| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| package org.apache.sling.discovery; |
| |
| /** |
| * The <code>TopologyEventListener</code> service interface may be implemented by |
| * components interested in being made aware of changes in the topology. |
| * <p> |
| * Upon registration and whenever changes in the topology occur, this |
| * service is informed. |
| */ |
| public interface TopologyEventListener { |
| |
| /** |
| * Inform the service about an event in the topology - or in the discovery |
| * of the topology. |
| * <p> |
| * The <code>TopologyEvent</code> contains details about what changed. |
| * The supported event types are: |
| * <ul> |
| * <li><code>TOPOLOGY_INIT</code> sent when the <code>TopologyEventListener</code> |
| * was first bound to the discovery service - represents the initial state |
| * of the topology at that time.</li> |
| * <li><code>TOPOLOGY_CHANGING</code> sent when the discovery service |
| * discovered a change in the topology and has started to settle the change. |
| * This event is sent before <code>TOPOLOGY_CHANGED</code> but is optional</li> |
| * <li><code>TOPOLOGY_CHANGED</code> sent when the discovery service |
| * discovered a change in the topology and has settled it.</li> |
| * <li><code>PROPERTIES_CHANGED</code> sent when the one or many properties |
| * have changed in an instance in the current topology</li> |
| * </ul> |
| * A note on instance restarts: it is currently not a requirement on the |
| * discovery service to send a TopologyEvent should an instance restart |
| * occur rapidly (ie within the change detection timeout). A TopologyEvent |
| * is only sent if the number of instances or any property changes. |
| * Should there be a requirement to detect a restart in a guaranteed fashion, |
| * it is always possible to set a particular property (using the PropertyProvider) |
| * to the instance start time and have others detect a change in that property. |
| * @param event The topology event |
| */ |
| void handleTopologyEvent(TopologyEvent event); |
| |
| } |