package org.apache.solr.common.util;
/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
import org.apache.lucene.util.PriorityQueue;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.TreeSet;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.ReentrantLock;
import java.lang.ref.WeakReference;
/**
* A LRU cache implementation based upon ConcurrentHashMap and other techniques to reduce
* contention and synchronization overhead to utilize multiple CPU cores more effectively.
* <p/>
* Note that the implementation does not follow a true LRU (least-recently-used) eviction
* strategy. Instead it strives to remove least recently used items but when the initial
* cleanup does not remove enough items to reach the 'acceptableWaterMark' limit, it can
* remove more items forcefully regardless of access order.
*
* @version $Id: ConcurrentLRUCache.java 922957 2010-03-14 20:58:32Z markrmiller $
* @since solr 1.4
*/
public class ConcurrentLRUCache<K,V> {
private static Logger log = LoggerFactory.getLogger(ConcurrentLRUCache.class);
private final ConcurrentHashMap<Object, CacheEntry<K,V>> map;
private final int upperWaterMark, lowerWaterMark;
private final ReentrantLock markAndSweepLock = new ReentrantLock(true);
private boolean isCleaning = false; // not volatile... piggybacked on other volatile vars
private final boolean newThreadForCleanup;
private volatile boolean islive = true;
private final Stats stats = new Stats();
private final int acceptableWaterMark;
private long oldestEntry = 0; // not volatile, only accessed in the cleaning method
private final EvictionListener<K,V> evictionListener;
private CleanupThread cleanupThread ;
public ConcurrentLRUCache(int upperWaterMark, final int lowerWaterMark, int acceptableWatermark,
int initialSize, boolean runCleanupThread, boolean runNewThreadForCleanup,
EvictionListener<K,V> evictionListener) {
if (upperWaterMark < 1) throw new IllegalArgumentException("upperWaterMark must be > 0");
if (lowerWaterMark >= upperWaterMark)
throw new IllegalArgumentException("lowerWaterMark must be < upperWaterMark");
map = new ConcurrentHashMap<Object, CacheEntry<K,V>>(initialSize);
newThreadForCleanup = runNewThreadForCleanup;
this.upperWaterMark = upperWaterMark;
this.lowerWaterMark = lowerWaterMark;
this.acceptableWaterMark = acceptableWatermark;
this.evictionListener = evictionListener;
if (runCleanupThread) {
cleanupThread = new CleanupThread(this);
cleanupThread.start();
}
}
public ConcurrentLRUCache(int size, int lowerWatermark) {
this(size, lowerWatermark, (int) Math.floor((lowerWatermark + size) / 2),
(int) Math.ceil(0.75 * size), false, false, null);
}
public void setAlive(boolean live) {
islive = live;
}
public V get(K key) {
CacheEntry<K,V> e = map.get(key);
if (e == null) {
if (islive) stats.missCounter.incrementAndGet();
return null;
}
if (islive) e.lastAccessed = stats.accessCounter.incrementAndGet();
return e.value;
}
public V remove(K key) {
CacheEntry<K,V> cacheEntry = map.remove(key);
if (cacheEntry != null) {
stats.size.decrementAndGet();
return cacheEntry.value;
}
return null;
}
public V put(K key, V val) {
if (val == null) return null;
CacheEntry<K,V> e = new CacheEntry<K,V>(key, val, stats.accessCounter.incrementAndGet());
CacheEntry<K,V> oldCacheEntry = map.put(key, e);
int currentSize;
if (oldCacheEntry == null) {
currentSize = stats.size.incrementAndGet();
} else {
currentSize = stats.size.get();
}
if (islive) {
stats.putCounter.incrementAndGet();
} else {
stats.nonLivePutCounter.incrementAndGet();
}
// Check if we need to clear out old entries from the cache.
// isCleaning variable is checked instead of markAndSweepLock.isLocked()
// for performance because every put invokation will check until
// the size is back to an acceptable level.
//
// There is a race between the check and the call to markAndSweep, but
// it's unimportant because markAndSweep actually aquires the lock or returns if it can't.
//
// Thread safety note: isCleaning read is piggybacked (comes after) other volatile reads
// in this method.
if (currentSize > upperWaterMark && !isCleaning) {
if (newThreadForCleanup) {
new Thread() {
public void run() {
markAndSweep();
}
}.start();
} else if (cleanupThread != null){
cleanupThread.wakeThread();
} else {
markAndSweep();
}
}
return oldCacheEntry == null ? null : oldCacheEntry.value;
}
/**
* Removes items from the cache to bring the size down
* to an acceptable value ('acceptableWaterMark').
* <p/>
* It is done in two stages. In the first stage, least recently used items are evicted.
* If, after the first stage, the cache size is still greater than 'acceptableSize'
* config parameter, the second stage takes over.
