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.
   */
  
  /**
   * A utility for executing 2-phase commit on several objects.
   * 
   * @see TwoPhaseCommit
   * @lucene.experimental
   */
  public final class TwoPhaseCommitTool {
  
    /**
     * A wrapper of a {@link TwoPhaseCommit}, which delegates all calls to the
     * wrapped object, passing the specified commitData. This object is useful for
     * use with {@link TwoPhaseCommitTool#execute(TwoPhaseCommit...)} if one would
     * like to store commitData as part of the commit.
     */
    public static final class TwoPhaseCommitWrapper implements TwoPhaseCommit {
  
      private final TwoPhaseCommit tpc;
      private  final Map<String, String> commitData;
  
      public TwoPhaseCommitWrapper(TwoPhaseCommit tpc, Map<String, String> commitData) {
        this.tpc = tpc;
        this.commitData = commitData;
      }
  
      public void prepareCommit() throws IOException {
        prepareCommit(commitData);
      }
  
      public void prepareCommit(Map<String, String> commitData) throws IOException {
        tpc.prepareCommit(this.commitData);
      }
  
      public void commit() throws IOException {
        commit(commitData);
      }
  
      public void commit(Map<String, String> commitData) throws IOException {
        tpc.commit(this.commitData);
      }
  
      public void rollback() throws IOException {
        tpc.rollback();
      }
    }
    
    /**
     * Thrown by {@link TwoPhaseCommitTool#execute(TwoPhaseCommit...)} when an
     * object fails to prepareCommit().
     */
    public static class PrepareCommitFailException extends IOException {
      
      public PrepareCommitFailException(Throwable cause, TwoPhaseCommit obj) {
        super("prepareCommit() failed on " + obj);
        initCause(cause);
      }
      
    }
  
    /**
     * Thrown by {@link TwoPhaseCommitTool#execute(TwoPhaseCommit...)} when an
     * object fails to commit().
     */
    public static class CommitFailException extends IOException {
      
      public CommitFailException(Throwable cause, TwoPhaseCommit obj) {
        super("commit() failed on " + obj);
        initCause(cause);
      }
      
    }
  
    /** rollback all objects, discarding any exceptions that occur. */
    private static void rollback(TwoPhaseCommit... objects) {
      for (TwoPhaseCommit tpc : objects) {
        // ignore any exception that occurs during rollback - we want to ensure
        // all objects are rolled-back.
        if (tpc != null) {
          try {
            tpc.rollback();
          } catch (Throwable t) {}
        }
      }
    }
  
    /**
     * Executes a 2-phase commit algorithm by first
     * {@link TwoPhaseCommit#prepareCommit()} all objects and only if all succeed,
     * it proceeds with {@link TwoPhaseCommit#commit()}. If any of the objects
     * fail on either the preparation or actual commit, it terminates and
     * {@link TwoPhaseCommit#rollback()} all of them.
     * <p>
     * <b>NOTE:</b> it may happen that an object fails to commit, after few have
     * already successfully committed. This tool will still issue a rollback
     * instruction on them as well, but depending on the implementation, it may
     * not have any effect.
     * <p>
     * <b>NOTE:</b> if any of the objects are {@code null}, this method simply
     * skips over them.
     * 
     * @throws PrepareCommitFailException
     *           if any of the objects fail to
     *           {@link TwoPhaseCommit#prepareCommit()}
     * @throws CommitFailException
     *           if any of the objects fail to {@link TwoPhaseCommit#commit()}
     */
    public static void execute(TwoPhaseCommit... objects)
        throws PrepareCommitFailException, CommitFailException {
      TwoPhaseCommit tpc = null;
      try {
        // first, all should successfully prepareCommit()
        for (int i = 0; i < objects.length; i++) {
          tpc = objects[i];
          if (tpc != null) {
            tpc.prepareCommit();
          }
        }
      } catch (Throwable t) {
        // first object that fails results in rollback all of them and
        // throwing an exception.
        rollback(objects);
        throw new PrepareCommitFailException(t, tpc);
      }
      
      // If all successfully prepareCommit(), attempt the actual commit()
      try {
        for (int i = 0; i < objects.length; i++) {
          tpc = objects[i];
          if (tpc != null) {
            tpc.commit();
          }
        }
      } catch (Throwable t) {
        // first object that fails results in rollback all of them and
        // throwing an exception.
        rollback(objects);
        throw new CommitFailException(t, tpc);
      }
    }
  
  }
  