org.apache.flink.runtime.webmonitor.retriever.LeaderRetriever 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.flink.runtime.webmonitor.retriever;

import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.runtime.leaderretrieval.LeaderRetrievalListener;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Optional;
import java.util.UUID;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.atomic.AtomicReference;

/**
 * Retrieves and stores the current leader address.
 */
public class LeaderRetriever implements LeaderRetrievalListener {
	protected final Logger log = LoggerFactory.getLogger(getClass());

	private AtomicReference>> atomicLeaderFuture;

	public LeaderRetriever() {
		atomicLeaderFuture = new AtomicReference<>(new CompletableFuture<>());
	}

	/**
	 * Returns the current leader information if available. Otherwise it returns an
	 * empty optional.
	 *
	 * @return The current leader information if available. Otherwise it returns an
	 * empty optional.
	 * @throws Exception if the leader future has been completed with an exception
	 */
	public Optional> getLeaderNow() throws Exception {
		CompletableFuture> leaderFuture = this.atomicLeaderFuture.get();
		if (leaderFuture != null) {
			if (leaderFuture.isDone()) {
				return Optional.of(leaderFuture.get());
			} else {
				return Optional.empty();
			}
		} else {
			return Optional.empty();
		}
	}

	/**
	 * Returns the current JobManagerGateway future.
	 */
	public CompletableFuture> getLeaderFuture() {
		return atomicLeaderFuture.get();
	}

	@Override
	public void notifyLeaderAddress(final String leaderAddress, final UUID leaderSessionID) {
		final CompletableFuture> newLeaderFuture;

		if (isEmptyAddress(leaderAddress)) {
			newLeaderFuture = new CompletableFuture<>();
		} else {
			newLeaderFuture = CompletableFuture.completedFuture(Tuple2.of(leaderAddress, leaderSessionID));
		}

		try {
			final CompletableFuture> oldLeaderFuture = atomicLeaderFuture.getAndSet(newLeaderFuture);

			if (!oldLeaderFuture.isDone()) {
				newLeaderFuture.whenComplete((stringUUIDTuple2, throwable) -> {
					if (throwable != null) {
						oldLeaderFuture.completeExceptionally(throwable);
					} else {
						oldLeaderFuture.complete(stringUUIDTuple2);
					}
				});
			}

			notifyNewLeaderAddress(newLeaderFuture);
		}
		catch (Exception e) {
			handleError(e);
		}
	}

	private boolean isEmptyAddress(String leaderAddress) {
		return leaderAddress == null || leaderAddress.equals("");
	}

	@Override
	public void handleError(Exception exception) {
		log.error("Received error from LeaderRetrievalService.", exception);

		atomicLeaderFuture.get().completeExceptionally(exception);
	}

	protected void notifyNewLeaderAddress(CompletableFuture> newLeaderAddressFuture) {}
}