/*
* Copyright (c) 1998-2011 Caucho Technology -- all rights reserved
*
* This file is part of Resin(R) Open Source
*
* Each copy or derived work must preserve the copyright notice and this
* notice unmodified.
*
* Resin Open Source is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* Resin Open Source is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE, or any warranty
* of NON-INFRINGEMENT. See the GNU General Public License for more
* details.
*
* You should have received a copy of the GNU General Public License
* along with Resin Open Source; if not, write to the
*
* Free Software Foundation, Inc.
* 59 Temple Place, Suite 330
* Boston, MA 02111-1307 USA
*
* @author Scott Ferguson
*/
package com.caucho.util;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
/**
* Fixed length cache with a LRU replacement policy. If cache items
* implement CacheListener, they will be informed when they're removed
* from the cache.
*
* <p>Null keys are not allowed. LruCache is synchronized.
*/
public final class LruCache<K,V> {
private static final Object NULL = new Object();
private static final Object MISMATCH = new Object();
// maximum allowed entries
private int _capacity;
// size 1 capacity is half the actual capacity
private int _capacity1;
// hash table containing the entries. Its size is twice the capacity
// so it will always remain at least half empty
private final CacheItem []_entries;
private final Object []_locks;
// mask for hash mapping
private int _prime;
private boolean _isEnableListeners = true;
//
// LRU
//
private final Object _lruLock = new Object();
// number of items in the cache seen once
private int _size1;
// head of the LRU list
private CacheItem<K,V> _head1;
// tail of the LRU list
private CacheItem<K,V> _tail1;
// number of items in the cache seen more than once
private int _size2;
// head of the LRU list
private CacheItem<K,V> _head2;
// tail of the LRU list
private CacheItem<K,V> _tail2;
// lru timeout reduces lru updates for the most used items
private final int _lruTimeout;
private final AtomicBoolean _isLruTailRemove = new AtomicBoolean();
// counts group 2 updates, rolling over at 0x3fffffff
private volatile int _lruCounter;
//
// statistics
//
private boolean _isEnableStatistics;
// hit count statistics
private volatile long _hitCount;
// miss count statistics
private volatile long _missCount;
/**
* Create the LRU cache with a specific capacity.
*
* @param initialCapacity minimum capacity of the cache
*/
public LruCache(int initialCapacity)
{
this(initialCapacity, false);
}
/**
* Create the LRU cache with a specific capacity.
*
* @param initialCapacity minimum capacity of the cache
*/
public LruCache(int initialCapacity, boolean isStatistics)
{
int capacity;
for (capacity = 16; capacity < 2 * initialCapacity; capacity *= 2) {
}
_entries = new CacheItem[capacity];
_prime = Primes.getBiggestPrime(_entries.length);
_locks = new Object[(_entries.length >> 3) + 1];
for (int i = 0; i < _locks.length; i++) {
_locks[i] = new Object();
}
_capacity = initialCapacity;
_capacity1 = _capacity / 2;
if (_capacity > 32)
_lruTimeout = _capacity / 32;
else
_lruTimeout = 1;
_isEnableStatistics = isStatistics;
/*
if (isStatistics) {
_hitCount = new AtomicLong();
_missCount = new AtomicLong();
}
*/
}
/**
* Disable the listeners
*/
public void setEnableListeners(boolean isEnable)
{
_isEnableListeners = isEnable;
}
public void setEnableStatistics(boolean isEnable)
{
_isEnableStatistics = isEnable;
}
/**
* Returns the current number of entries in the cache.
*/
public int size()
{
return _size1 + _size2;
}
/**
* Returns the LRU cache capacity
*/
public int getCapacity()
{
return _capacity;
}
/**
* Clears the cache
*/
public void clear()
{
if (_size1 == 0 && _size2 == 0)
return;
ArrayList<CacheListener> listeners = null;
for (int i = _entries.length - 1; i >= 0; i--) {
Object lock = getLock(i);
synchronized (lock) {
CacheItem<K,V> item = _entries[i];
_entries[i] = null;
if (_isEnableListeners) {
for (; item != null; item = item._nextHash) {
removeLruItem(item);
if (item._value instanceof CacheListener) {
if (listeners == null)
listeners = new ArrayList<CacheListener>();
listeners.add((CacheListener) item._value);
}
}
}
}
}
for (int i = listeners != null ? listeners.size() - 1 : -1;
i >= 0;
i--) {
CacheListener listener = listeners.get(i);
listener.removeEvent();
}
}
/**
* Get an item from the cache and make it most recently used.
