WatermarkTriggerScheduler.java

/**
 * Copyright 2016-2017 Seznam.cz, a.s.
 *
 * Licensed 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 cz.seznam.euphoria.inmem;

import cz.seznam.euphoria.core.client.dataset.windowing.Window;
import cz.seznam.euphoria.core.client.util.Pair;
import cz.seznam.euphoria.shaded.guava.com.google.common.collect.Iterables;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;
import java.util.stream.Collectors;

/**
 * Trigger scheduler based on watermarks. Uses event-time instead of real
 * wall-clock time.
 */
public class WatermarkTriggerScheduler<W extends Window, K>
    implements TriggerScheduler<W, K> {

  // how delayed is the watermark time after the event time (how long are
  // we going to accept latecomers)
  private final long watermarkDuration;
  
  // read-only accessed from multiple threads
  private volatile long currentWatermark;

  // following fields are accessed from owner thread only
  private final SortedMap<Long, List<Pair<KeyedWindow<W, K>, Triggerable<W, K>>>>
      scheduledEvents = new TreeMap<>();
  private final Map<KeyedWindow<W, K>, Set<Long>>
      eventStampsForWindow = new HashMap<>();
 
  /**
   * Create the triggering with specified duration in ms.
   * @param duration duration of the watermark in ms.
   */
  public WatermarkTriggerScheduler(long duration) {
    this.watermarkDuration = duration;
    this.currentWatermark = 0;
  }

  @Override
  @SuppressWarnings("unchecked")
  public void updateStamp(long stamp) {
    if (currentWatermark < stamp) {
      final long triggeringStamp = stamp - watermarkDuration;

      // fire all triggers that passed watermark duration

      SortedMap<Long, List<Pair<KeyedWindow<W, K>, Triggerable<W, K>>>> headMap;
      headMap = scheduledEvents.headMap(triggeringStamp);

      headMap.entrySet().stream()
          .flatMap(e -> e.getValue().stream().map(p -> Pair.of(e.getKey(), p)))
          // need to collect to list to prevent ConcurrentModificationException
          .collect(Collectors.toList())
          .forEach(p -> {
            // move the clock to the triggering time
            currentWatermark = p.getFirst();
            KeyedWindow<W, K> w = p.getSecond().getFirst();
            Triggerable<W, K> purged = purge(w, currentWatermark);
            purged.fire(currentWatermark, w);
          });

      // and set the final watermark
      currentWatermark = stamp;
    }
  }

  @Override
  public long getCurrentTimestamp() {
    return currentWatermark;
  }

  @Override
  public boolean scheduleAt(
      long stamp, KeyedWindow<W, K> window, Triggerable<W, K> trigger) {
    if (stamp <= currentWatermark - watermarkDuration) return false;
    purge(window, stamp);
    add(stamp, trigger, window);
    return true;
  }

  @Override
  public void cancelAll() {
    scheduledEvents.clear();
    eventStampsForWindow.clear();
  }

  @Override
  public void cancel(long timestamp, KeyedWindow<W, K> window) {
    purge(window, timestamp);
  }

  @Override
  public void close() {
    cancelAll();
  }

  /** Purge the scheduled event from all indices and return it (if exists). */
  private Triggerable purge(KeyedWindow<W, K> w, long stamp) {
    Set<Long> scheduled = eventStampsForWindow.get(w);
    if (scheduled == null || !scheduled.remove(stamp)) {
      return null;
    }

    List<Pair<KeyedWindow<W, K>, Triggerable<W, K>>> eventsForWindow;
    eventsForWindow = scheduledEvents.get(stamp);

    List<Pair<KeyedWindow<W, K>, Triggerable<W, K>>> filtered
        = eventsForWindow.stream()
        .filter(p -> w.equals(p.getFirst()))
        .collect(Collectors.toList());

    Pair<KeyedWindow<W, K>, Triggerable<W, K>> event =
        Iterables.getOnlyElement(filtered);

    eventsForWindow.remove(event);

    if (eventsForWindow.isEmpty()) {
      scheduledEvents.remove(stamp);
    }

    if (scheduled.isEmpty()) {
      eventStampsForWindow.remove(w);
    }


    return event.getSecond();
  }


  private void add(long stamp, Triggerable<W, K> trigger, KeyedWindow<W, K> w) {
    List<Pair<KeyedWindow<W, K>, Triggerable<W, K>>> scheduledForTime =
        scheduledEvents.get(stamp);
    if (scheduledForTime == null) {
      scheduledEvents.put(stamp, scheduledForTime = new ArrayList<>());
    }
    scheduledForTime.add(Pair.of(w, trigger));
    Set<Long> stamps = eventStampsForWindow.get(w);
    if (stamps == null) {
      eventStampsForWindow.put(w, stamps = new HashSet<>());
    }
    stamps.add(stamp);
  }

  public long getWatermarkDuration() {
    return watermarkDuration;
  }

}