/*
* 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.logging.Logger;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* 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>LongKeyLruCache is synchronized.
*/
public class LongKeyLruCache<V> {
private static final Logger log
= Logger.getLogger(LongKeyLruCache.class.getName());
private static final int LRU_MASK = 0x3fffffff;
// maximum allowed entries
private final int _capacity;
// size 1 capacity is half the actual capacity
private final 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<V> []_entries;
private final Object []_locks;
// mask for the hash
private final int _prime;
//
// 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<V> _head1;
// tail of the LRU list
private CacheItem<V> _tail1;
// number of items in the cache seen more than once
private int _size2;
// head of the LRU list
private CacheItem<V> _head2;
// tail of the LRU list
private CacheItem<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;
// 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 LongKeyLruCache(int initialCapacity)
{
int capacity = calculateCapacity(initialCapacity);
_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;
}
/**
* Returns the current number of entries in the cache.
*/
public int size()
{
return _size1 + _size2;
}
/**
* Returns the capacity.
*/
public int getCapacity()
{
return _capacity;
}
/**
* Ensure the cache can contain the given value.
*/
public LongKeyLruCache<V> ensureCapacity(int newCapacity)
{
int capacity = calculateCapacity(newCapacity);
if (capacity <= _entries.length)
return this;
else
return setCapacity(newCapacity);
}
public LongKeyLruCache<V> setCapacity(int newCapacity)
{
int capacity = calculateCapacity(newCapacity);
if (capacity == _entries.length)
return this;
LongKeyLruCache<V> newCache = new LongKeyLruCache<V>(newCapacity);
for (int i = 0; i < _entries.length; i++) {
Object lock = getLock(i);
synchronized (lock) {
for (CacheItem<V> item = _entries[i];
item != null;
item = item._nextHash) {
newCache.put(item._key, (V) item._value);
}
_entries[i] = null;
}
}
return newCache;
}
private int calculateCapacity(int initialCapacity)
{
int capacity;
for (capacity = 16; capacity < 8 * initialCapacity; capacity *= 2) {
}
return capacity;
}
/**
* Clears the cache
*/
public void clear()
{
ArrayList<CacheListener> listeners = null;
ArrayList<SyncCacheListener> syncListeners = null;
for (int i = _entries.length - 1; i >= 0; i--) {
Object lock = getLock(i);
synchronized (lock) {
CacheItem<V> item = _entries[i];
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);
}
if (item._value instanceof SyncCacheListener) {
if (syncListeners == null)
syncListeners = new ArrayList<SyncCacheListener>();
syncListeners.add((SyncCacheListener) item._value);
}
}
_entries[i] = null;
}
}
for (int i = listeners == null ? -1 : listeners.size() - 1; i >= 0; i--) {
CacheListener listener = listeners.get(i);
listener.removeEvent();
}
for (int i = syncListeners == null ? -1 : syncListeners.size() - 1;
i >= 0;
i--) {
SyncCacheListener listener = syncListeners.get(i);
listener.syncRemoveEvent();
}
}
/**
* 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(long key)
{
int hash = hash(key) % _prime;
CacheItem<V> item;
for (item = _entries[hash];
item != null;
item = item._nextHash) {
if (item._key == key) {
updateLru(item);
_hitCount++;
return item._value;
}
}
_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(long key, V value)
{
V oldValue = put(key, value, true);
if (oldValue instanceof CacheListener)
((CacheListener) oldValue).removeEvent();
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(long key, V value)
{
V oldValue = put(key, value, false);
if (oldValue != null)
return oldValue;
else
return value;
}
/**
* 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 putIfAbsent(long key, V value)
{
return put(key, value, false);
}
/**
* 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
*/
private V put(long key, V value, boolean replace)
{
removeLru();
int hash = hash(key) % _prime;
V oldValue = null;
Object lock = getLock(hash);
synchronized (lock) {
CacheItem<V> item = _entries[hash];
for (;
item != null;
item = item._nextHash) {
// matching item gets replaced
if (item._key == key) {
updateLru(item);
oldValue = item._value;
if (replace) {
if (oldValue instanceof SyncCacheListener) {
((SyncCacheListener) oldValue).syncRemoveEvent();
}
item._value = value;
}
break;
}
}
// No matching item, so create one
if (item == null) {
CacheItem<V> next = _entries[hash];
item = new CacheItem<V>(key, value);
addNewLruItem(item);
item._nextHash = next;
_entries[hash] = item;
return null;
}
}
if (replace && oldValue instanceof CacheListener)
((CacheListener) oldValue).removeEvent();
return oldValue;
}
private void addNewLruItem(CacheItem<V> item)
{
synchronized (_lruLock) {
_lruCounter = (_lruCounter + 1) & LRU_MASK;
item._lruCounter = _lruCounter;
_size1++;
item._nextLru = _head1;
if (_head1 != null)
_head1._prevLru = item;
_head1 = item;
if (_tail1 == null)
_tail1 = item;
}
}
/**
* Put item at the head of the used-twice lru list.
* This is always called while synchronized.
*/
private void updateLru(CacheItem<V> item)
{
long lruCounter = _lruCounter;
long itemCounter = item._lruCounter;
long delta = (lruCounter - itemCounter) & LRU_MASK;
if (_lruTimeout < delta || delta < 0) {
// update LRU only if not used recently
updateLruImpl(item);
}
}
/**
* Put item at the head of the used-twice lru list.
