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/*
 * Copyright (C) 2009 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 static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Ascii;
import com.google.common.base.Equivalence;
import com.google.common.base.MoreObjects;
import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.common.base.Ticker;
import com.google.common.cache.AbstractCache.SimpleStatsCounter;
import com.google.common.cache.AbstractCache.StatsCounter;
import com.google.common.cache.LocalCache.Strength;
import com.google.errorprone.annotations.CheckReturnValue;
import com.google.j2objc.annotations.J2ObjCIncompatible;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.util.ConcurrentModificationException;
import java.util.IdentityHashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;

/**
 * A builder of {@link LoadingCache} and {@link Cache} instances having any combination of the
 * following features:
 *
 * 
 *   automatic loading of entries into the cache
 *   
least-recently-used eviction when a maximum size is exceeded
 *   
time-based expiration of entries, measured since last access or last write
 *   
keys automatically wrapped in {@linkplain WeakReference weak} references
 *   
values automatically wrapped in {@linkplain WeakReference weak} or {@linkplain
 *       SoftReference soft} references
 *   
notification of evicted (or otherwise removed) entries
 *   
accumulation of cache access statistics
 * 
 *
 *
 * These features are all optional; caches can be created using all or none of them. By default
 * cache instances created by {@code CacheBuilder} will not perform any type of eviction.
 *
 * 
Usage example:
 *
 * 
{@code
 * LoadingCache graphs = CacheBuilder.newBuilder()
 *     .maximumSize(10000)
 *     .expireAfterWrite(Duration.ofMinutes(10))
 *     .removalListener(MY_LISTENER)
 *     .build(
 *         new CacheLoader() {
 *           public Graph load(Key key) throws AnyException {
 *             return createExpensiveGraph(key);
 *           }
 *         });
 * }
 *
 * Or equivalently,
 *
 * 
{@code
 * // In real life this would come from a command-line flag or config file
 * String spec = "maximumSize=10000,expireAfterWrite=10m";
 *
 * LoadingCache graphs = CacheBuilder.from(spec)
 *     .removalListener(MY_LISTENER)
 *     .build(
 *         new CacheLoader() {
 *           public Graph load(Key key) throws AnyException {
 *             return createExpensiveGraph(key);
 *           }
 *         });
 * }
 *
 * The returned cache is implemented as a hash table with similar performance characteristics to
 * {@link ConcurrentHashMap}. It implements all optional operations of the {@link LoadingCache} and
 * {@link Cache} interfaces. The {@code asMap} view (and its collection views) have weakly
 * consistent iterators. This means that they are safe for concurrent use, but if other threads
 * modify the cache after the iterator is created, it is undefined which of these changes, if any,
 * are reflected in that iterator. These iterators never throw {@link
 * ConcurrentModificationException}.
 *
 * 
Note: by default, the returned cache uses equality comparisons (the {@link
 * Object#equals equals} method) to determine equality for keys or values. However, if {@link
 * #weakKeys} was specified, the cache uses identity ({@code ==}) comparisons instead for keys.
 * Likewise, if {@link #weakValues} or {@link #softValues} was specified, the cache uses identity
 * comparisons for values.
 *
 * 
Entries are automatically evicted from the cache when any of {@linkplain #maximumSize(long)
 * maximumSize}, {@linkplain #maximumWeight(long) maximumWeight}, {@linkplain #expireAfterWrite
 * expireAfterWrite}, {@linkplain #expireAfterAccess expireAfterAccess}, {@linkplain #weakKeys
 * weakKeys}, {@linkplain #weakValues weakValues}, or {@linkplain #softValues softValues} are
 * requested.
 *
 * 
If {@linkplain #maximumSize(long) maximumSize} or {@linkplain #maximumWeight(long)
 * maximumWeight} is requested entries may be evicted on each cache modification.
 *
 * 
If {@linkplain #expireAfterWrite expireAfterWrite} or {@linkplain #expireAfterAccess
 * expireAfterAccess} is requested entries may be evicted on each cache modification, on occasional
 * cache accesses, or on calls to {@link Cache#cleanUp}. Expired entries may be counted by {@link
 * Cache#size}, but will never be visible to read or write operations.
 *
 * 
If {@linkplain #weakKeys weakKeys}, {@linkplain #weakValues weakValues}, or {@linkplain
 * #softValues softValues} are requested, it is possible for a key or value present in the cache to
 * be reclaimed by the garbage collector. Entries with reclaimed keys or values may be removed from
 * the cache on each cache modification, on occasional cache accesses, or on calls to {@link
 * Cache#cleanUp}; such entries may be counted in {@link Cache#size}, but will never be visible to
 * read or write operations.
 *
 * 
Certain cache configurations will result in the accrual of periodic maintenance tasks which
 * will be performed during write operations, or during occasional read operations in the absence of
 * writes. The {@link Cache#cleanUp} method of the returned cache will also perform maintenance, but
 * calling it should not be necessary with a high throughput cache. Only caches built with
 * {@linkplain #removalListener removalListener}, {@linkplain #expireAfterWrite expireAfterWrite},
 * {@linkplain #expireAfterAccess expireAfterAccess}, {@linkplain #weakKeys weakKeys}, {@linkplain
 * #weakValues weakValues}, or {@linkplain #softValues softValues} perform periodic maintenance.
 *
 * 
The caches produced by {@code CacheBuilder} are serializable, and the deserialized caches
 * retain all the configuration properties of the original cache. Note that the serialized form does
 * not include cache contents, but only configuration.
 *
 * 
See the Guava User Guide article on caching for a higher-level
 * explanation.
 *
 * @param  the most general key type this builder will be able to create caches for. This is
 *     normally {@code Object} unless it is constrained by using a method like {@code
 *     #removalListener}
 * @param  the most general value type this builder will be able to create caches for. This is
 *     normally {@code Object} unless it is constrained by using a method like {@code
 *     #removalListener}
 * @author Charles Fry
 * @author Kevin Bourrillion
 * @since 10.0
 */
@GwtCompatible(emulated = true)
public final class CacheBuilder {
  private static final int DEFAULT_INITIAL_CAPACITY = 16;
  private static final int DEFAULT_CONCURRENCY_LEVEL = 4;

