contrib/kafka/src/java/com/twitter/heron/spouts/kafka/TransferCollector.java

/*
 * Copyright 2016 Twitter, Inc.
 *
 * 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 com.twitter.heron.spouts.kafka;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

import backtype.storm.metric.api.CountMetric;
import backtype.storm.metric.api.IMetric;
import backtype.storm.spout.ISpoutOutputCollector;


/**
 * Threadsafe collector which can be used to transfer message from async message-fetcher to
 * spout main-thread which calls nextTuple. Note that, collector doesn't guarantee that
 * any emitted message will be read.
 * Note: Counters are not thread-safe. No attempts are made to synchronize counter values.
 */
public class TransferCollector extends LinkedBlockingQueue<TransferCollector.EmitData>
    implements ISpoutOutputCollector, IMetric, Serializable {
  public static final Logger LOG = Logger.getLogger(TransferCollector.class.getName());
  public static class EmitData implements Serializable {
    public String streamId;
    public Object messageId;
    public List<Object> tuple;

    public EmitData(String streamId, List<Object> tuple, Object messageId) {
      this.streamId = streamId;
      this.messageId = messageId;
      this.tuple = tuple;
    }

    /**
     * No argument contructor.
     */
    public EmitData() {
    }
  }

  private final CountMetric getEmitItemsTimeoutCounter;

  private final CountMetric getEmitItemsCallCounter;

  private final CountMetric getEmitCallCounter;

  private final CountMetric exceptionCounter;

  /**
   * Collector to serialize multiple emit and make it thread safe.
   * @param emitQueueMaxSize Max size of emit buffer.
   */
  public TransferCollector(int emitQueueMaxSize) {
    super(emitQueueMaxSize);
    getEmitItemsTimeoutCounter = new CountMetric();
    getEmitItemsCallCounter = new CountMetric();
    getEmitCallCounter = new CountMetric();
    exceptionCounter = new CountMetric();
  }

  /**
   * Emits to in-memory thread-safe pending queue.
   */
  @Override
  public List<Integer> emit(String streamId, List<Object> tuple, Object messageId) {
    getEmitCallCounter.incr();
    // Block until emit is successful in adding item to the transfer collector.
    try {
      put(new EmitData(streamId, tuple, messageId));
    } catch (InterruptedException ie) {
      exceptionCounter.incr();
    }
    return new ArrayList<Integer>();  // No task receive message directly from this collector.
  }

  @Override
  public void emitDirect(int taskId, String streamId, List<Object> tuple, Object messageId) {
    throw new IllegalStateException("Transfer collectors are not supposed to emit directly");
  }

  @Override
  public void reportError(Throwable throwable) {
    throw new IllegalStateException("Transfer collectors are not to transfer error messages");
  }

  @Override
  public Object getValueAndReset() {
    HashMap<String, Object> metrics = new HashMap<String, Object>();
    metrics.put("pendingEmits", size());
    metrics.put("getEmitItemsTimeoutCounter", getEmitItemsTimeoutCounter.getValueAndReset());
    metrics.put("getEmitItemsCallCounter", getEmitItemsCallCounter.getValueAndReset());
    metrics.put("getEmitCallCounter", getEmitCallCounter.getValueAndReset());
    metrics.put("exceptionCounter", exceptionCounter.getValueAndReset());
    return metrics;
  }

  // Accessor methods.

  /**
   * Get an item to emit from emit queue with timeout.
   * @param timeout Duration of timeout.
   * @param unit Unit of timeout.
   * @return First item from emit queue. Null if times out.
   */
  public EmitData getEmitItems(long timeout, TimeUnit unit) {
    getEmitItemsCallCounter.incr();
    try {
      EmitData item = poll(timeout, unit);
      if (item == null) {
        getEmitItemsTimeoutCounter.incr();
      }
      return item;
    } catch (InterruptedException ie) {
      exceptionCounter.incr();
      return null;
    }
  }

  /**
   * Poll with immediate return. Removes returned item from queue.
   * @return First item on emit queue. Null if empty.
   */
  public EmitData getEmitItems() {
    getEmitItemsCallCounter.incr();
    return poll();
  }
}