/*
 * 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.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.cache.CacheBuilder.NULL_TICKER;
import static com.google.common.cache.CacheBuilder.UNSET_INT;
import static com.google.common.util.concurrent.Futures.transform;
import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
import static com.google.common.util.concurrent.Uninterruptibles.getUninterruptibly;
import static java.util.concurrent.TimeUnit.NANOSECONDS;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Equivalence;
import com.google.common.base.Stopwatch;
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.CacheBuilder.NullListener;
import com.google.common.cache.CacheBuilder.OneWeigher;
import com.google.common.cache.CacheLoader.InvalidCacheLoadException;
import com.google.common.cache.CacheLoader.UnsupportedLoadingOperationException;
import com.google.common.cache.LocalCache.AbstractCacheSet;
import com.google.common.collect.AbstractSequentialIterator;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterators;
import com.google.common.collect.Maps;
import com.google.common.collect.Sets;
import com.google.common.primitives.Ints;
import com.google.common.util.concurrent.ExecutionError;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.SettableFuture;
import com.google.common.util.concurrent.UncheckedExecutionException;
import com.google.common.util.concurrent.Uninterruptibles;
import com.google.errorprone.annotations.concurrent.GuardedBy;
import com.google.j2objc.annotations.Weak;
import com.google.j2objc.annotations.WeakOuter;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractQueue;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReferenceArray;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.BiFunction;
import java.util.function.BiPredicate;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

The concurrent hash map implementation built by CacheBuilder. 
This implementation is heavily derived from revision 1.96 of ConcurrentHashMap.java.
Author:
Charles Fry, Bob Lee (com.google.common.collect.MapMaker), Doug Lea (ConcurrentHashMap)/**
 * The concurrent hash map implementation built by {@link CacheBuilder}.
 *
 * <p>This implementation is heavily derived from revision 1.96 of <a
 * href="http://tinyurl.com/ConcurrentHashMap">ConcurrentHashMap.java</a>.
 *
 * @author Charles Fry
 * @author Bob Lee ({@code com.google.common.collect.MapMaker})
 * @author Doug Lea ({@code ConcurrentHashMap})
 */
@GwtCompatible(emulated = true)
class LocalCache<K, V> extends AbstractMap<K, V> implements ConcurrentMap<K, V> {

  /*
   * The basic strategy is to subdivide the table among Segments, each of which itself is a
   * concurrently readable hash table. The map supports non-blocking reads and concurrent writes
   * across different segments.
   *
   * If a maximum size is specified, a best-effort bounding is performed per segment, using a
   * page-replacement algorithm to determine which entries to evict when the capacity has been
   * exceeded.
   *
   * The page replacement algorithm's data structures are kept casually consistent with the map. The
   * ordering of writes to a segment is sequentially consistent. An update to the map and recording
   * of reads may not be immediately reflected on the algorithm's data structures. These structures
   * are guarded by a lock and operations are applied in batches to avoid lock contention. The
   * penalty of applying the batches is spread across threads so that the amortized cost is slightly
   * higher than performing just the operation without enforcing the capacity constraint.
   *
   * This implementation uses a per-segment queue to record a memento of the additions, removals,
   * and accesses that were performed on the map. The queue is drained on writes and when it exceeds
   * its capacity threshold.
   *
   * The Least Recently Used page replacement algorithm was chosen due to its simplicity, high hit
   * rate, and ability to be implemented with O(1) time complexity. The initial LRU implementation
   * operates per-segment rather than globally for increased implementation simplicity. We expect
   * the cache hit rate to be similar to that of a global LRU algorithm.
   */

  // Constants

  
The maximum capacity, used if a higher value is implicitly specified by either of the constructors with arguments. MUST be a power of two <= 1<<30 to ensure that entries are indexable using ints. /**
   * The maximum capacity, used if a higher value is implicitly specified by either of the
   * constructors with arguments. MUST be a power of two {@code <= 1<<30} to ensure that entries are
   * indexable using ints.
   */
  static final int MAXIMUM_CAPACITY = 1 << 30;

  
The maximum number of segments to allow; used to bound constructor arguments. /** The maximum number of segments to allow; used to bound constructor arguments. */
  static final int MAX_SEGMENTS = 1 << 16; // slightly conservative

  
Number of (unsynchronized) retries in the containsValue method. /** Number of (unsynchronized) retries in the containsValue method. */
  static final int CONTAINS_VALUE_RETRIES = 3;

  
Number of cache access operations that can be buffered per segment before the cache's recency
ordering information is updated. This is used to avoid lock contention by recording a memento
of reads and delaying a lock acquisition until the threshold is crossed or a mutation occurs.
This must be a (2^n)-1 as it is used as a mask.
/**
   * Number of cache access operations that can be buffered per segment before the cache's recency
   * ordering information is updated. This is used to avoid lock contention by recording a memento
   * of reads and delaying a lock acquisition until the threshold is crossed or a mutation occurs.
   *
   * <p>This must be a (2^n)-1 as it is used as a mask.
   */
  static final int DRAIN_THRESHOLD = 0x3F;

  
Maximum number of entries to be drained in a single cleanup run. This applies independently to
the cleanup queue and both reference queues.
/**
   * Maximum number of entries to be drained in a single cleanup run. This applies independently to
   * the cleanup queue and both reference queues.
   */
  // TODO(fry): empirically optimize this
  static final int DRAIN_MAX = 16;

  // Fields

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

  
Mask value for indexing into segments. The upper bits of a key's hash code are used to choose
the segment.
/**
   * Mask value for indexing into segments. The upper bits of a key's hash code are used to choose
   * the segment.
   */
  final int segmentMask;

  
Shift value for indexing within segments. Helps prevent entries that end up in the same segment
from also ending up in the same bucket.
/**
   * Shift value for indexing within segments. Helps prevent entries that end up in the same segment
   * from also ending up in the same bucket.
   */
  final int segmentShift;

  
The segments, each of which is a specialized hash table. /** The segments, each of which is a specialized hash table. */
  final Segment<K, V>[] segments;

  
The concurrency level. /** The concurrency level. */
  final int concurrencyLevel;

  
Strategy for comparing keys. /** Strategy for comparing keys. */
  final Equivalence<Object> keyEquivalence;

  
Strategy for comparing values. /** Strategy for comparing values. */
  final Equivalence<Object> valueEquivalence;

  
Strategy for referencing keys. /** Strategy for referencing keys. */
  final Strength keyStrength;

  
Strategy for referencing values. /** Strategy for referencing values. */
  final Strength valueStrength;

  
The maximum weight of this map. UNSET_INT if there is no maximum. /** The maximum weight of this map. UNSET_INT if there is no maximum. */
  final long maxWeight;

  
Weigher to weigh cache entries. /** Weigher to weigh cache entries. */
  final Weigher<K, V> weigher;

  
How long after the last access to an entry the map will retain that entry. /** How long after the last access to an entry the map will retain that entry. */
  final long expireAfterAccessNanos;

  
How long after the last write to an entry the map will retain that entry. /** How long after the last write to an entry the map will retain that entry. */
  final long expireAfterWriteNanos;

  
How long after the last write an entry becomes a candidate for refresh. /** How long after the last write an entry becomes a candidate for refresh. */
  final long refreshNanos;

  
Entries waiting to be consumed by the removal listener. /** Entries waiting to be consumed by the removal listener. */
  // TODO(fry): define a new type which creates event objects and automates the clear logic
  final Queue<RemovalNotification<K, V>> removalNotificationQueue;

  
A listener that is invoked when an entry is removed due to expiration or garbage collection of
soft/weak entries.
/**
   * A listener that is invoked when an entry is removed due to expiration or garbage collection of
   * soft/weak entries.
   */
  final RemovalListener<K, V> removalListener;

  
Measures time in a testable way. /** Measures time in a testable way. */
  final Ticker ticker;

  
Factory used to create new entries. /** Factory used to create new entries. */
  final EntryFactory entryFactory;

  
Accumulates global cache statistics. Note that there are also per-segments stats counters which
must be aggregated to obtain a global stats view.
/**
   * Accumulates global cache statistics. Note that there are also per-segments stats counters which
   * must be aggregated to obtain a global stats view.
   */
  final StatsCounter globalStatsCounter;

  
The default cache loader to use on loading operations. /** The default cache loader to use on loading operations. */
  final @Nullable CacheLoader<? super K, V> defaultLoader;

  
Creates a new, empty map with the specified strategy, initial capacity and concurrency level.
/**
   * Creates a new, empty map with the specified strategy, initial capacity and concurrency level.
   */
  LocalCache(
      CacheBuilder<? super K, ? super V> builder, @Nullable CacheLoader<? super K, V> loader) {
    concurrencyLevel = Math.min(builder.getConcurrencyLevel(), MAX_SEGMENTS);

    keyStrength = builder.getKeyStrength();
    valueStrength = builder.getValueStrength();

    keyEquivalence = builder.getKeyEquivalence();
    valueEquivalence = builder.getValueEquivalence();

    maxWeight = builder.getMaximumWeight();
    weigher = builder.getWeigher();
    expireAfterAccessNanos = builder.getExpireAfterAccessNanos();
    expireAfterWriteNanos = builder.getExpireAfterWriteNanos();
    refreshNanos = builder.getRefreshNanos();

    removalListener = builder.getRemovalListener();
    removalNotificationQueue =
        (removalListener == NullListener.INSTANCE)
            ? LocalCache.<RemovalNotification<K, V>>discardingQueue()
            : new ConcurrentLinkedQueue<RemovalNotification<K, V>>();

    ticker = builder.getTicker(recordsTime());
    entryFactory = EntryFactory.getFactory(keyStrength, usesAccessEntries(), usesWriteEntries());
    globalStatsCounter = builder.getStatsCounterSupplier().get();
    defaultLoader = loader;

    int initialCapacity = Math.min(builder.getInitialCapacity(), MAXIMUM_CAPACITY);
    if (evictsBySize() && !customWeigher()) {
      initialCapacity = Math.min(initialCapacity, (int) maxWeight);
    }

