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 */
018
019 package org.apache.hadoop.service;
020
021 import org.apache.hadoop.classification.InterfaceAudience.Public;
022 import org.apache.hadoop.classification.InterfaceStability.Stable;
023
024 /**
025 * Interface to notify state changes of a service.
026 */
027 @Public
028 @Stable
029 public interface ServiceStateChangeListener {
030
031 /**
032 * Callback to notify of a state change. The service will already
033 * have changed state before this callback is invoked.
034 *
035 * This operation is invoked on the thread that initiated the state change,
036 * while the service itself in in a sychronized section.
037 * <ol>
038 * <li>Any long-lived operation here will prevent the service state
039 * change from completing in a timely manner.</li>
040 * <li>If another thread is somehow invoked from the listener, and
041 * that thread invokes the methods of the service (including
042 * subclass-specific methods), there is a risk of a deadlock.</li>
043 * </ol>
044 *
045 *
046 * @param service the service that has changed.
047 */
048 void stateChanged(Service service);
049
050 }