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.examples.utils.wake;
020
021import org.apache.reef.wake.EventHandler;
022
023import java.util.ArrayList;
024import java.util.List;
025
026/**
027 * An EventHandler that blocks until a set number of Events has been received.
028 * Once they have been received, the downstream event handler is called with an
029 * Iterable of the events spooled.
030 *
031 * @param <T>
032 */
033public final class BlockingEventHandler<T> implements EventHandler<T> {
034
035  private final int expectedSize;
036  private List<T> events = new ArrayList<>();
037  private final EventHandler<Iterable<T>> destination;
038
039  public BlockingEventHandler(final int expectedSize, final EventHandler<Iterable<T>> destination) {
040    this.expectedSize = expectedSize;
041    this.destination = destination;
042  }
043
044  @Override
045  public void onNext(final T event) {
046    if (this.isComplete()) {
047      throw new IllegalStateException("Received more Events than expected");
048    }
049    this.events.add(event);
050    if (this.isComplete()) {
051      this.destination.onNext(events);
052      this.reset();
053    }
054  }
055
056  private boolean isComplete() {
057    return this.events.size() >= expectedSize;
058  }
059
060  private void reset() {
061    this.events = new ArrayList<>();
062  }
063}