    // Find the lowest power-of-two segmentCount that exceeds concurrencyLevel, unless
    // maximumSize/Weight is specified in which case ensure that each segment gets at least 10
    // entries. The special casing for size-based eviction is only necessary because that eviction
    // happens per segment instead of globally, so too many segments compared to the maximum size
    // will result in random eviction behavior.
    int segmentShift = 0;
    int segmentCount = 1;
    while (segmentCount < concurrencyLevel && (!evictsBySize() || segmentCount * 20 <= maxWeight)) {
      ++segmentShift;
      segmentCount <<= 1;
    }
    this.segmentShift = 32 - segmentShift;
    segmentMask = segmentCount - 1;

    this.segments = newSegmentArray(segmentCount);

    int segmentCapacity = initialCapacity / segmentCount;
    if (segmentCapacity * segmentCount < initialCapacity) {
      ++segmentCapacity;
    }

    int segmentSize = 1;
    while (segmentSize < segmentCapacity) {
      segmentSize <<= 1;
    }

    if (evictsBySize()) {
      // Ensure sum of segment max weights = overall max weights
      long maxSegmentWeight = maxWeight / segmentCount + 1;
      long remainder = maxWeight % segmentCount;
      for (int i = 0; i < this.segments.length; ++i) {
        if (i == remainder) {
          maxSegmentWeight--;
        }
        this.segments[i] =
            createSegment(segmentSize, maxSegmentWeight, builder.getStatsCounterSupplier().get());
      }
    } else {
      for (int i = 0; i < this.segments.length; ++i) {
        this.segments[i] =
            createSegment(segmentSize, UNSET_INT, builder.getStatsCounterSupplier().get());
      }
    }
  }

  boolean evictsBySize() {
    return maxWeight >= 0;
  }

  boolean customWeigher() {
    return weigher != OneWeigher.INSTANCE;
  }

  boolean expires() {
    return expiresAfterWrite() || expiresAfterAccess();
  }

  boolean expiresAfterWrite() {
    return expireAfterWriteNanos > 0;
  }

  boolean expiresAfterAccess() {
    return expireAfterAccessNanos > 0;
  }

  boolean refreshes() {
    return refreshNanos > 0;
  }

  boolean usesAccessQueue() {
    return expiresAfterAccess() || evictsBySize();
  }

  boolean usesWriteQueue() {
    return expiresAfterWrite();
  }

  boolean recordsWrite() {
    return expiresAfterWrite() || refreshes();
  }

  boolean recordsAccess() {
    return expiresAfterAccess();
  }

  boolean recordsTime() {
    return recordsWrite() || recordsAccess();
  }

  boolean usesWriteEntries() {
    return usesWriteQueue() || recordsWrite();
  }

  boolean usesAccessEntries() {
    return usesAccessQueue() || recordsAccess();
  }

  boolean usesKeyReferences() {
    return keyStrength != Strength.STRONG;
  }

  boolean usesValueReferences() {
    return valueStrength != Strength.STRONG;
  }

  enum Strength {
    /*
     * TODO(kevinb): If we strongly reference the value and aren't loading, we needn't wrap the
     * value. This could save ~8 bytes per entry.
     */

    STRONG {
      @Override
      <K, V> ValueReference<K, V> referenceValue(
          Segment<K, V> segment, ReferenceEntry<K, V> entry, V value, int weight) {
        return (weight == 1)
            ? new StrongValueReference<K, V>(value)
            : new WeightedStrongValueReference<K, V>(value, weight);
      }

      @Override
      Equivalence<Object> defaultEquivalence() {
        return Equivalence.equals();
      }
    },
    SOFT {
      @Override
      <K, V> ValueReference<K, V> referenceValue(
          Segment<K, V> segment, ReferenceEntry<K, V> entry, V value, int weight) {
        return (weight == 1)
            ? new SoftValueReference<K, V>(segment.valueReferenceQueue, value, entry)
            : new WeightedSoftValueReference<K, V>(
                segment.valueReferenceQueue, value, entry, weight);
      }

      @Override
      Equivalence<Object> defaultEquivalence() {
        return Equivalence.identity();
      }
    },
    WEAK {
      @Override
      <K, V> ValueReference<K, V> referenceValue(
          Segment<K, V> segment, ReferenceEntry<K, V> entry, V value, int weight) {
        return (weight == 1)
            ? new WeakValueReference<K, V>(segment.valueReferenceQueue, value, entry)
            : new WeightedWeakValueReference<K, V>(
                segment.valueReferenceQueue, value, entry, weight);
      }

      @Override
      Equivalence<Object> defaultEquivalence() {
        return Equivalence.identity();
      }
    };

    
Creates a reference for the given value according to this value strength. /** Creates a reference for the given value according to this value strength. */
    abstract <K, V> ValueReference<K, V> referenceValue(
        Segment<K, V> segment, ReferenceEntry<K, V> entry, V value, int weight);

    
Returns the default equivalence strategy used to compare and hash keys or values referenced
at this strength. This strategy will be used unless the user explicitly specifies an
alternate strategy.
/**
     * Returns the default equivalence strategy used to compare and hash keys or values referenced
     * at this strength. This strategy will be used unless the user explicitly specifies an
     * alternate strategy.
     */
    abstract Equivalence<Object> defaultEquivalence();
  }

  
Creates new entries. /** Creates new entries. */
  enum EntryFactory {
    STRONG {
      @Override
      <K, V> ReferenceEntry<K, V> newEntry(
          Segment<K, V> segment, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
        return new StrongEntry<>(key, hash, next);
      }
    },
    STRONG_ACCESS {
      @Override
      <K, V> ReferenceEntry<K, V> newEntry(
          Segment<K, V> segment, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
        return new StrongAccessEntry<>(key, hash, next);
      }

      @Override
      <K, V> ReferenceEntry<K, V> copyEntry(
          Segment<K, V> segment, ReferenceEntry<K, V> original, ReferenceEntry<K, V> newNext) {
        ReferenceEntry<K, V> newEntry = super.copyEntry(segment, original, newNext);
        copyAccessEntry(original, newEntry);
        return newEntry;
      }
    },
    STRONG_WRITE {
      @Override
      <K, V> ReferenceEntry<K, V> newEntry(
          Segment<K, V> segment, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
        return new StrongWriteEntry<>(key, hash, next);
      }

      @Override
      <K, V> ReferenceEntry<K, V> copyEntry(
          Segment<K, V> segment, ReferenceEntry<K, V> original, ReferenceEntry<K, V> newNext) {
        ReferenceEntry<K, V> newEntry = super.copyEntry(segment, original, newNext);
        copyWriteEntry(original, newEntry);
        return newEntry;
      }
    },
    STRONG_ACCESS_WRITE {
      @Override
      <K, V> ReferenceEntry<K, V> newEntry(
          Segment<K, V> segment, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
        return new StrongAccessWriteEntry<>(key, hash, next);
      }

      @Override
      <K, V> ReferenceEntry<K, V> copyEntry(
          Segment<K, V> segment, ReferenceEntry<K, V> original, ReferenceEntry<K, V> newNext) {
        ReferenceEntry<K, V> newEntry = super.copyEntry(segment, original, newNext);
        copyAccessEntry(original, newEntry);
        copyWriteEntry(original, newEntry);
        return newEntry;
      }
    },
    WEAK {
      @Override
      <K, V> ReferenceEntry<K, V> newEntry(
          Segment<K, V> segment, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
        return new WeakEntry<>(segment.keyReferenceQueue, key, hash, next);
      }
    },
    WEAK_ACCESS {
      @Override
      <K, V> ReferenceEntry<K, V> newEntry(
          Segment<K, V> segment, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
        return new WeakAccessEntry<>(segment.keyReferenceQueue, key, hash, next);
      }

      @Override
      <K, V> ReferenceEntry<K, V> copyEntry(
          Segment<K, V> segment, ReferenceEntry<K, V> original, ReferenceEntry<K, V> newNext) {
        ReferenceEntry<K, V> newEntry = super.copyEntry(segment, original, newNext);
        copyAccessEntry(original, newEntry);
        return newEntry;
      }
    },
    WEAK_WRITE {
      @Override
      <K, V> ReferenceEntry<K, V> newEntry(
          Segment<K, V> segment, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
        return new WeakWriteEntry<>(segment.keyReferenceQueue, key, hash, next);
      }

      @Override
      <K, V> ReferenceEntry<K, V> copyEntry(
          Segment<K, V> segment, ReferenceEntry<K, V> original, ReferenceEntry<K, V> newNext) {
        ReferenceEntry<K, V> newEntry = super.copyEntry(segment, original, newNext);
        copyWriteEntry(original, newEntry);
        return newEntry;
      }
    },
    WEAK_ACCESS_WRITE {
      @Override
      <K, V> ReferenceEntry<K, V> newEntry(
          Segment<K, V> segment, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
        return new WeakAccessWriteEntry<>(segment.keyReferenceQueue, key, hash, next);
      }

