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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.CanIgnoreReturnValue;
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.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.CheckForNull;

/**
 * A builder of {@link LoadingCache} and {@link Cache} instances.
 *
 * 
Prefer Caffeine over Guava's caching
 * API

 *
 * 
The successor to Guava's caching API is Caffeine. Its API is designed to make it a
 * nearly drop-in replacement. It requires Java 8+, and is not available for Android or GWT/J2CL,
 * and may have different (usually
 * better) behavior when multiple threads attempt concurrent mutations. Its equivalent to {@code
 * CacheBuilder} is its {@code
 * Caffeine} class. Caffeine offers better performance, more features (including asynchronous
 * loading), and fewer bugs.
 *
 * 
Caffeine defines its own interfaces ({@code
 * Cache}, {@code
 * LoadingCache}, {@code
 * CacheLoader}, etc.), so you can use Caffeine without needing to use any Guava types.
 * Caffeine's types are better than Guava's, especially for their
 * deep support for asynchronous operations. But if you want to migrate to Caffeine with minimal
 * code changes, you can use its
 * {@code CaffeinatedGuava} adapter class, which lets you build a Guava {@code Cache} or a Guava
 * {@code LoadingCache} backed by a Guava {@code CacheLoader}.
 *
 * 
Caffeine's API for asynchronous operations uses {@code CompletableFuture}: {@code
 * AsyncLoadingCache.get} returns a {@code CompletableFuture}, and implementations of {@code
 * AsyncCacheLoader.asyncLoad} must return a {@code CompletableFuture}. Users of Guava's {@link
 * com.google.common.util.concurrent.ListenableFuture} can adapt between the two {@code Future}
 * types by using {@code
 * net.javacrumbs.futureconverter.java8guava.FutureConverter}.
 *
 * 
More on {@code CacheBuilder}

 *
 * {@code CacheBuilder} builds caches with any combination of the following features:
 *
 * 
    
 *   
  • automatic loading of entries into the cache
 *   
  • least-recently-used eviction when a maximum size is exceeded (note that the cache is
 *       divided into segments, each of which does LRU internally)
 *   
  • time-based expiration of entries, measured since last access or last write
 *   
  • keys automatically wrapped in {@code WeakReference}
 *   
  • values automatically wrapped in {@code WeakReference} or {@code SoftReference}
 *   
  • 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 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 {@link #maximumSize(long)
 * maximumSize}, {@link #maximumWeight(long) maximumWeight}, {@link #expireAfterWrite
 * expireAfterWrite}, {@link #expireAfterAccess expireAfterAccess}, {@link #weakKeys weakKeys},
 * {@link #weakValues weakValues}, or {@link #softValues softValues} are requested.
 *
 * 
If {@link #maximumSize(long) maximumSize} or {@link #maximumWeight(long) maximumWeight} is
 * requested entries may be evicted on each cache modification.
 *
 * 
If {@link #expireAfterWrite expireAfterWrite} or {@link #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 {@link #weakKeys weakKeys}, {@link #weakValues weakValues}, or {@link #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 {@link
 * #removalListener removalListener}, {@link #expireAfterWrite expireAfterWrite}, {@link
 * #expireAfterAccess expireAfterAccess}, {@link #weakKeys weakKeys}, {@link #weakValues
 * weakValues}, or {@link #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}. Cache keys may not be null.
 * @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}. Cache values may not be null.
 * @author Charles Fry
 * @author Kevin Bourrillion
 * @since 10.0
 */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
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);

  /*
   * We avoid using a method reference or lambda here for now:
   *
   * - method reference: Inside Google, CacheBuilder is used from the implementation of a custom
   *   ClassLoader that is sometimes used as a system classloader. That's a problem because
   *   method-reference linking tries to look up the system classloader, and it fails because there
   *   isn't one yet.
   *
   * - lambda: Outside Google, we got a report of a similar problem in
   *   https://github.com/google/guava/issues/6565
   */
  @SuppressWarnings("AnonymousToLambda")
  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;
        }
      };

  // We use a holder class to delay initialization: https://github.com/google/guava/issues/6566
  private static final class LoggerHolder {
    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;
  @CheckForNull Weigher weigher;

  @CheckForNull Strength keyStrength;
  @CheckForNull 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;

  @CheckForNull Equivalence keyEquivalence;
  @CheckForNull Equivalence valueEquivalence;

  @CheckForNull RemovalListener removalListener;
  @CheckForNull Ticker ticker;

