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RotatingMap.java
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/
RotatingMap.java
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/**
* 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.utils;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import java.util.Map.Entry;
/**
* 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.
*
* <p>get, put, remove, containsKey, and size take O(numBuckets) time to run.
*
* <p>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 gets/puts.
*
* <p>Note: This class is not thread-safe since it does not protect against changes to buckets while it is being read
*/
public class RotatingMap<K, V> {
//this default ensures things expire at most 50% past the expiration time
private static final int DEFAULT_NUM_BUCKETS = 3;
private final LinkedList<HashMap<K, V>> buckets;
private final ExpiredCallback<K, V> callback;
public RotatingMap(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;
}
public RotatingMap(ExpiredCallback<K, V> callback) {
this(DEFAULT_NUM_BUCKETS, callback);
}
public RotatingMap(int numBuckets) {
this(numBuckets, null);
}
public Map<K, V> rotate() {
Map<K, V> dead = buckets.removeLast();
buckets.addFirst(new HashMap<K, V>());
if (callback != null) {
for (Entry<K, V> entry : dead.entrySet()) {
callback.expire(entry.getKey(), entry.getValue());
}
}
return dead;
}
public boolean containsKey(K key) {
for (HashMap<K, V> bucket : buckets) {
if (bucket.containsKey(key)) {
return true;
}
}
return false;
}
public V get(K key) {
for (HashMap<K, V> bucket : buckets) {
if (bucket.containsKey(key)) {
return bucket.get(key);
}
}
return null;
}
public void put(K key, V value) {
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);
}
}
public V remove(K key) {
for (HashMap<K, V> bucket : buckets) {
if (bucket.containsKey(key)) {
return bucket.remove(key);
}
}
return null;
}
public int size() {
int size = 0;
for (HashMap<K, V> bucket : buckets) {
size += bucket.size();
}
return size;
}
public interface ExpiredCallback<K, V> {
void expire(K key, V val);
}
}