      @Override
      <K, V> ReferenceEntry<K, V> copyEntry(
          Segment<K, V> segment, ReferenceEntry<K, V> original, ReferenceEntry<K, V> newNext) {
        ReferenceEntry<K, V> newEntry = super.copyEntry(segment, original, newNext);
        copyAccessEntry(original, newEntry);
        copyWriteEntry(original, newEntry);
        return newEntry;
      }
    };

    // Masks used to compute indices in the following table.

    static final int ACCESS_MASK = 1;
    static final int WRITE_MASK = 2;
    static final int WEAK_MASK = 4;

    
Look-up table for factories. /** Look-up table for factories. */
    static final EntryFactory[] factories = {
      STRONG,
      STRONG_ACCESS,
      STRONG_WRITE,
      STRONG_ACCESS_WRITE,
      WEAK,
      WEAK_ACCESS,
      WEAK_WRITE,
      WEAK_ACCESS_WRITE,
    };

    static EntryFactory getFactory(
        Strength keyStrength, boolean usesAccessQueue, boolean usesWriteQueue) {
      int flags =
          ((keyStrength == Strength.WEAK) ? WEAK_MASK : 0)
              | (usesAccessQueue ? ACCESS_MASK : 0)
              | (usesWriteQueue ? WRITE_MASK : 0);
      return factories[flags];
    }

    
Creates a new entry.
Params:
segment – to create the entry for
key – of the entry
hash – of the key
next – entry in the same bucket/**
     * Creates a new entry.
     *
     * @param segment to create the entry for
     * @param key of the entry
     * @param hash of the key
     * @param next entry in the same bucket
     */
    abstract <K, V> ReferenceEntry<K, V> newEntry(
        Segment<K, V> segment, K key, int hash, @Nullable ReferenceEntry<K, V> next);

    
Copies an entry, assigning it a new next entry. 
Params:
original – the entry to copy
newNext – entry in the same bucket/**
     * Copies an entry, assigning it a new {@code next} entry.
     *
     * @param original the entry to copy
     * @param newNext entry in the same bucket
     */
    // Guarded By Segment.this
    <K, V> ReferenceEntry<K, V> copyEntry(
        Segment<K, V> segment, ReferenceEntry<K, V> original, ReferenceEntry<K, V> newNext) {
      return newEntry(segment, original.getKey(), original.getHash(), newNext);
    }

    // Guarded By Segment.this
    <K, V> void copyAccessEntry(ReferenceEntry<K, V> original, ReferenceEntry<K, V> newEntry) {
      // TODO(fry): when we link values instead of entries this method can go
      // away, as can connectAccessOrder, nullifyAccessOrder.
      newEntry.setAccessTime(original.getAccessTime());

      connectAccessOrder(original.getPreviousInAccessQueue(), newEntry);
      connectAccessOrder(newEntry, original.getNextInAccessQueue());

      nullifyAccessOrder(original);
    }

    // Guarded By Segment.this
    <K, V> void copyWriteEntry(ReferenceEntry<K, V> original, ReferenceEntry<K, V> newEntry) {
      // TODO(fry): when we link values instead of entries this method can go
      // away, as can connectWriteOrder, nullifyWriteOrder.
      newEntry.setWriteTime(original.getWriteTime());

      connectWriteOrder(original.getPreviousInWriteQueue(), newEntry);
      connectWriteOrder(newEntry, original.getNextInWriteQueue());

      nullifyWriteOrder(original);
    }
  }

  
A reference to a value. /** A reference to a value. */
  interface ValueReference<K, V> {
    
Returns the value. Does not block or throw exceptions. /** Returns the value. Does not block or throw exceptions. */
    @Nullable
    V get();

    
Waits for a value that may still be loading. Unlike get(), this method can block (in the case
of FutureValueReference).
Throws:
ExecutionException – if the loading thread throws an exception
ExecutionError – if the loading thread throws an error/**
     * Waits for a value that may still be loading. Unlike get(), this method can block (in the case
     * of FutureValueReference).
     *
     * @throws ExecutionException if the loading thread throws an exception
     * @throws ExecutionError if the loading thread throws an error
     */
    V waitForValue() throws ExecutionException;

    
Returns the weight of this entry. This is assumed to be static between calls to setValue. /** Returns the weight of this entry. This is assumed to be static between calls to setValue. */
    int getWeight();

    
Returns the entry associated with this value reference, or null if this value reference is independent of any entry. /**
     * Returns the entry associated with this value reference, or {@code null} if this value
     * reference is independent of any entry.
     */
    @Nullable
    ReferenceEntry<K, V> getEntry();

    
Creates a copy of this reference for the given entry.
value may be null only for a loading reference. /**
     * Creates a copy of this reference for the given entry.
     *
     * <p>{@code value} may be null only for a loading reference.
     */
    ValueReference<K, V> copyFor(
        ReferenceQueue<V> queue, @Nullable V value, ReferenceEntry<K, V> entry);

    
Notify pending loads that a new value was set. This is only relevant to loading value
references.
/**
     * Notify pending loads that a new value was set. This is only relevant to loading value
     * references.
     */
    void notifyNewValue(@Nullable V newValue);

    
Returns true if a new value is currently loading, regardless of whether or not there is an
existing value. It is assumed that the return value of this method is constant for any given
ValueReference instance.
/**
     * Returns true if a new value is currently loading, regardless of whether or not there is an
     * existing value. It is assumed that the return value of this method is constant for any given
     * ValueReference instance.
     */
    boolean isLoading();

    
Returns true if this reference contains an active value, meaning one that is still considered
present in the cache. Active values consist of live values, which are returned by cache
lookups, and dead values, which have been evicted but awaiting removal. Non-active values
consist strictly of loading values, though during refresh a value may be both active and
loading.
/**
     * Returns true if this reference contains an active value, meaning one that is still considered
     * present in the cache. Active values consist of live values, which are returned by cache
     * lookups, and dead values, which have been evicted but awaiting removal. Non-active values
     * consist strictly of loading values, though during refresh a value may be both active and
     * loading.
     */
    boolean isActive();
  }

  
Placeholder. Indicates that the value hasn't been set yet. /** Placeholder. Indicates that the value hasn't been set yet. */
  static final ValueReference<Object, Object> UNSET =
      new ValueReference<Object, Object>() {
        @Override
        public Object get() {
          return null;
        }

        @Override
        public int getWeight() {
          return 0;
        }

        @Override
        public ReferenceEntry<Object, Object> getEntry() {
          return null;
        }

        @Override
        public ValueReference<Object, Object> copyFor(
            ReferenceQueue<Object> queue,
            @Nullable Object value,
            ReferenceEntry<Object, Object> entry) {
          return this;
        }

        @Override
        public boolean isLoading() {
          return false;
        }

        @Override
        public boolean isActive() {
          return false;
        }

        @Override
        public Object waitForValue() {
          return null;
        }

        @Override
        public void notifyNewValue(Object newValue) {}
      };

  
Singleton placeholder that indicates a value is being loaded. /** Singleton placeholder that indicates a value is being loaded. */
  @SuppressWarnings("unchecked") // impl never uses a parameter or returns any non-null value
  static <K, V> ValueReference<K, V> unset() {
    return (ValueReference<K, V>) UNSET;
  }

  private enum NullEntry implements ReferenceEntry<Object, Object> {
    INSTANCE;

    @Override
    public ValueReference<Object, Object> getValueReference() {
      return null;
    }

    @Override
    public void setValueReference(ValueReference<Object, Object> valueReference) {}

    @Override
    public ReferenceEntry<Object, Object> getNext() {
      return null;
    }

    @Override
    public int getHash() {
      return 0;
    }

    @Override
    public Object getKey() {
      return null;
    }

    @Override
    public long getAccessTime() {
      return 0;
    }

    @Override
    public void setAccessTime(long time) {}

    @Override
    public ReferenceEntry<Object, Object> getNextInAccessQueue() {
      return this;
    }

    @Override
    public void setNextInAccessQueue(ReferenceEntry<Object, Object> next) {}

    @Override
    public ReferenceEntry<Object, Object> getPreviousInAccessQueue() {
      return this;
    }

    @Override
    public void setPreviousInAccessQueue(ReferenceEntry<Object, Object> previous) {}

    @Override
    public long getWriteTime() {
      return 0;
    }

    @Override
    public void setWriteTime(long time) {}

    @Override
    public ReferenceEntry<Object, Object> getNextInWriteQueue() {
      return this;
    }

    @Override
    public void setNextInWriteQueue(ReferenceEntry<Object, Object> next) {}

    @Override
    public ReferenceEntry<Object, Object> getPreviousInWriteQueue() {
      return this;
    }

    @Override
    public void setPreviousInWriteQueue(ReferenceEntry<Object, Object> previous) {}
  }

  abstract static class AbstractReferenceEntry<K, V> implements ReferenceEntry<K, V> {
    @Override
    public ValueReference<K, V> getValueReference() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setValueReference(ValueReference<K, V> valueReference) {
      throw new UnsupportedOperationException();
    }

    @Override
    public ReferenceEntry<K, V> getNext() {
      throw new UnsupportedOperationException();
    }

    @Override
    public int getHash() {
      throw new UnsupportedOperationException();
    }

    @Override
    public K getKey() {
      throw new UnsupportedOperationException();
    }

    @Override
    public long getAccessTime() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setAccessTime(long time) {
      throw new UnsupportedOperationException();
    }