  Supplier statsCounterSupplier = NULL_STATS_COUNTER;

  private CacheBuilder() {}

  /**
   * Constructs a new {@code CacheBuilder} instance with default settings, including strong keys,
   * strong values, and no automatic eviction of any kind.
   *
   * 
Note that while this return type is {@code CacheBuilder}, type parameters on
   * the {@link #build} methods allow you to create a cache of any key and value type desired.
   */
  public static CacheBuilder newBuilder() {
    return new CacheBuilder<>();
  }

  /**
   * Constructs a new {@code CacheBuilder} instance with the settings specified in {@code spec}.
   *
   * @since 12.0
   */
  @GwtIncompatible // To be supported
  public static CacheBuilder from(CacheBuilderSpec spec) {
    return spec.toCacheBuilder().lenientParsing();
  }

  /**
   * Constructs a new {@code CacheBuilder} instance with the settings specified in {@code spec}.
   * This is especially useful for command-line configuration of a {@code CacheBuilder}.
   *
   * @param spec a String in the format specified by {@link CacheBuilderSpec}
   * @since 12.0
   */
  @GwtIncompatible // To be supported
  public static CacheBuilder from(String spec) {
    return from(CacheBuilderSpec.parse(spec));
  }

  /**
   * Enables lenient parsing. Useful for tests and spec parsing.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   */
  @GwtIncompatible // To be supported
  @CanIgnoreReturnValue
  CacheBuilder lenientParsing() {
    strictParsing = false;
    return this;
  }

  /**
   * Sets a custom {@code Equivalence} strategy for comparing keys.
   *
   * 
By default, the cache uses {@link Equivalence#identity} to determine key equality when
   * {@link #weakKeys} is specified, and {@link Equivalence#equals()} otherwise.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   */
  @GwtIncompatible // To be supported
  @CanIgnoreReturnValue
  CacheBuilder keyEquivalence(Equivalence equivalence) {
    checkState(keyEquivalence == null, "key equivalence was already set to %s", keyEquivalence);
    keyEquivalence = checkNotNull(equivalence);
    return this;
  }

  Equivalence getKeyEquivalence() {
    return MoreObjects.firstNonNull(keyEquivalence, getKeyStrength().defaultEquivalence());
  }

  /**
   * Sets a custom {@code Equivalence} strategy for comparing values.
   *
   * 
By default, the cache uses {@link Equivalence#identity} to determine value equality when
   * {@link #weakValues} or {@link #softValues} is specified, and {@link Equivalence#equals()}
   * otherwise.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   */
  @GwtIncompatible // To be supported
  @CanIgnoreReturnValue
  CacheBuilder valueEquivalence(Equivalence equivalence) {
    checkState(
        valueEquivalence == null, "value equivalence was already set to %s", valueEquivalence);
    this.valueEquivalence = checkNotNull(equivalence);
    return this;
  }

  Equivalence getValueEquivalence() {
    return MoreObjects.firstNonNull(valueEquivalence, getValueStrength().defaultEquivalence());
  }

  /**
   * Sets the minimum total size for the internal hash tables. For example, if the initial capacity
   * is {@code 60}, and the concurrency level is {@code 8}, then eight segments are created, each
   * having a hash table of size eight. Providing a large enough estimate at construction time
   * avoids the need for expensive resizing operations later, but setting this value unnecessarily
   * high wastes memory.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code initialCapacity} is negative
   * @throws IllegalStateException if an initial capacity was already set
   */
  @CanIgnoreReturnValue
  public CacheBuilder initialCapacity(int initialCapacity) {
    checkState(
        this.initialCapacity == UNSET_INT,
        "initial capacity was already set to %s",
        this.initialCapacity);
    checkArgument(initialCapacity >= 0);
    this.initialCapacity = initialCapacity;
    return this;
  }

  int getInitialCapacity() {
    return (initialCapacity == UNSET_INT) ? DEFAULT_INITIAL_CAPACITY : initialCapacity;
  }