*
* @param key key to lookup the item
* @return the matching object in the cache
*/
public V get(K key)
{
Object okey = key;
if (okey == null)
okey = NULL;
int hash = (okey.hashCode() & 0x7fffffff) % _prime;
CacheItem<K,V> item;
for (item = _entries[hash];
item != null;
item = item._nextHash) {
Object itemKey = item._key;
if (itemKey == okey || itemKey.equals(okey)) {
updateLru(item);
if (_isEnableStatistics)
_hitCount++;
return item._value;
}
}
if (_isEnableStatistics)
_missCount++;
return null;
}
/**
* Puts a new item in the cache. If the cache is full, remove the
* LRU item.
*
* @param key key to store data
* @param value value to be stored
*
* @return old value stored under the key
*/
public V put(K key, V value)
{
V oldValue = compareAndPut(null, key, value, false);
return oldValue;
}
/**
* Puts a new item in the cache. If the cache is full, remove the
* LRU item.
*
* @param key key to store data
* @param value value to be stored
*
* @return the value actually stored
*/
public V putIfNew(K key, V value)
{
V oldValue = compareAndPut(null, key, value, true);
if (oldValue != null)
return oldValue;
else
return value;
}
/**
* Puts a new item in the cache if the current value matches oldValue.
*
* @param key the key
* @param value the new value
* @param testValue the value to test against the current
*
* @return true if the put succeeds
*/
public boolean compareAndPut(V testValue, K key, V value)
{
V result = compareAndPut(testValue, key, value, true);
return testValue == result;
}
/**
* Puts a new item in the cache. If the cache is full, remove the
* LRU item.
*
* @param key key to store data
* @param value value to be stored
* @param testValue tests the current value in the cache
* @param isCompare if true, this is a compare and put
*
* @return old value stored under the key
*/
private V compareAndPut(V testValue, K key, V value, boolean isCompare)
{
Object okey = key;
if (okey == null)
okey = NULL;
// remove LRU items until we're below capacity
removeLru();
int hash = (okey.hashCode() & 0x7fffffff) % _prime;
V oldValue = null;
Object lock = getLock(hash);
synchronized (lock) {
CacheItem<K,V> item = _entries[hash];
for (;
item != null;
item = item._nextHash) {
// matching item gets replaced
if (okey == item._key || okey.equals(item._key)) {
updateLru(item);
oldValue = item._value;
if (isCompare && testValue != oldValue) {
return oldValue;
}
item._value = value;
if (value == oldValue)
oldValue = null;
break;
}
}
if (isCompare && testValue != oldValue) {
return null;
}
if (item == null) {
CacheItem<K,V> next = _entries[hash];
item = new CacheItem<K,V>((K) okey, value);
// item must be added to lru first, because a get() hit can update
// the lru, and the item must be in the lru before that happens
synchronized (_lruLock) {
assert(item._hitCount == 1);
// server/1401
_lruCounter = (_lruCounter + 1) & 0x3fffffff;
_size1++;
// server/1406 - the item's lruCounter is not updated
// because the next hit needs to move it to head2
item._lruCounter = - (_lruTimeout + 16);
item._nextLru = _head1;
if (_head1 != null)
_head1._prevLru = item;
_head1 = item;
if (_tail1 == null)
_tail1 = item;
}
item._nextHash = next;
_entries[hash] = item;
return null;
}
if (_isEnableListeners
&& oldValue instanceof SyncCacheListener)
((SyncCacheListener) oldValue).syncRemoveEvent();
}
if (_isEnableListeners && oldValue instanceof CacheListener)
((CacheListener) oldValue).removeEvent();
return oldValue;
}
/**
* Put item at the head of the used-twice lru list.
* This is always called while synchronized.