    @Override
    public ReferenceEntry<K, V> getNextInAccessQueue() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setNextInAccessQueue(ReferenceEntry<K, V> next) {
      throw new UnsupportedOperationException();
    }

    @Override
    public ReferenceEntry<K, V> getPreviousInAccessQueue() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setPreviousInAccessQueue(ReferenceEntry<K, V> previous) {
      throw new UnsupportedOperationException();
    }

    @Override
    public long getWriteTime() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setWriteTime(long time) {
      throw new UnsupportedOperationException();
    }

    @Override
    public ReferenceEntry<K, V> getNextInWriteQueue() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setNextInWriteQueue(ReferenceEntry<K, V> next) {
      throw new UnsupportedOperationException();
    }

    @Override
    public ReferenceEntry<K, V> getPreviousInWriteQueue() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setPreviousInWriteQueue(ReferenceEntry<K, V> previous) {
      throw new UnsupportedOperationException();
    }
  }

  @SuppressWarnings("unchecked") // impl never uses a parameter or returns any non-null value
  static <K, V> ReferenceEntry<K, V> nullEntry() {
    return (ReferenceEntry<K, V>) NullEntry.INSTANCE;
  }

  static final Queue<?> DISCARDING_QUEUE =
      new AbstractQueue<Object>() {
        @Override
        public boolean offer(Object o) {
          return true;
        }

        @Override
        public Object peek() {
          return null;
        }

        @Override
        public Object poll() {
          return null;
        }

        @Override
        public int size() {
          return 0;
        }

        @Override
        public Iterator<Object> iterator() {
          return ImmutableSet.of().iterator();
        }
      };

  
Queue that discards all elements. /** Queue that discards all elements. */
  @SuppressWarnings("unchecked") // impl never uses a parameter or returns any non-null value
  static <E> Queue<E> discardingQueue() {
    return (Queue) DISCARDING_QUEUE;
  }

  /*
   * Note: All of this duplicate code sucks, but it saves a lot of memory. If only Java had mixins!
   * To maintain this code, make a change for the strong reference type. Then, cut and paste, and
   * replace "Strong" with "Soft" or "Weak" within the pasted text. The primary difference is that
   * strong entries store the key reference directly while soft and weak entries delegate to their
   * respective superclasses.
   */

  
Used for strongly-referenced keys. /** Used for strongly-referenced keys. */
  static class StrongEntry<K, V> extends AbstractReferenceEntry<K, V> {
    final K key;

    StrongEntry(K key, int hash, @Nullable ReferenceEntry<K, V> next) {
      this.key = key;
      this.hash = hash;
      this.next = next;
    }

    @Override
    public K getKey() {
      return this.key;
    }

    // The code below is exactly the same for each entry type.

    final int hash;
    final @Nullable ReferenceEntry<K, V> next;
    volatile ValueReference<K, V> valueReference = unset();

    @Override
    public ValueReference<K, V> getValueReference() {
      return valueReference;
    }

    @Override
    public void setValueReference(ValueReference<K, V> valueReference) {
      this.valueReference = valueReference;
    }

    @Override
    public int getHash() {
      return hash;
    }

    @Override
    public ReferenceEntry<K, V> getNext() {
      return next;
    }
  }

  static final class StrongAccessEntry<K, V> extends StrongEntry<K, V> {
    StrongAccessEntry(K key, int hash, @Nullable ReferenceEntry<K, V> next) {
      super(key, hash, next);
    }

    // The code below is exactly the same for each access entry type.

    volatile long accessTime = Long.MAX_VALUE;

    @Override
    public long getAccessTime() {
      return accessTime;
    }

    @Override
    public void setAccessTime(long time) {
      this.accessTime = time;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> nextAccess = nullEntry();

    @Override
    public ReferenceEntry<K, V> getNextInAccessQueue() {
      return nextAccess;
    }

    @Override
    public void setNextInAccessQueue(ReferenceEntry<K, V> next) {
      this.nextAccess = next;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> previousAccess = nullEntry();

    @Override
    public ReferenceEntry<K, V> getPreviousInAccessQueue() {
      return previousAccess;
    }

    @Override
    public void setPreviousInAccessQueue(ReferenceEntry<K, V> previous) {
      this.previousAccess = previous;
    }
  }

  static final class StrongWriteEntry<K, V> extends StrongEntry<K, V> {
    StrongWriteEntry(K key, int hash, @Nullable ReferenceEntry<K, V> next) {
      super(key, hash, next);
    }

    // The code below is exactly the same for each write entry type.

    volatile long writeTime = Long.MAX_VALUE;

    @Override
    public long getWriteTime() {
      return writeTime;
    }

    @Override
    public void setWriteTime(long time) {
      this.writeTime = time;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> nextWrite = nullEntry();

    @Override
    public ReferenceEntry<K, V> getNextInWriteQueue() {
      return nextWrite;
    }

    @Override
    public void setNextInWriteQueue(ReferenceEntry<K, V> next) {
      this.nextWrite = next;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> previousWrite = nullEntry();

    @Override
    public ReferenceEntry<K, V> getPreviousInWriteQueue() {
      return previousWrite;
    }

    @Override
    public void setPreviousInWriteQueue(ReferenceEntry<K, V> previous) {
      this.previousWrite = previous;
    }
  }

  static final class StrongAccessWriteEntry<K, V> extends StrongEntry<K, V> {
    StrongAccessWriteEntry(K key, int hash, @Nullable ReferenceEntry<K, V> next) {
      super(key, hash, next);
    }

    // The code below is exactly the same for each access entry type.

    volatile long accessTime = Long.MAX_VALUE;

    @Override
    public long getAccessTime() {
      return accessTime;
    }

    @Override
    public void setAccessTime(long time) {
      this.accessTime = time;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> nextAccess = nullEntry();

    @Override
    public ReferenceEntry<K, V> getNextInAccessQueue() {
      return nextAccess;
    }

    @Override
    public void setNextInAccessQueue(ReferenceEntry<K, V> next) {
      this.nextAccess = next;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> previousAccess = nullEntry();

    @Override
    public ReferenceEntry<K, V> getPreviousInAccessQueue() {
      return previousAccess;
    }

    @Override
    public void setPreviousInAccessQueue(ReferenceEntry<K, V> previous) {
      this.previousAccess = previous;
    }

    // The code below is exactly the same for each write entry type.

    volatile long writeTime = Long.MAX_VALUE;

    @Override
    public long getWriteTime() {
      return writeTime;
    }

    @Override
    public void setWriteTime(long time) {
      this.writeTime = time;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> nextWrite = nullEntry();

    @Override
    public ReferenceEntry<K, V> getNextInWriteQueue() {
      return nextWrite;
    }

    @Override
    public void setNextInWriteQueue(ReferenceEntry<K, V> next) {
      this.nextWrite = next;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> previousWrite = nullEntry();

    @Override
    public ReferenceEntry<K, V> getPreviousInWriteQueue() {
      return previousWrite;
    }

    @Override
    public void setPreviousInWriteQueue(ReferenceEntry<K, V> previous) {
      this.previousWrite = previous;
    }
  }

  
Used for weakly-referenced keys. /** Used for weakly-referenced keys. */
  static class WeakEntry<K, V> extends WeakReference<K> implements ReferenceEntry<K, V> {
    WeakEntry(ReferenceQueue<K> queue, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
      super(key, queue);
      this.hash = hash;
      this.next = next;
    }

    @Override
    public K getKey() {
      return get();
    }

    /*
     * It'd be nice to get these for free from AbstractReferenceEntry, but we're already extending
     * WeakReference<K>.
     */

    // null access

    @Override
    public long getAccessTime() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setAccessTime(long time) {
      throw new UnsupportedOperationException();
    }

    @Override
    public ReferenceEntry<K, V> getNextInAccessQueue() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setNextInAccessQueue(ReferenceEntry<K, V> next) {
      throw new UnsupportedOperationException();
    }

    @Override
    public ReferenceEntry<K, V> getPreviousInAccessQueue() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setPreviousInAccessQueue(ReferenceEntry<K, V> previous) {
      throw new UnsupportedOperationException();
    }

    // null write

    @Override
    public long getWriteTime() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setWriteTime(long time) {
      throw new UnsupportedOperationException();
    }

    @Override
    public ReferenceEntry<K, V> getNextInWriteQueue() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setNextInWriteQueue(ReferenceEntry<K, V> next) {
      throw new UnsupportedOperationException();
    }

    @Override
    public ReferenceEntry<K, V> getPreviousInWriteQueue() {
      throw new UnsupportedOperationException();
    }

    @Override
    public void setPreviousInWriteQueue(ReferenceEntry<K, V> previous) {
      throw new UnsupportedOperationException();
    }

    // The code below is exactly the same for each entry type.

    final int hash;
    final @Nullable ReferenceEntry<K, V> next;
    volatile ValueReference<K, V> valueReference = unset();

    @Override
    public ValueReference<K, V> getValueReference() {
      return valueReference;
    }

    @Override
    public void setValueReference(ValueReference<K, V> valueReference) {
      this.valueReference = valueReference;
    }

    @Override
    public int getHash() {
      return hash;
    }

    @Override
    public ReferenceEntry<K, V> getNext() {
      return next;
    }
  }

  static final class WeakAccessEntry<K, V> extends WeakEntry<K, V> {
    WeakAccessEntry(ReferenceQueue<K> queue, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
      super(queue, key, hash, next);
    }

    // The code below is exactly the same for each access entry type.

    volatile long accessTime = Long.MAX_VALUE;