* <p/>
* The second stage is more intensive and tries to bring down the cache size
* to the 'lowerWaterMark' config parameter.
*/
private void markAndSweep() {
// if we want to keep at least 1000 entries, then timestamps of
// current through current-1000 are guaranteed not to be the oldest (but that does
// not mean there are 1000 entries in that group... it's acutally anywhere between
// 1 and 1000).
// Also, if we want to remove 500 entries, then
// oldestEntry through oldestEntry+500 are guaranteed to be
// removed (however many there are there).
if (!markAndSweepLock.tryLock()) return;
try {
long oldestEntry = this.oldestEntry;
isCleaning = true;
this.oldestEntry = oldestEntry; // volatile write to make isCleaning visible
long timeCurrent = stats.accessCounter.get();
int sz = stats.size.get();
int numRemoved = 0;
int numKept = 0;
long newestEntry = timeCurrent;
long newNewestEntry = -1;
long newOldestEntry = Long.MAX_VALUE;
int wantToKeep = lowerWaterMark;
int wantToRemove = sz - lowerWaterMark;
CacheEntry<K,V>[] eset = new CacheEntry[sz];
int eSize = 0;
// System.out.println("newestEntry="+newestEntry + " oldestEntry="+oldestEntry);
// System.out.println("items removed:" + numRemoved + " numKept=" + numKept + " esetSz="+ eSize + " sz-numRemoved=" + (sz-numRemoved));
for (CacheEntry<K,V> ce : map.values()) {
// set lastAccessedCopy to avoid more volatile reads
ce.lastAccessedCopy = ce.lastAccessed;
long thisEntry = ce.lastAccessedCopy;
// since the wantToKeep group is likely to be bigger than wantToRemove, check it first
if (thisEntry > newestEntry - wantToKeep) {
// this entry is guaranteed not to be in the bottom
// group, so do nothing.
numKept++;
newOldestEntry = Math.min(thisEntry, newOldestEntry);
} else if (thisEntry < oldestEntry + wantToRemove) { // entry in bottom group?
// this entry is guaranteed to be in the bottom group
// so immediately remove it from the map.
evictEntry(ce.key);
numRemoved++;
} else {
// This entry *could* be in the bottom group.
// Collect these entries to avoid another full pass... this is wasted
// effort if enough entries are normally removed in this first pass.
// An alternate impl could make a full second pass.
if (eSize < eset.length-1) {
eset[eSize++] = ce;
newNewestEntry = Math.max(thisEntry, newNewestEntry);
newOldestEntry = Math.min(thisEntry, newOldestEntry);
}
}
}
// System.out.println("items removed:" + numRemoved + " numKept=" + numKept + " esetSz="+ eSize + " sz-numRemoved=" + (sz-numRemoved));
// TODO: allow this to be customized in the constructor?
int numPasses=1; // maximum number of linear passes over the data
// if we didn't remove enough entries, then make more passes
// over the values we collected, with updated min and max values.
while (sz - numRemoved > acceptableWaterMark && --numPasses>=0) {
oldestEntry = newOldestEntry == Long.MAX_VALUE ? oldestEntry : newOldestEntry;
newOldestEntry = Long.MAX_VALUE;
newestEntry = newNewestEntry;
newNewestEntry = -1;
wantToKeep = lowerWaterMark - numKept;
wantToRemove = sz - lowerWaterMark - numRemoved;
// iterate backward to make it easy to remove items.
for (int i=eSize-1; i>=0; i--) {
CacheEntry<K,V> ce = eset[i];
long thisEntry = ce.lastAccessedCopy;
if (thisEntry > newestEntry - wantToKeep) {
// this entry is guaranteed not to be in the bottom
// group, so do nothing but remove it from the eset.
numKept++;
// remove the entry by moving the last element to it's position
eset[i] = eset[eSize-1];
eSize--;
newOldestEntry = Math.min(thisEntry, newOldestEntry);
} else if (thisEntry < oldestEntry + wantToRemove) { // entry in bottom group?
// this entry is guaranteed to be in the bottom group
// so immediately remove it from the map.
evictEntry(ce.key);
numRemoved++;
// remove the entry by moving the last element to it's position
eset[i] = eset[eSize-1];
eSize--;
} else {
// This entry *could* be in the bottom group, so keep it in the eset,
// and update the stats.
