common/src/main/java/org/apache/flink/training/exercises/common/sources/TaxiRideGenerator.java

/*
 * 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.training.exercises.common.sources;

import org.apache.flink.streaming.api.functions.source.SourceFunction;
import org.apache.flink.streaming.api.watermark.Watermark;
import org.apache.flink.training.exercises.common.datatypes.TaxiRide;

import java.util.ArrayList;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Random;

/**
 * This SourceFunction generates a data stream of TaxiRide records that include event time
 * timestamps.
 *
 * <p>The stream is produced out-of-order, and includes Watermarks (with no late events).
 *
 */
public class TaxiRideGenerator implements SourceFunction<TaxiRide> {

	public static final int SLEEP_MILLIS_PER_EVENT = 10;
	private static final int BATCH_SIZE = 5;
	private volatile boolean running = true;

	@Override
	public void run(SourceContext<TaxiRide> ctx) throws Exception {

		PriorityQueue<TaxiRide> endEventQ = new PriorityQueue<>(100);
		long id = 0;
		long maxStartTime = 0;

		while (running) {

			// generate a batch of START events
			List<TaxiRide> startEvents = new ArrayList<TaxiRide>(BATCH_SIZE);
			for (int i = 1; i <= BATCH_SIZE; i++) {
				TaxiRide ride = new TaxiRide(id + i, true);
				startEvents.add(ride);
				// the start times may be in order, but let's not assume that
				maxStartTime = Math.max(maxStartTime, ride.startTime.toEpochMilli());
			}

			// enqueue the corresponding END events
			for (int i = 1; i <= BATCH_SIZE; i++) {
				endEventQ.add(new TaxiRide(id + i, false));
			}

			// release the END events coming before the end of this new batch
			// (this allows a few END events to precede their matching START event)
			while (endEventQ.peek().getEventTime() <= maxStartTime) {
				TaxiRide ride = endEventQ.poll();
				ctx.collectWithTimestamp(ride, ride.getEventTime());
			}

			// then emit the new START events (out-of-order)
			java.util.Collections.shuffle(startEvents, new Random(id));
			startEvents.iterator().forEachRemaining(r -> ctx.collectWithTimestamp(r, r.getEventTime()));

			// produce a Watermark
			ctx.emitWatermark(new Watermark(maxStartTime));

			// prepare for the next batch
			id += BATCH_SIZE;

			// don't go too fast
			Thread.sleep(BATCH_SIZE * SLEEP_MILLIS_PER_EVENT);
		}
	}

	@Override
	public void cancel() {
		running = false;
	}
}