  /**
   * Guides the allowed concurrency among update operations. Used as a hint for internal sizing. The
   * table is internally partitioned to try to permit the indicated number of concurrent updates
   * without contention. Because assignment of entries to these partitions is not necessarily
   * uniform, the actual concurrency observed may vary. Ideally, you should choose a value to
   * accommodate as many threads as will ever concurrently modify the table. Using a significantly
   * higher value than you need can waste space and time, and a significantly lower value can lead
   * to thread contention. But overestimates and underestimates within an order of magnitude do not
   * usually have much noticeable impact. A value of one permits only one thread to modify the cache
   * at a time, but since read operations and cache loading computations can proceed concurrently,
   * this still yields higher concurrency than full synchronization.
   *
   * 
Defaults to 4. Note:The default may change in the future. If you care about this
   * value, you should always choose it explicitly.
   *
   * 
The current implementation uses the concurrency level to create a fixed number of hashtable
   * segments, each governed by its own write lock. The segment lock is taken once for each explicit
   * write, and twice for each cache loading computation (once prior to loading the new value, and
   * once after loading completes). Much internal cache management is performed at the segment
   * granularity. For example, access queues and write queues are kept per segment when they are
   * required by the selected eviction algorithm. As such, when writing unit tests it is not
   * uncommon to specify {@code concurrencyLevel(1)} in order to achieve more deterministic eviction
   * behavior.
   *
   * 
Note that future implementations may abandon segment locking in favor of more advanced
   * concurrency controls.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code concurrencyLevel} is nonpositive
   * @throws IllegalStateException if a concurrency level was already set
   */
  @CanIgnoreReturnValue
  public CacheBuilder concurrencyLevel(int concurrencyLevel) {
    checkState(
        this.concurrencyLevel == UNSET_INT,
        "concurrency level was already set to %s",
        this.concurrencyLevel);
    checkArgument(concurrencyLevel > 0);
    this.concurrencyLevel = concurrencyLevel;
    return this;
  }

  int getConcurrencyLevel() {
    return (concurrencyLevel == UNSET_INT) ? DEFAULT_CONCURRENCY_LEVEL : concurrencyLevel;
  }

  /**
   * Specifies the maximum number of entries the cache may contain.
   *
   * 
Note that the cache may evict an entry before this limit is exceeded. For example, in
   * the current implementation, when {@code concurrencyLevel} is greater than {@code 1}, each
   * resulting segment inside the cache independently limits its own size to approximately
   * {@code maximumSize / concurrencyLevel}.
   *
   * 
When eviction is necessary, the cache evicts entries that are less likely to be used again.
   * For example, the cache may evict an entry because it hasn't been used recently or very often.
   *
   * 
If {@code maximumSize} is zero, elements will be evicted immediately after being loaded into
   * cache. This can be useful in testing, or to disable caching temporarily.
   *
   * 
This feature cannot be used in conjunction with {@link #maximumWeight}.
   *
   * @param maximumSize the maximum size of the cache
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code maximumSize} is negative
   * @throws IllegalStateException if a maximum size or weight was already set
   */
  @CanIgnoreReturnValue
  public CacheBuilder maximumSize(long maximumSize) {
    checkState(
        this.maximumSize == UNSET_INT, "maximum size was already set to %s", this.maximumSize);
    checkState(
        this.maximumWeight == UNSET_INT,
        "maximum weight was already set to %s",
        this.maximumWeight);
    checkState(this.weigher == null, "maximum size can not be combined with weigher");
    checkArgument(maximumSize >= 0, "maximum size must not be negative");
    this.maximumSize = maximumSize;
    return this;
  }

  /**
   * Specifies the maximum weight of entries the cache may contain. Weight is determined using the
   * {@link Weigher} specified with {@link #weigher}, and use of this method requires a
   * corresponding call to {@link #weigher} prior to calling {@link #build}.
   *
   * 
Note that the cache may evict an entry before this limit is exceeded. For example, in
   * the current implementation, when {@code concurrencyLevel} is greater than {@code 1}, each
   * resulting segment inside the cache independently limits its own weight to approximately
   * {@code maximumWeight / concurrencyLevel}.
   *
   * 
When eviction is necessary, the cache evicts entries that are less likely to be used again.
   * For example, the cache may evict an entry because it hasn't been used recently or very often.
   *
   * 
If {@code maximumWeight} is zero, elements will be evicted immediately after being loaded
   * into cache. This can be useful in testing, or to disable caching temporarily.
   *
   * 
Note that weight is only used to determine whether the cache is over capacity; it has no
   * effect on selecting which entry should be evicted next.
   *
   * 
This feature cannot be used in conjunction with {@link #maximumSize}.
   *
   * @param maximumWeight the maximum total weight of entries the cache may contain
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code maximumWeight} is negative
   * @throws IllegalStateException if a maximum weight or size was already set
   * @since 11.0
   */
  @GwtIncompatible // To be supported
  @CanIgnoreReturnValue
  public CacheBuilder maximumWeight(long maximumWeight) {
    checkState(
        this.maximumWeight == UNSET_INT,
        "maximum weight was already set to %s",
        this.maximumWeight);
    checkState(
        this.maximumSize == UNSET_INT, "maximum size was already set to %s", this.maximumSize);
    checkArgument(maximumWeight >= 0, "maximum weight must not be negative");
    this.maximumWeight = maximumWeight;
    return this;
  }