    @Override
    public long getAccessTime() {
      return accessTime;
    }

    @Override
    public void setAccessTime(long time) {
      this.accessTime = time;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> nextAccess = nullEntry();

    @Override
    public ReferenceEntry<K, V> getNextInAccessQueue() {
      return nextAccess;
    }

    @Override
    public void setNextInAccessQueue(ReferenceEntry<K, V> next) {
      this.nextAccess = next;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> previousAccess = nullEntry();

    @Override
    public ReferenceEntry<K, V> getPreviousInAccessQueue() {
      return previousAccess;
    }

    @Override
    public void setPreviousInAccessQueue(ReferenceEntry<K, V> previous) {
      this.previousAccess = previous;
    }
  }

  static final class WeakWriteEntry<K, V> extends WeakEntry<K, V> {
    WeakWriteEntry(ReferenceQueue<K> queue, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
      super(queue, key, hash, next);
    }

    // The code below is exactly the same for each write entry type.

    volatile long writeTime = Long.MAX_VALUE;

    @Override
    public long getWriteTime() {
      return writeTime;
    }

    @Override
    public void setWriteTime(long time) {
      this.writeTime = time;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> nextWrite = nullEntry();

    @Override
    public ReferenceEntry<K, V> getNextInWriteQueue() {
      return nextWrite;
    }

    @Override
    public void setNextInWriteQueue(ReferenceEntry<K, V> next) {
      this.nextWrite = next;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> previousWrite = nullEntry();

    @Override
    public ReferenceEntry<K, V> getPreviousInWriteQueue() {
      return previousWrite;
    }

    @Override
    public void setPreviousInWriteQueue(ReferenceEntry<K, V> previous) {
      this.previousWrite = previous;
    }
  }

  static final class WeakAccessWriteEntry<K, V> extends WeakEntry<K, V> {
    WeakAccessWriteEntry(
        ReferenceQueue<K> queue, K key, int hash, @Nullable ReferenceEntry<K, V> next) {
      super(queue, key, hash, next);
    }

    // The code below is exactly the same for each access entry type.

    volatile long accessTime = Long.MAX_VALUE;

    @Override
    public long getAccessTime() {
      return accessTime;
    }

    @Override
    public void setAccessTime(long time) {
      this.accessTime = time;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> nextAccess = nullEntry();

    @Override
    public ReferenceEntry<K, V> getNextInAccessQueue() {
      return nextAccess;
    }

    @Override
    public void setNextInAccessQueue(ReferenceEntry<K, V> next) {
      this.nextAccess = next;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> previousAccess = nullEntry();

    @Override
    public ReferenceEntry<K, V> getPreviousInAccessQueue() {
      return previousAccess;
    }

    @Override
    public void setPreviousInAccessQueue(ReferenceEntry<K, V> previous) {
      this.previousAccess = previous;
    }

    // The code below is exactly the same for each write entry type.

    volatile long writeTime = Long.MAX_VALUE;

    @Override
    public long getWriteTime() {
      return writeTime;
    }

    @Override
    public void setWriteTime(long time) {
      this.writeTime = time;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> nextWrite = nullEntry();

    @Override
    public ReferenceEntry<K, V> getNextInWriteQueue() {
      return nextWrite;
    }

    @Override
    public void setNextInWriteQueue(ReferenceEntry<K, V> next) {
      this.nextWrite = next;
    }

    // Guarded By Segment.this
    ReferenceEntry<K, V> previousWrite = nullEntry();

    @Override
    public ReferenceEntry<K, V> getPreviousInWriteQueue() {
      return previousWrite;
    }

    @Override
    public void setPreviousInWriteQueue(ReferenceEntry<K, V> previous) {
      this.previousWrite = previous;
    }
  }

  
References a weak value. /** References a weak value. */
  static class WeakValueReference<K, V> extends WeakReference<V> implements ValueReference<K, V> {
    final ReferenceEntry<K, V> entry;

    WeakValueReference(ReferenceQueue<V> queue, V referent, ReferenceEntry<K, V> entry) {
      super(referent, queue);
      this.entry = entry;
    }

    @Override
    public int getWeight() {
      return 1;
    }

    @Override
    public ReferenceEntry<K, V> getEntry() {
      return entry;
    }

    @Override
    public void notifyNewValue(V newValue) {}

    @Override
    public ValueReference<K, V> copyFor(
        ReferenceQueue<V> queue, V value, ReferenceEntry<K, V> entry) {
      return new WeakValueReference<>(queue, value, entry);
    }

    @Override
    public boolean isLoading() {
      return false;
    }

    @Override
    public boolean isActive() {
      return true;
    }

    @Override
    public V waitForValue() {
      return get();
    }
  }

  
References a soft value. /** References a soft value. */
  static class SoftValueReference<K, V> extends SoftReference<V> implements ValueReference<K, V> {
    final ReferenceEntry<K, V> entry;

    SoftValueReference(ReferenceQueue<V> queue, V referent, ReferenceEntry<K, V> entry) {
      super(referent, queue);
      this.entry = entry;
    }

    @Override
    public int getWeight() {
      return 1;
    }

    @Override
    public ReferenceEntry<K, V> getEntry() {
      return entry;
    }

    @Override
    public void notifyNewValue(V newValue) {}

    @Override
    public ValueReference<K, V> copyFor(
        ReferenceQueue<V> queue, V value, ReferenceEntry<K, V> entry) {
      return new SoftValueReference<>(queue, value, entry);
    }

    @Override
    public boolean isLoading() {
      return false;
    }

    @Override
    public boolean isActive() {
      return true;
    }

    @Override
    public V waitForValue() {
      return get();
    }
  }

  
References a strong value. /** References a strong value. */
  static class StrongValueReference<K, V> implements ValueReference<K, V> {
    final V referent;

    StrongValueReference(V referent) {
      this.referent = referent;
    }

    @Override
    public V get() {
      return referent;
    }

    @Override
    public int getWeight() {
      return 1;
    }

    @Override
    public ReferenceEntry<K, V> getEntry() {
      return null;
    }

    @Override
    public ValueReference<K, V> copyFor(
        ReferenceQueue<V> queue, V value, ReferenceEntry<K, V> entry) {
      return this;
    }

    @Override
    public boolean isLoading() {
      return false;
    }

    @Override
    public boolean isActive() {
      return true;
    }

    @Override
    public V waitForValue() {
      return get();
    }

    @Override
    public void notifyNewValue(V newValue) {}
  }

  
References a weak value. /** References a weak value. */
  static final class WeightedWeakValueReference<K, V> extends WeakValueReference<K, V> {
    final int weight;

    WeightedWeakValueReference(
        ReferenceQueue<V> queue, V referent, ReferenceEntry<K, V> entry, int weight) {
      super(queue, referent, entry);
      this.weight = weight;
    }

    @Override
    public int getWeight() {
      return weight;
    }

    @Override
    public ValueReference<K, V> copyFor(
        ReferenceQueue<V> queue, V value, ReferenceEntry<K, V> entry) {
      return new WeightedWeakValueReference<>(queue, value, entry, weight);
    }
  }

  
References a soft value. /** References a soft value. */
  static final class WeightedSoftValueReference<K, V> extends SoftValueReference<K, V> {
    final int weight;

    WeightedSoftValueReference(
        ReferenceQueue<V> queue, V referent, ReferenceEntry<K, V> entry, int weight) {
      super(queue, referent, entry);
      this.weight = weight;
    }

    @Override
    public int getWeight() {
      return weight;
    }

    @Override
    public ValueReference<K, V> copyFor(
        ReferenceQueue<V> queue, V value, ReferenceEntry<K, V> entry) {
      return new WeightedSoftValueReference<>(queue, value, entry, weight);
    }
  }

  
References a strong value. /** References a strong value. */
  static final class WeightedStrongValueReference<K, V> extends StrongValueReference<K, V> {
    final int weight;

    WeightedStrongValueReference(V referent, int weight) {
      super(referent);
      this.weight = weight;
    }

    @Override
    public int getWeight() {
      return weight;
    }
  }

  
Applies a supplemental hash function to a given hash code, which defends against poor quality
hash functions. This is critical when the concurrent hash map uses power-of-two length hash
tables, that otherwise encounter collisions for hash codes that do not differ in lower or upper
bits.
Params:
h – hash code/**
   * Applies a supplemental hash function to a given hash code, which defends against poor quality
   * hash functions. This is critical when the concurrent hash map uses power-of-two length hash
   * tables, that otherwise encounter collisions for hash codes that do not differ in lower or upper
   * bits.
   *
   * @param h hash code
   */
  static int rehash(int h) {
    // Spread bits to regularize both segment and index locations,
    // using variant of single-word Wang/Jenkins hash.
    // TODO(kevinb): use Hashing/move this to Hashing?
    h += (h << 15) ^ 0xffffcd7d;
    h ^= (h >>> 10);
    h += (h << 3);
    h ^= (h >>> 6);
    h += (h << 2) + (h << 14);
    return h ^ (h >>> 16);
  }

  
This method is a convenience for testing. Code should call Segment.newEntry directly. /**
   * This method is a convenience for testing. Code should call {@link Segment#newEntry} directly.
   */
  @VisibleForTesting
  ReferenceEntry<K, V> newEntry(K key, int hash, @Nullable ReferenceEntry<K, V> next) {
    Segment<K, V> segment = segmentFor(hash);
    segment.lock();
    try {
      return segment.newEntry(key, hash, next);
    } finally {
      segment.unlock();
    }
  }

