| /** |
| * 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 org.apache.storm.windowing; |
| |
| import java.util.concurrent.atomic.AtomicLong; |
| |
| /** |
| * An eviction policy that tracks event counts and can evict based on a threshold count. |
| * |
| * @param <T> the type of event tracked by this policy. |
| */ |
| public class CountEvictionPolicy<T> implements EvictionPolicy<T, Long> { |
| protected final int threshold; |
| protected final AtomicLong currentCount; |
| private EvictionContext context; |
| |
| public CountEvictionPolicy(int count) { |
| this.threshold = count; |
| this.currentCount = new AtomicLong(); |
| } |
| |
| @Override |
| public Action evict(Event<T> event) { |
| /* |
| * atomically decrement the count if its greater than threshold and |
| * return if the event should be evicted |
| */ |
| while (true) { |
| long curVal = currentCount.get(); |
| if (curVal > threshold) { |
| if (currentCount.compareAndSet(curVal, curVal - 1)) { |
| return Action.EXPIRE; |
| } |
| } else { |
| break; |
| } |
| } |
| return Action.PROCESS; |
| } |
| |
| @Override |
| public void track(Event<T> event) { |
| if (!event.isWatermark()) { |
| currentCount.incrementAndGet(); |
| } |
| } |
| |
| @Override |
| public EvictionContext getContext() { |
| return context; |
| } |
| |
| @Override |
| public void setContext(EvictionContext context) { |
| this.context = context; |
| } |
| |
| @Override |
| public String toString() { |
| return "CountEvictionPolicy{" |
| + "threshold=" + threshold |
| + ", currentCount=" + currentCount |
| + '}'; |
| } |
| |
| @Override |
| public void reset() { |
| // NOOP |
| } |
| |
| @Override |
| public Long getState() { |
| return currentCount.get(); |
| } |
| |
| @Override |
| public void restoreState(Long state) { |
| currentCount.set(state); |
| } |
| } |