001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.errorhandling;
019
020import org.apache.yetus.audience.InterfaceAudience;
021
022/**
023 * This is an interface for a cooperative exception throwing mechanism.  Implementations are
024 * containers that holds an exception from a separate thread. This can be used to receive
025 * exceptions from 'foreign' threads or from separate 'foreign' processes.
026 * <p>
027 * To use, one would pass an implementation of this object to a long running method and
028 * periodically check by calling {@link #rethrowException()}.  If any foreign exceptions have
029 * been received, the calling thread is then responsible for handling the rethrown exception.
030 * <p>
031 * One could use the boolean {@link #hasException()} to determine if there is an exceptoin as well.
032 * <p>
033 * NOTE: This is very similar to the InterruptedException/interrupt/interrupted pattern.  There,
034 * the notification state is bound to a Thread.  Using this, applications receive Exceptions in
035 * the snare.  The snare is referenced and checked by multiple threads which enables exception 
036 * notification in all the involved threads/processes. 
037 */
038@InterfaceAudience.Private
039public interface ForeignExceptionSnare {
040
041  /**
042   * Rethrow an exception currently held by the {@link ForeignExceptionSnare}. If there is
043   * no exception this is a no-op
044   *
045   * @throws ForeignException
046   *           all exceptions from remote sources are procedure exceptions
047   */
048  void rethrowException() throws ForeignException;
049
050  /**
051   * Non-exceptional form of {@link #rethrowException()}. Checks to see if any
052   * process to which the exception checkers is bound has created an error that
053   * would cause a failure.
054   *
055   * @return <tt>true</tt> if there has been an error,<tt>false</tt> otherwise
056   */
057  boolean hasException();
058
059  /**
060   * Get the value of the captured exception.
061   *
062   * @return the captured foreign exception or null if no exception captured.
063   */
064  ForeignException getException();
065}