newNewestEntry = Math.max(thisEntry, newNewestEntry);
newOldestEntry = Math.min(thisEntry, newOldestEntry);
}
}
// System.out.println("items removed:" + numRemoved + " numKept=" + numKept + " esetSz="+ eSize + " sz-numRemoved=" + (sz-numRemoved));
}
// if we still didn't remove enough entries, then make another pass while
// inserting into a priority queue
if (sz - numRemoved > acceptableWaterMark) {
oldestEntry = newOldestEntry == Long.MAX_VALUE ? oldestEntry : newOldestEntry;
newOldestEntry = Long.MAX_VALUE;
newestEntry = newNewestEntry;
newNewestEntry = -1;
wantToKeep = lowerWaterMark - numKept;
wantToRemove = sz - lowerWaterMark - numRemoved;
PQueue queue = new PQueue(wantToRemove);
for (int i=eSize-1; i>=0; i--) {
CacheEntry<K,V> ce = eset[i];
long thisEntry = ce.lastAccessedCopy;
if (thisEntry > newestEntry - wantToKeep) {
// this entry is guaranteed not to be in the bottom
// group, so do nothing but remove it from the eset.
numKept++;
// removal not necessary on last pass.
// eset[i] = eset[eSize-1];
// eSize--;
newOldestEntry = Math.min(thisEntry, newOldestEntry);
} else if (thisEntry < oldestEntry + wantToRemove) { // entry in bottom group?
// this entry is guaranteed to be in the bottom group
// so immediately remove it.
evictEntry(ce.key);
numRemoved++;
// removal not necessary on last pass.
// eset[i] = eset[eSize-1];
// eSize--;
} else {
// This entry *could* be in the bottom group.
// add it to the priority queue
// everything in the priority queue will be removed, so keep track of
// the lowest value that ever comes back out of the queue.
// first reduce the size of the priority queue to account for
// the number of items we have already removed while executing
// this loop so far.
queue.myMaxSize = sz - lowerWaterMark - numRemoved;
while (queue.size() > queue.myMaxSize && queue.size() > 0) {
CacheEntry otherEntry = (CacheEntry) queue.pop();
newOldestEntry = Math.min(otherEntry.lastAccessedCopy, newOldestEntry);
}
if (queue.myMaxSize <= 0) break;
Object o = queue.myInsertWithOverflow(ce);
if (o != null) {
newOldestEntry = Math.min(((CacheEntry)o).lastAccessedCopy, newOldestEntry);
}
}
}
// Now delete everything in the priority queue.
// avoid using pop() since order doesn't matter anymore
for (Object o : queue.getValues()) {
if (o==null) continue;
CacheEntry<K,V> ce = (CacheEntry)o;
evictEntry(ce.key);
numRemoved++;
}
// System.out.println("items removed:" + numRemoved + " numKept=" + numKept + " initialQueueSize="+ wantToRemove + " finalQueueSize=" + queue.size() + " sz-numRemoved=" + (sz-numRemoved));
}
oldestEntry = newOldestEntry == Long.MAX_VALUE ? oldestEntry : newOldestEntry;
this.oldestEntry = oldestEntry;
} finally {
isCleaning = false; // set before markAndSweep.unlock() for visibility
markAndSweepLock.unlock();
}
}
private static class PQueue extends PriorityQueue {
int myMaxSize;
PQueue(int maxSz) {
super.initialize(maxSz);
myMaxSize = maxSz;
}
Object[] getValues() { return heap; }
protected boolean lessThan(Object a, Object b) {
// reverse the parameter order so that the queue keeps the oldest items
return ((CacheEntry)b).lastAccessedCopy < ((CacheEntry)a).lastAccessedCopy;
}
// necessary because maxSize is private in base class
public Object myInsertWithOverflow(Object element) {
if (size() < myMaxSize) {
add(element);
return null;
} else if (size() > 0 && !lessThan(element, heap[1])) {
Object ret = heap[1];
heap[1] = element;
updateTop();
return ret;
} else {
return element;
}
}
}
private void evictEntry(K key) {
CacheEntry<K,V> o = map.remove(key);
if (o == null) return;
stats.size.decrementAndGet();
stats.evictionCounter.incrementAndGet();
if(evictionListener != null) evictionListener.evictedEntry(o.key,o.value);
}
/**
* Returns 'n' number of oldest accessed entries present in this cache.
*
* This uses a TreeSet to collect the 'n' oldest items ordered by ascending last access time
* and returns a LinkedHashMap containing 'n' or less than 'n' entries.
