Java tutorial
/* * 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.twill.internal; import com.google.common.collect.HashMultimap; import com.google.common.collect.Multimap; import com.google.common.collect.Multimaps; import org.apache.twill.api.ElectionHandler; import org.apache.twill.common.Cancellable; import org.apache.twill.internal.zookeeper.LeaderElection; import org.apache.twill.zookeeper.ZKClient; /** * Tracks currently active leader elections within the Twill container. */ public class ElectionRegistry { private final ZKClient zkClient; private final Multimap<String, LeaderElection> registry; public ElectionRegistry(ZKClient zkClient) { this.zkClient = zkClient; Multimap<String, LeaderElection> multimap = HashMultimap.create(); this.registry = Multimaps.synchronizedMultimap(multimap); } /** * Creates a new {@link LeaderElection} for the given arguments, starts the service, and adds it to the registry. * @param name Name for the election. * @param handler Callback to handle leader and follower transitions. * @return An object to cancel the election participation. */ public Cancellable register(String name, ElectionHandler handler) { LeaderElection election = new LeaderElection(zkClient, name, handler); election.start(); registry.put(name, election); return new CancellableElection(name, election); } /** * Stops all active {@link LeaderElection} processes. */ public void shutdown() { for (LeaderElection election : registry.values()) { election.stop(); } } private class CancellableElection implements Cancellable { private final String name; private final LeaderElection election; public CancellableElection(String name, LeaderElection election) { this.name = name; this.election = election; } @Override public void cancel() { election.stop(); registry.remove(name, election); } } }