  
This method is a convenience for testing. Code should call Segment.copyEntry directly. /**
   * This method is a convenience for testing. Code should call {@link Segment#copyEntry} directly.
   */
  // Guarded By Segment.this
  @VisibleForTesting
  ReferenceEntry<K, V> copyEntry(ReferenceEntry<K, V> original, ReferenceEntry<K, V> newNext) {
    int hash = original.getHash();
    return segmentFor(hash).copyEntry(original, newNext);
  }

  
This method is a convenience for testing. Code should call Segment.setValue instead. /**
   * This method is a convenience for testing. Code should call {@link Segment#setValue} instead.
   */
  // Guarded By Segment.this
  @VisibleForTesting
  ValueReference<K, V> newValueReference(ReferenceEntry<K, V> entry, V value, int weight) {
    int hash = entry.getHash();
    return valueStrength.referenceValue(segmentFor(hash), entry, checkNotNull(value), weight);
  }

  int hash(@Nullable Object key) {
    int h = keyEquivalence.hash(key);
    return rehash(h);
  }

  void reclaimValue(ValueReference<K, V> valueReference) {
    ReferenceEntry<K, V> entry = valueReference.getEntry();
    int hash = entry.getHash();
    segmentFor(hash).reclaimValue(entry.getKey(), hash, valueReference);
  }

  void reclaimKey(ReferenceEntry<K, V> entry) {
    int hash = entry.getHash();
    segmentFor(hash).reclaimKey(entry, hash);
  }

  
This method is a convenience for testing. Code should call Segment.getLiveValue instead. /**
   * This method is a convenience for testing. Code should call {@link Segment#getLiveValue}
   * instead.
   */
  @VisibleForTesting
  boolean isLive(ReferenceEntry<K, V> entry, long now) {
    return segmentFor(entry.getHash()).getLiveValue(entry, now) != null;
  }

  
Returns the segment that should be used for a key with the given hash.
Params:
hash – the hash code for the key
Returns:
the segment/**
   * Returns the segment that should be used for a key with the given hash.
   *
   * @param hash the hash code for the key
   * @return the segment
   */
  Segment<K, V> segmentFor(int hash) {
    // TODO(fry): Lazily create segments?
    return segments[(hash >>> segmentShift) & segmentMask];
  }

  Segment<K, V> createSegment(
      int initialCapacity, long maxSegmentWeight, StatsCounter statsCounter) {
    return new Segment<>(this, initialCapacity, maxSegmentWeight, statsCounter);
  }

  
Gets the value from an entry. Returns null if the entry is invalid, partially-collected, loading, or expired. Unlike Segment.getLiveValue this method does not attempt to cleanup stale entries. As such it should only be called outside of a segment context, such as during iteration. /**
   * Gets the value from an entry. Returns null if the entry is invalid, partially-collected,
   * loading, or expired. Unlike {@link Segment#getLiveValue} this method does not attempt to
   * cleanup stale entries. As such it should only be called outside of a segment context, such as
   * during iteration.
   */
  @Nullable
  V getLiveValue(ReferenceEntry<K, V> entry, long now) {
    if (entry.getKey() == null) {
      return null;
    }
    V value = entry.getValueReference().get();
    if (value == null) {
      return null;
    }

    if (isExpired(entry, now)) {
      return null;
    }
    return value;
  }

  // expiration

  
Returns true if the entry has expired. /** Returns true if the entry has expired. */
  boolean isExpired(ReferenceEntry<K, V> entry, long now) {
    checkNotNull(entry);
    if (expiresAfterAccess() && (now - entry.getAccessTime() >= expireAfterAccessNanos)) {
      return true;
    }
    if (expiresAfterWrite() && (now - entry.getWriteTime() >= expireAfterWriteNanos)) {
      return true;
    }
    return false;
  }

  // queues

  // Guarded By Segment.this
  static <K, V> void connectAccessOrder(ReferenceEntry<K, V> previous, ReferenceEntry<K, V> next) {
    previous.setNextInAccessQueue(next);
    next.setPreviousInAccessQueue(previous);
  }

  // Guarded By Segment.this
  static <K, V> void nullifyAccessOrder(ReferenceEntry<K, V> nulled) {
    ReferenceEntry<K, V> nullEntry = nullEntry();
    nulled.setNextInAccessQueue(nullEntry);
    nulled.setPreviousInAccessQueue(nullEntry);
  }

  // Guarded By Segment.this
  static <K, V> void connectWriteOrder(ReferenceEntry<K, V> previous, ReferenceEntry<K, V> next) {
    previous.setNextInWriteQueue(next);
    next.setPreviousInWriteQueue(previous);
  }

  // Guarded By Segment.this
  static <K, V> void nullifyWriteOrder(ReferenceEntry<K, V> nulled) {
    ReferenceEntry<K, V> nullEntry = nullEntry();
    nulled.setNextInWriteQueue(nullEntry);
    nulled.setPreviousInWriteQueue(nullEntry);
  }

  
Notifies listeners that an entry has been automatically removed due to expiration, eviction, or
eligibility for garbage collection. This should be called every time expireEntries or
evictEntry is called (once the lock is released).
/**
   * Notifies listeners that an entry has been automatically removed due to expiration, eviction, or
   * eligibility for garbage collection. This should be called every time expireEntries or
   * evictEntry is called (once the lock is released).
   */
  void processPendingNotifications() {
    RemovalNotification<K, V> notification;
    while ((notification = removalNotificationQueue.poll()) != null) {
      try {
        removalListener.onRemoval(notification);
      } catch (Throwable e) {
        logger.log(Level.WARNING, "Exception thrown by removal listener", e);
      }
    }
  }

  @SuppressWarnings("unchecked")
  final Segment<K, V>[] newSegmentArray(int ssize) {
    return new Segment[ssize];
  }

  // Inner Classes

  
Segments are specialized versions of hash tables. This subclass inherits from ReentrantLock
opportunistically, just to simplify some locking and avoid separate construction.
/**
   * Segments are specialized versions of hash tables. This subclass inherits from ReentrantLock
   * opportunistically, just to simplify some locking and avoid separate construction.
   */
  @SuppressWarnings("serial") // This class is never serialized.
  static class Segment<K, V> extends ReentrantLock {

    /*
     * TODO(fry): Consider copying variables (like evictsBySize) from outer class into this class.
     * It will require more memory but will reduce indirection.
     */

    /*
     * Segments maintain a table of entry lists that are ALWAYS kept in a consistent state, so can
     * be read without locking. Next fields of nodes are immutable (final). All list additions are
     * performed at the front of each bin. This makes it easy to check changes, and also fast to
     * traverse. When nodes would otherwise be changed, new nodes are created to replace them. This
     * works well for hash tables since the bin lists tend to be short. (The average length is less
     * than two.)
     *
     * Read operations can thus proceed without locking, but rely on selected uses of volatiles to
     * ensure that completed write operations performed by other threads are noticed. For most
     * purposes, the "count" field, tracking the number of elements, serves as that volatile
     * variable ensuring visibility. This is convenient because this field needs to be read in many
     * read operations anyway:
     *
     * - All (unsynchronized) read operations must first read the "count" field, and should not look
     * at table entries if it is 0.
     *
     * - All (synchronized) write operations should write to the "count" field after structurally
     * changing any bin. The operations must not take any action that could even momentarily cause a
     * concurrent read operation to see inconsistent data. This is made easier by the nature of the
     * read operations in Map. For example, no operation can reveal that the table has grown but the
     * threshold has not yet been updated, so there are no atomicity requirements for this with
     * respect to reads.
     *
     * As a guide, all critical volatile reads and writes to the count field are marked in code
     * comments.
     */

    @Weak final LocalCache<K, V> map;

    
The number of live elements in this segment's region. /** The number of live elements in this segment's region. */
    volatile int count;

    
The weight of the live elements in this segment's region. /** The weight of the live elements in this segment's region. */
    @GuardedBy("this")
    long totalWeight;

    
Number of updates that alter the size of the table. This is used during bulk-read methods to
make sure they see a consistent snapshot: If modCounts change during a traversal of segments
loading size or checking containsValue, then we might have an inconsistent view of state so
(usually) must retry.
/**
     * Number of updates that alter the size of the table. This is used during bulk-read methods to
     * make sure they see a consistent snapshot: If modCounts change during a traversal of segments
     * loading size or checking containsValue, then we might have an inconsistent view of state so
     * (usually) must retry.
     */
    int modCount;

    
The table is expanded when its size exceeds this threshold. (The value of this field is always (int) (capacity * 0.75).) /**
     * The table is expanded when its size exceeds this threshold. (The value of this field is
     * always {@code (int) (capacity * 0.75)}.)
     */
    int threshold;

    
The per-segment table. /** The per-segment table. */
    volatile @MonotonicNonNull AtomicReferenceArray<ReferenceEntry<K, V>> table;

    
The maximum weight of this segment. UNSET_INT if there is no maximum. /** The maximum weight of this segment. UNSET_INT if there is no maximum. */
    final long maxSegmentWeight;

    
The key reference queue contains entries whose keys have been garbage collected, and which
need to be cleaned up internally.
/**
     * The key reference queue contains entries whose keys have been garbage collected, and which
     * need to be cleaned up internally.
     */
    final @Nullable ReferenceQueue<K> keyReferenceQueue;