* @param n the number of oldest items needed
* @return a LinkedHashMap containing 'n' or less than 'n' entries
*/
public Map<K, V> getOldestAccessedItems(int n) {
Map<K, V> result = new LinkedHashMap<K, V>();
TreeSet<CacheEntry> tree = new TreeSet<CacheEntry>();
markAndSweepLock.lock();
try {
for (Map.Entry<Object, CacheEntry<K,V>> entry : map.entrySet()) {
CacheEntry ce = entry.getValue();
ce.lastAccessedCopy = ce.lastAccessed;
if (tree.size() < n) {
tree.add(ce);
} else {
if (ce.lastAccessedCopy < tree.first().lastAccessedCopy) {
tree.remove(tree.first());
tree.add(ce);
}
}
}
} finally {
markAndSweepLock.unlock();
}
for (CacheEntry<K, V> e : tree) {
result.put(e.key, e.value);
}
return result;
}
public Map<K,V> getLatestAccessedItems(int n) {
Map<K,V> result = new LinkedHashMap<K,V>();
TreeSet<CacheEntry> tree = new TreeSet<CacheEntry>();
// we need to grab the lock since we are changing lastAccessedCopy
markAndSweepLock.lock();
try {
for (Map.Entry<Object, CacheEntry<K,V>> entry : map.entrySet()) {
CacheEntry<K,V> ce = entry.getValue();
ce.lastAccessedCopy = ce.lastAccessed;
if (tree.size() < n) {
tree.add(ce);
} else {
if (ce.lastAccessedCopy > tree.last().lastAccessedCopy) {
tree.remove(tree.last());
tree.add(ce);
}
}
}
} finally {
markAndSweepLock.unlock();
}
for (CacheEntry<K,V> e : tree) {
result.put(e.key, e.value);
}
return result;
}
public int size() {
return stats.size.get();
}
public void clear() {
map.clear();
}
public Map<Object, CacheEntry<K,V>> getMap() {
return map;
}
private static class CacheEntry<K,V> implements Comparable<CacheEntry<K,V>> {
K key;
V value;
volatile long lastAccessed = 0;
long lastAccessedCopy = 0;
public CacheEntry(K key, V value, long lastAccessed) {
this.key = key;
this.value = value;
this.lastAccessed = lastAccessed;
}
public void setLastAccessed(long lastAccessed) {
this.lastAccessed = lastAccessed;
}
public int compareTo(CacheEntry<K,V> that) {
if (this.lastAccessedCopy == that.lastAccessedCopy) return 0;
return this.lastAccessedCopy < that.lastAccessedCopy ? 1 : -1;
}
public int hashCode() {
return value.hashCode();
}
public boolean equals(Object obj) {
return value.equals(obj);
}
public String toString() {
return "key: " + key + " value: " + value + " lastAccessed:" + lastAccessed;
}
}
private boolean isDestroyed = false;
public void destroy() {
try {
if(cleanupThread != null){
cleanupThread.stopThread();
}
} finally {
isDestroyed = true;
}
}
public Stats getStats() {
return stats;
}
public static class Stats {
private final AtomicLong accessCounter = new AtomicLong(0),
putCounter = new AtomicLong(0),
nonLivePutCounter = new AtomicLong(0),
missCounter = new AtomicLong();
private final AtomicInteger size = new AtomicInteger();
private AtomicLong evictionCounter = new AtomicLong();
public long getCumulativeLookups() {
return (accessCounter.get() - putCounter.get() - nonLivePutCounter.get()) + missCounter.get();
}
public long getCumulativeHits() {
return accessCounter.get() - putCounter.get() - nonLivePutCounter.get();
}
public long getCumulativePuts() {
return putCounter.get();
}
public long getCumulativeEvictions() {
return evictionCounter.get();
}
public int getCurrentSize() {
return size.get();
}
public long getCumulativeNonLivePuts() {
return nonLivePutCounter.get();
}
public long getCumulativeMisses() {
return missCounter.get();
}
public void add(Stats other) {
accessCounter.addAndGet(other.accessCounter.get());
putCounter.addAndGet(other.putCounter.get());
nonLivePutCounter.addAndGet(other.nonLivePutCounter.get());
missCounter.addAndGet(other.missCounter.get());
evictionCounter.addAndGet(other.evictionCounter.get());
size.set(Math.max(size.get(), other.size.get()));
}
}
public static interface EvictionListener<K,V>{
public void evictedEntry(K key, V value);
}
private static class CleanupThread extends Thread {
private WeakReference<ConcurrentLRUCache> cache;
private boolean stop = false;
public CleanupThread(ConcurrentLRUCache c) {
cache = new WeakReference<ConcurrentLRUCache>(c);
}
public void run() {
while (true) {
synchronized (this) {
if (stop) break;
try {
this.wait();
} catch (InterruptedException e) {}
}
if (stop) break;
ConcurrentLRUCache c = cache.get();
if(c == null) break;
c.markAndSweep();
}
}
void wakeThread() {
synchronized(this){
this.notify();
}
}
void stopThread() {
synchronized(this){
stop=true;
this.notify();
}
}
}
protected void finalize() throws Throwable {
try {
if(!isDestroyed){
log.error("ConcurrentLRUCache was not destroyed prior to finalize(), indicates a bug -- POSSIBLE RESOURCE LEAK!!!");
destroy();
}
} finally {
super.finalize();
}
}
}