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Diffstat (limited to 'src/org/jivesoftware/smack/util/Cache.java')
| -rw-r--r-- | src/org/jivesoftware/smack/util/Cache.java | 678 |
1 files changed, 678 insertions, 0 deletions
diff --git a/src/org/jivesoftware/smack/util/Cache.java b/src/org/jivesoftware/smack/util/Cache.java new file mode 100644 index 0000000..964ac23 --- /dev/null +++ b/src/org/jivesoftware/smack/util/Cache.java @@ -0,0 +1,678 @@ +/** + * $Revision: 1456 $ + * $Date: 2005-06-01 22:04:54 -0700 (Wed, 01 Jun 2005) $ + * + * Copyright 2003-2005 Jive Software. + * + * All rights reserved. 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 org.jivesoftware.smack.util; + +import org.jivesoftware.smack.util.collections.AbstractMapEntry; + +import java.util.*; + +/** + * A specialized Map that is size-limited (using an LRU algorithm) and + * has an optional expiration time for cache items. The Map is thread-safe.<p> + * + * The algorithm for cache is as follows: a HashMap is maintained for fast + * object lookup. Two linked lists are maintained: one keeps objects in the + * order they are accessed from cache, the other keeps objects in the order + * they were originally added to cache. When objects are added to cache, they + * are first wrapped by a CacheObject which maintains the following pieces + * of information:<ul> + * <li> A pointer to the node in the linked list that maintains accessed + * order for the object. Keeping a reference to the node lets us avoid + * linear scans of the linked list. + * <li> A pointer to the node in the linked list that maintains the age + * of the object in cache. Keeping a reference to the node lets us avoid + * linear scans of the linked list.</ul> + * <p/> + * To get an object from cache, a hash lookup is performed to get a reference + * to the CacheObject that wraps the real object we are looking for. + * The object is subsequently moved to the front of the accessed linked list + * and any necessary cache cleanups are performed. Cache deletion and expiration + * is performed as needed. + * + * @author Matt Tucker + */ +public class Cache<K, V> implements Map<K, V> { + + /** + * The map the keys and values are stored in. + */ + protected Map<K, CacheObject<V>> map; + + /** + * Linked list to maintain order that cache objects are accessed + * in, most used to least used. + */ + protected LinkedList lastAccessedList; + + /** + * Linked list to maintain time that cache objects were initially added + * to the cache, most recently added to oldest added. + */ + protected LinkedList ageList; + + /** + * Maximum number of items the cache will hold. + */ + protected int maxCacheSize; + + /** + * Maximum length of time objects can exist in cache before expiring. + */ + protected long maxLifetime; + + /** + * Maintain the number of cache hits and misses. A cache hit occurs every + * time the get method is called and the cache contains the requested + * object. A cache miss represents the opposite occurence.<p> + * + * Keeping track of cache hits and misses lets one measure how efficient + * the cache is; the higher the percentage of hits, the more efficient. + */ + protected long cacheHits, cacheMisses = 0L; + + /** + * Create a new cache and specify the maximum size of for the cache in + * bytes, and the maximum lifetime of objects. + * + * @param maxSize the maximum number of objects the cache will hold. -1 + * means the cache has no max size. + * @param maxLifetime the maximum amount of time (in ms) objects can exist in + * cache before being deleted. -1 means objects never expire. + */ + public Cache(int maxSize, long maxLifetime) { + if (maxSize == 0) { + throw new IllegalArgumentException("Max cache size cannot be 0."); + } + this.maxCacheSize = maxSize; + this.maxLifetime = maxLifetime; + + // Our primary data structure is a hash map. The default capacity of 11 + // is too small in almost all cases, so we set it bigger. + map = new HashMap<K, CacheObject<V>>(103); + + lastAccessedList = new LinkedList(); + ageList = new LinkedList(); + } + + public synchronized V put(K key, V value) { + V oldValue = null; + // Delete an old entry if it exists. + if (map.containsKey(key)) { + oldValue = remove(key, true); + } + + CacheObject<V> cacheObject = new CacheObject<V>(value); + map.put(key, cacheObject); + // Make an entry into the cache order list. + // Store the cache order list entry so that we can get back to it + // during later lookups. + cacheObject.lastAccessedListNode = lastAccessedList.addFirst(key); + // Add the object to the age list + LinkedListNode ageNode = ageList.addFirst(key); + ageNode.timestamp = System.currentTimeMillis(); + cacheObject.ageListNode = ageNode; + + // If cache is too full, remove least used cache entries until it is not too full. + cullCache(); + + return oldValue; + } + + public synchronized V get(Object key) { + // First, clear all entries that have been in cache longer than the + // maximum defined age. + deleteExpiredEntries(); + + CacheObject<V> cacheObject = map.get(key); + if (cacheObject == null) { + // The object didn't exist in cache, so increment cache misses. + cacheMisses++; + return null; + } + // Remove the object from it's current place in the cache order list, + // and re-insert it at the front of the list. + cacheObject.lastAccessedListNode.remove(); + lastAccessedList.addFirst(cacheObject.lastAccessedListNode); + + // The object exists in cache, so increment cache