/*******************************************************************************
* Copyright 2010 Cees De Groot, Alex Boisvert, Jan Kotek
*
* 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.apache.jdbm;
import javax.crypto.Cipher;
import java.io.IOException;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.util.Iterator;
import java.util.concurrent.atomic.AtomicInteger;
/**
* A DB wrapping and caching another DB.
*
* @author Jan Kotek
* @author Alex Boisvert
* @author Cees de Groot
*
* TODO add 'cache miss' statistics
*/
public class DBCacheRef
extends DBCache {
private static final boolean debug = false;
/**
* If Soft Cache is enabled, this contains softly referenced clean entries.
* If entry became dirty, it is moved to _hash with limited size.
* This map is accessed from SoftCache Disposer thread, so all access must be
* synchronized
*/
protected LongHashMap _softHash;
/**
* Reference queue used to collect Soft Cache entries
*/
protected ReferenceQueue<ReferenceCacheEntry> _refQueue;
/**
* Thread in which Soft Cache references are disposed
*/
protected Thread _softRefThread;
protected static AtomicInteger threadCounter = new AtomicInteger(0);
/** counter which counts number of insert since last 'action'*/
protected int insertCounter = 0;
private final boolean _autoClearReferenceCacheOnLowMem;
private final byte _cacheType;
/**
* Construct a CacheRecordManager wrapping another DB and
* using a given cache policy.
*/
public DBCacheRef(String filename, boolean readonly, boolean transactionDisabled,
Cipher cipherIn, Cipher cipherOut, boolean useRandomAccessFile,
boolean deleteFilesAfterClose,
byte cacheType, boolean cacheAutoClearOnLowMem, boolean lockingDisabled) {
super(filename, readonly, transactionDisabled,
cipherIn, cipherOut, useRandomAccessFile,
deleteFilesAfterClose, lockingDisabled);
this._cacheType = cacheType;
_autoClearReferenceCacheOnLowMem = cacheAutoClearOnLowMem;
_softHash = new LongHashMap<ReferenceCacheEntry>();
_refQueue = new ReferenceQueue<ReferenceCacheEntry>();
_softRefThread = new Thread(
new SoftRunnable(this, _refQueue),
"JDBM Soft Cache Disposer " + (threadCounter.incrementAndGet()));
_softRefThread.setDaemon(true);
_softRefThread.start();
}
void clearCacheIfLowOnMem() {
insertCounter = 0;
if(!_autoClearReferenceCacheOnLowMem)
return;
Runtime r = Runtime.getRuntime();
long max = r.maxMemory();
if(max == Long.MAX_VALUE)
return;
double free = r.freeMemory();
double total = r.totalMemory();
//We believe that free refers to total not max.
//Increasing heap size to max would increase to max
free = free + (max-total);
if(debug)
System.err.println("DBCache: freemem = " +free + " = "+(free/max)+"%");
if(free<1e7 || free*4 <max)
clearCache();
}
public synchronized <A> A fetch(long recid, Serializer<A> serializer, boolean disableCache) throws IOException {
if (disableCache)
return super.fetch(recid, serializer, disableCache);
else
return fetch(recid, serializer);
}
public synchronized void delete(long recid)
throws IOException {
checkNotClosed();
super.delete(recid);
synchronized (_hashDirties){
_hashDirties.remove(recid);
}
synchronized (_softHash) {
Object e = _softHash.remove(recid);
if (e != null && e instanceof ReferenceCacheEntry) {
((ReferenceCacheEntry)e).clear();
}
}
if(needsAutoCommit())
commit();
}
public synchronized <A> void update(final long recid, A obj, Serializer<A> serializer) throws IOException {
checkNotClosed();
synchronized (_softHash) {
//soft cache can not contain dirty objects
Object e = _softHash.remove(recid);
if (e != null && e instanceof ReferenceCacheEntry) {
((ReferenceCacheEntry)e).clear();
}
}
synchronized (_hashDirties){
//put into dirty cache
final DirtyCacheEntry e = new DirtyCacheEntry();
e._recid = recid;
e._obj = obj;
e._serializer = serializer;
_hashDirties.put(recid,e);
