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/**
* Copyright 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.hibernate.strategy;
import java.io.Serializable;
import java.util.Comparator;
import java.util.UUID;
import java.util.concurrent.atomic.AtomicLong;
import net.sf.ehcache.hibernate.regions.EhcacheTransactionalDataRegion;
import org.hibernate.cache.CacheException;
import org.hibernate.cache.access.SoftLock;
import org.hibernate.cfg.Settings;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Superclass for all Ehcache specific read/write AccessStrategy implementations.
*
* @param the type of the enclosed cache region
*
* @author Chris Dennis
*/
abstract class AbstractReadWriteEhcacheAccessStrategy extends AbstractEhcacheAccessStrategy {
private static final Logger LOG = LoggerFactory.getLogger(AbstractReadWriteEhcacheAccessStrategy.class);
private final UUID uuid = UUID.randomUUID();
private final AtomicLong nextLockId = new AtomicLong();
private final Comparator versionComparator;
/**
* Creates a read/write cache access strategy around the given cache region.
*/
public AbstractReadWriteEhcacheAccessStrategy(T region, Settings settings) {
super(region, settings);
this.versionComparator = region.getCacheDataDescription().getVersionComparator();
}
/**
* Returns null if the item is not readable. Locked items are not readable, nor are items created
* after the start of this transaction.
*
* @see org.hibernate.cache.access.EntityRegionAccessStrategy#get(java.lang.Object, long)
* @see org.hibernate.cache.access.CollectionRegionAccessStrategy#get(java.lang.Object, long)
*/
public final Object get(Object key, long txTimestamp) throws CacheException {
readLockIfNeeded(key);
try {
Lockable item = (Lockable) region.get(key);
boolean readable = item != null && item.isReadable(txTimestamp);
if (readable) {
return item.getValue();
} else {
return null;
}
} finally {
readUnlockIfNeeded(key);
}
}
/**
* Returns false and fails to put the value if there is an existing un-writeable item mapped to this
* key.
*
* @see org.hibernate.cache.access.EntityRegionAccessStrategy#putFromLoad(java.lang.Object, java.lang.Object, long, java.lang.Object, boolean)
* @see org.hibernate.cache.access.CollectionRegionAccessStrategy#putFromLoad(java.lang.Object, java.lang.Object, long, java.lang.Object, boolean)
*/
@Override
public final boolean putFromLoad(Object key, Object value, long txTimestamp, Object version, boolean minimalPutOverride)
throws CacheException {
region.writeLock(key);
try {
Lockable item = (Lockable) region.get(key);
boolean writeable = item == null || item.isWriteable(txTimestamp, version, versionComparator);
if (writeable) {
region.put(key, new Item(value, version, region.nextTimestamp()));
return true;
} else {
return false;
}
} finally {
region.writeUnlock(key);
}
}
/**
* Soft-lock a cache item.
*
* @see org.hibernate.cache.access.EntityRegionAccessStrategy#lockItem(java.lang.Object, java.lang.Object)
* @see org.hibernate.cache.access.CollectionRegionAccessStrategy#lockItem(java.lang.Object, java.lang.Object)
*/
public final SoftLock lockItem(Object key, Object version) throws CacheException {
region.writeLock(key);
try {
Lockable item = (Lockable) region.get(key);
long timeout = region.nextTimestamp() + region.getTimeout();
final Lock lock = (item == null) ? new Lock(timeout, uuid, nextLockId(), version) : item.lock(timeout, uuid, nextLockId());
putLock(key, lock);
return lock;
} finally {
region.writeUnlock(key);
}
}
/**
* Soft-unlock a cache item.
*
* @see org.hibernate.cache.access.EntityRegionAccessStrategy#unlockItem(java.lang.Object, org.hibernate.cache.access.SoftLock)
* @see org.hibernate.cache.access.CollectionRegionAccessStrategy#unlockItem(java.lang.Object, org.hibernate.cache.access.SoftLock)
*/
public final void unlockItem(Object key, SoftLock lock) throws CacheException {
region.writeLock(key);
try {
Lockable item = (Lockable) region.get(key);
if ((item != null) && item.isUnlockable(lock)) {
decrementLock(key, (Lock) item);
} else {
handleMissingLock(key, item);
}
} finally {
region.writeUnlock(key);
}
}
private long nextLockId() {
return nextLockId.getAndIncrement();
}
/**
* Unlock and re-put the given key, lock combination.
*/
protected void decrementLock(Object key, Lock lock) {
lock.unlock(region.nextTimestamp());
putLock(key, lock);
}
/**
* Handle the timeout of a previous lock mapped to this key
*/
protected void handleMissingLock(Object key, Lockable lock) {
LOG.error("Cache " + region.getName() + " Key " + key + " Lockable : " + lock + "\n"
+ "A soft-locked cache entry was removed already. Out of balance lock/unlock sequences ?");
long ts = region.nextTimestamp() + region.getTimeout();
// create new lock that times out immediately
Lock newLock = new Lock(ts, uuid, nextLockId.getAndIncrement(), null);
newLock.unlock(ts);
// This isn't really necessary, could be a simple put, but for completeness, though given pinning, this also should never happen
putLock(key, newLock);
}
private void putLock(final Object key, final Lock newLock) {
if (newLock.isLocked()) {
region.putPinned(key, newLock);
} else {
region.put(key, newLock);
}
}
/**
* Read lock the entry for the given key if internal cache locks will not provide correct exclusion.
