jstorm-core/src/main/java/com/alibaba/jstorm/utils/TimeCacheQueue.java

/**
 * 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.alibaba.jstorm.utils;

import java.util.Iterator;
import java.util.LinkedList;
import java.util.concurrent.LinkedBlockingDeque;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Expires keys that have not been updated in the configured number of seconds. The algorithm used will take between expirationSecs and expirationSecs * (1 + 1
 * / (numBuckets-1)) to actually expire the message.
 * 
 * get, put, remove, containsKey, and size take O(numBuckets) time to run.
 * 
 * The advantage of this design is that the expiration thread only locks the object for O(1) time, meaning the object is essentially always available for
 * poll/offer
 */
public class TimeCacheQueue<K> {
    // this default ensures things expire at most 50% past the expiration time
    public static final int DEFAULT_NUM_BUCKETS = 3;

    public static interface ExpiredCallback<K> {
        public void expire(K entry);
    }

    public static class DefaultExpiredCallback<K> implements ExpiredCallback<K> {
        protected static final Logger LOG = LoggerFactory.getLogger(DefaultExpiredCallback.class);

        protected String queueName;

        public DefaultExpiredCallback(String queueName) {
            this.queueName = queueName;
        }

        public void expire(K entry) {
            LOG.info("TimeCacheQueue " + queueName + " entry:" + entry + ", timeout");
        }
    }

    protected LinkedList<LinkedBlockingDeque<K>> _buckets;

    protected final Object _lock = new Object();
    protected Thread _cleaner;
    protected ExpiredCallback _callback;

    public TimeCacheQueue(int expirationSecs, int numBuckets, ExpiredCallback<K> callback) {
        if (numBuckets < 2) {
            throw new IllegalArgumentException("numBuckets must be >= 2");
        }
        _buckets = new LinkedList<LinkedBlockingDeque<K>>();
        for (int i = 0; i < numBuckets; i++) {
            _buckets.add(new LinkedBlockingDeque<K>());
        }

        _callback = callback;
        final long expirationMillis = expirationSecs * 1000L;
        final long sleepTime = expirationMillis / (numBuckets - 1);
        _cleaner = new Thread(new Runnable() {
            public void run() {
                try {
                    while (true) {
                        LinkedBlockingDeque<K> dead = null;

                        Thread.sleep(sleepTime);

                        synchronized (_lock) {
                            dead = _buckets.removeLast();
                            _buckets.addFirst(new LinkedBlockingDeque<K>());
                        }
                        if (_callback != null) {
                            for (K entry : dead) {
                                _callback.expire(entry);
                            }
                        }
                    }
                } catch (InterruptedException ex) {

                }
            }
        });
        _cleaner.setDaemon(true);
        _cleaner.start();
    }

    public TimeCacheQueue(int expirationSecs, ExpiredCallback<K> callback) {
        this(expirationSecs, DEFAULT_NUM_BUCKETS, callback);
    }

    public TimeCacheQueue(int expirationSecs) {
        this(expirationSecs, DEFAULT_NUM_BUCKETS, null);
    }

    public TimeCacheQueue(int expirationSecs, int numBuckets) {
        this(expirationSecs, numBuckets, null);
    }

    public boolean containsKey(K entry) {
        synchronized (_lock) {
            for (LinkedBlockingDeque<K> bucket : _buckets) {
                if (bucket.contains(entry)) {
                    return true;
                }
            }
            return false;
        }
    }

    public K poll() {
        synchronized (_lock) {
            Iterator<LinkedBlockingDeque<K>> itor = _buckets.descendingIterator();
            while (itor.hasNext()) {
                LinkedBlockingDeque<K> bucket = itor.next();
                K entry = bucket.poll();
                if (entry != null) {
                    return entry;
                }
            }

            return null;
        }
    }

    public void offer(K entry) {
        synchronized (_lock) {
            LinkedBlockingDeque<K> bucket = _buckets.getFirst();

            bucket.offer(entry);
        }
    }

    public void remove(K entry) {
        synchronized (_lock) {
            for (LinkedBlockingDeque<K> bucket : _buckets) {
                if (bucket.contains(entry)) {
                    bucket.remove(entry);
                    return;
                }
            }
            return;
        }
    }

    public int size() {
        synchronized (_lock) {
            int size = 0;
            for (LinkedBlockingDeque<K> bucket : _buckets) {
                size += bucket.size();
            }
            return size;
        }
    }

    @Override
    protected void finalize() throws Throwable {
        try {
            _cleaner.interrupt();
        } finally {
            super.finalize();
        }
    }

}