  /**
   * Specifies the weigher to use in determining the weight of entries. Entry weight is taken into
   * consideration by {@link #maximumWeight(long)} when determining which entries to evict, and use
   * of this method requires a corresponding call to {@link #maximumWeight(long)} prior to calling
   * {@link #build}. Weights are measured and recorded when entries are inserted into the cache, and
   * are thus effectively static during the lifetime of a cache entry.
   *
   * 
When the weight of an entry is zero it will not be considered for size-based eviction
   * (though it still may be evicted by other means).
   *
   * 
Important note: Instead of returning this as a {@code CacheBuilder}
   * instance, this method returns {@code CacheBuilder}. From this point on, either the
   * original reference or the returned reference may be used to complete configuration and build
   * the cache, but only the "generic" one is type-safe. That is, it will properly prevent you from
   * building caches whose key or value types are incompatible with the types accepted by the
   * weigher already provided; the {@code CacheBuilder} type cannot do this. For best results,
   * simply use the standard method-chaining idiom, as illustrated in the documentation at top,
   * configuring a {@code CacheBuilder} and building your {@link Cache} all in a single statement.
   *
   * 
Warning: if you ignore the above advice, and use this {@code CacheBuilder} to build a
   * cache whose key or value type is incompatible with the weigher, you will likely experience a
   * {@link ClassCastException} at some undefined point in the future.
   *
   * @param weigher the weigher to use in calculating the weight of cache entries
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if a weigher was already set or {@link #maximumSize} was
   *     previously called
   * @since 11.0
   */
  @GwtIncompatible // To be supported
  @CanIgnoreReturnValue // TODO(b/27479612): consider removing this
  public  CacheBuilder weigher(
      Weigher weigher) {
    checkState(this.weigher == null);
    if (strictParsing) {
      checkState(
          this.maximumSize == UNSET_INT,
          "weigher can not be combined with maximum size (%s provided)",
          this.maximumSize);
    }

    // safely limiting the kinds of caches this can produce
    @SuppressWarnings("unchecked")
    CacheBuilder me = (CacheBuilder) this;
    me.weigher = checkNotNull(weigher);
    return me;
  }

  long getMaximumWeight() {
    if (expireAfterWriteNanos == 0 || expireAfterAccessNanos == 0) {
      return 0;
    }
    return (weigher == null) ? maximumSize : maximumWeight;
  }

  // Make a safe contravariant cast now so we don't have to do it over and over.
  @SuppressWarnings("unchecked")
   Weigher getWeigher() {
    return (Weigher) MoreObjects.firstNonNull(weigher, OneWeigher.INSTANCE);
  }

  /**
   * Specifies that each key (not value) stored in the cache should be wrapped in a {@link
   * WeakReference} (by default, strong references are used).
   *
   * 
Warning: when this method is used, the resulting cache will use identity ({@code ==})
   * comparison to determine equality of keys. Its {@link Cache#asMap} view will therefore
   * technically violate the {@link Map} specification (in the same way that {@link IdentityHashMap}
   * does).
   *
   * 
Entries with keys that have been garbage collected may be counted in {@link Cache#size}, but
   * will never be visible to read or write operations; such entries are cleaned up as part of the
   * routine maintenance described in the class javadoc.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if the key strength was already set
   */
  @GwtIncompatible // java.lang.ref.WeakReference
  @CanIgnoreReturnValue
  public CacheBuilder weakKeys() {
    return setKeyStrength(Strength.WEAK);
  }

  @CanIgnoreReturnValue
  CacheBuilder setKeyStrength(Strength strength) {
    checkState(keyStrength == null, "Key strength was already set to %s", keyStrength);
    keyStrength = checkNotNull(strength);
    return this;
  }

  Strength getKeyStrength() {
    return MoreObjects.firstNonNull(keyStrength, Strength.STRONG);
  }

  /**
   * Specifies that each value (not key) stored in the cache should be wrapped in a {@link
   * WeakReference} (by default, strong references are used).
   *
   * 
Weak values will be garbage collected once they are weakly reachable. This makes them a poor
   * candidate for caching; consider {@link #softValues} instead.
   *
   * 
Note: when this method is used, the resulting cache will use identity ({@code ==})
   * comparison to determine equality of values.
   *
   * 
Entries with values that have been garbage collected may be counted in {@link Cache#size},
   * but will never be visible to read or write operations; such entries are cleaned up as part of
   * the routine maintenance described in the class javadoc.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if the value strength was already set
   */
  @GwtIncompatible // java.lang.ref.WeakReference
  @CanIgnoreReturnValue
  public CacheBuilder weakValues() {
    return setValueStrength(Strength.WEAK);
  }

