.
 * DrupalDatabaseCache provides the default implementation, which can be
 * consulted as an example.
 *
 * To make Drupal use your implementation for a certain cache bin, you have to
 * set a variable with the name of the cache bin as its key and the name of
 * your class as its value. For example, if your implementation of
 * DrupalCacheInterface was called MyCustomCache, the following line would make
 * Drupal use it for the 'cache_page' bin:
 * @code
 *  variable_set('cache_class_cache_page', 'MyCustomCache');
 * @endcode
 *
 * Additionally, you can register your cache implementation to be used by
 * default for all cache bins by setting the variable 'cache_default_class' to
 * the name of your implementation of the DrupalCacheInterface, e.g.
 * @code
 *  variable_set('cache_default_class', 'MyCustomCache');
 * @endcode
 *
 * To implement a completely custom cache bin, use the same variable format:
 * @code
 *  variable_set('cache_class_custom_bin', 'MyCustomCache');
 * @endcode
 * To access your custom cache bin, specify the name of the bin when storing
 * or retrieving cached data:
 * @code
 *  cache_set($cid, $data, 'custom_bin', $expire);
 *  cache_get($cid, 'custom_bin');
 * @endcode
 *
 * @see _cache_get_object()
 * @see DrupalDatabaseCache
 */
interface DrupalCacheInterface {
  /**
   * Constructor.
   *
   * @param $bin
   *   The cache bin for which the object is created.
   */
  function __construct($bin);

  /**
   * Return data from the persistent cache. Data may be stored as either plain
   * text or as serialized data. cache_get will automatically return
   * unserialized objects and arrays.
   *
   * @param $cid
   *   The cache ID of the data to retrieve.
   * @return
   *   The cache or FALSE on failure.
   */
  function get($cid);

  /**
   * Return data from the persistent cache when given an array of cache IDs.
   *
   * @param $cids
   *   An array of cache IDs for the data to retrieve. This is passed by
   *   reference, and will have the IDs successfully returned from cache
   *   removed.
   * @return
   *   An array of the items successfully returned from cache indexed by cid.
   */
   function getMultiple(&$cids);

  /**
   * Store data in the persistent cache.
   *
   * @param $cid
   *   The cache ID of the data to store.
   * @param $data
   *   The data to store in the cache. Complex data types will be automatically
   *   serialized before insertion.
   *   Strings will be stored as plain text and not serialized.
   * @param $expire
   *   One of the following values:
   *   - CACHE_PERMANENT: Indicates that the item should never be removed unless
   *     explicitly told to using cache_clear_all() with a cache ID.
   *   - CACHE_TEMPORARY: Indicates that the item should be removed at the next
   *     general cache wipe.
   *   - A Unix timestamp: Indicates that the item should be kept at least until
   *     the given time, after which it behaves like CACHE_TEMPORARY.
   */
  function set($cid, $data, $expire = CACHE_PERMANENT);


  /**
   * Expire data from the cache. If called without arguments, expirable
   * entries will be cleared from the cache_page and cache_block bins.
   *
   * @param $cid
   *   If set, the cache ID to delete. Otherwise, all cache entries that can
   *   expire are deleted.
   * @param $wildcard
   *   If set to TRUE, the $cid is treated as a substring
   *   to match rather than a complete ID. The match is a right hand
   *   match. If '*' is given as $cid, the bin $bin will be emptied.
   */
  function clear($cid = NULL, $wildcard = FALSE);

  /**
   * Check if a cache bin is empty.
   *
   * A cache bin is considered empty if it does not contain any valid data for
   * any cache ID.
   *
   * @return
   *   TRUE if the cache bin specified is empty.
   */
  function isEmpty();
}

/**
 * Default cache implementation.
 *
 * This is Drupal's default cache implementation. It uses the database to store
 * cached data. Each cache bin corresponds to a database table by the same name.
 */
class DrupalDatabaseCache implements DrupalCacheInterface {
  protected $bin;

  function __construct($bin) {
    $this->bin = $bin;
  }

  function get($cid) {
    $cids = array($cid);
    $cache = $this->getMultiple($cids);
    return reset($cache);
  }

  function getMultiple(&$cids) {
    try {
      // Garbage collection necessary when enforcing a minimum cache lifetime.
      $this->garbageCollection($this->bin);
      $query = db_select($this->bin);
      $query->fields($this->bin, array('cid', 'data', 'created', 'expire', 'serialized'));
      $query->condition($this->bin . '.cid', $cids, 'IN');
      $result = $query->execute();
      $cache = array();
      foreach ($result as $item) {
        $item = $this->prepareItem($item);
        if ($item) {
          $cache[$item->cid] = $item;
        }
      }
      $cids = array_diff($cids, array_keys($cache));
      return $cache;
    }
    catch (Exception $e) {
      // If the database is never going to be available, cache requests should
      // return FALSE in order to allow exception handling to occur.
      return array();
    }
  }

