/*
 * 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.
 */
package org.apache.lucene.index;

import java.io.IOException;



A utility for executing 2-phase commit on several objects.
See Also:
TwoPhaseCommit
@lucene.experimental
/**
 * A utility for executing 2-phase commit on several objects.
 * 
 * @see TwoPhaseCommit
 * @lucene.experimental
 */
public final class TwoPhaseCommitTool {
  
  
No instance /** No instance */
  private TwoPhaseCommitTool() {}

  
Thrown by TwoPhaseCommitTool.execute(TwoPhaseCommit...) when an object fails to prepareCommit(). /**
   * Thrown by {@link TwoPhaseCommitTool#execute(TwoPhaseCommit...)} when an
   * object fails to prepareCommit().
   */
  public static class PrepareCommitFailException extends IOException {

    
Sole constructor. /** Sole constructor. */
    public PrepareCommitFailException(Throwable cause, TwoPhaseCommit obj) {
      super("prepareCommit() failed on " + obj, cause);
    }
  }

  
Thrown by TwoPhaseCommitTool.execute(TwoPhaseCommit...) when an object fails to commit(). /**
   * Thrown by {@link TwoPhaseCommitTool#execute(TwoPhaseCommit...)} when an
   * object fails to commit().
   */
  public static class CommitFailException extends IOException {

    
Sole constructor. /** Sole constructor. */
    public CommitFailException(Throwable cause, TwoPhaseCommit obj) {
      super("commit() failed on " + obj, cause);
    }
    
  }

  
rollback all objects, discarding any exceptions that occur. /** 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 TwoPhaseCommit.prepareCommit() all objects and only if all succeed, it proceeds with TwoPhaseCommit.commit(). If any of the objects fail on either the preparation or actual commit, it terminates and TwoPhaseCommit.rollback() all of them. 

NOTE: 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.

NOTE: if any of the objects are null, this method simply skips over them. 
Throws:
PrepareCommitFailException –  if any of the objects fail to TwoPhaseCommit.prepareCommit()
CommitFailException –  if any of the objects fail to TwoPhaseCommit.commit()/**
   * 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);
    }
  }

}