  /**
   * Specifies that each value (not key) stored in the cache should be wrapped in a {@link
   * SoftReference} (by default, strong references are used). Softly-referenced objects will be
   * garbage-collected in a globally least-recently-used manner, in response to memory
   * demand.
   *
   * 
Warning: in most circumstances it is better to set a per-cache {@linkplain
   * #maximumSize(long) maximum size} instead of using soft references. You should only use this
   * method if you are well familiar with the practical consequences of soft references.
   *
   * 
Note: when this method is used, the resulting cache will use identity ({@code ==})
   * comparison to determine equality of values.
   *
   * 
Entries with values that have been garbage collected may be counted in {@link Cache#size},
   * but will never be visible to read or write operations; such entries are cleaned up as part of
   * the routine maintenance described in the class javadoc.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if the value strength was already set
   */
  @GwtIncompatible // java.lang.ref.SoftReference
  @CanIgnoreReturnValue
  public CacheBuilder softValues() {
    return setValueStrength(Strength.SOFT);
  }

  @CanIgnoreReturnValue
  CacheBuilder setValueStrength(Strength strength) {
    checkState(valueStrength == null, "Value strength was already set to %s", valueStrength);
    valueStrength = checkNotNull(strength);
    return this;
  }

  Strength getValueStrength() {
    return MoreObjects.firstNonNull(valueStrength, Strength.STRONG);
  }

  /**
   * Specifies that each entry should be automatically removed from the cache once a fixed duration
   * has elapsed after the entry's creation, or the most recent replacement of its value.
   *
   * 
When {@code duration} is zero, this method hands off to {@link #maximumSize(long)
   * maximumSize}{@code (0)}, ignoring any otherwise-specified maximum size or weight. This can be
   * useful in testing, or to disable caching temporarily without a code change.
   *
   * 
Expired entries may be counted in {@link Cache#size}, but will never be visible to read or
   * write operations. Expired entries are cleaned up as part of the routine maintenance described
   * in the class javadoc.
   *
   * @param duration the length of time after an entry is created that it should be automatically
   *     removed
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if {@link #expireAfterWrite} was already set
   * @throws ArithmeticException for durations greater than +/- approximately 292 years
   * @since 25.0
   */
  @J2ObjCIncompatible
  @GwtIncompatible // java.time.Duration
  @SuppressWarnings("GoodTime") // java.time.Duration decomposition
  @CanIgnoreReturnValue
  public CacheBuilder expireAfterWrite(java.time.Duration duration) {
    return expireAfterWrite(toNanosSaturated(duration), TimeUnit.NANOSECONDS);
  }

  /**
   * Specifies that each entry should be automatically removed from the cache once a fixed duration
   * has elapsed after the entry's creation, or the most recent replacement of its value.
   *
   * 
When {@code duration} is zero, this method hands off to {@link #maximumSize(long)
   * maximumSize}{@code (0)}, ignoring any otherwise-specified maximum size or weight. This can be
   * useful in testing, or to disable caching temporarily without a code change.
   *
   * 
Expired entries may be counted in {@link Cache#size}, but will never be visible to read or
   * write operations. Expired entries are cleaned up as part of the routine maintenance described
   * in the class javadoc.
   *
   * 
If you can represent the duration as a {@link java.time.Duration} (which should be preferred
   * when feasible), use {@link #expireAfterWrite(Duration)} instead.
   *
   * @param duration the length of time after an entry is created that it should be automatically
   *     removed
   * @param unit the unit that {@code duration} is expressed in
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if {@link #expireAfterWrite} was already set
   */
  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
  @CanIgnoreReturnValue
  public CacheBuilder expireAfterWrite(long duration, TimeUnit unit) {
    checkState(
        expireAfterWriteNanos == UNSET_INT,
        "expireAfterWrite was already set to %s ns",
        expireAfterWriteNanos);
    checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
    this.expireAfterWriteNanos = unit.toNanos(duration);
    return this;
  }

  @SuppressWarnings("GoodTime") // nanos internally, should be Duration
  long getExpireAfterWriteNanos() {
    return (expireAfterWriteNanos == UNSET_INT) ? DEFAULT_EXPIRATION_NANOS : expireAfterWriteNanos;
  }

