content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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 org.apache.cassandra.cache;
  
  import static com.google.common.base.Preconditions.checkState;
  
  import java.util.Iterator;
  
  import com.github.benmanes.caffeine.cache.Cache;
  import com.github.benmanes.caffeine.cache.Caffeine;
  import com.github.benmanes.caffeine.cache.Policy.Eviction;
  import com.github.benmanes.caffeine.cache.Weigher;
  import org.apache.cassandra.concurrent.ImmediateExecutor;
  
  /**
   * An adapter from a Caffeine cache to the ICache interface. This provides an on-heap cache using
   * the W-TinyLFU eviction policy (http://arxiv.org/pdf/1512.00727.pdf), which has a higher hit rate
   * than an LRU.
   */
  public class CaffeineCache<K extends IMeasurableMemory, V extends IMeasurableMemory> implements ICache<K, V>
  {
      private final Cache<K, V> cache;
      private final Eviction<K, V> policy;
  
      private CaffeineCache(Cache<K, V> cache)
      {
          this.cache = cache;
          this.policy = cache.policy().eviction().orElseThrow(() -> 
              new IllegalArgumentException("Expected a size bounded cache"));
          checkState(policy.isWeighted(), "Expected a weighted cache");
      }
  
      /**
       * Initialize a cache with initial capacity with weightedCapacity
       */
      public static <K extends IMeasurableMemory, V extends IMeasurableMemory> CaffeineCache<K, V> create(long weightedCapacity, Weigher<K, V> weigher)
      {
          Cache<K, V> cache = Caffeine.newBuilder()
                  .maximumWeight(weightedCapacity)
                  .weigher(weigher)
                  .executor(ImmediateExecutor.INSTANCE)
                  .build();
          return new CaffeineCache<>(cache);
      }
  
      public static <K extends IMeasurableMemory, V extends IMeasurableMemory> CaffeineCache<K, V> create(long weightedCapacity)
      {
          return create(weightedCapacity, (key, value) -> {
              long size = key.unsharedHeapSize() + value.unsharedHeapSize();
              if (size > Integer.MAX_VALUE) {
                  throw new IllegalArgumentException("Serialized size cannot be more than 2GiB/Integer.MAX_VALUE");
              }
              return (int) size;
          });
      }
  
      public long capacity()
      {
          return policy.getMaximum();
      }
  
      public void setCapacity(long capacity)
      {
          policy.setMaximum(capacity);
      }
  
      public boolean isEmpty()
      {
          return cache.asMap().isEmpty();
      }
  
      public int size()
      {
          return cache.asMap().size();
      }
  
      public long weightedSize()
      {
          return policy.weightedSize().getAsLong();
      }
  
      public void clear()
      {
          cache.invalidateAll();
      }
  
      public V get(K key)
      {
          return cache.getIfPresent(key);
      }
  
      public void put(K key, V value)
      {
          cache.put(key, value);
      }
  
      public boolean putIfAbsent(K key, V value)
      {
          return cache.asMap().putIfAbsent(key, value) == null;
      }
  
      public boolean replace(K key, V old, V value)
      {
          return cache.asMap().replace(key, old, value);
      }
  
      public void remove(K key)
      {
          cache.invalidate(key);
      }
  
      public Iterator<K> keyIterator()
      {
          return cache.asMap().keySet().iterator();
      }
  
      public Iterator<K> hotKeyIterator(int n)
      {
          return policy.hottest(n).keySet().iterator();
      }
  
      public boolean containsKey(K key)
      {
          return cache.asMap().containsKey(key);
      }
  }
  