747 lines
25 KiB
Java
747 lines
25 KiB
Java
/**
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*
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* Copyright 2003-2005 Jive Software.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.jivesoftware.smack.util;
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import java.util.AbstractCollection;
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import java.util.AbstractSet;
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import java.util.Collection;
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import java.util.Collections;
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.Map;
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import java.util.Set;
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import java.util.logging.Logger;
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/**
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* A specialized Map that is size-limited (using an LRU algorithm) and
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* has an optional expiration time for cache items. The Map is thread-safe.<p>
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*
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* The algorithm for cache is as follows: a HashMap is maintained for fast
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* object lookup. Two linked lists are maintained: one keeps objects in the
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* order they are accessed from cache, the other keeps objects in the order
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* they were originally added to cache. When objects are added to cache, they
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* are first wrapped by a CacheObject which maintains the following pieces
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* of information:<ul>
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* <li> A pointer to the node in the linked list that maintains accessed
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* order for the object. Keeping a reference to the node lets us avoid
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* linear scans of the linked list.
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* <li> A pointer to the node in the linked list that maintains the age
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* of the object in cache. Keeping a reference to the node lets us avoid
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* linear scans of the linked list.</ul>
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* <p/>
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* To get an object from cache, a hash lookup is performed to get a reference
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* to the CacheObject that wraps the real object we are looking for.
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* The object is subsequently moved to the front of the accessed linked list
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* and any necessary cache cleanups are performed. Cache deletion and expiration
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* is performed as needed.
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*
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* @author Matt Tucker
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*/
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public class Cache<K, V> implements Map<K, V> {
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private static final Logger LOGGER = Logger.getLogger(Cache.class.getName());
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/**
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* The map the keys and values are stored in.
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*/
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protected Map<K, CacheObject<V>> map;
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/**
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* Linked list to maintain order that cache objects are accessed
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* in, most used to least used.
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*/
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protected LinkedList lastAccessedList;
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/**
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* Linked list to maintain time that cache objects were initially added
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* to the cache, most recently added to oldest added.
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*/
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protected LinkedList ageList;
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/**
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* Maximum number of items the cache will hold.
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*/
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protected int maxCacheSize;
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/**
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* Maximum length of time objects can exist in cache before expiring.
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*/
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protected long maxLifetime;
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/**
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* Maintain the number of cache hits and misses. A cache hit occurs every
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* time the get method is called and the cache contains the requested
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* object. A cache miss represents the opposite occurence.<p>
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*
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* Keeping track of cache hits and misses lets one measure how efficient
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* the cache is; the higher the percentage of hits, the more efficient.
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*/
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protected long cacheHits, cacheMisses = 0L;
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/**
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* Create a new cache and specify the maximum size of for the cache in
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* bytes, and the maximum lifetime of objects.
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*
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* @param maxSize the maximum number of objects the cache will hold. -1
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* means the cache has no max size.
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* @param maxLifetime the maximum amount of time (in ms) objects can exist in
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* cache before being deleted. -1 means objects never expire.
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*/
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public Cache(int maxSize, long maxLifetime) {
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if (maxSize == 0) {
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throw new IllegalArgumentException("Max cache size cannot be 0.");
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}
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this.maxCacheSize = maxSize;
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this.maxLifetime = maxLifetime;
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// Our primary data structure is a hash map. The default capacity of 11
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// is too small in almost all cases, so we set it bigger.
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map = new HashMap<K, CacheObject<V>>(103);
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lastAccessedList = new LinkedList();
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ageList = new LinkedList();
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}
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public synchronized V put(K key, V value) {
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V oldValue = null;
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// Delete an old entry if it exists.
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if (map.containsKey(key)) {
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oldValue = remove(key, true);
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}
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CacheObject<V> cacheObject = new CacheObject<V>(value);
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map.put(key, cacheObject);
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// Make an entry into the cache order list.
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// Store the cache order list entry so that we can get back to it
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// during later lookups.
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cacheObject.lastAccessedListNode = lastAccessedList.addFirst(key);
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// Add the object to the age list
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LinkedListNode ageNode = ageList.addFirst(key);
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ageNode.timestamp = System.currentTimeMillis();
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cacheObject.ageListNode = ageNode;
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// If cache is too full, remove least used cache entries until it is not too full.