*/
private void updateLru(CacheItem<K,V> item)
{
long lruCounter = _lruCounter;
long itemCounter = item._lruCounter;
long delta = (lruCounter - itemCounter) & 0x3fffffff;
if (_lruTimeout < delta || delta < 0) {
// update LRU only if not used recently
updateLruImpl(item);
}
}
private void updateLruImpl(CacheItem<K,V> item)
{
synchronized (_lruLock) {
_lruCounter = (_lruCounter + 1) & 0x3fffffff;
item._lruCounter = _lruCounter;
CacheItem<K,V> prevLru = item._prevLru;
CacheItem<K,V> nextLru = item._nextLru;
if (item._hitCount <= 0) {
// item deleted before update
return;
}
else if (item._hitCount++ == 1) {
item._prevLru = null;
item._nextLru = _head2;
if (prevLru != null)
prevLru._nextLru = nextLru;
else {
assert(_head1 == item);
_head1 = nextLru;
}
if (nextLru != null)
nextLru._prevLru = prevLru;
else {
assert(_tail1 == item);
_tail1 = prevLru;
}
if (_head2 != null)
_head2._prevLru = item;
else {
assert(_tail2 == null);
_tail2 = item;
}
_head2 = item;
_size1--;
_size2++;
}
else {
assert(item._hitCount > 1);
if (item == _head2)
return;
item._prevLru = null;
item._nextLru = _head2;
prevLru._nextLru = nextLru;
_head2._prevLru = item;
_head2 = item;
if (nextLru != null)
nextLru._prevLru = prevLru;
else {
assert(_tail2 == item);
_tail2 = prevLru;
}
}
}
}
private void removeLru()
{
int overflow = _size1 + _size2 - _capacity;
if (overflow >= 0) {
if (_isLruTailRemove.compareAndSet(false, true)) {
try {
// remove LRU items until we're below capacity
for (; overflow >= 0 && removeTail(); overflow--) {
}
} finally {
_isLruTailRemove.set(false);
}
}
}
}
/**
* Remove the last item in the LRU
*/
public boolean removeTail()
{
CacheItem<K,V> tail = null;
if (_capacity1 <= _size1)
tail = _tail1;
if (tail == null) {
tail = _tail2;
if (tail == null) {
tail = _tail1;
if (tail == null)
return false;
}
}
V oldValue = tail._value;
if (oldValue instanceof LruListener)
((LruListener) oldValue).lruEvent();
V value = remove(tail._key);
return true;
}
/**
* Remove the last item in the LRU. In this case, remove from the
* list with the longest length.
*
* For functions like Cache disk space, this is a better solution
* than the struct LRU removal.
*/
public boolean removeLongestTail()
{
CacheItem<K,V> tail;
if (_size1 <= _size2)
tail = _tail2;
else
tail = _tail1;
if (tail == null)
return false;
V oldValue = tail._value;
if (oldValue instanceof LruListener)
((LruListener) oldValue).lruEvent();
V value = remove(tail._key);
return true;
}
/**
* Removes an item from the cache
*
* @param key the key to remove
*
* @return the value removed
*/
public V remove(K key)
{
Object okey = key;
if (okey == null)
okey = NULL;
int hash = (okey.hashCode() & 0x7fffffff) % _prime;
Object lock = getLock(hash);
V value = null;
synchronized (lock) {
CacheItem<K,V> prevItem = null;
for (CacheItem<K,V> item = _entries[hash];
item != null;
item = item._nextHash) {
if (item._key == okey || item._key.equals(okey)) {
removeLruItem(item);
CacheItem<K,V> nextHash = item._nextHash;
if (prevItem != null)
prevItem._nextHash = nextHash;
else {
assert(_entries[hash] == item);
_entries[hash] = nextHash;
}
value = item._value;
break;
}
prevItem = item;
}
if (_isEnableListeners && value instanceof SyncCacheListener)
((SyncCacheListener) value).syncRemoveEvent();
}
if (_isEnableListeners && value instanceof CacheListener)
((CacheListener) value).removeEvent();
return value;
}
private void removeLruItem(CacheItem<K,V> item)
{
synchronized (_lruLock) {
_lruCounter = (_lruCounter + 1) & 0x3fffffff;
CacheItem<K,V> prevLru = item._prevLru;
CacheItem<K,V> nextLru = item._nextLru;
item._prevLru = null;
item._nextLru = null;
int hitCount = item._hitCount;
item._hitCount = -1;
if (hitCount <= 0)
return;
else if (hitCount == 1) {
_size1--;
if (prevLru != null)
prevLru._nextLru = nextLru;
else {
assert(_head1 == item);
_head1 = nextLru;
}
if (nextLru != null)
nextLru._prevLru = prevLru;
else {
assert(_tail1 == item);
_tail1 = prevLru;
}
}
else {
_size2--;
if (prevLru != null)
prevLru._nextLru = nextLru;
else {
assert(_head2 == item);
_head2 = nextLru;
}
if (nextLru != null)
nextLru._prevLru = prevLru;
else {
assert(_tail2 == item);
_tail2 = prevLru;
}
}
}
}
private Object getLock(int hash)
{
return _locks[hash >> 3];
}
/**
* Returns the keys stored in the cache
*/
public Iterator<K> keys()
{
KeyIterator<K,V> iter = new KeyIterator<K,V>(this);
iter.init(this);
return iter;
}
/**
* Returns keys stored in the cache using an old iterator
*/
public Iterator<K> keys(Iterator<K> oldIter)
{
KeyIterator<K,V> iter = (KeyIterator<K,V>) oldIter;
iter.init(this);
return oldIter;
}
/**
* Returns the values in the cache
*/
public Iterator<V> values()
{
ValueIterator<K,V> iter = new ValueIterator<K,V>(this);
iter.init(this);
return iter;
}
@SuppressWarnings("unchecked")
public Iterator<V> values(Iterator<V> oldIter)
{
ValueIterator<K,V> iter = (ValueIterator<K,V>) oldIter;
iter.init(this);
return oldIter;
}
/**
* Returns the entries
*/
public Iterator<Entry<K,V>> iterator()
{
return new EntryIterator();
}
/**
* Returns the hit count.