  @SuppressWarnings("GoodTime") // should be a java.time.Duration
  private static final int DEFAULT_EXPIRATION_NANOS = 0;

  @SuppressWarnings("GoodTime") // should be a java.time.Duration
  private static final int DEFAULT_REFRESH_NANOS = 0;

  static final Supplier NULL_STATS_COUNTER =
      Suppliers.ofInstance(
          new StatsCounter() {
            @Override
            public void recordHits(int count) {}

            @Override
            public void recordMisses(int count) {}

            @SuppressWarnings("GoodTime") // b/122668874
            @Override
            public void recordLoadSuccess(long loadTime) {}

            @SuppressWarnings("GoodTime") // b/122668874
            @Override
            public void recordLoadException(long loadTime) {}

            @Override
            public void recordEviction() {}

            @Override
            public CacheStats snapshot() {
              return EMPTY_STATS;
            }
          });
  static final CacheStats EMPTY_STATS = new CacheStats(0, 0, 0, 0, 0, 0);

  static final Supplier CACHE_STATS_COUNTER =
      new Supplier() {
        @Override
        public StatsCounter get() {
          return new SimpleStatsCounter();
        }
      };

  enum NullListener implements RemovalListener {
    INSTANCE;

    @Override
    public void onRemoval(RemovalNotification notification) {}
  }

  enum OneWeigher implements Weigher {
    INSTANCE;

    @Override
    public int weigh(Object key, Object value) {
      return 1;
    }
  }

  static final Ticker NULL_TICKER =
      new Ticker() {
        @Override
        public long read() {
          return 0;
        }
      };

  private static final Logger logger = Logger.getLogger(CacheBuilder.class.getName());

  static final int UNSET_INT = -1;

  boolean strictParsing = true;

  int initialCapacity = UNSET_INT;
  int concurrencyLevel = UNSET_INT;
  long maximumSize = UNSET_INT;
  long maximumWeight = UNSET_INT;
  @MonotonicNonNull Weigher weigher;

  @MonotonicNonNull Strength keyStrength;
  @MonotonicNonNull Strength valueStrength;

  @SuppressWarnings("GoodTime") // should be a java.time.Duration
  long expireAfterWriteNanos = UNSET_INT;

  @SuppressWarnings("GoodTime") // should be a java.time.Duration
  long expireAfterAccessNanos = UNSET_INT;

  @SuppressWarnings("GoodTime") // should be a java.time.Duration
  long refreshNanos = UNSET_INT;

  @MonotonicNonNull Equivalence