heron/api/src/java/com/twitter/heron/api/windowing/triggers/CountTriggerPolicy.java

//  Copyright 2017 Twitter. All rights reserved.
//
//  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.api.windowing.triggers;

import java.util.concurrent.atomic.AtomicInteger;

import com.twitter.heron.api.windowing.DefaultEvictionContext;
import com.twitter.heron.api.windowing.Event;
import com.twitter.heron.api.windowing.EvictionPolicy;
import com.twitter.heron.api.windowing.TriggerHandler;
import com.twitter.heron.api.windowing.TriggerPolicy;

/**
 * A trigger that tracks event counts and calls back {@link TriggerHandler#onTrigger()}
 * when the count threshold is hit.
 *
 * @param <T> the type of event tracked by this policy.
 */
public class CountTriggerPolicy<T> implements TriggerPolicy<T> {
  private final int count;
  private final AtomicInteger currentCount;
  private final TriggerHandler handler;
  private final EvictionPolicy<T> evictionPolicy;
  private boolean started;

  public CountTriggerPolicy(int count, TriggerHandler handler, EvictionPolicy<T>
      evictionPolicy) {
    this.count = count;
    this.currentCount = new AtomicInteger();
    this.handler = handler;
    this.evictionPolicy = evictionPolicy;
    this.started = false;
  }

  @Override
  public void track(Event<T> event) {
    if (started && !event.isWatermark()) {
      if (currentCount.incrementAndGet() >= count) {
        evictionPolicy.setContext(new DefaultEvictionContext(System.currentTimeMillis()));
        handler.onTrigger();
      }
    }
  }

  @Override
  public void reset() {
    currentCount.set(0);
  }

  @Override
  public void start() {
    started = true;
  }

  @Override
  public void shutdown() {
    // NOOP
  }

  @Override
  public String toString() {
    return "CountTriggerPolicy{" + "count=" + count + ", currentCount=" + currentCount
        + ", started=" + started + '}';
  }
}