    
The value reference queue contains value references whose values have been garbage collected,
and which need to be cleaned up internally.
/**
     * The value reference queue contains value references whose values have been garbage collected,
     * and which need to be cleaned up internally.
     */
    final @Nullable ReferenceQueue<V> valueReferenceQueue;

    
The recency queue is used to record which entries were accessed for updating the access
list's ordering. It is drained as a batch operation when either the DRAIN_THRESHOLD is
crossed or a write occurs on the segment.
/**
     * The recency queue is used to record which entries were accessed for updating the access
     * list's ordering. It is drained as a batch operation when either the DRAIN_THRESHOLD is
     * crossed or a write occurs on the segment.
     */
    final Queue<ReferenceEntry<K, V>> recencyQueue;

    
A counter of the number of reads since the last write, used to drain queues on a small
fraction of read operations.
/**
     * A counter of the number of reads since the last write, used to drain queues on a small
     * fraction of read operations.
     */
    final AtomicInteger readCount = new AtomicInteger();

    
A queue of elements currently in the map, ordered by write time. Elements are added to the
tail of the queue on write.
/**
     * A queue of elements currently in the map, ordered by write time. Elements are added to the
     * tail of the queue on write.
     */
    @GuardedBy("this")
    final Queue<ReferenceEntry<K, V>> writeQueue;

    
A queue of elements currently in the map, ordered by access time. Elements are added to the
tail of the queue on access (note that writes count as accesses).
/**
     * A queue of elements currently in the map, ordered by access time. Elements are added to the
     * tail of the queue on access (note that writes count as accesses).
     */
    @GuardedBy("this")
    final Queue<ReferenceEntry<K, V>> accessQueue;

    
Accumulates cache statistics. /** Accumulates cache statistics. */
    final StatsCounter statsCounter;

    Segment(
        LocalCache<K, V> map,
        int initialCapacity,
        long maxSegmentWeight,
        StatsCounter statsCounter) {
      this.map = map;
      this.maxSegmentWeight = maxSegmentWeight;
      this.statsCounter = checkNotNull(statsCounter);
      initTable(newEntryArray(initialCapacity));

      keyReferenceQueue = map.usesKeyReferences() ? new ReferenceQueue<K>() : null;

      valueReferenceQueue = map.usesValueReferences() ? new ReferenceQueue<V>() : null;

      recencyQueue =
          map.usesAccessQueue()
              ? new ConcurrentLinkedQueue<ReferenceEntry<K, V>>()
              : LocalCache.<ReferenceEntry<K, V>>discardingQueue();

      writeQueue =
          map.usesWriteQueue()
              ? new WriteQueue<K, V>()
              : LocalCache.<ReferenceEntry<K, V>>discardingQueue();

      accessQueue =
          map.usesAccessQueue()
              ? new AccessQueue<K, V>()
              : LocalCache.<ReferenceEntry<K, V>>discardingQueue();
    }

    AtomicReferenceArray<ReferenceEntry<K, V>> newEntryArray(int size) {
      return new AtomicReferenceArray<>(size);
    }

    void initTable(AtomicReferenceArray<ReferenceEntry<K, V>> newTable) {
      this.threshold = newTable.length() * 3 / 4; // 0.75
      if (!map.customWeigher() && this.threshold == maxSegmentWeight) {
        // prevent spurious expansion before eviction
        this.threshold++;
      }
      this.table = newTable;
    }

    @GuardedBy("this")
    ReferenceEntry<K, V> newEntry(K key, int hash, @Nullable ReferenceEntry<K, V> next) {
      return map.entryFactory.newEntry(this, checkNotNull(key), hash, next);
    }

    
Copies original into a new entry chained to newNext. Returns the new entry, or null if original was already garbage collected. /**
     * Copies {@code original} into a new entry chained to {@code newNext}. Returns the new entry,
     * or {@code null} if {@code original} was already garbage collected.
     */
    @GuardedBy("this")
    ReferenceEntry<K, V> copyEntry(ReferenceEntry<K, V> original, ReferenceEntry<K, V> newNext) {
      if (original.getKey() == null) {
        // key collected
        return null;
      }

      ValueReference<K, V> valueReference = original.getValueReference();
      V value = valueReference.get();
      if ((value == null) && valueReference.isActive()) {
        // value collected
        return null;
      }

      ReferenceEntry<K, V> newEntry = map.entryFactory.copyEntry(this, original, newNext);
      newEntry.setValueReference(valueReference.copyFor(this.valueReferenceQueue, value, newEntry));
      return newEntry;
    }

    
Sets a new value of an entry. Adds newly created entries at the end of the access queue. /** Sets a new value of an entry. Adds newly created entries at the end of the access queue. */
    @GuardedBy("this")
    void setValue(ReferenceEntry<K, V> entry, K key, V value, long now) {
      ValueReference<K, V> previous = entry.getValueReference();
      int weight = map.weigher.weigh(key, value);
      checkState(weight >= 0, "Weights must be non-negative");

      ValueReference<K, V> valueReference =
          map.valueStrength.referenceValue(this, entry, value, weight);
      entry.setValueReference(valueReference);
      recordWrite(entry, weight, now);
      previous.notifyNewValue(value);
    }

    // loading

    V get(K key, int hash, CacheLoader<? super K, V> loader) throws ExecutionException {
      checkNotNull(key);
      checkNotNull(loader);
      try {
        if (count != 0) { // read-volatile
          // don't call getLiveEntry, which would ignore loading values
          ReferenceEntry<K, V> e = getEntry(key, hash);
          if (e != null) {
            long now = map.ticker.read();
            V value = getLiveValue(e, now);
            if (value != null) {
              recordRead(e, now);
              statsCounter.recordHits(1);
              return scheduleRefresh(e, key, hash, value, now, loader);
            }
            ValueReference<K, V> valueReference = e.getValueReference();
            if (valueReference.isLoading()) {
              return waitForLoadingValue(e, key, valueReference);
            }
          }
        }

        // at this point e is either null or expired;
        return lockedGetOrLoad(key, hash, loader);
      } catch (ExecutionException ee) {
        Throwable cause = ee.getCause();
        if (cause instanceof Error) {
          throw new ExecutionError((Error) cause);
        } else if (cause instanceof RuntimeException) {
          throw new UncheckedExecutionException(cause);
        }
        throw ee;
      } finally {
        postReadCleanup();
      }
    }

    @Nullable
    V get(Object key, int hash) {
      try {
        if (count != 0) { // read-volatile
          long now = map.ticker.read();
          ReferenceEntry<K, V> e = getLiveEntry(key, hash, now);
          if (e == null) {
            return null;
          }

          V value = e.getValueReference().get();
          if (value != null) {
            recordRead(e, now);
            return scheduleRefresh(e, e.getKey(), hash, value, now, map.defaultLoader);
          }
          tryDrainReferenceQueues();
        }
        return null;
      } finally {
        postReadCleanup();
      }
    }

    V lockedGetOrLoad(K key, int hash, CacheLoader<? super K, V> loader) throws ExecutionException {
      ReferenceEntry<K, V> e;
      ValueReference<K, V> valueReference = null;
      LoadingValueReference<K, V> loadingValueReference = null;
      boolean createNewEntry = true;

      lock();
      try {
        // re-read ticker once inside the lock
        long now = map.ticker.read();
        preWriteCleanup(now);

        int newCount = this.count - 1;
        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        for (e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            valueReference = e.getValueReference();
            if (valueReference.isLoading()) {
              createNewEntry = false;
            } else {
              V value = valueReference.get();
              if (value == null) {
                enqueueNotification(
                    entryKey, hash, value, valueReference.getWeight(), RemovalCause.COLLECTED);
              } else if (map.isExpired(e, now)) {
                // This is a duplicate check, as preWriteCleanup already purged expired
                // entries, but let's accomodate an incorrect expiration queue.
                enqueueNotification(
                    entryKey, hash, value, valueReference.getWeight(), RemovalCause.EXPIRED);
              } else {
                recordLockedRead(e, now);
                statsCounter.recordHits(1);
                // we were concurrent with loading; don't consider refresh
                return value;
              }

              // immediately reuse invalid entries
              writeQueue.remove(e);
              accessQueue.remove(e);
              this.count = newCount; // write-volatile
            }
            break;
          }
        }

        if (createNewEntry) {
          loadingValueReference = new LoadingValueReference<>();

          if (e == null) {
            e = newEntry(key, hash, first);
            e.setValueReference(loadingValueReference);
            table.set(index, e);
          } else {
            e.setValueReference(loadingValueReference);
          }
        }
      } finally {
        unlock();
        postWriteCleanup();
      }

      if (createNewEntry) {
        try {
          // Synchronizes on the entry to allow failing fast when a recursive load is
          // detected. This may be circumvented when an entry is copied, but will fail fast most
          // of the time.
          synchronized (e) {
            return loadSync(key, hash, loadingValueReference, loader);
          }
        } finally {
          statsCounter.recordMisses(1);
        }
      } else {
        // The entry already exists. Wait for loading.
        return waitForLoadingValue(e, key, valueReference);
      }
    }

    V waitForLoadingValue(ReferenceEntry<K, V> e, K key, ValueReference<K, V> valueReference)
        throws ExecutionException {
      if (!valueReference.isLoading()) {
        throw new AssertionError();
      }

      checkState(!Thread.holdsLock(e), "Recursive load of: %s", key);
      // don't consider expiration as we're concurrent with loading
      try {
        V value = valueReference.waitForValue();
        if (value == null) {
          throw new InvalidCacheLoadException("CacheLoader returned null for key " + key + ".");
        }
        // re-read ticker now that loading has completed
        long now = map.ticker.read();
        recordRead(e, now);
        return value;
      } finally {
        statsCounter.recordMisses(1);
      }
    }

