class BackendChain in Zircon Profile 8

Defines a chained cache implementation for combining multiple cache backends.

Can be used to combine two or more backends together to behave as if they were a single backend.

For example a slower, persistent storage engine could be combined with a faster, volatile storage engine. When retrieving items from cache, they will be fetched from the volatile backend first, only falling back to the persistent backend if an item is not available. An item not present in the volatile backend but found in the persistent one will be propagated back up to ensure fast retrieval on the next request. On cache sets and deletes, both backends will be invoked to ensure consistency.

Hierarchy

• class \Drupal\Core\Cache\BackendChain implements CacheBackendInterface, CacheTagsInvalidatorInterface

See also

\Drupal\Core\Cache\ChainedFastBackend

Related topics

Cache API

Information about the Drupal Cache API

2 files declare their use of BackendChain

BackendChainImplementationUnitTest.php in core/tests/Drupal/Tests/Core/Cache/BackendChainImplementationUnitTest.php

Contains \Drupal\Tests\Core\Cache\BackendChainImplementationUnitTest.

BackendChainUnitTest.php in core/modules/system/src/Tests/Cache/BackendChainUnitTest.php

Contains \Drupal\system\Tests\Cache\BackendChainUnitTest.

File

core/lib/Drupal/Core/Cache/BackendChain.php, line 28

Contains \Drupal\Core\Cache\BackendChain.

Namespace

Drupal\Core\Cache

class BackendChain implements CacheBackendInterface, CacheTagsInvalidatorInterface {

  /**
   * Ordered list of CacheBackendInterface instances.
   *
   * @var array
   */
  protected $backends = array();

  /**
   * Constructs a DatabaseBackend object.
   *
   * @param string $bin
   *   The cache bin for which the object is created.
   */
  public function __construct($bin) {
  }

  /**
   * Appends a cache backend to the cache chain.
   *
   * @param CacheBackendInterface $backend
   *   The cache backend to be appended to the cache chain.
   *
   * @return \Drupal\Core\Cache\BackendChain
   *   The called object.
   */
  public function appendBackend(CacheBackendInterface $backend) {
    $this->backends[] = $backend;
    return $this;
  }

  /**
   * Prepends a cache backend to the cache chain.
   *
   * @param CacheBackendInterface $backend
   *   The backend to be prepended to the cache chain.
   *
   * @return \Drupal\Core\Cache\BackendChain
   *   The called object.
   */
  public function prependBackend(CacheBackendInterface $backend) {
    array_unshift($this->backends, $backend);
    return $this;
  }

  /**
   * {@inheritdoc}
   */
  public function get($cid, $allow_invalid = FALSE) {
    foreach ($this->backends as $index => $backend) {
      if (($return = $backend
        ->get($cid, $allow_invalid)) !== FALSE) {

        // We found a result, propagate it to all missed backends.
        if ($index > 0) {
          for ($i = $index - 1; 0 <= $i; --$i) {
            $this->backends[$i]
              ->set($cid, $return->data, $return->expire, $return->tags);
          }
        }
        return $return;
      }
    }
    return FALSE;
  }

  /**
   * {@inheritdoc}
   */
  public function getMultiple(&$cids, $allow_invalid = FALSE) {
    $return = array();
    foreach ($this->backends as $index => $backend) {
      $items = $backend
        ->getMultiple($cids, $allow_invalid);

      // Propagate the values that could be retrieved from the current cache
      // backend to all missed backends.
      if ($index > 0 && !empty($items)) {
        for ($i = $index - 1; 0 <= $i; --$i) {
          foreach ($items as $cached) {
            $this->backends[$i]
              ->set($cached->cid, $cached->data, $cached->expire, $cached->tags);
          }
        }
      }

      // Append the values to the previously retrieved ones.
      $return += $items;
      if (empty($cids)) {

        // No need to go further if we don't have any cid to fetch left.
        break;
      }
    }
    return $return;
  }

  /**
   * {@inheritdoc}
   */
  public function set($cid, $data, $expire = Cache::PERMANENT, array $tags = array()) {
    foreach ($this->backends as $backend) {
      $backend
        ->set($cid, $data, $expire, $tags);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function setMultiple(array $items) {
    foreach ($this->backends as $backend) {
      $backend
        ->setMultiple($items);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function delete($cid) {
    foreach ($this->backends as $backend) {
      $backend
        ->delete($cid);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function deleteMultiple(array $cids) {
    foreach ($this->backends as $backend) {
      $backend
        ->deleteMultiple($cids);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function deleteAll() {
    foreach ($this->backends as $backend) {
      $backend
        ->deleteAll();
    }
  }

  /**
   * {@inheritdoc}
   */
  public function invalidate($cid) {
    foreach ($this->backends as $backend) {
      $backend
        ->invalidate($cid);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function invalidateMultiple(array $cids) {
    foreach ($this->backends as $backend) {
      $backend
        ->invalidateMultiple($cids);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function invalidateTags(array $tags) {
    foreach ($this->backends as $backend) {
      if ($backend instanceof CacheTagsInvalidatorInterface) {
        $backend
          ->invalidateTags($tags);
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public function invalidateAll() {
    foreach ($this->backends as $backend) {
      $backend
        ->invalidateAll();
    }
  }

  /**
   * {@inheritdoc}
   */
  public function garbageCollection() {
    foreach ($this->backends as $backend) {
      $backend
        ->garbageCollection();
    }
  }

  /**
   * {@inheritdoc}
   */
  public function removeBin() {
    foreach ($this->backends as $backend) {
      $backend
        ->removeBin();
    }
  }

}

Members

Name	Modifiers	Type	Description	Overrides
BackendChain::$backends	protected	property	Ordered list of CacheBackendInterface instances.
BackendChain::appendBackend	public	function	Appends a cache backend to the cache chain.
BackendChain::delete	public	function	Deletes an item from the cache. Overrides CacheBackendInterface::delete
BackendChain::deleteAll	public	function	Deletes all cache items in a bin. Overrides CacheBackendInterface::deleteAll
BackendChain::deleteMultiple	public	function	Deletes multiple items from the cache. Overrides CacheBackendInterface::deleteMultiple
BackendChain::garbageCollection	public	function	Performs garbage collection on a cache bin. Overrides CacheBackendInterface::garbageCollection
BackendChain::get	public	function	Returns data from the persistent cache. Overrides CacheBackendInterface::get
BackendChain::getMultiple	public	function	Returns data from the persistent cache when given an array of cache IDs. Overrides CacheBackendInterface::getMultiple
BackendChain::invalidate	public	function	Marks a cache item as invalid. Overrides CacheBackendInterface::invalidate
BackendChain::invalidateAll	public	function	Marks all cache items as invalid. Overrides CacheBackendInterface::invalidateAll
BackendChain::invalidateMultiple	public	function	Marks cache items as invalid. Overrides CacheBackendInterface::invalidateMultiple
BackendChain::invalidateTags	public	function	Marks cache items with any of the specified tags as invalid. Overrides CacheTagsInvalidatorInterface::invalidateTags
BackendChain::prependBackend	public	function	Prepends a cache backend to the cache chain.
BackendChain::removeBin	public	function	Remove a cache bin. Overrides CacheBackendInterface::removeBin
BackendChain::set	public	function	Stores data in the persistent cache. Overrides CacheBackendInterface::set
BackendChain::setMultiple	public	function	Store multiple items in the persistent cache. Overrides CacheBackendInterface::setMultiple
BackendChain::__construct	public	function	Constructs a DatabaseBackend object.
CacheBackendInterface::CACHE_PERMANENT		constant	Indicates that the item should never be removed unless explicitly deleted.