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.wake.EventHandler;
022
023import java.util.concurrent.atomic.AtomicInteger;
024
025/**
026 * An EventHandler that blocks until a set number of Events has been received.
027 * Once they have been received, the downstream event handler is called with
028 * the <i>last event</i> received. The handler resets atomically to start
029 * receiving the next batch of events.
030 * <p>
031 * onNext is thread safe
032 *
033 * @param <T> type of events
034 * @see BlockingEventHandler
035 */
036public final class BlockingSignalEventHandler<T> implements EventHandler<T> {
037
038  private final int expectedSize;
039  private final EventHandler<T> destination;
040  private final AtomicInteger cursor;
041
042  public BlockingSignalEventHandler(final int expectedSize, final EventHandler<T> destination) {
043    this.expectedSize = expectedSize;
044    this.destination = destination;
045    this.cursor = new AtomicInteger(0);
046  }
047
048  @Override
049  public void onNext(final T event) {
050    final int newSize = this.cursor.incrementAndGet();
051
052    if (newSize % expectedSize == 0) {
053      this.destination.onNext(event);
054    }
055  }
056}