Club Drupal

<?php

/**

 * @file

 * Functions and interfaces for cache handling.

 */

/**

 * Gets 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.

 *

 * @param $bin

 *   The cache bin for which the cache object should be returned.

 *

 * @return DrupalCacheInterface

 *   The cache object associated with the specified bin.

 *

 * @see DrupalCacheInterface

 */

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];

}

/**

 * Returns 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.

 *

 * @see cache_set()

 */

function cache_get($cid, $bin = 'cache') {

  return _cache_get_object($bin)->get($cid);

}

/**

 * Returns 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);

}

/**

 * Stores 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. The

 * other bins are expired automatically by core. Contributed modules can add

 * additional bins and get them expired automatically by implementing

 * hook_flush_caches().

 *

 * 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 are

 *   not serialized. Some storage engines only allow objects up to a maximum of

 *   1MB in size to be stored by default. When caching large arrays or similar,

 *   take care to ensure $data does not exceed this size.

 * @param $bin

 *   (optional) The cache bin to store the data in. Valid core values are:

 *   - cache: (default) Generic cache storage bin (used for theme registry,

 *     locale date, list of simpletest tests, etc.).

 *   - cache_block: Stores the content of various blocks.

 *   - cache_bootstrap: Stores the class registry, the system list of modules,

 *     the list of which modules implement which hooks, and the Drupal variable

 *     list.

 *   - 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. This bin should not be flushed before its expired time.

 *   - 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 node 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.

 * @param $expire

 *   (optional) Controls the maximum lifetime of this cache entry. Note that

 *   caches might be subject to clearing at any time, so this setting does not

 *   guarantee a minimum lifetime. With this in mind, the cache should not be

 *   used for data that must be kept during a cache clear, like sessions.

 *

 *   Use 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.

 *

 * @see _update_cache_set()

 * @see cache_get()

 */

function cache_set($cid, $data, $bin = 'cache', $expire = CACHE_PERMANENT) {

  return _cache_get_object($bin)->set($cid, $data, $expire);

}

/**

 * Expires data from the cache.

 *

 * If called with the arguments $cid and $bin set to NULL or omitted, then

 * expirable entries will be cleared from the cache_page and cache_block bins,

 * and the $wildcard argument is ignored.

 *

 * @param $cid

 *   If set, the cache ID or an array of cache IDs. Otherwise, all cache entries

 *   that can expire are deleted. The $wildcard argument will be ignored if set

 *   to NULL.

 * @param $bin

 *   If set, the cache bin to delete from. Mandatory argument if $cid is set.

 * @param $wildcard

 *   If TRUE, the $cid argument must contain a string value and cache IDs

 *   starting with $cid are deleted in addition to the exact cache ID specified

 *   by $cid. If $wildcard is TRUE and $cid is '*', the entire cache 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);

}

/**

 * Checks 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();

}

/**

 * Defines an 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 {

  /**

   * Returns 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);

  /**

   * Returns 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);

  /**

   * Stores 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. Some storage engines only allow objects up to a maximum of

   *   1MB in size to be stored by default. When caching large arrays or

   *   similar, take care to ensure $data does not exceed this size.

   * @param $expire

   *   (optional) Controls the maximum lifetime of this cache entry. Note that

   *   caches might be subject to clearing at any time, so this setting does not

   *   guarantee a minimum lifetime. With this in mind, the cache should not be

   *   used for data that must be kept during a cache clear, like sessions.

   *

   *   Use 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);

  /**

   * Expires 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 or an array of cache IDs. Otherwise, all cache

   *   entries that can expire are deleted. The $wildcard argument will be

   *   ignored if set to NULL.

   * @param $wildcard

   *   If TRUE, the $cid argument must contain a string value and cache IDs

   *   starting with $cid are deleted in addition to the exact cache ID

   *   specified by $cid. If $wildcard is TRUE and $cid is '*', the entire

   *   cache is emptied.

   */

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

  /**

   * Checks 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();

}

/**

 * Defines a 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;

  /**

   * Constructs a DrupalDatabaseCache object.

   *

   * @param $bin

   *   The cache bin for which the object is created.

   */

  function __construct($bin) {

    $this->bin = $bin;

  }

  /**

   * Implements DrupalCacheInterface::get().

   */

  function get($cid) {

    $cids = array($cid);

    $cache = $this->getMultiple($cids);

    return reset($cache);

  }

  /**

   * Implements DrupalCacheInterface::getMultiple().

