TimeCacheMap.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.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import java.util.Map.Entry;

import com.alibaba.jstorm.callback.AsyncLoopRunnable;

/**
 * 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.
 */
public class TimeCacheMap<K, V> implements TimeOutMap<K, V> {
    // this default ensures things expire at most 50% past the expiration time
    private static final int DEFAULT_NUM_BUCKETS = 3;

    private LinkedList<HashMap<K, V>> buckets;

    private final Object lock = new Object();
    private Thread cleaner;
    private ExpiredCallback callback;

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

        this.callback = callback;
        final long expirationMillis = expirationSecs * 1000L;
        final long sleepTime = expirationMillis / (numBuckets - 1);
        cleaner = new Thread(new Runnable() {
            public void run() {
                while (!AsyncLoopRunnable.getShutdown().get()) {
                    Map<K, V> dead;
                    JStormUtils.sleepMs(sleepTime);
                    synchronized (lock) {
                        dead = buckets.removeLast();
                        buckets.addFirst(new HashMap<K, V>());
                    }
                    if (TimeCacheMap.this.callback != null) {
                        for (Entry<K, V> entry : dead.entrySet()) {
                            TimeCacheMap.this.callback.expire(entry.getKey(), entry.getValue());
                        }
                    }
                }
            }
        });
        cleaner.setDaemon(true);
        cleaner.start();
    }

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

    public TimeCacheMap(int expirationSecs) {
        this(expirationSecs, DEFAULT_NUM_BUCKETS);
    }

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

    @Override
    public boolean containsKey(K key) {
        synchronized (lock) {
            for (HashMap<K, V> bucket : buckets) {
                if (bucket.containsKey(key)) {
                    return true;
                }
            }
            return false;
        }
    }

    @Override
    public V get(K key) {
        synchronized (lock) {
            for (HashMap<K, V> bucket : buckets) {
                if (bucket.containsKey(key)) {
                    return bucket.get(key);
                }
            }
            return null;
        }
    }

    @Override
    public void putHead(K key, V value) {
        synchronized (lock) {
            buckets.getFirst().put(key, value);
        }
    }

    @Override
    public void put(K key, V value) {
        synchronized (lock) {
            Iterator<HashMap<K, V>> it = buckets.iterator();
            HashMap<K, V> bucket = it.next();
            bucket.put(key, value);
            while (it.hasNext()) {
                bucket = it.next();
                bucket.remove(key);
            }
        }
    }

    @Override
    public Object remove(K key) {
        synchronized (lock) {
            for (HashMap<K, V> bucket : buckets) {
                if (bucket.containsKey(key)) {
                    return bucket.remove(key);
                }
            }
            return null;
        }
    }

    @Override
    public int size() {
        synchronized (lock) {
            int size = 0;
            for (HashMap<K, V> bucket : buckets) {
                size += bucket.size();
            }
            return size;
        }
    }

    public void cleanup() {
        cleaner.interrupt();
    }

    public Map<K, V> buildMap() {
        Map<K, V> ret = new HashMap<>();
        synchronized (lock) {
            for (HashMap<K, V> bucket : buckets) {
                ret.putAll(bucket);
            }
            return ret;
        }
    }

}