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 019package org.apache.hadoop.service; 020 021import org.apache.hadoop.classification.InterfaceAudience.Public; 022import org.apache.hadoop.classification.InterfaceStability.Stable; 023 024/** 025 * Interface to notify state changes of a service. 026 */ 027@Public 028@Stable 029public 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}