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1   /**
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  package org.apache.hadoop.hbase.errorhandling;
19  
20  import org.apache.hadoop.classification.InterfaceAudience;
21  import org.apache.hadoop.classification.InterfaceStability;
22  
23  /**
24   * This is an interface for a cooperative exception throwing mechanism.  Implementations are
25   * containers that holds an exception from a separate thread. This can be used to receive
26   * exceptions from 'foreign' threads or from separate 'foreign' processes.
27   * <p>
28   * To use, one would pass an implementation of this object to a long running method and
29   * periodically check by calling {@link #rethrowException()}.  If any foreign exceptions have
30   * been received, the calling thread is then responsible for handling the rethrown exception.
31   * <p>
32   * One could use the boolean {@link #hasException()} to determine if there is an exceptoin as well.
33   * <p>
34   * NOTE: This is very similar to the InterruptedException/interrupt/interrupted pattern.  There,
35   * the notification state is bound to a Thread.  Using this, applications receive Exceptions in
36   * the snare.  The snare is referenced and checked by multiple threads which enables exception 
37   * notification in all the involved threads/processes. 
38   */
39  @InterfaceAudience.Private
40  public interface ForeignExceptionSnare {
41  
42    /**
43     * Rethrow an exception currently held by the {@link ForeignExceptionSnare}. If there is
44     * no exception this is a no-op
45     *
46     * @throws ForeignException
47     *           all exceptions from remote sources are procedure exceptions
48     */
49    void rethrowException() throws ForeignException;
50  
51    /**
52     * Non-exceptional form of {@link #rethrowException()}. Checks to see if any
53     * process to which the exception checkers is bound has created an error that
54     * would cause a failure.
55     *
56     * @return <tt>true</tt> if there has been an error,<tt>false</tt> otherwise
57     */
58    boolean hasException();
59  
60    /**
61     * Get the value of the captured exception.
62     *
63     * @return the captured foreign exception or null if no exception captured.
64     */
65    ForeignException getException();
66  }