  /**
   * Specifies that each entry should be automatically removed from the cache once a fixed duration
   * has elapsed after the entry's creation, the most recent replacement of its value, or its last
   * access. Access time is reset by all cache read and write operations (including {@code
   * Cache.asMap().get(Object)} and {@code Cache.asMap().put(K, V)}), but not by {@code
   * containsKey(Object)}, nor by operations on the collection-views of {@link Cache#asMap}}. So,
   * for example, iterating through {@code Cache.asMap().entrySet()} does not reset access time for
   * the entries you retrieve.
   *
   * 
When {@code duration} is zero, this method hands off to {@link #maximumSize(long)
   * maximumSize}{@code (0)}, ignoring any otherwise-specified maximum size or weight. This can be
   * useful in testing, or to disable caching temporarily without a code change.
   *
   * 
Expired entries may be counted in {@link Cache#size}, but will never be visible to read or
   * write operations. Expired entries are cleaned up as part of the routine maintenance described
   * in the class javadoc.
   *
   * @param duration the length of time after an entry is last accessed that it should be
   *     automatically removed
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if {@link #expireAfterAccess} was already set
   * @throws ArithmeticException for durations greater than +/- approximately 292 years
   * @since 25.0
   */
  @J2ObjCIncompatible
  @GwtIncompatible // java.time.Duration
  @SuppressWarnings("GoodTime") // java.time.Duration decomposition
  @CanIgnoreReturnValue
  public CacheBuilder expireAfterAccess(java.time.Duration duration) {
    return expireAfterAccess(toNanosSaturated(duration), TimeUnit.NANOSECONDS);
  }

  /**
   * Specifies that each entry should be automatically removed from the cache once a fixed duration
   * has elapsed after the entry's creation, the most recent replacement of its value, or its last
   * access. Access time is reset by all cache read and write operations (including {@code
   * Cache.asMap().get(Object)} and {@code Cache.asMap().put(K, V)}), but not by {@code
   * containsKey(Object)}, nor by operations on the collection-views of {@link Cache#asMap}. So, for
   * example, iterating through {@code Cache.asMap().entrySet()} does not reset access time for the
   * entries you retrieve.
   *
   * 
When {@code duration} is zero, this method hands off to {@link #maximumSize(long)
   * maximumSize}{@code (0)}, ignoring any otherwise-specified maximum size or weight. This can be
   * useful in testing, or to disable caching temporarily without a code change.
   *
   * 
Expired entries may be counted in {@link Cache#size}, but will never be visible to read or
   * write operations. Expired entries are cleaned up as part of the routine maintenance described
   * in the class javadoc.
   *
   * 
If you can represent the duration as a {@link java.time.Duration} (which should be preferred
   * when feasible), use {@link #expireAfterAccess(Duration)} instead.
   *
   * @param duration the length of time after an entry is last accessed that it should be
   *     automatically removed
   * @param unit the unit that {@code duration} is expressed in
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if {@link #expireAfterAccess} was already set
   */
  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
  @CanIgnoreReturnValue
  public CacheBuilder expireAfterAccess(long duration, TimeUnit unit) {
    checkState(
        expireAfterAccessNanos == UNSET_INT,
        "expireAfterAccess was already set to %s ns",
        expireAfterAccessNanos);
    checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
    this.expireAfterAccessNanos = unit.toNanos(duration);
    return this;
  }

  @SuppressWarnings("GoodTime") // nanos internally, should be Duration
  long getExpireAfterAccessNanos() {
    return (expireAfterAccessNanos == UNSET_INT)
        ? DEFAULT_EXPIRATION_NANOS
        : expireAfterAccessNanos;
  }

  /**
   * Specifies that active entries are eligible for automatic refresh once a fixed duration has
   * elapsed after the entry's creation, or the most recent replacement of its value. The semantics
   * of refreshes are specified in {@link LoadingCache#refresh}, and are performed by calling {@link
   * CacheLoader#reload}.
   *
   * 
As the default implementation of {@link CacheLoader#reload} is synchronous, it is
   * recommended that users of this method override {@link CacheLoader#reload} with an asynchronous
   * implementation; otherwise refreshes will be performed during unrelated cache read and write
   * operations.
   *
   * 
Currently automatic refreshes are performed when the first stale request for an entry
   * occurs. The request triggering refresh will make a synchronous call to {@link
   * CacheLoader#reload}
   * to obtain a future of the new value. If the returned future is already complete, it is returned
   * immediately. Otherwise, the old value is returned.
   *
   * 
Note: all exceptions thrown during refresh will be logged and then swallowed.
   *
   * @param duration the length of time after an entry is created that it should be considered
   *     stale, and thus eligible for refresh
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if {@link #refreshAfterWrite} was already set
   * @throws ArithmeticException for durations greater than +/- approximately 292 years
   * @since 25.0
   */
  @J2ObjCIncompatible
  @GwtIncompatible // java.time.Duration
  @SuppressWarnings("GoodTime") // java.time.Duration decomposition
  @CanIgnoreReturnValue
  public CacheBuilder refreshAfterWrite(java.time.Duration duration) {
    return refreshAfterWrite(toNanosSaturated(duration), TimeUnit.NANOSECONDS);
  }