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cullCache();
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return oldValue;
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}
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public synchronized V get(Object key) {
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// First, clear all entries that have been in cache longer than the
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// maximum defined age.
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deleteExpiredEntries();
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CacheObject<V> cacheObject = map.get(key);
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if (cacheObject == null) {
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// The object didn't exist in cache, so increment cache misses.
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cacheMisses++;
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return null;
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}
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// Remove the object from it's current place in the cache order list,
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// and re-insert it at the front of the list.
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cacheObject.lastAccessedListNode.remove();
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lastAccessedList.addFirst(cacheObject.lastAccessedListNode);
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// The object exists in cache, so increment cache hits. Also, increment
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// the object's read count.
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cacheHits++;
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cacheObject.readCount++;
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return cacheObject.object;
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}
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public synchronized V remove(Object key) {
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return remove(key, false);
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}
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/*
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* Remove operation with a flag so we can tell coherence if the remove was
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* caused by cache internal processing such as eviction or loading
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*/
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public synchronized V remove(Object key, boolean internal) {
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//noinspection SuspiciousMethodCalls
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CacheObject<V> cacheObject = map.remove(key);
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// If the object is not in cache, stop trying to remove it.
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if (cacheObject == null) {
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return null;
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}
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// Remove from the cache order list
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cacheObject.lastAccessedListNode.remove();
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cacheObject.ageListNode.remove();
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// Remove references to linked list nodes
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cacheObject.ageListNode = null;
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cacheObject.lastAccessedListNode = null;
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return cacheObject.object;
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}
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public synchronized void clear() {
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Object[] keys = map.keySet().toArray();
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for (Object key : keys) {
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remove(key);
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}
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// Now, reset all containers.
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map.clear();
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lastAccessedList.clear();
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ageList.clear();
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cacheHits = 0;
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cacheMisses = 0;
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}
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public synchronized int size() {
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// First, clear all entries that have been in cache longer than the
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// maximum defined age.
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deleteExpiredEntries();
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return map.size();
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}
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public synchronized boolean isEmpty() {
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// First, clear all entries that have been in cache longer than the
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// maximum defined age.
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deleteExpiredEntries();
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return map.isEmpty();
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}
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public synchronized Collection<V> values() {
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// First, clear all entries that have been in cache longer than the
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// maximum defined age.
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deleteExpiredEntries();
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return Collections.unmodifiableCollection(new AbstractCollection<V>() {
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Collection<CacheObject<V>> values = map.values();
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public Iterator<V> iterator() {
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return new Iterator<V>() {
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Iterator<CacheObject<V>> it = values.iterator();
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public boolean hasNext() {
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return it.hasNext();
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}
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public V next() {
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return it.next().object;
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}
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public void remove() {
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it.remove();
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}
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};
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}
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public int size() {
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return values.size();
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}
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});
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}
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public synchronized boolean containsKey(Object key) {
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// First, clear all entries that have been in cache longer than the
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// maximum defined age.
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deleteExpiredEntries();
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return map.containsKey(key);
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}
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@SuppressWarnings("unchecked")
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public void putAll(Map<? extends K, ? extends V> map) {
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for (Entry<? extends K, ? extends V> entry : map.entrySet()) {
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V value = entry.getValue();
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// If the map is another DefaultCache instance than the
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// entry values will be CacheObject instances that need
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// to be converted to the normal object form.
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if (value instanceof CacheObject) {
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//noinspection unchecked
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value = ((CacheObject<V>) value).object;
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}
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put(entry.getKey(), value);
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}
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}
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public synchronized boolean containsValue(Object value) {
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// First, clear all entries that have been in cache longer than the
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// maximum defined age.
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deleteExpiredEntries();
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//noinspection unchecked
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@SuppressWarnings("unchecked")
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CacheObject<V> cacheObject = new CacheObject<V>((V) value);
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return map.containsValue(cacheObject);
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}
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public synchronized Set<Map.Entry<K, V>> entrySet() {
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// Warning -- this method returns CacheObject instances and not Objects
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// in the same form they were put into cache.
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// First, clear all entries that have been in cache longer than the
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// maximum defined age.
