content: package org.apache.lucene.util;
  
  import java.io.IOException;
  import java.util.Map;
  
  /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  /**
   * An interface for implementations that support 2-phase commit. You can use
   * {@link TwoPhaseCommitTool} to execute a 2-phase commit algorithm over several
   * {@link TwoPhaseCommit}s.
   * 
   * @lucene.experimental
   */
  public interface TwoPhaseCommit {
  
    /**
     * The first stage of a 2-phase commit. Implementations should do as much work
     * as possible in this method, but avoid actual committing changes. If the
     * 2-phase commit fails, {@link #rollback()} is called to discard all changes
     * since last successful commit.
     */
    public void prepareCommit() throws IOException;
  
    /**
     * Like {@link #commit()}, but takes an additional commit data to be included
     * w/ the commit.
     * <p>
     * <b>NOTE:</b> some implementations may not support any custom data to be
     * included w/ the commit and may discard it altogether. Consult the actual
     * implementation documentation for verifying if this is supported.
     * 
     * @see #prepareCommit()
     */
    public void prepareCommit(Map<String, String> commitData) throws IOException;
  
    /**
     * The second phase of a 2-phase commit. Implementations should ideally do
     * very little work in this method (following {@link #prepareCommit()}, and
     * after it returns, the caller can assume that the changes were successfully
     * committed to the underlying storage.
     */
    public void commit() throws IOException;
  
    /**
     * Like {@link #commit()}, but takes an additional commit data to be included
     * w/ the commit.
     * 
     * @see #commit()
     * @see #prepareCommit(Map)
     */
    public void commit(Map<String, String> commitData) throws IOException;
  
    /**
     * Discards any changes that have occurred since the last commit. In a 2-phase
     * commit algorithm, where one of the objects failed to {@link #commit()} or
     * {@link #prepareCommit()}, this method is used to roll all other objects
     * back to their previous state.
     */
    public void rollback() throws IOException;
  
  }
  