com.google.gapid.util.FutureCache.java Source code

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Here is the source code for com.google.gapid.util.FutureCache.java

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/*
 * Copyright (C) 2017 Google Inc.
 *
 * 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.gapid.util;

import static com.google.gapid.util.Scheduler.EXECUTOR;

import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;

import java.util.function.Function;
import java.util.function.Predicate;

public class FutureCache<K, V> {
    private final Cache<K, V> cache;
    private final Function<K, ListenableFuture<V>> fetcher;
    private final Predicate<V> shouldCache;

    public FutureCache(Cache<K, V> cache, Function<K, ListenableFuture<V>> fetcher, Predicate<V> shouldCache) {
        this.cache = cache;
        this.fetcher = fetcher;
        this.shouldCache = shouldCache;
    }

    public static <K, V> FutureCache<K, V> softCache(Function<K, ListenableFuture<V>> fetcher,
            Predicate<V> shouldCache) {
        return new FutureCache<K, V>(CacheBuilder.newBuilder().softValues().build(), fetcher, shouldCache);
    }

    public static <K, V> FutureCache<K, V> hardCache(Function<K, ListenableFuture<V>> fetcher,
            Predicate<V> shouldCache) {
        return new FutureCache<K, V>(CacheBuilder.newBuilder().build(), fetcher, shouldCache);
    }

    public ListenableFuture<V> get(K key) {
        // Look up the value in the cache using the executor.
        ListenableFuture<V> cacheLookUp = EXECUTOR.submit(() -> cache.getIfPresent(key));
        return Futures.transformAsync(cacheLookUp, fromCache -> {
            if (fromCache != null) {
                return Futures.immediateFuture(fromCache);
            }

            return Futures.transform(fetcher.apply(key), value -> {
                if (shouldCache.test(value)) {
                    cache.put(key, value);
                }
                return value;
            });
        });
    }

    public V getIfPresent(K key) {
        return cache.getIfPresent(key);
    }
}