  /**
   * Garbage collection for get() and getMultiple().
   *
   * @param $bin
   *   The bin being requested.
   */
  protected function garbageCollection() {
    global $user;

    // Garbage collection necessary when enforcing a minimum cache lifetime.
    $cache_flush = variable_get('cache_flush_' . $this->bin, 0);
    if ($cache_flush && ($cache_flush + variable_get('cache_lifetime', 0) <= REQUEST_TIME)) {
      // Reset the variable immediately to prevent a meltdown in heavy load situations.
      variable_set('cache_flush_' . $this->bin, 0);
      // Time to flush old cache data
      db_delete($this->bin)
        ->condition('expire', CACHE_PERMANENT, '<>')
        ->condition('expire', $cache_flush, '<=')
        ->execute();
    }
  }

  /**
   * Prepare a cached item.
   *
   * Checks that items are either permanent or did not expire, and unserializes
   * data as appropriate.
   *
   * @param $cache
   *   An item loaded from cache_get() or cache_get_multiple().
   * @return
   *   The item with data unserialized as appropriate or FALSE if there is no
   *   valid item to load.
   */
  protected function prepareItem($cache) {
    global $user;

    if (!isset($cache->data)) {
      return FALSE;
    }
    // If enforcing a minimum cache lifetime, validate that the data is
    // currently valid for this user before we return it by making sure the cache
    // entry was created before the timestamp in the current session's cache
    // timer. The cache variable is loaded into the $user object by _drupal_session_read()
    // in session.inc. If the data is permanent or we're not enforcing a minimum
    // cache lifetime always return the cached data.
    if ($cache->expire != CACHE_PERMANENT && variable_get('cache_lifetime', 0) && $user->cache > $cache->created) {
      // This cache data is too old and thus not valid for us, ignore it.
      return FALSE;
    }

    if ($cache->serialized) {
      $cache->data = unserialize($cache->data);
    }

    return $cache;
  }

  function set($cid, $data, $expire = CACHE_PERMANENT) {
    $fields = array(
      'serialized' => 0,
      'created' => REQUEST_TIME,
      'expire' => $expire,
    );
    if (!is_string($data)) {
      $fields['data'] = serialize($data);
      $fields['serialized'] = 1;
    }
    else {
      $fields['data'] = $data;
      $fields['serialized'] = 0;
    }

    try {
      db_merge($this->bin)
        ->key(array('cid' => $cid))
        ->fields($fields)
        ->execute();
    }
    catch (Exception $e) {
      // The database may not be available, so we'll ignore cache_set requests.
    }
  }

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

    if (empty($cid)) {
      if (variable_get('cache_lifetime', 0)) {
        // We store the time in the current user's $user->cache variable which
        // will be saved into the sessions bin by _drupal_session_write(). We then
        // simulate that the cache was flushed for this user by not returning
        // cached data that was cached before the timestamp.
        $user->cache = REQUEST_TIME;

        $cache_flush = variable_get('cache_flush_' . $this->bin, 0);
        if ($cache_flush == 0) {
          // This is the first request to clear the cache, start a timer.
          variable_set('cache_flush_' . $this->bin, REQUEST_TIME);
        }
        elseif (REQUEST_TIME > ($cache_flush + variable_get('cache_lifetime', 0))) {
          // Clear the cache for everyone, cache_lifetime seconds have
          // passed since the first request to clear the cache.
          db_delete($this->bin)
            ->condition('expire', CACHE_PERMANENT, '<>')
            ->condition('expire', REQUEST_TIME, '<')
            ->execute();
          variable_set('cache_flush_' . $this->bin, 0);
        }
      }
      else {
        // No minimum cache lifetime, flush all temporary cache entries now.
        db_delete($this->bin)
          ->condition('expire', CACHE_PERMANENT, '<>')
          ->condition('expire', REQUEST_TIME, '<')
          ->execute();
      }
    }
    else {
      if ($wildcard) {
        if ($cid == '*') {
          db_truncate($this->bin)->execute();
        }
        else {
          db_delete($this->bin)
            ->condition('cid', db_like($cid) . '%', 'LIKE')
            ->execute();
        }
      }
      elseif (is_array($cid)) {
        // Delete in chunks when a large array is passed.
        do {
          db_delete($this->bin)
            ->condition('cid', array_splice($cid, 0, 1000), 'IN')
            ->execute();
        }
        while (count($cid));
      }
      else {
        db_delete($this->bin)
          ->condition('cid', $cid)
          ->execute();
      }
    }
  }

  function isEmpty() {
    $this->garbageCollection();
    $query = db_select($this->bin);
    $query->addExpression('1');
    $result = $query->range(0, 1)
      ->execute()
      ->fetchField();
    return empty($result);
  }
}

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