hits. Also, increment + // the object's read count. + cacheHits++; + cacheObject.readCount++; + + return cacheObject.object; + } + + public synchronized V remove(Object key) { + return remove(key, false); + } + + /* + * Remove operation with a flag so we can tell coherence if the remove was + * caused by cache internal processing such as eviction or loading + */ + public synchronized V remove(Object key, boolean internal) { + //noinspection SuspiciousMethodCalls + CacheObject<V> cacheObject = map.remove(key); + // If the object is not in cache, stop trying to remove it. + if (cacheObject == null) { + return null; + } + // Remove from the cache order list + cacheObject.lastAccessedListNode.remove(); + cacheObject.ageListNode.remove(); + // Remove references to linked list nodes + cacheObject.ageListNode = null; + cacheObject.lastAccessedListNode = null; + + return cacheObject.object; + } + + public synchronized void clear() { + Object[] keys = map.keySet().toArray(); + for (Object key : keys) { + remove(key); + } + + // Now, reset all containers. + map.clear(); + lastAccessedList.clear(); + ageList.clear(); + + cacheHits = 0; + cacheMisses = 0; + } + + public synchronized int size() { + // First, clear all entries that have been in cache longer than the + // maximum defined age. + deleteExpiredEntries(); + + return map.size(); + } + + public synchronized boolean isEmpty() { + // First, clear all entries that have been in cache longer than the + // maximum defined age. + deleteExpiredEntries(); + + return map.isEmpty(); + } + + public synchronized Collection<V> values() { + // First, clear all entries that have been in cache longer than the + // maximum defined age. + deleteExpiredEntries(); + + return Collections.unmodifiableCollection(new AbstractCollection<V>() { + Collection<CacheObject<V>> values = map.values(); + public Iterator<V> iterator() { + return new Iterator<V>() { + Iterator<CacheObject<V>> it = values.iterator(); + + public boolean hasNext() { + return it.hasNext(); + } + + public V next() { + return it.next().object; + } + + public void remove() { + it.remove(); + } + }; + } + + public int size() { + return values.size(); + } + }); + } + + public synchronized boolean containsKey(Object key) { + // First, clear all entries that have been in cache longer than the + // maximum defined age. + deleteExpiredEntries(); + + return map.containsKey(key); + } + + public void putAll(Map<? extends K, ? extends V> map) { + for (Entry<? extends K, ? extends V> entry : map.entrySet()) { + V value = entry.getValue(); + // If the map is another DefaultCache instance than the + // entry values will be CacheObject instances that need + // to be converted to the normal object form. + if (value instanceof CacheObject) { + //noinspection unchecked + value = ((CacheObject<V>) value).object; + } + put(entry.getKey(), value); + } + } + + public synchronized boolean containsValue(Object value) { + // First, clear all entries that have been in cache longer than the + // maximum defined age. + deleteExpiredEntries(); + + //noinspection unchecked + CacheObject<V> cacheObject = new CacheObject<V>((V) value); + + return map.containsValue(cacheObject); + } + + public synchronized Set<Map.Entry<K, V>> entrySet() { + // Warning -- this method returns CacheObject instances and not Objects + // in the same form they were put into cache. + + // First, clear all entries that have been in cache longer than the + // maximum defined age. + deleteExpiredEntries(); + + return new AbstractSet<Map.Entry<K, V>>() { + private final Set<Map.Entry<K, CacheObject<V>>> set = map.entrySet(); + + public Iterator<Entry<K, V>> iterator() { + return new Iterator<Entry<K, V>>() { + private final Iterator<Entry<K, CacheObject<V>>> it = set.iterator(); + public boolean hasNext() { + return it.hasNext(); + } + + public Entry<K, V> next() { + Map.Entry<K, CacheObject<V>> entry = it.next(); + return new AbstractMapEntry<K, V>(entry.getKey(), entry.getValue().object) { + @Override + public V setValue(V value) { + throw new UnsupportedOperationException("Cannot set"); + } + }; + } + + public void remove() { + it.remove(); + } + }; + + } + + public int size() { + return set.size(); + } + }; + } + + public synchronized Set<K> keySet() { + // First, clear all entries that have been in cache longer than the + // maximum defined age. + deleteExpiredEntries(); + + return Collections.unmodifiableSet(map.keySet()); + } + + public long getCacheHits() { + return cacheHits; + } + + public long getCacheMisses() { + return cacheMisses; + } + + public int getMaxCacheSize() { + return maxCacheSize; + } + + public synchronized void setMaxCacheSize(int maxCacheSize) { + this.maxCacheSize = maxCacheSize; + // It's possible that the new max size is smaller than our current cache + // size. If so, we need to delete infrequently used items. + cullCache(); + } + + public long getMaxLifetime() { + return maxLifetime; + } + + public void setMaxLifetime(long maxLifetime) { + this.maxLifetime = maxLifetime; + } + + /** + * Clears all entries out of cache where the entries are older than the + * maximum defined age. + */ + protected synchronized void deleteExpiredEntries() { + // Check if expiration is turned on. + if (maxLifetime <= 0) { + return; + } + + // Remove all old entries. To do this, we remove objects from the end + // of the linked list until they are no longer too old. We get to avoid + // any hash lookups or looking at