class BackendChain in Drupal 10

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 \Drupal\Core\Cache\CacheBackendInterface, \Drupal\Core\Cache\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

BackendChainTest.php in core/tests/Drupal/KernelTests/Core/Cache/BackendChainTest.php

2 string references to 'BackendChain'

book.services.yml in core/modules/book/book.services.yml

core/modules/book/book.services.yml

jsonapi.services.yml in core/modules/jsonapi/jsonapi.services.yml

core/modules/jsonapi/jsonapi.services.yml

2 services use BackendChain

book.backend_chained_cache in core/modules/book/book.services.yml

Drupal\Core\Cache\BackendChain

cache.jsonapi_resource_types in core/modules/jsonapi/jsonapi.services.yml

Drupal\Core\Cache\BackendChain

File

core/lib/Drupal/Core/Cache/BackendChain.php, line 23

Namespace

Drupal\Core\Cache

class BackendChain implements CacheBackendInterface, CacheTagsInvalidatorInterface {

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

  /**
   * Appends a cache backend to the cache chain.
   *
   * @param CacheBackendInterface $backend
   *   The cache backend to be appended to the cache chain.
   *
   * @return $this
   *   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 $this
   *   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) {
    $return = [];
    foreach ($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 $tags = []) {
    foreach ($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();
    }
  }

}