  /**
   * Specifies that active entries are eligible for automatic refresh once a fixed duration has
   * elapsed after the entry's creation, or the most recent replacement of its value. The semantics
   * of refreshes are specified in {@link LoadingCache#refresh}, and are performed by calling {@link
   * CacheLoader#reload}.
   *
   * 
As the default implementation of {@link CacheLoader#reload} is synchronous, it is
   * recommended that users of this method override {@link CacheLoader#reload} with an asynchronous
   * implementation; otherwise refreshes will be performed during unrelated cache read and write
   * operations.
   *
   * 
Currently automatic refreshes are performed when the first stale request for an entry
   * occurs. The request triggering refresh will make a synchronous call to {@link
   * CacheLoader#reload}
   * and immediately return the new value if the returned future is complete, and the old value
   * otherwise.
   *
   * 
Note: all exceptions thrown during refresh will be logged and then swallowed.
   *
   * 
If you can represent the duration as a {@link java.time.Duration} (which should be preferred
   * when feasible), use {@link #refreshAfterWrite(Duration)} instead.
   *
   * @param duration the length of time after an entry is created that it should be considered
   *     stale, and thus eligible for refresh
   * @param unit the unit that {@code duration} is expressed in
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if {@link #refreshAfterWrite} was already set
   * @since 11.0
   */
  @GwtIncompatible // To be supported (synchronously).
  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
  @CanIgnoreReturnValue
  public CacheBuilder refreshAfterWrite(long duration, TimeUnit unit) {
    checkNotNull(unit);
    checkState(refreshNanos == UNSET_INT, "refresh was already set to %s ns", refreshNanos);
    checkArgument(duration > 0, "duration must be positive: %s %s", duration, unit);
    this.refreshNanos = unit.toNanos(duration);
    return this;
  }

  @SuppressWarnings("GoodTime") // nanos internally, should be Duration
  long getRefreshNanos() {
    return (refreshNanos == UNSET_INT) ? DEFAULT_REFRESH_NANOS : refreshNanos;
  }

  /**
   * Specifies a nanosecond-precision time source for this cache. By default, {@link
   * System#nanoTime} is used.
   *
   * 
The primary intent of this method is to facilitate testing of caches with a fake or mock
   * time source.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if a ticker was already set
   */
  @CanIgnoreReturnValue
  public CacheBuilder ticker(Ticker ticker) {
    checkState(this.ticker == null);
    this.ticker = checkNotNull(ticker);
    return this;
  }

  Ticker getTicker(boolean recordsTime) {
    if (ticker != null) {
      return ticker;
    }
    return recordsTime ? Ticker.systemTicker() : NULL_TICKER;
  }

  /**
   * Specifies a listener instance that caches should notify each time an entry is removed for any
   * {@linkplain RemovalCause reason}. Each cache created by this builder will invoke this listener
   * as part of the routine maintenance described in the class documentation above.
   *
   * 
Warning: after invoking this method, do not continue to use this cache builder
   * reference; instead use the reference this method returns. At runtime, these point to the
   * same instance, but only the returned reference has the correct generic type information to
   * ensure type safety. For best results, use the standard method-chaining idiom illustrated in the
   * class documentation above, configuring a builder and building your cache in a single statement.
   * Failure to heed this advice can result in a {@link ClassCastException} being thrown by a cache
   * operation at some undefined point in the future.
   *
   * 
Warning: any exception thrown by {@code listener} will not be propagated to
   * the {@code Cache} user, only logged via a {@link Logger}.
   *
   * @return the cache builder reference that should be used instead of {@code this} for any
   *     remaining configuration and cache building
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if a removal listener was already set
   */
  public  CacheBuilder removalListener(
      RemovalListener listener) {
    checkState(this.removalListener == null);

    // safely limiting the kinds of caches this can produce
    @SuppressWarnings("unchecked")
    CacheBuilder me = (CacheBuilder) this;
    me.removalListener = checkNotNull(listener);
    return me;
  }

  // Make a safe contravariant cast now so we don't have to do it over and over.
  @SuppressWarnings("unchecked")
   RemovalListener getRemovalListener() {
    return (RemovalListener)
        MoreObjects.firstNonNull(removalListener, NullListener.INSTANCE);
  }

  /**
   * Enable the accumulation of {@link CacheStats} during the operation of the cache. Without this
   * {@link Cache#stats} will return zero for all statistics. Note that recording stats requires
   * bookkeeping to be performed with each operation, and thus imposes a performance penalty on
   * cache operation.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @since 12.0 (previously, stats collection was automatic)
   */
  @CanIgnoreReturnValue
  public CacheBuilder recordStats() {
    statsCounterSupplier = CACHE_STATS_COUNTER;
    return this;
  }

  boolean isRecordingStats() {
    return statsCounterSupplier == CACHE_STATS_COUNTER;
  }