any more objects than is strictly + // neccessary. + LinkedListNode node = ageList.getLast(); + // If there are no entries in the age list, return. + if (node == null) { + return; + } + + // Determine the expireTime, which is the moment in time that elements + // should expire from cache. Then, we can do an easy check to see + // if the expire time is greater than the expire time. + long expireTime = System.currentTimeMillis() - maxLifetime; + + while (expireTime > node.timestamp) { + if (remove(node.object, true) == null) { + System.err.println("Error attempting to remove(" + node.object.toString() + + ") - cacheObject not found in cache!"); + // remove from the ageList + node.remove(); + } + + // Get the next node. + node = ageList.getLast(); + // If there are no more entries in the age list, return. + if (node == null) { + return; + } + } + } + + /** + * Removes the least recently used elements if the cache size is greater than + * or equal to the maximum allowed size until the cache is at least 10% empty. + */ + protected synchronized void cullCache() { + // Check if a max cache size is defined. + if (maxCacheSize < 0) { + return; + } + + // See if the cache is too big. If so, clean out cache until it's 10% free. + if (map.size() > maxCacheSize) { + // First, delete any old entries to see how much memory that frees. + deleteExpiredEntries(); + // Next, delete the least recently used elements until 10% of the cache + // has been freed. + int desiredSize = (int) (maxCacheSize * .90); + for (int i=map.size(); i>desiredSize; i--) { + // Get the key and invoke the remove method on it. + if (remove(lastAccessedList.getLast().object, true) == null) { + System.err.println("Error attempting to cullCache with remove(" + + lastAccessedList.getLast().object.toString() + ") - " + + "cacheObject not found in cache!"); + lastAccessedList.getLast().remove(); + } + } + } + } + + /** + * Wrapper for all objects put into cache. It's primary purpose is to maintain + * references to the linked lists that maintain the creation time of the object + * and the ordering of the most used objects. + * + * This class is optimized for speed rather than strictly correct encapsulation. + */ + private static class CacheObject<V> { + + /** + * Underlying object wrapped by the CacheObject. + */ + public V object; + + /** + * A reference to the node in the cache order list. We keep the reference + * here to avoid linear scans of the list. Every time the object is + * accessed, the node is removed from its current spot in the list and + * moved to the front. + */ + public LinkedListNode lastAccessedListNode; + + /** + * A reference to the node in the age order list. We keep the reference + * here to avoid linear scans of the list. The reference is used if the + * object has to be deleted from the list. + */ + public LinkedListNode ageListNode; + + /** + * A count of the number of times the object has been read from cache. + */ + public int readCount = 0; + + /** + * Creates a new cache object wrapper. + * + * @param object the underlying Object to wrap. + */ + public CacheObject(V object) { + this.object = object; + } + + public boolean equals(Object o) { + if (this == o) { + return true; + } + if (!(o instanceof CacheObject)) { + return false; + } + + final CacheObject<?> cacheObject = (CacheObject<?>) o; + + return object.equals(cacheObject.object); + + } + + public int hashCode() { + return object.hashCode(); + } + } + + /** + * Simple LinkedList implementation. The main feature is that list nodes + * are public, which allows very fast delete operations when one has a + * reference to the node that is to be deleted.<p> + */ + private static class LinkedList { + + /** + * The root of the list keeps a reference to both the first and last + * elements of the list. + */ + private LinkedListNode head = new LinkedListNode("head", null, null); + + /** + * Creates a new linked list. + */ + public LinkedList() { + head.next = head.previous = head; + } + + /** + * Returns the first linked list node in the list. + * + * @return the first element of the list. + */ + public LinkedListNode getFirst() { + LinkedListNode node = head.next; + if (node == head) { + return null; + } + return node; + } + + /** + * Returns the last linked list node in the list. + * + * @return the last element of the list. + */ + public LinkedListNode getLast() { + LinkedListNode node = head.previous; + if (node == head) { + return null; + } + return node; + } + + /** + * Adds a node to the beginning of the list. + * + * @param node the node to add to the beginning of the list. + * @return the node + */ + public LinkedListNode addFirst(LinkedListNode node) { + node.next = head.next; + node.previous = head; + node.previous.next = node; + node.next.previous = node; + return node; + } + + /** + * Adds an object to the beginning of the list by automatically creating a + * a new node and adding it to the beginning of the list. + * + * @param object the object to add to the beginning of the list. + * @return the node created to wrap the object. + */ + public LinkedListNode addFirst(Object object) { + LinkedListNode node = new LinkedListNode(object, head.next, head); + node.previous.next = node; + node.next.previous = node; + return node; + } + + /** + * 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. + */ + 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(); + } + } +}
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