com.twitter.heron.api.windowing.evictors.TimeEvictionPolicy Maven / Gradle / Ivy

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// 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.

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.evictors;

import java.io.Serializable;
import java.util.logging.Logger;

import com.twitter.heron.api.windowing.Event;
import com.twitter.heron.api.windowing.EvictionContext;
import com.twitter.heron.api.windowing.EvictionPolicy;

/**
 * Eviction policy that evicts events based on time duration.
 */
public class TimeEvictionPolicy
    implements EvictionPolicy {
  private static final Logger LOG = Logger.getLogger(TimeEvictionPolicy.class.getName());

  private final long windowLength;
  protected volatile EvictionContext evictionContext;
  private long delta;

  /**
   * Constructs a TimeEvictionPolicy that evicts events older
   * than the given window length in millis
   *
   * @param windowLength the duration in milliseconds
   */
  public TimeEvictionPolicy(long windowLength) {
    this.windowLength = windowLength;
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public EvictionPolicy.Action evict(Event event) {
    long now =
        evictionContext == null ? System.currentTimeMillis() : evictionContext.getReferenceTime();
    long diff = now - event.getTimestamp();
    if (diff >= (windowLength + delta)) {
      return Action.EXPIRE;
    } else if (diff < 0) { // do not process events beyond current ts
      return Action.KEEP;
    }
    return Action.PROCESS;
  }

  @Override
  public void track(Event event) {
    // NOOP
  }

  @Override
  public void setContext(EvictionContext context) {
    EvictionContext prevContext = evictionContext;
    evictionContext = context;
    // compute window length adjustment (delta) to account for time drift
    if (context.getSlidingInterval() != null) {
      if (prevContext == null) {
        delta = Integer.MAX_VALUE; // consider all events for the initial window
      } else {
        delta = context.getReferenceTime() - prevContext.getReferenceTime()
            - context.getSlidingInterval();
        if (Math.abs(delta) > 100) {
          LOG.warning(String.format("Possible clock drift or long running computation in window; "
              + "Previous eviction time: %s, current eviction time: %s", prevContext
              .getReferenceTime(), context.getReferenceTime()));
        }
      }
    }
  }

  @Override
  public EvictionContext getContext() {
    return evictionContext;
  }

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

  @Override
  public EvictionContext getState() {
    return evictionContext;
  }

  @Override
  public void restoreState(EvictionContext state) {
    this.evictionContext = state;
  }

  @Override
  public String toString() {
    return "TimeEvictionPolicy{" + "windowLength=" + windowLength + ", evictionContext="
        + evictionContext + '}';
  }
}