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 }