/**
* Copyright 2003-2010 Terracotta, 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.sf.ehcache.store;
import net.sf.ehcache.CacheEntry;
import net.sf.ehcache.CacheException;
import net.sf.ehcache.Ehcache;
import net.sf.ehcache.Element;
import net.sf.ehcache.Status;
import net.sf.ehcache.writer.CacheWriterManager;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
/**
* An implementation of a LruMemoryStore.
* <p/>
* This uses {@link java.util.LinkedHashMap} as its backing map. It uses the {@link java.util.LinkedHashMap} LRU
* feature. LRU for this implementation means least recently accessed.
*
* @author <a href="mailto:gluck@thoughtworks.com">Greg Luck</a>
* @version $Id$
*/
public class LruMemoryStore extends AbstractStore {
private static final Logger LOG = LoggerFactory.getLogger(LruMemoryStore.class.getName());
/**
* The cache this store is associated with.
*/
protected Ehcache cache;
/**
* Map where items are stored by key.
*/
protected Map map;
/**
* The DiskStore associated with this MemoryStore.
*/
protected final Store diskStore;
/**
* status.
*/
protected Status status;
/**
* The maximum size of the store (0 == no limit)
*/
protected int maximumSize;
/**
* Constructor for the LruMemoryStore object
* The backing {@link java.util.LinkedHashMap} is created with LRU by access order.
*/
public LruMemoryStore(Ehcache cache, Store diskStore) {
status = Status.STATUS_UNINITIALISED;
this.maximumSize = cache.getCacheConfiguration().getMaxElementsInMemory();
this.cache = cache;
this.diskStore = diskStore;
map = new SpoolingLinkedHashMap();
status = Status.STATUS_ALIVE;
}
/**
* Puts an item in the cache. Note that this automatically results in
* {@link net.sf.ehcache.store.LruMemoryStore.SpoolingLinkedHashMap#removeEldestEntry} being called.
*
* @param element the element to add
*/
public final boolean put(Element element) throws CacheException {
return putInternal(element, null);
}
/**
* {@inheritDoc}
*/
public final boolean putWithWriter(Element element, CacheWriterManager writerManager) throws CacheException {
return putInternal(element, writerManager);
}
private synchronized boolean putInternal(Element element, CacheWriterManager writerManager) throws CacheException {
boolean newPut = true;
if (element != null) {
newPut = map.put(element.getObjectKey(), element) == null;
if (writerManager != null) {
writerManager.put(element);
}
doPut(element);
}
return newPut;
}
/**
* Allow specialised actions over adding the element to the map.
*
* @param element
*/
protected void doPut(Element element) throws CacheException {
//empty
}
/**
* Gets an item from the cache.
* <p/>
* The last access time in {@link net.sf.ehcache.Element} is updated.
*
* @param key the cache key
* @return the element, or null if there was no match for the key
*/
public final synchronized Element get(Object key) {
return (Element) map.get(key);
}
/**
* Gets an item from the cache, without updating statistics.
*
* @param key the cache key
* @return the element, or null if there was no match for the key
*/
public final synchronized Element getQuiet(Object key) {
return get(key);
}
/**
* Removes an Element from the store.
*
* @param key the key of the Element, usually a String
* @return the Element if one was found, else null
*/
public final Element remove(Object key) {
return removeInternal(key, null);
}
/**
* {@inheritDoc}
*/
public final Element removeWithWriter(Object key, CacheWriterManager writerManager) throws CacheException {
return removeInternal(key, writerManager);
}
private synchronized Element removeInternal(Object key, CacheWriterManager writerManager) throws CacheException {
// remove single item.
Element element = (Element) map.remove(key);
if (writerManager != null) {
writerManager.remove(new CacheEntry(key, element));
}
if (element != null) {
return element;
} else {
return null;
}
}
/**
* Remove all of the elements from the store.
*/
public final synchronized void removeAll() throws CacheException {
clear();
}
/**
* Clears any data structures and places it back to its state when it was first created.
*/
protected final void clear() {
map.clear();
}
/**
* Prepares for shutdown.
*/
public final synchronized void dispose() {
if (status.equals(Status.STATUS_SHUTDOWN)) {
return;
}
status = Status.STATUS_SHUTDOWN;
flush();
//release reference to cache
cache = null;
}
/**
* Flush to disk only if the cache is diskPersistent.
*/
public final void flush() {
if (cache.getCacheConfiguration().isDiskPersistent()) {
if (LOG.isDebugEnabled()) {
LOG.debug(cache.getName() + " is persistent. Spooling " + map.size() + " elements to the disk store.");
}
spoolAllToDisk();
}
//should be emptied if clearOnFlush is true
if (cache.getCacheConfiguration().isClearOnFlush()) {
clear();
}
}
/**
* Spools all elements to disk, in preparation for shutdown.