*/
public long getHitCount()
{
return _hitCount;
}
/**
* Returns the miss count.
*/
public long getMissCount()
{
return _missCount;
}
/**
* A cache item
*/
static class CacheItem<K,V> {
volatile CacheItem<K,V> _nextHash;
CacheItem<K,V> _prevLru;
CacheItem<K,V> _nextLru;
volatile int _lruCounter; // LRU only updated after expire time
final K _key;
V _value;
int _index;
int _hitCount = 1;
CacheItem(K key, V value)
{
if (key == null)
throw new NullPointerException();
_key = key;
_value = value;
}
}
/**
* Iterator of cache keys
*/
static class KeyIterator<K,V> implements Iterator<K> {
private LruCache<K,V> _cache;
private CacheItem<K,V> _item;
private boolean _isHead1;
KeyIterator(LruCache<K,V> cache)
{
init(cache);
}
void init(LruCache<K,V> cache)
{
_cache = cache;
_item = _cache._head2;
_isHead1 = false;
if (_item == null) {
_item = _cache._head1;
_isHead1 = true;
}
}
/**
* Returns the next entry in the cache.
*/
@Override
public boolean hasNext()
{
return _item != null;
}
/**
* Returns the next key.
*/
@Override
public K next()
{
CacheItem<K,V> entry = _item;
if (_item != null)
_item = _item._nextLru;
if (_item == null && ! _isHead1) {
_isHead1 = true;
_item = _cache._head1;
}
if (entry != null)
return entry._key;
else
return null;
}
@Override
public void remove()
{
throw new UnsupportedOperationException();
}
}
/**
* Iterator of cache values
*/
static class ValueIterator<K,V> implements Iterator<V> {
private LruCache<K,V> _cache;
private CacheItem<K,V> _item;
private boolean _isHead1;
ValueIterator(LruCache<K,V> cache)
{
init(cache);
}
void init(LruCache<K,V> cache)
{
_cache = cache;
_item = _cache._head2;
_isHead1 = false;
if (_item == null) {
_item = _cache._head1;
_isHead1 = true;
}
}
/**
* Returns the next entry in the cache.
*/
public boolean hasNext()
{
return _item != null;
}
/**
* Returns the next value.
*/
public V next()
{
CacheItem<K,V> entry = _item;
if (_item != null)
_item = _item._nextLru;
if (_item == null && ! _isHead1) {
_isHead1 = true;
_item = _cache._head1;
}
if (entry != null)
return entry._value;
else
return null;
}
public void remove()
{
throw new UnsupportedOperationException();
}
}
/**
* Interface for entry iterator;
*/
public interface Entry<K,V> {
/**
* Returns the key.
*/
public K getKey();
/**
* Returns the value.
*/
public V getValue();
}
/**
* Iterator of cache values
*/
class EntryIterator implements Iterator<Entry<K,V>>, Entry<K,V> {
private int _i = -1;
public boolean hasNext()
{
int i = _i + 1;
CacheItem<K,V> []entries = _entries;
int length = entries.length;
for (; i < length && entries[i] == null; i++) {
}
_i = i - 1;
return i < length;
}
public Entry<K,V> next()
{
int i = _i + 1;
CacheItem<K,V> []entries = _entries;
int length = entries.length;
for (; i < length && entries[i] == null; i++) {
}
_i = i;
if (_i < length) {
return this;
}
else
return null;
}
/**
* Returns the key.
*/
public K getKey()
{
if (_i < _entries.length) {
CacheItem<K,V> entry = _entries[_i];
if (entry == null)
return null;
else if (entry._key == NULL)
return null;
else
return entry._key;
}
return null;
}
/**
* Returns the value.
*/
public V getValue()
{
if (_i < _entries.length) {
CacheItem<K,V> entry = _entries[_i];
return entry != null ? entry._value : null;
}
return null;
}
public void remove()
{
if (_i < _entries.length) {
CacheItem<K,V> entry = _entries[_i];
if (entry != null)
LruCache.this.remove(entry._key);
}
}
}
}