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 java.util.ArrayList;
21 import java.util.List;
22
23 import org.apache.commons.logging.Log;
24 import org.apache.commons.logging.LogFactory;
25 import org.apache.hadoop.classification.InterfaceAudience;
26 import org.apache.hadoop.classification.InterfaceStability;
27
28 /**
29 * The dispatcher acts as the state holding entity for foreign error handling. The first
30 * exception received by the dispatcher get passed directly to the listeners. Subsequent
31 * exceptions are dropped.
32 * <p>
33 * If there are multiple dispatchers that are all in the same foreign exception monitoring group,
34 * ideally all these monitors are "peers" -- any error on one dispatcher should get propagated to
35 * all others (via rpc, or some other mechanism). Due to racing error conditions the exact reason
36 * for failure may be different on different peers, but the fact that they are in error state
37 * should eventually hold on all.
38 * <p>
39 * This is thread-safe and must be because this is expected to be used to propagate exceptions
40 * from foreign threads.
41 */
42 @InterfaceAudience.Public
43 @InterfaceStability.Evolving
44 public class ForeignExceptionDispatcher implements ForeignExceptionListener, ForeignExceptionSnare {
45 public static final Log LOG = LogFactory.getLog(ForeignExceptionDispatcher.class);
46 protected final String name;
47 protected final List<ForeignExceptionListener> listeners =
48 new ArrayList<ForeignExceptionListener>();
49 private ForeignException exception;
50
51 public ForeignExceptionDispatcher(String name) {
52 this.name = name;
53 }
54
55 public ForeignExceptionDispatcher() {
56 this("");
57 }
58
59 public String getName() {
60 return name;
61 }
62
63 @Override
64 public synchronized void receive(ForeignException e) {
65 // if we already have an exception, then ignore it
66 if (exception != null) return;
67
68 LOG.debug(name + " accepting received exception" , e);
69 // mark that we got the error
70 if (e != null) {
71 exception = e;
72 } else {
73 exception = new ForeignException(name, "");
74 }
75
76 // notify all the listeners
77 dispatch(e);
78 }
79
80 @Override
81 public synchronized void rethrowException() throws ForeignException {
82 if (exception != null) {
83 // This gets the stack where this is caused, (instead of where it was deserialized).
84 // This is much more useful for debugging
85 throw new ForeignException(exception.getSource(), exception.getCause());
86 }
87 }
88
89 @Override
90 public synchronized boolean hasException() {
91 return exception != null;
92 }
93
94 @Override
95 synchronized public ForeignException getException() {
96 return exception;
97 }
98
99 /**
100 * Sends an exception to all listeners.
101 * @param message human readable message passed to the listener
102 * @param e {@link ForeignException} containing the cause. Can be null.
103 */
104 private void dispatch(ForeignException e) {
105 // update all the listeners with the passed error
106 for (ForeignExceptionListener l: listeners) {
107 l.receive(e);
108 }
109 }
110
111 /**
112 * Listen for failures to a given process. This method should only be used during
113 * initialization and not added to after exceptions are accepted.
114 * @param errorable listener for the errors. may be null.
115 */
116 public synchronized void addListener(ForeignExceptionListener errorable) {
117 this.listeners.add(errorable);
118 }
119 }