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.journal.checkpoint;
  
  import alluxio.exception.runtime.AlluxioRuntimeException;
  import alluxio.grpc.ErrorType;
  
  import io.grpc.Status;
  import org.apache.ratis.io.MD5Hash;
  import org.apache.ratis.util.MD5FileUtil;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.File;
  import java.io.IOException;
  import java.io.OutputStream;
  import java.security.MessageDigest;
  import java.util.concurrent.CompletableFuture;
  import java.util.concurrent.ExecutorService;
  
  /**
   * Base class for Alluxio classes which can be written to and read from metadata checkpoints.
   */
  public interface Checkpointed {
    Logger LOG = LoggerFactory.getLogger(Checkpointed.class);
    /**
     * @return a name for this checkpointed class
     */
    CheckpointName getCheckpointName();
  
    /**
     * Writes a checkpoint to the specified directory asynchronously using the provided executor.
     *
     * @param directory       where the checkpoint will be written
     * @param executorService to use when running tasks asynchronously
     * @return a future that processes the computation
     */
    default CompletableFuture<Void> writeToCheckpoint(File directory,
                                                      ExecutorService executorService) {
      return CompletableFuture.runAsync(() -> {
        LOG.debug("taking {} snapshot started", getCheckpointName());
        File file = new File(directory, getCheckpointName().toString());
        try {
          MessageDigest md5 = MD5Hash.getDigester();
          try (OutputStream outputStream = new OptimizedCheckpointOutputStream(file, md5)) {
            writeToCheckpoint(outputStream);
          }
          MD5FileUtil.saveMD5File(file, new MD5Hash(md5.digest()));
        } catch (Exception e) {
          throw new AlluxioRuntimeException(Status.INTERNAL,
              String.format("Failed to take snapshot %s", getCheckpointName()),
              e, ErrorType.Internal, false);
        }
        LOG.debug("taking {} snapshot finished", getCheckpointName());
      }, executorService);
    }
  
    /**
     * Writes a checkpoint of all state to the given output stream.
     *
     * Implementations should make an effort to throw {@link InterruptedException} if they get
     * interrupted while running.
     *
     * @param output the output stream to write to
     */
    void writeToCheckpoint(OutputStream output) throws IOException, InterruptedException;
  
    /**
     * Restores state from a checkpoint asynchronously.
     * @param directory where the checkpoint will be located
     * @param executorService to use when running asynchronous tasks
     * @return a future to track the progress
     */
    default CompletableFuture<Void> restoreFromCheckpoint(File directory,
                                                          ExecutorService executorService) {
      return CompletableFuture.runAsync(() -> {
        LOG.debug("loading {} snapshot started", getCheckpointName());
        File file = new File(directory, getCheckpointName().toString());
        try {
          MessageDigest md5 = MD5Hash.getDigester();
          try (CheckpointInputStream is = new OptimizedCheckpointInputStream(file, md5)) {
            restoreFromCheckpoint(is);
          }
          MD5FileUtil.verifySavedMD5(file, new MD5Hash(md5.digest()));
        } catch (Exception e) {
          throw new AlluxioRuntimeException(Status.INTERNAL,
              String.format("Failed to restore snapshot %s", getCheckpointName()),
              e, ErrorType.Internal, false);
        }
        LOG.debug("loading {} snapshot finished", getCheckpointName());
      }, executorService);
    }
  
    /**
     * Restores state from a checkpoint.
     *
     * @param input an input stream with checkpoint data
     */
    void restoreFromCheckpoint(CheckpointInputStream input) throws IOException;
  }
  