org.apache.sling.discovery.DiscoveryService Maven / Gradle / Ivy
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/*
* 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;
import aQute.bnd.annotation.ProviderType;
/**
* The discovery service can be used to get the current topology view.
*
* The discovery service is in charge of managing live instances that
* have announced themselves as being part of a topology view. The exact
* details of how this announcement occurs is implementation dependent.
*/
@ProviderType
public interface DiscoveryService {
/**
* Returns the topology that was last discovered by this service.
*
* If for some reason the service is currently not able to do topology discovery
* it will return the last valid topology marked with false in the call
* to . This is also true if the service
* has noticed a potential change in the topology and is in the process of
* settling the change in the topology (eg with peers, ie voting).
*
* Note that this call is synchronized with TopologyEventListener.handleTopologyEvent()
* calls: ie if calls to TopologyEventListener.handleTopologyEvent() are currently
* ongoing, then the call to this method will block until all TopologyEventListeners
* have been called. Be careful not to cause deadlock situations.
*
* @return the topology that was last discovered by this service. This will never
* be null (ie even if a change in the topology is ongoing at the moment or the
* cluster consists only of the local instance).
*/
TopologyView getTopology();
}