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Grails Web Application Framework
/*
* Copyright 2011 the original author or authors.
*
* 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 grails.util;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.concurrent.Callable;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* Wrapper for a value inside a cache that adds timestamp information
* for expiration and prevents "cache storms" with a Lock.
*
* JMM happens-before is ensured with AtomicReference.
*
* Objects in cache are assumed to not change after publication.
*
* @author Lari Hotari
* @since 2.3.4
*/
public class CacheEntry {
private static final Logger LOG = LoggerFactory.getLogger(CacheEntry.class);
private final AtomicReference valueRef=new AtomicReference(null);
private long createdMillis;
private final ReadWriteLock lock=new ReentrantReadWriteLock();
private final Lock readLock=lock.readLock();
private final Lock writeLock=lock.writeLock();
private volatile boolean initialized=false;
public CacheEntry() {
expire();
}
public CacheEntry(V value) {
setValue(value);
}
/**
* Gets a value from cache. If the key doesn't exist, it will create the value using the updater callback
* Prevents cache storms with a lock
*
* The key is always added to the cache. Null return values will also be cached.
* You can use this together with ConcurrentLinkedHashMap to create a bounded LRU cache
*
* @param map the cache map
* @param key the key to look up
* @param timeoutMillis cache entry timeout
* @param updater callback to create/update value
* @param cacheEntryClass CacheEntry implementation class to use
* @param returnExpiredWhileUpdating when true, return expired value while updating new value
* @param cacheRequestObject context object that gets passed to hasExpired, shouldUpdate and updateValue methods, not used in default implementation
* @return
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
public static V getValue(ConcurrentMap> map, K key, long timeoutMillis, Callable updater, Callable cacheEntryFactory, boolean returnExpiredWhileUpdating, Object cacheRequestObject) {
CacheEntry cacheEntry = map.get(key);
if(cacheEntry==null) {
try {
cacheEntry = cacheEntryFactory.call();
}
catch (Exception e) {
throw new UpdateException(e);
}
CacheEntry previousEntry = map.putIfAbsent(key, cacheEntry);
if(previousEntry != null) {
cacheEntry = previousEntry;
}
}
try {
return cacheEntry.getValue(timeoutMillis, updater, returnExpiredWhileUpdating, cacheRequestObject);
}
catch (UpdateException e) {
e.rethrowRuntimeException();
// make compiler happy
return null;
}
}
@SuppressWarnings("rawtypes")
private static final Callable DEFAULT_CACHE_ENTRY_FACTORY = new Callable() {
@Override
public CacheEntry call() throws Exception {
return new CacheEntry();
}
};
public static V getValue(ConcurrentMap> map, K key, long timeoutMillis, Callable updater) {
return getValue(map, key, timeoutMillis, updater, DEFAULT_CACHE_ENTRY_FACTORY, true, null);
}
public static V getValue(ConcurrentMap> map, K key, long timeoutMillis, Callable updater, boolean returnExpiredWhileUpdating) {
return getValue(map, key, timeoutMillis, updater, DEFAULT_CACHE_ENTRY_FACTORY, returnExpiredWhileUpdating, null);
}
public V getValue(long timeout, Callable updater) {
return getValue(timeout, updater, true, null);
}
/**
* gets the current value from the entry and updates it if it's older than timeout
*
* updater is a callback for creating an updated value.
*
* @param timeout
* @param updater
* @param returnExpiredWhileUpdating
* @param cacheRequestObject
* @return the current value
*/
public V getValue(long timeout, Callable updater, boolean returnExpiredWhileUpdating, Object cacheRequestObject) {
if (!isInitialized() || hasExpired(timeout, cacheRequestObject)) {
boolean lockAcquired = false;
try {
long beforeLockingCreatedMillis = createdMillis;
if(returnExpiredWhileUpdating) {
if(!writeLock.tryLock()) {
if(isInitialized()) {
return getValueWhileUpdating(cacheRequestObject);
} else {
if(LOG.isDebugEnabled()) {
LOG.debug("Locking cache for update");
}
writeLock.lock();
}
}
} else {
LOG.debug("Locking cache for update");
writeLock.lock();
}
lockAcquired = true;
V value;
if (!isInitialized() || shouldUpdate(beforeLockingCreatedMillis, cacheRequestObject)) {
try {
value = updateValue(getValue(), updater, cacheRequestObject);
if(LOG.isDebugEnabled()) {
LOG.debug("Updating cache for value [{}]", value);
}
setValue(value);
}
catch (Exception e) {
throw new UpdateException(e);
}
} else {
value = getValue();
resetTimestamp(false);
}
return value;
} finally {
if(lockAcquired) {
if(LOG.isDebugEnabled()) {
LOG.debug("Unlocking cache for update");
}
writeLock.unlock();
}
}
} else {
return getValue();
}
}
protected V getValueWhileUpdating(Object cacheRequestObject) {
return valueRef.get();
}
protected V updateValue(V oldValue, Callable updater, Object cacheRequestObject) throws Exception {
return updater != null ? updater.call() : oldValue;
}
public V getValue() {
try {
readLock.lock();
return valueRef.get();
} finally {
readLock.unlock();
}
}
public void setValue(V val) {
try{
writeLock.lock();
valueRef.set(val);
setInitialized(true);
resetTimestamp(true);
} finally {
writeLock.unlock();
}
}
protected boolean hasExpired(long timeout, Object cacheRequestObject) {
return timeout >= 0 && System.currentTimeMillis() - timeout > createdMillis;
}
protected boolean shouldUpdate(long beforeLockingCreatedMillis, Object cacheRequestObject) {
return beforeLockingCreatedMillis == createdMillis || createdMillis == 0L;
}
protected void resetTimestamp(boolean updated) {
if(updated) {
createdMillis = System.currentTimeMillis();
}
}
public long getCreatedMillis() {
return createdMillis;
}
public void expire() {
createdMillis = 0L;
}
public boolean isInitialized() {
return initialized;
}
public void setInitialized(boolean initialized) {
this.initialized = initialized;
}
public static final class UpdateException extends RuntimeException {
private static final long serialVersionUID = 1L;
public UpdateException(String message, Throwable cause) {
super(message, cause);
}
public UpdateException(Throwable cause) {
super(cause);
}
public void rethrowCause() throws Exception {
if (getCause() instanceof Exception) {
throw (Exception)getCause();
}
throw this;
}
public void rethrowRuntimeException() {
if (getCause() instanceof RuntimeException) {
throw (RuntimeException)getCause();
}
throw this;
}
}
}
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