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deleteExpiredEntries();
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return new AbstractSet<Map.Entry<K, V>>() {
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private final Set<Map.Entry<K, CacheObject<V>>> set = map.entrySet();
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public Iterator<Entry<K, V>> iterator() {
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return new Iterator<Entry<K, V>>() {
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private final Iterator<Entry<K, CacheObject<V>>> it = set.iterator();
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public boolean hasNext() {
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return it.hasNext();
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}
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public Entry<K, V> next() {
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Map.Entry<K, CacheObject<V>> entry = it.next();
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return new AbstractMapEntry<K, V>(entry.getKey(), entry.getValue().object) {
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@Override
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public V setValue(V value) {
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throw new UnsupportedOperationException("Cannot set");
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}
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};
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}
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public void remove() {
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it.remove();
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}
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};
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}
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public int size() {
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return set.size();
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}
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};
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}
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public synchronized Set<K> keySet() {
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// First, clear all entries that have been in cache longer than the
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// maximum defined age.
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deleteExpiredEntries();
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return Collections.unmodifiableSet(map.keySet());
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}
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public long getCacheHits() {
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return cacheHits;
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}
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public long getCacheMisses() {
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return cacheMisses;
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}
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public int getMaxCacheSize() {
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return maxCacheSize;
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}
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public synchronized void setMaxCacheSize(int maxCacheSize) {
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this.maxCacheSize = maxCacheSize;
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// It's possible that the new max size is smaller than our current cache
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// size. If so, we need to delete infrequently used items.
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cullCache();
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}
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public long getMaxLifetime() {
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return maxLifetime;
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}
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public void setMaxLifetime(long maxLifetime) {
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this.maxLifetime = maxLifetime;
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}
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/**
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* Clears all entries out of cache where the entries are older than the
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* maximum defined age.
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*/
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protected synchronized void deleteExpiredEntries() {
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// Check if expiration is turned on.
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if (maxLifetime <= 0) {
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return;
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}
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// Remove all old entries. To do this, we remove objects from the end
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// of the linked list until they are no longer too old. We get to avoid
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// any hash lookups or looking at any more objects than is strictly
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// neccessary.
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LinkedListNode node = ageList.getLast();
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// If there are no entries in the age list, return.
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if (node == null) {
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return;
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}
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// Determine the expireTime, which is the moment in time that elements
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// should expire from cache. Then, we can do an easy check to see
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// if the expire time is greater than the expire time.
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long expireTime = System.currentTimeMillis() - maxLifetime;
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while (expireTime > node.timestamp) {
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if (remove(node.object, true) == null) {
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LOGGER.warning("Error attempting to remove(" + node.object.toString() + ") - cacheObject not found in cache!");
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// remove from the ageList
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node.remove();
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}
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// Get the next node.
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node = ageList.getLast();
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// If there are no more entries in the age list, return.
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if (node == null) {
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return;
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}
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}
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}
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/**
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* Removes the least recently used elements if the cache size is greater than
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* or equal to the maximum allowed size until the cache is at least 10% empty.
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*/
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protected synchronized void cullCache() {
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// Check if a max cache size is defined.
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if (maxCacheSize < 0) {
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return;
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}
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// See if the cache is too big. If so, clean out cache until it's 10% free.
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if (map.size() > maxCacheSize) {
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// First, delete any old entries to see how much memory that frees.
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deleteExpiredEntries();
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// Next, delete the least recently used elements until 10% of the cache
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// has been freed.
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int desiredSize = (int) (maxCacheSize * .90);
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for (int i=map.size(); i>desiredSize; i--) {
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// Get the key and invoke the remove method on it.
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if (remove(lastAccessedList.getLast().object, true) == null) {
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LOGGER.warning("Error attempting to cullCache with remove(" + lastAccessedList.getLast().object.toString() + ") - cacheObject not found in cache!");
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lastAccessedList.getLast().remove();
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}
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}
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}
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}
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/**
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* Wrapper for all objects put into cache. It's primary purpose is to maintain
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* references to the linked lists that maintain the creation time of the object
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* and the ordering of the most used objects.
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*
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* This class is optimized for speed rather than strictly correct encapsulation.
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*/
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private static class CacheObject<V> {
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/**
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* Underlying object wrapped by the CacheObject.
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*/
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public V object;
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/**
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* A reference to the node in the cache order list. We keep the reference
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* here to avoid linear scans of the list. Every time the object is
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* accessed, the node is removed from its current spot in the list and
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* moved to the front.