  Supplier getStatsCounterSupplier() {
    return statsCounterSupplier;
  }

  /**
   * Builds a cache, which either returns an already-loaded value for a given key or atomically
   * computes or retrieves it using the supplied {@code CacheLoader}. If another thread is currently
   * loading the value for this key, simply waits for that thread to finish and returns its loaded
   * value. Note that multiple threads can concurrently load values for distinct keys.
   *
   * 
This method does not alter the state of this {@code CacheBuilder} instance, so it can be
   * invoked again to create multiple independent caches.
   *
   * @param loader the cache loader used to obtain new values
   * @return a cache having the requested features
   */
  public  LoadingCache build(
      CacheLoader loader) {
    checkWeightWithWeigher();
    return new LocalCache.LocalLoadingCache<>(this, loader);
  }

  /**
   * Builds a cache which does not automatically load values when keys are requested.
   *
   * 
Consider {@link #build(CacheLoader)} instead, if it is feasible to implement a {@code
   * CacheLoader}.
   *
   * 
This method does not alter the state of this {@code CacheBuilder} instance, so it can be
   * invoked again to create multiple independent caches.
   *
   * @return a cache having the requested features
   * @since 11.0
   */
  public  Cache build() {
    checkWeightWithWeigher();
    checkNonLoadingCache();
    return new LocalCache.LocalManualCache<>(this);
  }

  private void checkNonLoadingCache() {
    checkState(refreshNanos == UNSET_INT, "refreshAfterWrite requires a LoadingCache");
  }

  private void checkWeightWithWeigher() {
    if (weigher == null) {
      checkState(maximumWeight == UNSET_INT, "maximumWeight requires weigher");
    } else {
      if (strictParsing) {
        checkState(maximumWeight != UNSET_INT, "weigher requires maximumWeight");
      } else {
        if (maximumWeight == UNSET_INT) {
          LoggerHolder.logger.log(
              Level.WARNING, "ignoring weigher specified without maximumWeight");
        }
      }
    }
  }

  /**
   * Returns a string representation for this CacheBuilder instance. The exact form of the returned
   * string is not specified.
   */
  @Override
  public String toString() {
    MoreObjects.ToStringHelper s = MoreObjects.toStringHelper(this);
    if (initialCapacity != UNSET_INT) {
      s.add("initialCapacity", initialCapacity);
    }
    if (concurrencyLevel != UNSET_INT) {
      s.add("concurrencyLevel", concurrencyLevel);
    }
    if (maximumSize != UNSET_INT) {
      s.add("maximumSize", maximumSize);
    }
    if (maximumWeight != UNSET_INT) {
      s.add("maximumWeight", maximumWeight);
    }
    if (expireAfterWriteNanos != UNSET_INT) {
      s.add("expireAfterWrite", expireAfterWriteNanos + "ns");
    }
    if (expireAfterAccessNanos != UNSET_INT) {
      s.add("expireAfterAccess", expireAfterAccessNanos + "ns");
    }
    if (keyStrength != null) {
      s.add("keyStrength", Ascii.toLowerCase(keyStrength.toString()));
    }
    if (valueStrength != null) {
      s.add("valueStrength", Ascii.toLowerCase(valueStrength.toString()));
    }
    if (keyEquivalence != null) {
      s.addValue("keyEquivalence");
    }
    if (valueEquivalence != null) {
      s.addValue("valueEquivalence");
    }
    if (removalListener != null) {
      s.addValue("removalListener");
    }
    return s.toString();
  }

  /**
   * Returns the number of nanoseconds of the given duration without throwing or overflowing.
   *
   * 
Instead of throwing {@link ArithmeticException}, this method silently saturates to either
   * {@link Long#MAX_VALUE} or {@link Long#MIN_VALUE}. This behavior can be useful when decomposing
   * a duration in order to call a legacy API which requires a {@code long, TimeUnit} pair.
   */
  @GwtIncompatible // java.time.Duration
  @SuppressWarnings("GoodTime") // duration decomposition
  private static long toNanosSaturated(java.time.Duration duration) {
    // Using a try/catch seems lazy, but the catch block will rarely get invoked (except for
    // durations longer than approximately +/- 292 years).
    try {
      return duration.toNanos();
    } catch (ArithmeticException tooBig) {
      return duration.isNegative() ? Long.MIN_VALUE : Long.MAX_VALUE;
    }
  }
}
    

    

    
            
    
            







    
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