com.github.benmanes.caffeine.cache.simulator.policy.opt.ClairvoyantPolicy.java Source code

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Here is the source code for com.github.benmanes.caffeine.cache.simulator.policy.opt.ClairvoyantPolicy.java

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/*
 * 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>Bldy'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.rem(data.lastInt());
        policyStats.recordEviction();
    }
}