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