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/*
* 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.
*/
package org.codehaus.groovy.runtime.memoize;
import javax.annotation.concurrent.ThreadSafe;
import java.io.Serializable;
import java.util.Collection;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.locks.StampedLock;
/**
* Represents a simple key-value cache, which is thread safe and backed by a {@link Map} instance.
* StampedCommonCache has better performance than {@link ConcurrentCommonCache},
* but it is not reentrant, in other words, it may cause deadlock if {@link #getAndPut(Object, MemoizeCache.ValueProvider)}
* or {@link #getAndPut(Object, MemoizeCache.ValueProvider, boolean)} is called recursively:
* readlock -> upgrade to writelock -> readlock (fails to get and waits forever)
*
* @param type of the keys
* @param type of the values
* @since 3.0.0
*/
@ThreadSafe
public class StampedCommonCache implements EvictableCache, ValueConvertable, Serializable {
private static final long serialVersionUID = 6760742552334555146L;
private final StampedLock sl = new StampedLock();
private final CommonCache commonCache;
/**
* Constructs a cache with unlimited size
*/
public StampedCommonCache() {
commonCache = new CommonCache();
}
/**
* Constructs a cache with limited size
*
* @param initialCapacity initial capacity of the cache
* @param maxSize max size of the cache
* @param evictionStrategy LRU or FIFO, see {@link EvictableCache.EvictionStrategy}
*/
public StampedCommonCache(int initialCapacity, int maxSize, EvictionStrategy evictionStrategy) {
commonCache = new CommonCache(initialCapacity, maxSize, evictionStrategy);
}
/**
* Constructs a LRU cache with the specified initial capacity and max size.
* The LRU cache is slower than {@link LRUCache}
*
* @param initialCapacity initial capacity of the LRU cache
* @param maxSize max size of the LRU cache
*/
public StampedCommonCache(int initialCapacity, int maxSize) {
commonCache = new CommonCache(initialCapacity, maxSize);
}
/**
* Constructs a LRU cache with the default initial capacity(16)
*
* @param maxSize max size of the LRU cache
* @see #StampedCommonCache(int, int)
*/
public StampedCommonCache(int maxSize) {
commonCache = new CommonCache(maxSize);
}
/**
* Constructs a cache backed by the specified {@link Map} instance
*
* @param map the {@link Map} instance
*/
public StampedCommonCache(Map map) {
commonCache = new CommonCache(map);
}
/**
* {@inheritDoc}
*/
@Override
public V get(final Object key) {
return doWithReadLock(c -> c.get(key));
}
/**
* {@inheritDoc}
*/
@Override
public V put(final K key, final V value) {
return doWithWriteLock(c -> c.put(key, value));
}
/**
* {@inheritDoc}
*/
@Override
public V getAndPut(K key, ValueProvider valueProvider) {
return getAndPut(key, valueProvider, true);
}
public V getAndPut(K key, ValueProvider valueProvider, boolean shouldCache) {
V value;
// try optimistic read first, which is non-blocking
long optimisticReadStamp = sl.tryOptimisticRead();
value = commonCache.get(key);
if (sl.validate(optimisticReadStamp)) {
if (null != convertValue(value)) {
return value;
}
}
long stamp = sl.readLock();
try {
// if stale, read again
if (!sl.validate(optimisticReadStamp)) {
value = commonCache.get(key);
if (null != convertValue(value)) {
return value;
}
}
long ws = sl.tryConvertToWriteLock(stamp); // the new local variable `ws` is necessary here!
if (0L == ws) { // Failed to convert read lock to write lock
sl.unlockRead(stamp);
stamp = sl.writeLock();
// try to read again
value = commonCache.get(key);
if (null != convertValue(value)) {
return value;
}
} else {
stamp = ws;
}
value = compute(key, valueProvider, shouldCache);
} finally {
sl.unlock(stamp);
}
return value;
}
private V compute(K key, ValueProvider valueProvider, boolean shouldCache) {
V value = null == valueProvider ? null : valueProvider.provide(key);
if (shouldCache && null != convertValue(value)) {
commonCache.put(key, value);
}
return value;
}
/**
* {@inheritDoc}
*/
@Override
public Collection values() {
return doWithReadLock(c -> c.values());
}
@Override
public Set> entrySet() {
return doWithReadLock(c -> c.entrySet());
}
/**
* {@inheritDoc}
*/
@Override
public Set keys() {
return doWithReadLock(c -> c.keys());
}
/**
* {@inheritDoc}
*/
@Override
public boolean containsKey(final Object key) {
return doWithReadLock(c -> c.containsKey(key));
}
@Override
public boolean containsValue(Object value) {
return doWithReadLock(c -> c.containsValue(value));
}
/**
* {@inheritDoc}
*/
@Override
public int size() {
return doWithReadLock(c -> c.size());
}
@Override
public boolean isEmpty() {
return size() == 0;
}
/**
* {@inheritDoc}
*/
@Override
public V remove(final Object key) {
return doWithWriteLock(c -> c.remove(key));
}
@Override
public void putAll(Map m) {
doWithWriteLock(c -> {
c.putAll(m);
return null;
});
}
@Override
public Set keySet() {
return keys();
}
/**
* {@inheritDoc}
*/
@Override
public Map clearAll() {
return doWithWriteLock(c -> c.clearAll());
}
/**
* {@inheritDoc}
*/
@Override
public void cleanUpNullReferences() {
doWithWriteLock(c -> {
c.cleanUpNullReferences();
return null;
});
}
/**
* {@inheritDoc}
*/
@Override
public Object convertValue(V value) {
return value;
}
/**
* deal with the backed cache guarded by write lock
* @param action the content to complete
*/
private R doWithWriteLock(Action action) {
long stamp = sl.writeLock();
try {
return action.doWith(commonCache);
} finally {
sl.unlockWrite(stamp);
}
}
/**
* deal with the backed cache guarded by read lock
* @param action the content to complete
*/
private R doWithReadLock(Action action) {
long stamp = sl.tryOptimisticRead();
R result = action.doWith(commonCache);
if (!sl.validate(stamp)) {
stamp = sl.readLock();
try {
result = action.doWith(commonCache);
} finally {
sl.unlockRead(stamp);
}
}
return result;
}
}
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