class CachedStorage

class CachedStorage implements StorageInterface {

  /**
   * The configuration storage to be cached.
   *
   * @var Drupal\Core\Config\StorageInterface
   */
  protected $storage;

  /**
   * The instantiated Cache backend.
   *
   * @var Drupal\Core\Cache\CacheBackendInterface
   */
  protected $cache;

  /**
   * Constructs a new CachedStorage controller.
   *
   * @param Drupal\Core\Config\StorageInterface $storage
   *   A configuration storage controller to be cached.
   * @param Drupal\Core\Cache\CacheBackendInterface $cache
   *   A cache backend instance to use for caching.
   */
  public function __construct(StorageInterface $storage, CacheBackendInterface $cache) {
    $this->storage = $storage;
    $this->cache = $cache;
  }

  /**
   * Implements Drupal\Core\Config\StorageInterface::exists().
   */
  public function exists($name) {

    // The cache would read in the entire data (instead of only checking whether
    // any data exists), and on a potential cache miss, an additional storage
    // lookup would have to happen, so check the storage directly.
    return $this->storage
      ->exists($name);
  }

  /**
   * Implements Drupal\Core\Config\StorageInterface::read().
   */
  public function read($name) {
    if ($cache = $this->cache
      ->get($name)) {

      // The cache backend supports primitive data types, but only an array
      // represents valid config object data.
      if (is_array($cache->data)) {
        return $cache->data;
      }
    }

    // Read from the storage on a cache miss and cache the data, if any.
    $data = $this->storage
      ->read($name);
    if ($data !== FALSE) {
      $this->cache
        ->set($name, $data, CacheBackendInterface::CACHE_PERMANENT);
    }
    elseif ($cache) {
      $this->cache
        ->delete($name);
    }
    return $data;
  }

  /**
   * Implements Drupal\Core\Config\StorageInterface::write().
   */
  public function write($name, array $data) {
    if ($this->storage
      ->write($name, $data)) {

      // While not all written data is read back, setting the cache instead of
      // just deleting it avoids cache rebuild stampedes.
      $this->cache
        ->set($name, $data, CacheBackendInterface::CACHE_PERMANENT);
      return TRUE;
    }
    return FALSE;
  }

  /**
   * Implements Drupal\Core\Config\StorageInterface::delete().
   */
  public function delete($name) {

    // If the cache was the first to be deleted, another process might start
    // rebuilding the cache before the storage is gone.
    if ($this->storage
      ->delete($name)) {
      $this->cache
        ->delete($name);
      return TRUE;
    }
    return FALSE;
  }

  /**
   * Implements Drupal\Core\Config\StorageInterface::rename().
   */
  public function rename($name, $new_name) {

    // If the cache was the first to be deleted, another process might start
    // rebuilding the cache before the storage is renamed.
    if ($this->storage
      ->rename($name, $new_name)) {
      $this->cache
        ->delete($name);
      $this->cache
        ->delete($new_name);
      return TRUE;
    }
    return FALSE;
  }

  /**
   * Implements Drupal\Core\Config\StorageInterface::encode().
   */
  public function encode($data) {
    return $this->storage
      ->encode($data);
  }

  /**
   * Implements Drupal\Core\Config\StorageInterface::decode().
   */
  public function decode($raw) {
    return $this->storage
      ->decode($raw);
  }

  /**
   * Implements Drupal\Core\Config\StorageInterface::listAll().
   *
   * Not supported by CacheBackendInterface.
   */
  public function listAll($prefix = '') {
    return $this->storage
      ->listAll($prefix);
  }

}