* <p/>
* This revised implementation is a little slower but avoids using increased memory during the method.
*/
protected final void spoolAllToDisk() {
boolean clearOnFlush = cache.getCacheConfiguration().isClearOnFlush();
for (Object key : getKeys()) {
Element element = (Element) map.get(key);
if (element != null) {
if (!element.isSerializable()) {
if (LOG.isWarnEnabled()) {
LOG.warn("Object with key " + element.getObjectKey()
+ " is not Serializable and is not being overflowed to disk.");
}
} else {
spoolToDisk(element);
//Don't notify listeners. They are not being removed from the cache, only a store
//Leave it in the memory store for performance if do not want to clear on flush
if (clearOnFlush) {
remove(key);
}
}
}
}
}
/**
* Puts the element in the DiskStore.
* Should only be called if isOverflowToDisk is true
* <p/>
* Relies on being called from a synchronized method
*
* @param element The Element
*/
protected void spoolToDisk(Element element) {
diskStore.put(element);
if (LOG.isDebugEnabled()) {
LOG.debug(cache.getName() + "Cache: spool to disk done for: " + element.getObjectKey());
}
}
/**
* Gets the status of the MemoryStore.
*/
public final Status getStatus() {
return status;
}
/**
* Gets an Array of the keys for all elements in the memory cache.
* <p/>
* Does not check for expired entries
*
* @return An Object[]
*/
public final synchronized List getKeys() {
return new ArrayList(map.keySet());
}
/**
* Returns the current cache size.
*
* @return The size value
*/
public final int getSize() {
return map.size();
}
/**
* Returns nothing since a disk store isn't clustered
*
* @return returns 0
*/
public final int getTerracottaClusteredSize() {
return 0;
}
/**
* An unsynchronized check to see if a key is in the Store. No check is made to see if the Element is expired.
*
* @param key The Element key
* @return true if found. If this method return false, it means that an Element with the given key is definitely not in the MemoryStore.
* If it returns true, there is an Element there. An attempt to get it may return null if the Element has expired.
*/
public final boolean containsKey(Object key) {
return map.containsKey(key);
}
/**
* Measures the size of the memory store by measuring the serialized size of all elements.
* If the objects are not Serializable they count as 0.
* <p/>
* Warning: This method can be very expensive to run. Allow approximately 1 second
* per 1MB of entries. Running this method could create liveness problems
* because the object lock is held for a long period
*
* @return the size, in bytes
*/
public final synchronized long getSizeInBytes() throws CacheException {
long sizeInBytes = 0;
for (Iterator iterator = map.values().iterator(); iterator.hasNext();) {
Element element = (Element) iterator.next();
if (element != null) {
sizeInBytes += element.getSerializedSize();
}
}
return sizeInBytes;
}
/**
* Evict the <code>Element</code>.
* <p/>
* Evict means that the <code>Element</code> is:
* <ul>
* <li>if, the store is diskPersistent, the <code>Element</code> is spooled to the DiskStore
* <li>if not, the <code>Element</code> is removed.
* </ul>
*
* @param element the <code>Element</code> to be evicted.
*/
protected final void evict(Element element) throws CacheException {
boolean spooled = false;
if (cache.getCacheConfiguration().isOverflowToDisk()) {
if (!element.isSerializable()) {
if (LOG.isWarnEnabled()) {
LOG.warn(new StringBuilder("Object with key ").append(element.getObjectKey())
.append(" is not Serializable and cannot be overflowed to disk").toString());
}
} else {
spoolToDisk(element);
spooled = true;
}
}
if (!spooled) {
cache.getCacheEventNotificationService().notifyElementEvicted(element, false);
}
}
/**
* Before eviction elements are checked.
*
* @param element
*/
protected final void notifyExpiry(Element element) {
cache.getCacheEventNotificationService().notifyElementExpiry(element, false);
}
/**
* An algorithm to tell if the MemoryStore is at or beyond its carrying capacity.
*/
protected final boolean isFull() {
return maximumSize > 0 && map.size() > maximumSize;
}
/**
* Expire all elsments.
* <p/>
* This is a default implementation which does nothing. Expiry on demand is only
* implemented for disk stores.
*/
public void expireElements() {
//empty implementation
}
/**
* Memory stores are never backed up and always return false
*/
public boolean bufferFull() {
return false;
}
/**
* Package local access to the map for testing
*/
Map getBackingMap() {
return map;
}
/**
* {@inheritDoc}
*/
public Object getMBean() {
return null;
}
/**
* An extension of LinkedHashMap which overrides {@link #removeEldestEntry}
* to persist cache entries to the auxiliary cache before they are removed.
* <p/>
* This implementation also provides LRU by access order.
