/*
* Copyright 2015 Ben Manes. All Rights Reserved.
*
* 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.github.benmanes.caffeine.cache.simulator.policy.opt;
import java.util.Set;
import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
import com.github.benmanes.caffeine.cache.simulator.policy.Policy;
import com.github.benmanes.caffeine.cache.simulator.policy.PolicyStats;
import com.google.common.collect.ImmutableSet;
import com.typesafe.config.Config;
import it.unimi.dsi.fastutil.ints.IntArrayFIFOQueue;
import it.unimi.dsi.fastutil.ints.IntPriorityQueue;
import it.unimi.dsi.fastutil.ints.IntRBTreeSet;
import it.unimi.dsi.fastutil.ints.IntSortedSet;
import it.unimi.dsi.fastutil.longs.Long2ObjectMap;
import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
import it.unimi.dsi.fastutil.longs.LongArrayFIFOQueue;
/**
* <pre>Bélády's</pre> optimal page replacement policy. The upper bound of the hit rate is estimated
* by evicting from the cache the item that will next be used farthest into the future.
*
* @author ben.manes@gmail.com (Ben Manes)
*/
public final class ClairvoyantPolicy implements Policy {
private final Long2ObjectMap<IntPriorityQueue> accessTimes;
private final LongArrayFIFOQueue future;
private final PolicyStats policyStats;
private final IntSortedSet data;
private final int maximumSize;
private int infiniteTimestamp;
private int tick;
public ClairvoyantPolicy(Config config) {
BasicSettings settings = new BasicSettings(config);
policyStats = new PolicyStats("opt.Clairvoyant");
accessTimes = new Long2ObjectOpenHashMap<>();
infiniteTimestamp = Integer.MAX_VALUE;
maximumSize = settings.maximumSize();
future = new LongArrayFIFOQueue();
data = new IntRBTreeSet();
}
/** Returns all variations of this policy based on the configuration parameters. */
public static Set<Policy> policies(Config config) {
return ImmutableSet.of(new ClairvoyantPolicy(config));
}
@Override
public void record(long key) {
tick++;
future.enqueue(key);
IntPriorityQueue times = accessTimes.get(key);
if (times == null) {
times = new IntArrayFIFOQueue();
accessTimes.put(key, times);
}
times.enqueue(tick);
}
@Override
public PolicyStats stats() {
return policyStats;
}
@Override
public void finished() {
policyStats.stopwatch().start();
while (!future.isEmpty()) {
process(future.dequeueLong());
}
policyStats.stopwatch().stop();
}
/** Performs the cache operations for the given key. */
private void process(long key) {
IntPriorityQueue times = accessTimes.get(key);
int lastAccess = times.dequeueInt();
boolean found = data.remove(lastAccess);
if (times.isEmpty()) {
data.add(infiniteTimestamp--);
accessTimes.remove(key);
} else {
data.add(times.firstInt());
}
if (found) {
policyStats.recordHit();
} else {
policyStats.recordMiss();
if (data.size() > maximumSize) {
evict();
}
}
}
/** Removes the entry whose next access is farthest away into the future. */
private void evict() {
data.remove(data.lastInt());
policyStats.recordEviction();
}
}