content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.master.file.meta;
  
  import alluxio.AlluxioURI;
  
  import java.util.List;
  
  /**
   * Cache for block locations in the UFS.
   */
  public interface UfsBlockLocationCache {
    /**
     * @param blockId the block ID
     * @return the cached block locations or null if there is no cached locations for the block
     */
    List<String> get(long blockId);
  
    /**
     * If the locations exist in the cache, return them, otherwise, retrieves the block locations
     * from UFS, and caches the result.
     * If failed to get the locations from UFS, {@code null} is returned and nothing is cached.
     *
     * @param blockId the block ID
     * @param fileUri the URI of the file which contains the block
     * @param offset the block's offset in the file
     * @return the block locations or null if it fails to get the locations from UFS
     */
    List<String> get(long blockId, AlluxioURI fileUri, long offset);
  
    /**
     * Invalidates the UFS locations for the block.
     *
     * @param blockId the block ID
     */
    void invalidate(long blockId);
  
    /**
     * Factory class for {@link UfsBlockLocationCache}.
     */
    final class Factory {
      private Factory() {} // prevent instantiation
  
      /**
       * @param mountTable the mount table
       * @return {@link UfsBlockLocationCache}
       */
      public static UfsBlockLocationCache create(MountTable mountTable) {
        return new LazyUfsBlockLocationCache(mountTable);
      }
    }
  }
  