*/
private void readLockIfNeeded(Object key) {
if (region.locksAreIndependentOfCache()) {
region.readLock(key);
}
}
/**
* Read unlock the entry for the given key if internal cache locks will not provide correct exclusion.
*/
private void readUnlockIfNeeded(Object key) {
if (region.locksAreIndependentOfCache()) {
region.readUnlock(key);
}
}
/**
* Interface type implemented by all wrapper objects in the cache.
*/
protected static interface Lockable {
/**
* Returns true if the enclosed value can be read by a transaction started at the given time.
*/
public boolean isReadable(long txTimestamp);
/**
* Returns true if the enclosed value can be replaced with one of the given version by a
* transaction started at the given time.
*/
public boolean isWriteable(long txTimestamp, Object version, Comparator versionComparator);
/**
* Returns the enclosed value.
*/
public Object getValue();
/**
* Returns true if the given lock can be unlocked using the given SoftLock instance as a handle.
*/
public boolean isUnlockable(SoftLock lock);
/**
* Locks this entry, stamping it with the UUID and lockId given, with the lock timeout occuring at the specified
* time. The returned Lock object can be used to unlock the entry in the future.
*/
public Lock lock(long timeout, UUID uuid, long lockId);
}
/**
* Wrapper type representing unlocked items.
*/
protected static final class Item implements Serializable, Lockable {
private static final long serialVersionUID = 1L;
private final Object value;
private final Object version;
private final long timestamp;
/**
* Creates an unlocked item wrapping the given value with a version and creation timestamp.
*/
Item(Object value, Object version, long timestamp) {
this.value = value;
this.version = version;
this.timestamp = timestamp;
}
/**
* {@inheritDoc}
*/
public boolean isReadable(long txTimestamp) {
return txTimestamp > timestamp;
}
/**
* {@inheritDoc}
*/
public boolean isWriteable(long txTimestamp, Object newVersion, Comparator versionComparator) {
return version != null && versionComparator.compare(version, newVersion) < 0;
}
/**
* {@inheritDoc}
*/
public Object getValue() {
return value;
}
/**
* {@inheritDoc}
*/
public boolean isUnlockable(SoftLock lock) {
return false;
}
/**
* {@inheritDoc}
*/
public Lock lock(long timeout, UUID uuid, long lockId) {
return new Lock(timeout, uuid, lockId, version);
}
}
/**
* Wrapper type representing locked items.
*/
protected static final class Lock implements Serializable, Lockable, SoftLock {
private static final long serialVersionUID = 2L;
private final UUID sourceUuid;
private final long lockId;
private final Object version;
private long timeout;
private boolean concurrent;
private int multiplicity = 1;
private long unlockTimestamp;
/**
* Creates a locked item with the given identifiers and object version.
*/
Lock(long timeout, UUID sourceUuid, long lockId, Object version) {
this.timeout = timeout;
this.lockId = lockId;
this.version = version;
this.sourceUuid = sourceUuid;
}
/**
* {@inheritDoc}
*/
public boolean isReadable(long txTimestamp) {
return false;
}
/**
* {@inheritDoc}
*/
public boolean isWriteable(long txTimestamp, Object newVersion, Comparator versionComparator) {
if (txTimestamp > timeout) {
// if timedout then allow write
return true;
}
if (multiplicity > 0) {
// if still locked then disallow write
return false;
}
return version == null ? txTimestamp > unlockTimestamp : versionComparator.compare(version, newVersion) < 0;
}
/**
* {@inheritDoc}
*/
public Object getValue() {
return null;
}
/**
* {@inheritDoc}
*/
public boolean isUnlockable(SoftLock lock) {
return equals(lock);
}
/**
* {@inheritDoc}
*/
@Override
public boolean equals(Object o) {
if (o == this) {
return true;
} else if (o instanceof Lock) {
return (lockId == ((Lock) o).lockId) && sourceUuid.equals(((Lock) o).sourceUuid);
} else {
return false;
}
}
/**
* {@inheritDoc}
*/
@Override
public int hashCode() {
int hash = (sourceUuid != null ? sourceUuid.hashCode() : 0);
int temp = (int) lockId;
for (int i = 1; i < Long.SIZE / Integer.SIZE; i++) {
temp ^= (lockId >>> (i * Integer.SIZE));
}
return hash + temp;
}
/**
* Returns true if this Lock has been concurrently locked by more than one transaction.
*/
public boolean wasLockedConcurrently() {
return concurrent;
}
/**
* {@inheritDoc}
*/
public Lock lock(long timeout, UUID uuid, long lockId) {
concurrent = true;
multiplicity++;
this.timeout = timeout;
return this;
}
/**
* Unlocks this Lock, and timestamps the unlock event.
*/
public void unlock(long timestamp) {
if (--multiplicity == 0) {
unlockTimestamp = timestamp;
}
}
/**
* {@inheritDoc}
*/
@Override
public String toString() {
StringBuilder sb = new StringBuilder("Lock Source-UUID:" + sourceUuid + " Lock-ID:" + lockId);
return sb.toString();
}
/**
* Tells whether the Lock is currently held
* @return true if locked, false otherwise
*/
public boolean isLocked() {
return multiplicity != 0;
}
}
}