}
if(needsAutoCommit())
commit();
}
public synchronized <A> A fetch(long recid, Serializer<A> serializer)
throws IOException {
checkNotClosed();
synchronized (_softHash) {
Object e = _softHash.get(recid);
if (e != null) {
if(e instanceof ReferenceCacheEntry)
e = ((ReferenceCacheEntry)e).get();
if (e != null) {
return (A) e;
}
}
}
synchronized (_hashDirties){
DirtyCacheEntry e2 = _hashDirties.get(recid);
if(e2!=null){
return (A) e2._obj;
}
}
A value = super.fetch(recid, serializer);
if(needsAutoCommit())
commit();
synchronized (_softHash) {
if (_cacheType == SOFT)
_softHash.put(recid, new SoftCacheEntry(recid, value, _refQueue));
else if (_cacheType == WEAK)
_softHash.put(recid, new WeakCacheEntry(recid, value, _refQueue));
else
_softHash.put(recid,value);
}
return value;
}
public synchronized void close() {
checkNotClosed();
updateCacheEntries();
super.close();
_softHash = null;
_softRefThread.interrupt();
}
public synchronized void rollback() {
checkNotClosed();
// discard all cache entries since we don't know which entries
// where part of the transaction
synchronized (_softHash) {
Iterator<ReferenceCacheEntry> iter = _softHash.valuesIterator();
while (iter.hasNext()) {
ReferenceCacheEntry e = iter.next();
e.clear();
}
_softHash.clear();
}
super.rollback();
}
protected boolean isCacheEntryDirty(DirtyCacheEntry entry) {
return _hashDirties.get(entry._recid) != null;
}
protected void setCacheEntryDirty(DirtyCacheEntry entry, boolean dirty) {
if (dirty) {
_hashDirties.put(entry._recid, entry);
} else {
_hashDirties.remove(entry._recid);
}
}
interface ReferenceCacheEntry {
long getRecid();
void clear();
Object get();
}
@SuppressWarnings("unchecked")
static final class SoftCacheEntry extends SoftReference implements ReferenceCacheEntry {
protected final long _recid;
public long getRecid() {
return _recid;
}
SoftCacheEntry(long recid, Object obj, ReferenceQueue queue) {
super(obj, queue);
_recid = recid;
}
}
@SuppressWarnings("unchecked")
static final class WeakCacheEntry extends WeakReference implements ReferenceCacheEntry {
protected final long _recid;
public long getRecid() {
return _recid;
}
WeakCacheEntry(long recid, Object obj, ReferenceQueue queue) {
super(obj, queue);
_recid = recid;
}
}
/**
* Runs in separate thread and cleans SoftCache.
* Runnable auto exists when CacheRecordManager is GCed
*
* @author Jan Kotek
*/
static final class SoftRunnable implements Runnable {
private ReferenceQueue<ReferenceCacheEntry> entryQueue;
private WeakReference<DBCacheRef> db2;
public SoftRunnable(DBCacheRef db,
ReferenceQueue<ReferenceCacheEntry> entryQueue) {
this.db2 = new WeakReference<DBCacheRef>(db);
this.entryQueue = entryQueue;
}
public void run() {
while (true) try {
//collect next item from cache,
//limit 10000 ms is to keep periodically checking if db was GCed
ReferenceCacheEntry e = (ReferenceCacheEntry) entryQueue.remove(10000);
//check if db was GCed, cancel in that case
DBCacheRef db = db2.get();
if (db == null)
return;
if (e != null) {
synchronized (db._softHash) {
int counter = 0;
while (e != null) {
db._softHash.remove(e.getRecid());
e = (SoftCacheEntry) entryQueue.poll();
if(debug)
counter++;
}
if(debug)
System.err.println("DBCache: "+counter+" objects released from ref cache.");
}
}else{
//check memory consumption every 10 seconds
db.clearCacheIfLowOnMem();
}
} catch (InterruptedException e) {
return;
} catch (Throwable e) {
//this thread must keep spinning,
//otherwise SoftCacheEntries would not be disposed
e.printStackTrace();
}
}
}
public void clearCache() {
if(debug)
System.err.println("DBCache: Clear cache");
synchronized (_softHash) {
if(_cacheType!=HARD){
Iterator<ReferenceCacheEntry> iter = _softHash.valuesIterator();
while (iter.hasNext()) {
ReferenceCacheEntry e = iter.next();
e.clear();
}
}
_softHash.clear();
}
}
}