interface CacheBackendInterface

interface CacheBackendInterface {
    
    /**
     * Indicates that the item should never be removed unless explicitly deleted.
     */
    const CACHE_PERMANENT = -1;
    
    /**
     * Returns data from the persistent cache.
     *
     * @param string $cid
     *   The cache ID of the data to retrieve.
     * @param bool $allow_invalid
     *   (optional) If TRUE, a cache item may be returned even if it is expired or
     *   has been invalidated. Such items may sometimes be preferred, if the
     *   alternative is recalculating the value stored in the cache, especially
     *   if another concurrent request is already recalculating the same value.
     *   The "valid" property of the returned object indicates whether the item is
     *   valid or not. Defaults to FALSE.
     *
     * @return object|false
     *   The cache item or FALSE on failure.
     *
     * @see \Drupal\Core\Cache\CacheBackendInterface::getMultiple()
     */
    public function get($cid, $allow_invalid = FALSE);
    
    /**
     * Returns data from the persistent cache when given an array of cache IDs.
     *
     * @param array $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 bool $allow_invalid
     *   (optional) If TRUE, cache items may be returned even if they have expired
     *   or been invalidated. Such items may sometimes be preferred, if the
     *   alternative is recalculating the value stored in the cache, especially
     *   if another concurrent thread is already recalculating the same value. The
     *   "valid" property of the returned objects indicates whether the items are
     *   valid or not. Defaults to FALSE.
     *
     * @return array
     *   An array of cache item objects indexed by cache ID.
     *
     * @see \Drupal\Core\Cache\CacheBackendInterface::get()
     */
    public function getMultiple(&$cids, $allow_invalid = FALSE);
    
    /**
     * Stores data in the persistent cache.
     *
     * Core cache implementations set the created time on cache item with
     * microtime(TRUE) rather than REQUEST_TIME_FLOAT, because the created time
     * of cache items should match when they are created, not when the request
     * started. Apart from being more accurate, this increases the chance an
     * item will legitimately be considered valid.
     *
     * @param string $cid
     *   The cache ID of the data to store.
     * @param mixed $data
     *   The data to store in the cache.
     *   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 int $expire
     *   One of the following values:
     *   - CacheBackendInterface::CACHE_PERMANENT: Indicates that the item should
     *     not be removed unless it is deleted explicitly.
     *   - A Unix timestamp: Indicates that the item will be considered invalid
     *     after this time, i.e. it will not be returned by get() unless
     *     $allow_invalid has been set to TRUE. When the item has expired, it may
     *     be permanently deleted by the garbage collector at any time.
     * @param array $tags
     *   An array of tags to be stored with the cache item. These should normally
     *   identify objects used to build the cache item, which should trigger
     *   cache invalidation when updated. For example if a cached item represents
     *   a node, both the node ID and the author's user ID might be passed in as
     *   tags. For example ['node:123', 'node:456', 'user:789'].
     *
     * @see \Drupal\Core\Cache\CacheBackendInterface::get()
     * @see \Drupal\Core\Cache\CacheBackendInterface::getMultiple()
     */
    public function set($cid, $data, $expire = Cache::PERMANENT, array $tags = []);
    
    /**
     * Store multiple items in the persistent cache.
     *
     * @param array $items
     *   An array of cache items, keyed by cid. In the form:
     *   @code
     *   $items = array(
     *     $cid => array(
     *       // Required, will be automatically serialized if not a string.
     *       'data' => $data,
     *       // Optional, defaults to CacheBackendInterface::CACHE_PERMANENT.
     *       'expire' => CacheBackendInterface::CACHE_PERMANENT,
     *       // (optional) The cache tags for this item, see CacheBackendInterface::set().
     *       'tags' => array(),
     *     ),
     *   );
     *   @endcode
     */
    public function setMultiple(array $items);
    
    /**
     * Deletes an item from the cache.
     *
     * If the cache item is being deleted because it is no longer "fresh", you may
     * consider using invalidate() instead. This allows callers to retrieve the
     * invalid item by calling get() with $allow_invalid set to TRUE. In some cases
     * an invalid item may be acceptable rather than having to rebuild the cache.
     *
     * @param string $cid
     *   The cache ID to delete.
     *
     * @see \Drupal\Core\Cache\CacheBackendInterface::invalidate()
     * @see \Drupal\Core\Cache\CacheBackendInterface::deleteMultiple()
     * @see \Drupal\Core\Cache\CacheBackendInterface::deleteAll()
     */
    public function delete($cid);
    
    /**
     * Deletes multiple items from the cache.
     *
     * If the cache items are being deleted because they are no longer "fresh",
     * you may consider using invalidateMultiple() instead. This allows callers to
     * retrieve the invalid items by calling get() with $allow_invalid set to TRUE.
     * In some cases an invalid item may be acceptable rather than having to
     * rebuild the cache.
     *
     * @param array $cids
     *   An array of cache IDs to delete.
     *
     * @see \Drupal\Core\Cache\CacheBackendInterface::invalidateMultiple()
     * @see \Drupal\Core\Cache\CacheBackendInterface::delete()
     * @see \Drupal\Core\Cache\CacheBackendInterface::deleteAll()
     */
    public function deleteMultiple(array $cids);
    
    /**
     * Deletes all cache items in a bin.
     *
     * @see \Drupal\Core\Cache\CacheBackendInterface::invalidateAll()
     * @see \Drupal\Core\Cache\CacheBackendInterface::delete()
     * @see \Drupal\Core\Cache\CacheBackendInterface::deleteMultiple()
     */
    public function deleteAll();
    
    /**
     * Marks a cache item as invalid.
     *
     * Invalid items may be returned in later calls to get(), if the $allow_invalid
     * argument is TRUE.
     *
     * @param string $cid
     *   The cache ID to invalidate.
     *
     * @see \Drupal\Core\Cache\CacheBackendInterface::delete()
     * @see \Drupal\Core\Cache\CacheBackendInterface::invalidateMultiple()
     * @see \Drupal\Core\Cache\CacheBackendInterface::invalidateAll()
     */
    public function invalidate($cid);
    
    /**
     * Marks cache items as invalid.
     *
     * Invalid items may be returned in later calls to get(), if the $allow_invalid
     * argument is TRUE.
     *
     * @param string[] $cids
     *   An array of cache IDs to invalidate.
     *
     * @see \Drupal\Core\Cache\CacheBackendInterface::deleteMultiple()
     * @see \Drupal\Core\Cache\CacheBackendInterface::invalidate()
     * @see \Drupal\Core\Cache\CacheBackendInterface::invalidateAll()
     */
    public function invalidateMultiple(array $cids);
    
    /**
     * Marks all cache items as invalid.
     *
     * Invalid items may be returned in later calls to get(), if the $allow_invalid
     * argument is TRUE.
     *
     * @see \Drupal\Core\Cache\CacheBackendInterface::deleteAll()
     * @see \Drupal\Core\Cache\CacheBackendInterface::invalidate()
     * @see \Drupal\Core\Cache\CacheBackendInterface::invalidateMultiple()
     */
    public function invalidateAll();
    
    /**
     * Performs garbage collection on a cache bin.
     *
     * The backend may choose to delete expired or invalidated items.
     */
    public function garbageCollection();
    
    /**
     * Remove a cache bin.
     */
    public function removeBin();

}