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*/
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public LinkedListNode lastAccessedListNode;
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/**
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* A reference to the node in the age order list. We keep the reference
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* here to avoid linear scans of the list. The reference is used if the
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* object has to be deleted from the list.
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*/
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public LinkedListNode ageListNode;
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/**
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* A count of the number of times the object has been read from cache.
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*/
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@SuppressWarnings("unused")
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public int readCount = 0;
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/**
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* Creates a new cache object wrapper.
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*
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* @param object the underlying Object to wrap.
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*/
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public CacheObject(V object) {
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this.object = object;
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}
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public boolean equals(Object o) {
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if (this == o) {
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return true;
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}
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if (!(o instanceof CacheObject)) {
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return false;
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}
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final CacheObject<?> cacheObject = (CacheObject<?>) o;
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return object.equals(cacheObject.object);
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}
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public int hashCode() {
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return object.hashCode();
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}
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}
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/**
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* Simple LinkedList implementation. The main feature is that list nodes
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* are public, which allows very fast delete operations when one has a
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* reference to the node that is to be deleted.<p>
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*/
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private static class LinkedList {
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/**
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* The root of the list keeps a reference to both the first and last
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* elements of the list.
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*/
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private LinkedListNode head = new LinkedListNode("head", null, null);
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/**
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* Creates a new linked list.
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*/
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public LinkedList() {
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head.next = head.previous = head;
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}
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/**
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* Returns the first linked list node in the list.
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*
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* @return the first element of the list.
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*/
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@SuppressWarnings("unused")
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public LinkedListNode getFirst() {
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LinkedListNode node = head.next;
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if (node == head) {
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return null;
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}
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return node;
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}
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/**
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* Returns the last linked list node in the list.
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*
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* @return the last element of the list.
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*/
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public LinkedListNode getLast() {
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LinkedListNode node = head.previous;
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if (node == head) {
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return null;
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}
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return node;
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}
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/**
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* Adds a node to the beginning of the list.
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*
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* @param node the node to add to the beginning of the list.
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* @return the node
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*/
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public LinkedListNode addFirst(LinkedListNode node) {
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node.next = head.next;
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node.previous = head;
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node.previous.next = node;
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node.next.previous = node;
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return node;
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}
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/**
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* Adds an object to the beginning of the list by automatically creating a
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* a new node and adding it to the beginning of the list.
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*
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* @param object the object to add to the beginning of the list.
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* @return the node created to wrap the object.
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*/
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public LinkedListNode addFirst(Object object) {
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LinkedListNode node = new LinkedListNode(object, head.next, head);
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node.previous.next = node;
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node.next.previous = node;
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return node;
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}
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/**
|
|
* Adds an object to the end of the list by automatically creating a
|
|
* a new node and adding it to the end of the list.
|
|
*
|
|
* @param object the object to add to the end of the list.
|
|
* @return the node created to wrap the object.
|
|
*/
|
|
@SuppressWarnings("unused")
|
|
public LinkedListNode addLast(Object object) {
|
|
LinkedListNode node = new LinkedListNode(object, head, head.previous);
|
|
node.previous.next = node;
|
|
node.next.previous = node;
|
|
return node;
|
|
}
|
|
|
|
/**
|
|
* Erases all elements in the list and re-initializes it.
|
|
*/
|
|
public void clear() {
|
|
//Remove all references in the list.
|
|
LinkedListNode node = getLast();
|
|
while (node != null) {
|
|
node.remove();
|
|
node = getLast();
|
|
}
|
|
|
|
//Re-initialize.
|
|
head.next = head.previous = head;
|
|
}
|
|
|
|
/**
|
|
* Returns a String representation of the linked list with a comma
|
|
* delimited list of all the elements in the list.
|
|
*
|
|
* @return a String representation of the LinkedList.
|
|
*/
|
|
public String toString() {
|
|
LinkedListNode node = head.next;
|
|
StringBuilder buf = new StringBuilder();
|
|
while (node != head) {
|
|
buf.append(node.toString()).append(", ");
|
|
node = node.next;
|
|
}
|
|
return buf.toString();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Doubly linked node in a LinkedList. Most LinkedList implementations keep the
|
|
* equivalent of this class private. We make it public so that references
|
|
* to each node in the list can be maintained externally.
