Source code

001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.reef.wake.impl;
020
021import org.apache.reef.tang.annotations.Unit;
022import org.apache.reef.wake.EventHandler;
023
024import javax.inject.Inject;
025import java.util.logging.Level;
026import java.util.logging.Logger;
027
028/**
029 * An EventHandler combines two events of different types into a single Pair of events.
030 * Handler will block until both events are received.
031 * <p/>
032 * onNext is thread safe
033 *
034 * @param <L> type of event
035 * @param <R> type of event
036 * @see BlockingEventHandler
037 */
038@Unit
039public final class MergingEventHandler<L, R> {
040
041  private static Logger LOG = Logger.getLogger(MergingEventHandler.class.getName());
042  public final EventHandler<L> left = new Left();
043  public final EventHandler<R> right = new Right();
044  private final Object mutex = new Object();
045  private final EventHandler<Pair<L, R>> destination;
046  private L leftEvent;
047  private R rightEvent;
048
049  @Inject
050  public MergingEventHandler(final EventHandler<Pair<L, R>> destination) {
051    this.destination = destination;
052    reset();
053  }
054
055  /*
056   * Not thread safe. Must be externally synchronized.
057   */
058  private void reset() {
059    rightEvent = null;
060    leftEvent = null;
061  }
062
063  public static class Pair<S1, S2> {
064    public final S1 first;
065    public final S2 second;
066
067    private Pair(S1 s1, S2 s2) {
068      this.first = s1;
069      this.second = s2;
070    }
071  }
072
073  private class Left implements EventHandler<L> {
074
075    @Override
076    public void onNext(final L event) {
077
078      L leftRef = null;
079      R rightRef = null;
080
081      synchronized (mutex) {
082
083        while (leftEvent != null) {
084          try {
085            mutex.wait();
086          } catch (final InterruptedException e) {
087            LOG.log(Level.SEVERE, "Wait interrupted.", e);
088          }
089        }
090
091        if (LOG.isLoggable(Level.FINEST)) {
092          LOG.log(Level.FINEST, "{0} producing left {1}",
093              new Object[]{Thread.currentThread(), event});
094        }
095
096        leftEvent = event;
097        leftRef = event;
098
099        if (rightEvent != null) {
100          rightRef = rightEvent;
101          reset();
102          mutex.notifyAll();
103        }
104      }
105
106      if (rightRef != null) {
107        // I get to fire the event
108        destination.onNext(new Pair<L, R>(leftRef, rightRef));
109      }
110    }
111  }
112
113  private class Right implements EventHandler<R> {
114
115    @Override
116    public void onNext(final R event) {
117
118      L leftRef = null;
119      R rightRef = null;
120
121      synchronized (mutex) {
122
123        while (rightEvent != null) {
124          try {
125            mutex.wait();
126          } catch (final InterruptedException e) {
127            LOG.log(Level.SEVERE, "Wait interrupted.", e);
128          }
129        }
130
131        if (LOG.isLoggable(Level.FINEST)) {
132          LOG.log(Level.FINEST, "{0} producing right {1}",
133              new Object[]{Thread.currentThread(), event});
134        }
135
136        rightEvent = event;
137        rightRef = event;
138
139        if (leftEvent != null) {
140          leftRef = leftEvent;
141          reset();
142          mutex.notifyAll();
143        }
144      }
145
146      if (leftRef != null) {
147        // I get to fire the event
148        destination.onNext(new Pair<L, R>(leftRef, rightRef));
149      }
150    }
151  }
152}