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.journalv0;
  
  import java.io.IOException;
  import javax.annotation.concurrent.NotThreadSafe;
  
  /**
   * This class manages reading from the journal. The reading must occur in two phases:
   *
   * 1. First, the checkpoint must be read.
   *
   * 2. Afterwards, logs are read in order they were created. Only completed logs are read, so the
   * last log currently being written is not read until it is marked as complete.
   */
  @NotThreadSafe
  public interface JournalReader {
  
    /**
     * Checks to see if the journal checkpoint has not been updated. If it has been updated since the
     * creation of this reader, this reader is no longer valid.
     *
     * @return true if the checkpoint has not been updated
     */
    boolean isValid();
  
    /**
     * Gets the {@link JournalInputStream} for the journal checkpoint. This must be called before
     * calling {@link #getNextInputStream()}.
     *
     * @return the {@link JournalInputStream} for the journal checkpoint
     */
    JournalInputStream getCheckpointInputStream() throws IOException;
  
    /**
     * @return the input stream for the next completed log. Will return null if the next
     *         completed log does not exist yet.
     */
    JournalInputStream getNextInputStream() throws IOException;
  
    /**
     * @return the last modified time of the checkpoint in ms
     */
    long getCheckpointLastModifiedTimeMs() throws IOException;
  }
  