|
|
*
|
|
* Exposing this class lets us make remove operations very fast. Remove is
|
|
* built into this class and only requires two reference reassignments. If
|
|
* remove existed in the main LinkedList class, a linear scan would have to
|
|
* be performed to find the correct node to delete.
|
|
*
|
|
* The linked list implementation was specifically written for the Jive
|
|
* cache system. While it can be used as a general purpose linked list, for
|
|
* most applications, it is more suitable to use the linked list that is part
|
|
* of the Java Collections package.
|
|
*/
|
|
private static class LinkedListNode {
|
|
|
|
public LinkedListNode previous;
|
|
public LinkedListNode next;
|
|
public Object object;
|
|
|
|
/**
|
|
* This class is further customized for the Jive cache system. It
|
|
* maintains a timestamp of when a Cacheable object was first added to
|
|
* cache. Timestamps are stored as long values and represent the number
|
|
* of milliseconds passed since January 1, 1970 00:00:00.000 GMT.<p>
|
|
*
|
|
* The creation timestamp is used in the case that the cache has a
|
|
* maximum lifetime set. In that case, when
|
|
* [current time] - [creation time] > [max lifetime], the object will be
|
|
* deleted from cache.
|
|
*/
|
|
public long timestamp;
|
|
|
|
/**
|
|
* Constructs a new linked list node.
|
|
*
|
|
* @param object the Object that the node represents.
|
|
* @param next a reference to the next LinkedListNode in the list.
|
|
* @param previous a reference to the previous LinkedListNode in the list.
|
|
*/
|
|
public LinkedListNode(Object object, LinkedListNode next,
|
|
LinkedListNode previous)
|
|
{
|
|
this.object = object;
|
|
this.next = next;
|
|
this.previous = previous;
|
|
}
|
|
|
|
/**
|
|
* Removes this node from the linked list that it is a part of.
|
|
*/
|
|
public void remove() {
|
|
previous.next = next;
|
|
next.previous = previous;
|
|
}
|
|
|
|
/**
|
|
* Returns a String representation of the linked list node by calling the
|
|
* toString method of the node's object.
|
|
*
|
|
* @return a String representation of the LinkedListNode.
|
|
*/
|
|
public String toString() {
|
|
return object.toString();
|
|
}
|
|
}
|
|
|
|
static class AbstractMapEntry<K, V> implements Map.Entry<K, V> {
|
|
final K key;
|
|
V value;
|
|
|
|
AbstractMapEntry(K key, V value) {
|
|
this.key = key;
|
|
this.value = value;
|
|
}
|
|
|
|
@Override
|
|
public K getKey() {
|
|
return key;
|
|
}
|
|
|
|
@Override
|
|
public V getValue() {
|
|
return value;
|
|
}
|
|
|
|
@Override
|
|
public V setValue(V value) {
|
|
V answer = this.value;
|
|
this.value = value;
|
|
return answer;
|
|
}
|
|
|
|
/**
|
|
* Compares this Map Entry with another Map Entry.
|
|
* <p/>
|
|
* Implemented per API documentation of {@link java.util.Map.Entry#equals(Object)}
|
|
*
|
|
* @param obj the object to compare to
|
|
* @return true if equal key and value
|
|
*/
|
|
@SuppressWarnings("rawtypes")
|
|
@Override
|
|
public boolean equals(Object obj) {
|
|
if (obj == this) {
|
|
return true;
|
|
}
|
|
if (obj instanceof Map.Entry == false) {
|
|
return false;
|
|
}
|
|
Map.Entry other = (Map.Entry) obj;
|
|
return (getKey() == null ? other.getKey() == null : getKey().equals(other.getKey()))
|
|
&& (getValue() == null ? other.getValue() == null : getValue().equals(
|
|
other.getValue()));
|
|
}
|
|
|
|
/**
|
|
* Gets a hashCode compatible with the equals method.
|
|
* <p/>
|
|
* Implemented per API documentation of {@link java.util.Map.Entry#hashCode()}
|
|
*
|
|
* @return a suitable hash code
|
|
*/
|
|
@Override
|
|
public int hashCode() {
|
|
return (getKey() == null ? 0 : getKey().hashCode())
|
|
^ (getValue() == null ? 0 : getValue().hashCode());
|
|
}
|
|
}
|
|
}
|