/*
* Copyright (C) 2011 The Guava 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 com.google.common.cache;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ExecutionException;
/**
* This class provides a skeletal implementation of the {@code Cache} interface to minimize the
* effort required to implement this interface.
*
* <p>To implement a cache, the programmer needs only to extend this class and provide an
* implementation for the {@link #put} and {@link #getIfPresent} methods. {@link #getAllPresent} is
* implemented in terms of {@link #getIfPresent}; {@link #putAll} is implemented in terms of
* {@link #put}, {@link #invalidateAll(Iterable)} is implemented in terms of {@link #invalidate}.
* The method {@link #cleanUp} is a no-op. All other methods throw an
* {@link UnsupportedOperationException}.
*
* @author Charles Fry
* @since 10.0
*/
@Beta
@GwtCompatible
public abstract class AbstractCache<K, V> implements Cache<K, V> {
/** Constructor for use by subclasses. */
protected AbstractCache() {}
/**
* @since 11.0
*/
@Override
public V get(K key, Callable<? extends V> valueLoader) throws ExecutionException {
throw new UnsupportedOperationException();
}
/**
* This implementation of {@code getAllPresent} lacks any insight into the internal cache data
* structure, and is thus forced to return the query keys instead of the cached keys. This is only
* possible with an unsafe cast which requires {@code keys} to actually be of type {@code K}.
*
* {@inheritDoc}
*
* @since 11.0
*/
@Override
public ImmutableMap<K, V> getAllPresent(Iterable<?> keys) {
Map<K, V> result = Maps.newLinkedHashMap();
for (Object key : keys) {
if (!result.containsKey(key)) {
@SuppressWarnings("unchecked")
K castKey = (K) key;
V value = getIfPresent(key);
if (value != null) {
result.put(castKey, value);
}
}
}
return ImmutableMap.copyOf(result);
}
/**
* @since 11.0
*/
@Override
public void put(K key, V value) {
throw new UnsupportedOperationException();
}
/**
* @since 12.0
*/
@Override
public void putAll(Map<? extends K, ? extends V> m) {
for (Map.Entry<? extends K, ? extends V> entry : m.entrySet()) {
put(entry.getKey(), entry.getValue());
}
}
@Override
public void cleanUp() {}
@Override
public long size() {
throw new UnsupportedOperationException();
}
@Override
public void invalidate(Object key) {
throw new UnsupportedOperationException();
}
/**
* @since 11.0
*/
@Override
public void invalidateAll(Iterable<?> keys) {
for (Object key : keys) {
invalidate(key);
}
}
@Override
public void invalidateAll() {
throw new UnsupportedOperationException();
}
@Override
public CacheStats stats() {
throw new UnsupportedOperationException();
}
@Override
public ConcurrentMap<K, V> asMap() {
throw new UnsupportedOperationException();
}
/**
* Accumulates statistics during the operation of a {@link Cache} for presentation by {@link
* Cache#stats}. This is solely intended for consumption by {@code Cache} implementors.
*
* @since 10.0
*/
@Beta
public interface StatsCounter {
/**
* Records cache hits. This should be called when a cache request returns a cached value.
*
* @param count the number of hits to record
* @since 11.0
*/
void recordHits(int count);
/**
* Records cache misses. This should be called when a cache request returns a value that was
* not found in the cache. This method should be called by the loading thread, as well as by
* threads blocking on the load. Multiple concurrent calls to {@link Cache} lookup methods with
* the same key on an absent value should result in a single call to either
* {@code recordLoadSuccess} or {@code recordLoadException} and multiple calls to this method,
* despite all being served by the results of a single load operation.
*
* @param count the number of misses to record
* @since 11.0
*/
void recordMisses(int count);
/**
* Records the successful load of a new entry. This should be called when a cache request
* causes an entry to be loaded, and the loading completes successfully. In contrast to
* {@link #recordMisses}, this method should only be called by the loading thread.
*
* @param loadTime the number of nanoseconds the cache spent computing or retrieving the new
* value
*/
void recordLoadSuccess(long loadTime);
/**
* Records the failed load of a new entry. This should be called when a cache request causes
* an entry to be loaded, but an exception is thrown while loading the entry. In contrast to
* {@link #recordMisses}, this method should only be called by the loading thread.
*
* @param loadTime the number of nanoseconds the cache spent computing or retrieving the new
* value prior to an exception being thrown
*/
void recordLoadException(long loadTime);
/**
* Records the eviction of an entry from the cache. This should only been called when an entry
* is evicted due to the cache's eviction strategy, and not as a result of manual {@linkplain
* Cache#invalidate invalidations}.
*/
void recordEviction();
/**
* Returns a snapshot of this counter's values. Note that this may be an inconsistent view, as
* it may be interleaved with update operations.
*/
CacheStats snapshot();
}
/**
* A thread-safe {@link StatsCounter} implementation for use by {@link Cache} implementors.
*
* @since 10.0
*/
@Beta
public static final class SimpleStatsCounter implements StatsCounter {
private final LongAddable hitCount = LongAddables.create();
private final LongAddable missCount = LongAddables.create();
private final LongAddable loadSuccessCount = LongAddables.create();
private final LongAddable loadExceptionCount = LongAddables.create();
private final LongAddable totalLoadTime = LongAddables.create();
private final LongAddable evictionCount = LongAddables.create();
/**
* Constructs an instance with all counts initialized to zero.
*/
public SimpleStatsCounter() {}
/**
* @since 11.0
*/
@Override
public void recordHits(int count) {
hitCount.add(count);
}
/**
* @since 11.0
*/
@Override
public void recordMisses(int count) {
missCount.add(count);
}
@Override
public void recordLoadSuccess(long loadTime) {
loadSuccessCount.increment();
totalLoadTime.add(loadTime);
}
@Override
public void recordLoadException(long loadTime) {
loadExceptionCount.increment();
totalLoadTime.add(loadTime);
}
@Override
public void recordEviction() {
evictionCount.increment();
}
@Override
public CacheStats snapshot() {
return new CacheStats(
hitCount.sum(),
missCount.sum(),
loadSuccessCount.sum(),
loadExceptionCount.sum(),
totalLoadTime.sum(),
evictionCount.sum());
}
/**
* Increments all counters by the values in {@code other}.
*/
public void incrementBy(StatsCounter other) {
CacheStats otherStats = other.snapshot();
hitCount.add(otherStats.hitCount());
missCount.add(otherStats.missCount());
loadSuccessCount.add(otherStats.loadSuccessCount());
loadExceptionCount.add(otherStats.loadExceptionCount());
totalLoadTime.add(otherStats.totalLoadTime());
evictionCount.add(otherStats.evictionCount());
}
}
}