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NavigableMapEvictionQueue.java
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/**
*
* Copyright 2012, Stoyan Rachev
*
* 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 com.stoyanr.evictor.queue;
import java.util.NoSuchElementException;
import java.util.concurrent.ConcurrentNavigableMap;
import java.util.concurrent.ConcurrentSkipListMap;
import com.stoyanr.evictor.EvictionQueue;
import com.stoyanr.evictor.map.EvictibleEntry;
/**
* An {@link EvictionQueue} which uses a
* {@link java.util.concurrent.ConcurrentNavigableMap} to store its entries. The
* key in the map is the eviction time of the entry, and the value is the entry
* itself.
*
* @author Stoyan Rachev
*
* @param <K>
* the type of keys maintained by this map
*
* @param <V>
* the type of mapped values
*/
public class NavigableMapEvictionQueue<K, V> implements EvictionQueue<K, V> {
private final ConcurrentNavigableMap<Long, EvictibleEntry<K, V>> map;
/**
* Creates a navigable map eviction queue with a
* {@link java.util.concurrent.ConcurrentSkipListMap}.
*/
public NavigableMapEvictionQueue() {
this(new ConcurrentSkipListMap<Long, EvictibleEntry<K, V>>());
}
/**
* Creates a navigable map eviction queue with the specified map.
*
* @param map
* the map to be used
*
* @throws NullPointerException
* if the map is <code>null</code>
*/
public NavigableMapEvictionQueue(ConcurrentNavigableMap<Long, EvictibleEntry<K, V>> map) {
if (map == null) {
throw new NullPointerException("Map instnace cannot be null");
}
this.map = map;
}
/**
* {@inheritDoc}
*
* <p>
* This implementation simply returns true if the map is non-empty and vice
* versa.
* </p>
*/
@Override
public boolean hasEntries() {
return !map.isEmpty();
}
/**
* {@inheritDoc}
*
* <p>
* This implementation simply returns the first key in the map if it is
* non-empty, or 0 otherwise.
* </p>
*/
@Override
public long getNextEvictionTime() {
try {
return (!map.isEmpty()) ? map.firstKey() : 0;
} catch (NoSuchElementException e) {
// Safeguard in a concurrent environment
return 0;
}
}
/**
* {@inheritDoc}
*
* <p>
* This implementation simply invokes the <tt>put</tt> method on the map.
*/
@Override
public void putEntry(EvictibleEntry<K, V> e) {
map.put(e.getEvictionTime(), e);
}
/**
* {@inheritDoc}
*
* <p>
* This implementation simply invokes the <tt>remove</tt> method on the map.
* </p>
*/
@Override
public void removeEntry(EvictibleEntry<K, V> e) {
map.remove(e.getEvictionTime(), e);
}
/**
* {@inheritDoc}
*
* <p>
* This implementation uses the <tt>headMap</tt> method on the map to find
* all entries that should be evicted, and then calls the <tt>evict</tt>
* method on each one of them and removes them from the map.
* </p>
*/
@Override
public boolean evictEntries() {
boolean result = false;
ConcurrentNavigableMap<Long, EvictibleEntry<K, V>> head = map.headMap(System.nanoTime());
if (!head.isEmpty()) {
for (EvictibleEntry<K, V> e : head.values()) {
e.evict(false);
}
head.clear();
result = true;
}
return result;
}
}