*/
public final class SpoolingLinkedHashMap extends java.util.LinkedHashMap {
private static final int INITIAL_CAPACITY = 100;
private static final float GROWTH_FACTOR = .75F;
/**
* Default constructor.
* Will create an initial capacity of 100, a loading of .75 and
* LRU by access order.
*/
public SpoolingLinkedHashMap() {
super(INITIAL_CAPACITY, GROWTH_FACTOR, true);
}
/**
* Returns <tt>true</tt> if this map should remove its eldest entry.
* This method is invoked by <tt>put</tt> and <tt>putAll</tt> after
* inserting a new entry into the map. It provides the implementer
* with the opportunity to remove the eldest entry each time a new one
* is added. This is useful if the map represents a cache: it allows
* the map to reduce memory consumption by deleting stale entries.
* <p/>
* Will return true if:
* <ol>
* <li> the element has expired
* <li> the cache size is greater than the in-memory actual.
* In this case we spool to disk before returning.
* </ol>
*
* @param eldest The least recently inserted entry in the map, or if
* this is an access-ordered map, the least recently accessed
* entry. This is the entry that will be removed it this
* method returns <tt>true</tt>. If the map was empty prior
* to the <tt>put</tt> or <tt>putAll</tt> invocation resulting
* in this invocation, this will be the entry that was just
* inserted; in other words, if the map contains a single
* entry, the eldest entry is also the newest.
* @return true if the eldest entry should be removed
* from the map; <tt>false</t> if it should be retained.
*/
@Override
protected final boolean removeEldestEntry(Map.Entry eldest) {
Element element = (Element) eldest.getValue();
return element != null && removeLeastRecentlyUsedElement(element);
}
/**
* Relies on being called from a synchronized method
*
* @param element
* @return true if the LRU element should be removed
*/
private boolean removeLeastRecentlyUsedElement(Element element) throws CacheException {
//check for expiry and remove before going to the trouble of spooling it
if (element.isExpired()) {
notifyExpiry(element);
return true;
}
if (isFull()) {
evict(element);
return true;
} else {
return false;
}
}
}
/**
* @return the current eviction policy. This may not be the configured policy, if it has been
* dynamically set.
* @see #setEvictionPolicy(Policy)
*/
public Policy getEvictionPolicy() {
return new LruPolicy();
}
/**
* Sets the eviction policy strategy. The Store will use a policy at startup. The store may allow changing
* the eviction policy strategy dynamically. Otherwise implementations will throw an exception if this method
* is called.
*
* @param policy the new policy
*/
public void setEvictionPolicy(Policy policy) {
throw new UnsupportedOperationException("This store is LRU only. It does not support changing the eviction" +
" strategy.");
}
/**
* {@inheritDoc}
*/
public Object getInternalContext() {
return null;
}
/**
* {@inheritDoc}
*/
public boolean containsKeyInMemory(Object key) {
return containsKey(key);
}
/**
* {@inheritDoc}
*/
public boolean containsKeyOffHeap(Object key) {
return false;
}
/**
* {@inheritDoc}
*/
public boolean containsKeyOnDisk(Object key) {
return false;
}
/**
* {@inheritDoc}
*/
public Policy getInMemoryEvictionPolicy() {
return getEvictionPolicy();
}
/**
* {@inheritDoc}
*/
public int getInMemorySize() {
return getSize();
}
/**
* {@inheritDoc}
*/
public long getInMemorySizeInBytes() {
return getSizeInBytes();
}
/**
* {@inheritDoc}
*/
public int getOffHeapSize() {
return 0;
}
/**
* {@inheritDoc}
*/
public long getOffHeapSizeInBytes() {
return 0;
}
/**
* {@inheritDoc}
*/
public int getOnDiskSize() {
return 0;
}
/**
* {@inheritDoc}
*/
public long getOnDiskSizeInBytes() {
return 0;
}
/**
* {@inheritDoc}
*/
public void setInMemoryEvictionPolicy(Policy policy) {
setEvictionPolicy(policy);
}
/**
* Unsupported in LruMemoryStore
*/
public Element putIfAbsent(Element element) throws NullPointerException {
throw new UnsupportedOperationException();
}
/**
* Unsupported in LruMemoryStore
*/
public Element removeElement(Element element, ElementValueComparator comparator) throws NullPointerException {
throw new UnsupportedOperationException();
}
/**
* Unsupported in LruMemoryStore
*/
public boolean replace(Element old, Element element, ElementValueComparator comparator)
throws NullPointerException, IllegalArgumentException {
throw new UnsupportedOperationException();
}
/**
* Unsupported in LruMemoryStore
*/
public Element replace(Element element) throws NullPointerException {
throw new UnsupportedOperationException();
}
}