/*
* 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.util.concurrent.UncheckedExecutionException;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.atomic.AtomicLong;
/**
* 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 {@code get} method. This implementation throws an
* {@link UnsupportedOperationException} on calls to {@link #size}, {@link #invalidate},
* {@link #invalidateAll}, {@link #stats}, and {@link #asMap}. The methods
* {@link #getUnchecked} and {@link #apply} are implemented in terms of {@link #get}. The method
* {@link #cleanUp} is a no-op.
*
* @author Charles Fry
* @since 10.0
*/
@Beta
public abstract class AbstractCache<K, V> implements Cache<K, V> {
/** Constructor for use by subclasses. */
protected AbstractCache() {}
@Override
public V getUnchecked(K key) {
try {
return get(key);
} catch (ExecutionException e) {
throw new UncheckedExecutionException(e.getCause());
}
}
@Override
public final V apply(K key) {
return getUnchecked(key);
}
@Override
public void cleanUp() {}
@Override
public long size() {
throw new UnsupportedOperationException();
}
@Override
public void invalidate(Object key) {
throw new UnsupportedOperationException();
}
@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 a single hit. This should be called when a cache request returns a cached value.
*/
public void recordHit();
/**
* 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 succesfully. In contrast to
* {@link #recordConcurrentMiss}, 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
*/
public 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 #recordConcurrentMiss}, 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
*/
public void recordLoadException(long loadTime);
/**
* Records a single concurrent miss. This should be called when a cache request returns a
* value which was loaded by a different thread. In contrast to {@link #recordLoadSuccess}
* and {@link #recordLoadException}, this method should never be called by the loading
* thread. 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.
*/
public void recordConcurrentMiss();
/**
* 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}.
*/
public 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.
*/
public CacheStats snapshot();
}
/**
* A thread-safe {@link StatsCounter} implementation for use by {@link Cache} implementors.
*
* @since 10.0
*/
@Beta
public static class SimpleStatsCounter implements StatsCounter {
private final AtomicLong hitCount = new AtomicLong();
private final AtomicLong missCount = new AtomicLong();
private final AtomicLong loadSuccessCount = new AtomicLong();
private final AtomicLong loadExceptionCount = new AtomicLong();
private final AtomicLong totalLoadTime = new AtomicLong();
private final AtomicLong evictionCount = new AtomicLong();
@Override
public void recordHit() {
hitCount.incrementAndGet();
}
@Override
public void recordLoadSuccess(long loadTime) {
missCount.incrementAndGet();
loadSuccessCount.incrementAndGet();
totalLoadTime.addAndGet(loadTime);
}
@Override
public void recordLoadException(long loadTime) {
missCount.incrementAndGet();
loadExceptionCount.incrementAndGet();
totalLoadTime.addAndGet(loadTime);
}
@Override
public void recordConcurrentMiss() {
missCount.incrementAndGet();
}
@Override
public void recordEviction() {
evictionCount.incrementAndGet();
}
@Override
public CacheStats snapshot() {
return new CacheStats(
hitCount.get(),
missCount.get(),
loadSuccessCount.get(),
loadExceptionCount.get(),
totalLoadTime.get(),
evictionCount.get());
}
/**
* Increments all counters by the values in {@code other}.
*/
public void incrementBy(StatsCounter other) {
CacheStats otherStats = other.snapshot();
hitCount.addAndGet(otherStats.hitCount());
missCount.addAndGet(otherStats.missCount());
loadSuccessCount.addAndGet(otherStats.loadSuccessCount());
loadExceptionCount.addAndGet(otherStats.loadExceptionCount());
totalLoadTime.addAndGet(otherStats.totalLoadTime());
evictionCount.addAndGet(otherStats.evictionCount());
}
}
}
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