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/**
* Copyright 2009 Google Inc.
*
* 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.
*/
package net.appjet.common.util;
import java.util.*;
// this class is synchronized
public class ExpiringMapping<K,V> {
private Map<K,TimeStampedValue> keyToValue =
new HashMap<K,TimeStampedValue>();
private SortedMap<Long,K> timeToKey= new TreeMap<Long,K>();
private long lastTimeStamp = 0;
private ExpiryPolicy policy;
public ExpiringMapping(final long maxAgeMillis) {
this(new ExpiryPolicy() {
public boolean hasExpired(long timeStamp, long now, int rank) {
return now - timeStamp > maxAgeMillis;
}
});
}
protected ExpiringMapping(ExpiryPolicy policy) {
this.policy = policy;
}
public synchronized void clear() {
keyToValue.clear();
timeToKey.clear();
}
public synchronized void put(K key, V value) {
TimeStampedValue old = keyToValue.get(key);
if (old != null) {
timeToKey.remove(old.getTimeStamp());
}
TimeStampedValue newVal = new TimeStampedValue(value);
keyToValue.put(key, newVal);
timeToKey.put(newVal.getTimeStamp(), key);
checkExpiry();
}
public synchronized void touch(K key) {
TimeStampedValue old = keyToValue.get(key);
if (old != null) {
put(key, old.getValue());
}
}
public synchronized void remove(Object key) {
TimeStampedValue old = keyToValue.get(key);
if (old != null) {
keyToValue.remove(key);
timeToKey.remove(old.getTimeStamp());
}
}
// doesn't "touch" key or trigger expiry of expired items
public synchronized V get(Object key) {
if (keyToValue.containsKey(key)) {
return keyToValue.get(key).getValue();
} else {
return null;
}
}
public synchronized boolean containsKey(Object key) {
return keyToValue.containsKey(key);
}
public synchronized void checkExpiry() {
while (timeToKey.size() > 0) {
long oldestTime = timeToKey.firstKey();
if (hasExpired(oldestTime, timeToKey.size())) {
remove(timeToKey.get(oldestTime));
}
else {
break;
}
}
}
// lists keys in time order, oldest to newest
public synchronized List<K> listAllKeys() {
List<K> keyList = new java.util.ArrayList<K>(timeToKey.size());
for(Map.Entry<Long,K> entry : timeToKey.entrySet()) {
keyList.add(entry.getValue());
}
return Collections.unmodifiableList(keyList);
}
// result must be monotonic
private boolean hasExpired(long time, int rank) {
return policy.hasExpired(time, System.currentTimeMillis(), rank);
}
private long nowTimeStamp() {
// return "now", but unique
long now = System.currentTimeMillis();
if (now <= lastTimeStamp) {
now = lastTimeStamp+1;
}
lastTimeStamp = now;
return now;
}
private class TimeStampedValue {
private final V value;
private long timeStamp;
private TimeStampedValue(V value) {
this(value, nowTimeStamp());
}
private TimeStampedValue(V value, long timeStamp) {
this.value = value; this.timeStamp = timeStamp;
}
public void setTimeStamp(long ts) {
timeStamp = ts;
}
public long getTimeStamp() {
return timeStamp;
}
public V getValue() {
return value;
}
public String toString() {
return "("+value+", "+new Date(timeStamp)+")";
}
}
public synchronized String toString() {
return keyToValue.toString();
}
protected interface ExpiryPolicy {
// result must be monotonic wrt timeStamp given now
boolean hasExpired(long timeStamp, long now, int rank);
}
}
/*private static int compareLongs(long a, long b) {
if (a < b) return -1;
if (a > b) return 1;
return 0;
}*/
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