   */

  function getMultiple(&$cids) {

    try {

      // Garbage collection necessary when enforcing a minimum cache lifetime.

      $this->garbageCollection($this->bin);

      // When serving cached pages, the overhead of using db_select() was found

      // to add around 30% overhead to the request. Since $this->bin is a

      // variable, this means the call to db_query() here uses a concatenated

      // string. This is highly discouraged under any other circumstances, and

      // is used here only due to the performance overhead we would incur

      // otherwise. When serving an uncached page, the overhead of using

      // db_select() is a much smaller proportion of the request.

      $result = db_query('SELECT cid, data, created, expire, serialized FROM {' . db_escape_table($this->bin) . '} WHERE cid IN (:cids)', array(':cids' => $cids));

      $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() {

    $cache_lifetime = variable_get('cache_lifetime', 0);

    // Clean-up the per-user cache expiration session data, so that the session

    // handler can properly clean-up the session data for anonymous users.

    if (isset($_SESSION['cache_expiration'])) {

      $expire = REQUEST_TIME - $cache_lifetime;

      foreach ($_SESSION['cache_expiration'] as $bin => $timestamp) {

        if ($timestamp < $expire) {

          unset($_SESSION['cache_expiration'][$bin]);

        }

      }

      if (!$_SESSION['cache_expiration']) {

        unset($_SESSION['cache_expiration']);

      }

    }

    // Garbage collection of temporary items is only necessary when enforcing

    // a minimum cache lifetime.

    if (!$cache_lifetime) {

      return;

    }

    // When cache lifetime is in force, avoid running garbage collection too

    // often since this will remove temporary cache items indiscriminately.

    $cache_flush = variable_get('cache_flush_' . $this->bin, 0);

    if ($cache_flush && ($cache_flush + $cache_lifetime <= 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();

    }

  }

  /**

   * Prepares 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 the cached data is temporary and subject to a per-user minimum

    // lifetime, compare the cache entry timestamp with the user session

    // cache_expiration timestamp. If the cache entry is too old, ignore it.

    if ($cache->expire != CACHE_PERMANENT && variable_get('cache_lifetime', 0) && isset($_SESSION['cache_expiration'][$this->bin]) && $_SESSION['cache_expiration'][$this->bin] > $cache->created) {

      // Ignore cache data that is too old and thus not valid for this user.

      return FALSE;

    }

    // If the data is permanent or not subject to a minimum cache lifetime,

    // unserialize and return the cached data.

    if ($cache->serialized) {

      $cache->data = unserialize($cache->data);

    }

    return $cache;

  }

  /**

   * Implements DrupalCacheInterface::set().

   */

  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.

    }

  }

  /**

   * Implements DrupalCacheInterface::clear().

   */

  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 session. We then simulate

        // that the cache was flushed for this user by not returning cached

        // data that was cached before the timestamp.

        $_SESSION['cache_expiration'][$this->bin] = 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 == '*') {

          // Check if $this->bin is a cache table before truncating. Other

          // cache_clear_all() operations throw a PDO error in this situation,

          // so we don't need to verify them first. This ensures that non-cache

          // tables cannot be truncated accidentally.

          if ($this->isValidBin()) {

            db_truncate($this->bin)->execute();

          }

          else {

            throw new Exception(t('Invalid or missing cache bin specified: %bin', array('%bin' => $this->bin)));

          }

        }

        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();

      }

    }

  }

  /**

   * Implements DrupalCacheInterface::isEmpty().

   */

  function isEmpty() {

    $this->garbageCollection();

    $query = db_select($this->bin);

    $query->addExpression('1');

    $result = $query->range(0, 1)

      ->execute()

      ->fetchField();

    return empty($result);

  }

  /**

   * Checks if $this->bin represents a valid cache table.

   *

   * This check is required to ensure that non-cache tables are not truncated

   * accidentally when calling cache_clear_all().

   *

   * @return boolean

   */

  function isValidBin() {

    if ($this->bin == 'cache' || substr($this->bin, 0, 6) == 'cache_') {

      // Skip schema check for bins with standard table names.

      return TRUE;

    }

    // These fields are required for any cache table.

    $fields = array('cid', 'data', 'expire', 'created', 'serialized');

    // Load the table schema.

    $schema = drupal_get_schema($this->bin);

    // Confirm that all fields are present.

    return isset($schema['fields']) && !array_diff($fields, array_keys($schema['fields']));

  }

}