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 alluxio.conf.Configuration;
  import alluxio.conf.PropertyKey;
  import alluxio.exception.InvalidPathException;
  import alluxio.resource.CloseableResource;
  import alluxio.underfs.UnderFileSystem;
  import alluxio.underfs.options.FileLocationOptions;
  
  import com.google.common.cache.Cache;
  import com.google.common.cache.CacheBuilder;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.IOException;
  import java.util.List;
  import javax.annotation.Nullable;
  import javax.annotation.concurrent.ThreadSafe;
  
  /**
   * Lazily cache the block locations only when needed.
   */
  @ThreadSafe
  public class LazyUfsBlockLocationCache implements UfsBlockLocationCache {
    private static final Logger LOG = LoggerFactory.getLogger(LazyUfsBlockLocationCache.class);
  
    /** Number of blocks to cache. */
    private static final int MAX_BLOCKS =
        Configuration.getInt(PropertyKey.MASTER_UFS_BLOCK_LOCATION_CACHE_CAPACITY);
  
    /** Cache of ufs block locations, key is block ID, value is block locations. */
    private Cache<Long, List<String>> mCache;
    private MountTable mMountTable;
  
    /**
     * Creates a new instance of {@link UfsBlockLocationCache}.
     *
     * @param mountTable the mount table
     */
    public LazyUfsBlockLocationCache(MountTable mountTable) {
      mCache = CacheBuilder.newBuilder().maximumSize(MAX_BLOCKS).build();
      mMountTable = mountTable;
    }
  
    @Override
    public void invalidate(long blockId) {
      mCache.invalidate(blockId);
    }
  
    @Override
    public List<String> get(long blockId) {
      return mCache.getIfPresent(blockId);
    }
  
    @Override
    @Nullable
    public List<String> get(long blockId, AlluxioURI fileUri, long offset) {
      List<String> locations = mCache.getIfPresent(blockId);
      if (locations != null) {
        return locations;
      }
      try {
        MountTable.Resolution resolution = mMountTable.resolve(fileUri);
        String ufsUri = resolution.getUri().toString();
        try (CloseableResource<UnderFileSystem> ufsResource = resolution.acquireUfsResource()) {
          UnderFileSystem ufs = ufsResource.get();
          locations = ufs.getFileLocations(ufsUri, FileLocationOptions.defaults().setOffset(offset));
        }
        if (locations != null) {
          mCache.put(blockId, locations);
          return locations;
        }
      } catch (InvalidPathException | IOException e) {
        LOG.warn("Failed to get locations for block {} in file {} with offset {}: {}",
            blockId, fileUri, offset, e);
      }
      return null;
    }
  }
  