* This is always called while synchronized.
*/
private void updateLruImpl(CacheItem<V> item)
{
synchronized (_lruLock) {
_lruCounter = (_lruCounter + 1) & LRU_MASK;
item._lruCounter = _lruCounter;
CacheItem<V> prevLru = item._prevLru;
CacheItem<V> nextLru = item._nextLru;
if (item._hitCount <= 0) {
// item deleted before update
return;
}
else if (item._hitCount == 1) {
item._hitCount = 2;
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 {
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
while (overflow-- > 0 && removeTail()) {
}
} finally {
_isLruTailRemove.set(false);
}
}
}
}
/**
* Remove the last item in the LRU
*/
public boolean removeTail()
{
CacheItem<V> tail = null;
if (_capacity1 <= _size1)
tail = _tail1;
if (tail == null) {
tail = _tail2;
if (tail == null) {
tail = _tail1;
if (tail == null)
return false;
}
}
if (tail == null)
return false;
Object value = remove(tail._key, true);
return value != null;
}
/**
* Removes an item from the cache
*
* @param key the key to remove
*
* @return the value removed
*/
public V remove(long key)
{
return remove(key, false);
}
/**
* Removes an item from the cache
*
* @param key the key to remove
*
* @return the value removed
*/
private V remove(long key, boolean isTail)
{
int hash = hash(key) % _prime;
V value = null;
Object lock = getLock(hash);
synchronized (lock) {
CacheItem<V> prevItem = null;
for (CacheItem<V> item = _entries[hash];
item != null;
item = item._nextHash) {
if (item._key == key) {
value = item._value;
SyncCacheListener syncListener = null;
// sync must occur before remove because get() is non-locking
if (value instanceof SyncCacheListener) {
syncListener = (SyncCacheListener) value;
if (isTail && ! syncListener.startLruRemove()) {
item._lruCounter = _lruCounter - _lruTimeout - 2;
updateLruImpl(item);
return null;
}
}
removeLruItem(item);
// sync must occur before remove because get() is non-locking
if (syncListener != null) {
if (isTail)
syncListener.syncLruRemoveEvent();
else
syncListener.syncRemoveEvent();
}
CacheItem<V> nextHash = item._nextHash;
if (prevItem != null)
prevItem._nextHash = nextHash;
else {
assert(_entries[hash] == item);
_entries[hash] = nextHash;
}
break;
}
prevItem = item;
}
}
if (value instanceof CacheListener)
((CacheListener) value).removeEvent();
return value;
}
private void removeLruItem(CacheItem<V> item)
{
synchronized (_lruLock) {
_lruCounter = (_lruCounter + 1) & 0x3fffffff;
CacheItem<V> prevLru = item._prevLru;
CacheItem<V> nextLru = item._nextLru;
item._prevLru = null;
item._nextLru = null;
int hitCount = item._hitCount;
item._hitCount = -1;
if (hitCount <= 0) {
return; // item already removed
}
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 static int hash(long key)
{
long hash = key;
hash = 65537 * hash + (key >>> 8);
hash = 65537 * hash + (key >>> 16);
hash = 65537 * hash + (key >>> 32);
hash = 65537 * hash + (key >>> 48);
return (int) (hash & 0x7fffffff);
}
private Object getLock(int hash)
{
return _locks[hash >> 3];
}
/**
* Returns the values in the cache
*/
public Iterator<V> values()
{
ValueIterator iter = new ValueIterator<V>(this);
iter.init(this);
return iter;
}
public Iterator<V> values(Iterator<V> oldIter)
{
ValueIterator iter = (ValueIterator) oldIter;
iter.init(this);
return oldIter;
}
/**
* Returns the hit count.
*/
public long getHitCount()
{
return _hitCount;
}
/**
* Returns the miss count.
*/
public long getMissCount()
{
return _missCount;
}
/**
* A cache item
*/
static class CacheItem<V> {
CacheItem<V> _nextHash;
CacheItem<V> _prevLru;
CacheItem<V> _nextLru;
long _key;
V _value;
int _index;
int _hitCount = 1;
int _lruCounter;
CacheItem(long key, V value)
{
_key = key;
_value = value;
}
}
/**
* Iterator of cache values
*/
static class ValueIterator<V> implements Iterator<V> {
private LongKeyLruCache<V> _cache;
private CacheItem<V> _entry;
private int _i = -1;
ValueIterator(LongKeyLruCache<V> cache)
{
init(cache);
}
void init(LongKeyLruCache<V> cache)
{
_cache = cache;
_entry = null;
_i = -1;
}
/**
* Returns the next entry in the cache.
*/
public boolean hasNext()
{
if (_entry != null)
return true;
CacheItem<V> []entries = _cache._entries;
int length = entries.length;
int i = _i + 1;
for (; i < length; i++) {
if (entries[i] != null) {
_i = i - 1;
return true;
}
}
_i = i;
return false;
}
/**
* Returns the next value.
*/
public V next()
{
CacheItem<V> entry = _entry;
if (entry != null) {
_entry = entry._nextHash;
return entry._value;
}
CacheItem<V> []entries = _cache._entries;
int length = entries.length;
int i = _i + 1;
for (; i < length; i++) {
entry = entries[i];
if (entry != null) {
_entry = entry._nextHash;
_i = i;
return entry._value;
}
}
_i = i;
return null;
}
public void remove()
{
throw new UnsupportedOperationException();
}
}
}