    V compute(K key, int hash, BiFunction<? super K, ? super V, ? extends V> function) {
      ReferenceEntry<K, V> e;
      ValueReference<K, V> valueReference = null;
      LoadingValueReference<K, V> loadingValueReference = null;
      boolean createNewEntry = true;
      V newValue;

      lock();
      try {
        // re-read ticker once inside the lock
        long now = map.ticker.read();
        preWriteCleanup(now);

        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        for (e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            valueReference = e.getValueReference();
            if (map.isExpired(e, now)) {
              // This is a duplicate check, as preWriteCleanup already purged expired
              // entries, but let's accomodate an incorrect expiration queue.
              enqueueNotification(
                  entryKey,
                  hash,
                  valueReference.get(),
                  valueReference.getWeight(),
                  RemovalCause.EXPIRED);
            }

            // immediately reuse invalid entries
            writeQueue.remove(e);
            accessQueue.remove(e);
            createNewEntry = false;
            break;
          }
        }

        // note valueReference can be an existing value or even itself another loading value if
        // the value for the key is already being computed.
        loadingValueReference = new LoadingValueReference<>(valueReference);

        if (e == null) {
          createNewEntry = true;
          e = newEntry(key, hash, first);
          e.setValueReference(loadingValueReference);
          table.set(index, e);
        } else {
          e.setValueReference(loadingValueReference);
        }

        newValue = loadingValueReference.compute(key, function);
        if (newValue != null) {
          if (valueReference != null && newValue == valueReference.get()) {
            loadingValueReference.set(newValue);
            setValue(e, key, newValue, now);
            return newValue;
          }
          try {
            return getAndRecordStats(
                key, hash, loadingValueReference, Futures.immediateFuture(newValue));
          } catch (ExecutionException exception) {
            throw new AssertionError("impossible; Futures.immediateFuture can't throw");
          }
        } else if (createNewEntry) {
          removeLoadingValue(key, hash, loadingValueReference);
          return null;
        } else {
          removeEntry(e, hash, RemovalCause.EXPLICIT);
          return null;
        }
      } finally {
        unlock();
        postWriteCleanup();
      }
    }

    // at most one of loadSync/loadAsync may be called for any given LoadingValueReference

    V loadSync(
        K key,
        int hash,
        LoadingValueReference<K, V> loadingValueReference,
        CacheLoader<? super K, V> loader)
        throws ExecutionException {
      ListenableFuture<V> loadingFuture = loadingValueReference.loadFuture(key, loader);
      return getAndRecordStats(key, hash, loadingValueReference, loadingFuture);
    }

    ListenableFuture<V> loadAsync(
        final K key,
        final int hash,
        final LoadingValueReference<K, V> loadingValueReference,
        CacheLoader<? super K, V> loader) {
      final ListenableFuture<V> loadingFuture = loadingValueReference.loadFuture(key, loader);
      loadingFuture.addListener(
          new Runnable() {
            @Override
            public void run() {
              try {
                getAndRecordStats(key, hash, loadingValueReference, loadingFuture);
              } catch (Throwable t) {
                logger.log(Level.WARNING, "Exception thrown during refresh", t);
                loadingValueReference.setException(t);
              }
            }
          },
          directExecutor());
      return loadingFuture;
    }

    
Waits uninterruptibly for newValue to be loaded, and then records loading stats. /** Waits uninterruptibly for {@code newValue} to be loaded, and then records loading stats. */
    V getAndRecordStats(
        K key,
        int hash,
        LoadingValueReference<K, V> loadingValueReference,
        ListenableFuture<V> newValue)
        throws ExecutionException {
      V value = null;
      try {
        value = getUninterruptibly(newValue);
        if (value == null) {
          throw new InvalidCacheLoadException("CacheLoader returned null for key " + key + ".");
        }
        statsCounter.recordLoadSuccess(loadingValueReference.elapsedNanos());
        storeLoadedValue(key, hash, loadingValueReference, value);
        return value;
      } finally {
        if (value == null) {
          statsCounter.recordLoadException(loadingValueReference.elapsedNanos());
          removeLoadingValue(key, hash, loadingValueReference);
        }
      }
    }

    V scheduleRefresh(
        ReferenceEntry<K, V> entry,
        K key,
        int hash,
        V oldValue,
        long now,
        CacheLoader<? super K, V> loader) {
      if (map.refreshes()
          && (now - entry.getWriteTime() > map.refreshNanos)
          && !entry.getValueReference().isLoading()) {
        V newValue = refresh(key, hash, loader, true);
        if (newValue != null) {
          return newValue;
        }
      }
      return oldValue;
    }

    
Refreshes the value associated with key, unless another thread is already doing so. Returns the newly refreshed value associated with key if it was refreshed inline, or null if another thread is performing the refresh or if an error occurs during refresh. /**
     * Refreshes the value associated with {@code key}, unless another thread is already doing so.
     * Returns the newly refreshed value associated with {@code key} if it was refreshed inline, or
     * {@code null} if another thread is performing the refresh or if an error occurs during
     * refresh.
     */
    @Nullable
    V refresh(K key, int hash, CacheLoader<? super K, V> loader, boolean checkTime) {
      final LoadingValueReference<K, V> loadingValueReference =
          insertLoadingValueReference(key, hash, checkTime);
      if (loadingValueReference == null) {
        return null;
      }

      ListenableFuture<V> result = loadAsync(key, hash, loadingValueReference, loader);
      if (result.isDone()) {
        try {
          return Uninterruptibles.getUninterruptibly(result);
        } catch (Throwable t) {
          // don't let refresh exceptions propagate; error was already logged
        }
      }
      return null;
    }

    
Returns a newly inserted LoadingValueReference, or null if the live value reference is already loading. /**
     * Returns a newly inserted {@code LoadingValueReference}, or null if the live value reference
     * is already loading.
     */
    @Nullable
    LoadingValueReference<K, V> insertLoadingValueReference(
        final K key, final int hash, boolean checkTime) {
      ReferenceEntry<K, V> e = null;
      lock();
      try {
        long now = map.ticker.read();
        preWriteCleanup(now);

        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        // Look for an existing entry.
        for (e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            // We found an existing entry.

            ValueReference<K, V> valueReference = e.getValueReference();
            if (valueReference.isLoading()
                || (checkTime && (now - e.getWriteTime() < map.refreshNanos))) {
              // refresh is a no-op if loading is pending
              // if checkTime, we want to check *after* acquiring the lock if refresh still needs
              // to be scheduled
              return null;
            }

            // continue returning old value while loading
            ++modCount;
            LoadingValueReference<K, V> loadingValueReference =
                new LoadingValueReference<>(valueReference);
            e.setValueReference(loadingValueReference);
            return loadingValueReference;
          }
        }

        ++modCount;
        LoadingValueReference<K, V> loadingValueReference = new LoadingValueReference<>();
        e = newEntry(key, hash, first);
        e.setValueReference(loadingValueReference);
        table.set(index, e);
        return loadingValueReference;
      } finally {
        unlock();
        postWriteCleanup();
      }
    }

    // reference queues, for garbage collection cleanup

    
Cleanup collected entries when the lock is available. /** Cleanup collected entries when the lock is available. */
    void tryDrainReferenceQueues() {
      if (tryLock()) {
        try {
          drainReferenceQueues();
        } finally {
          unlock();
        }
      }
    }

    
Drain the key and value reference queues, cleaning up internal entries containing garbage
collected keys or values.
/**
     * Drain the key and value reference queues, cleaning up internal entries containing garbage
     * collected keys or values.
     */
    @GuardedBy("this")
    void drainReferenceQueues() {
      if (map.usesKeyReferences()) {
        drainKeyReferenceQueue();
      }
      if (map.usesValueReferences()) {
        drainValueReferenceQueue();
      }
    }

    @GuardedBy("this")
    void drainKeyReferenceQueue() {
      Reference<? extends K> ref;
      int i = 0;
      while ((ref = keyReferenceQueue.poll()) != null) {
        @SuppressWarnings("unchecked")
        ReferenceEntry<K, V> entry = (ReferenceEntry<K, V>) ref;
        map.reclaimKey(entry);
        if (++i == DRAIN_MAX) {
          break;
        }
      }
    }

    @GuardedBy("this")
    void drainValueReferenceQueue() {
      Reference<? extends V> ref;
      int i = 0;
      while ((ref = valueReferenceQueue.poll()) != null) {
        @SuppressWarnings("unchecked")
        ValueReference<K, V> valueReference = (ValueReference<K, V>) ref;
        map.reclaimValue(valueReference);
        if (++i == DRAIN_MAX) {
          break;
        }
      }
    }

    
Clears all entries from the key and value reference queues. /** Clears all entries from the key and value reference queues. */
    void clearReferenceQueues() {
      if (map.usesKeyReferences()) {
        clearKeyReferenceQueue();
      }
      if (map.usesValueReferences()) {
        clearValueReferenceQueue();
      }
    }

    void clearKeyReferenceQueue() {
      while (keyReferenceQueue.poll() != null) {}
    }

    void clearValueReferenceQueue() {
      while (valueReferenceQueue.poll() != null) {}
    }

    // recency queue, shared by expiration and eviction

    
Records the relative order in which this read was performed by adding entry to the recency queue. At write-time, or when the queue is full past the threshold, the queue will be drained and the entries therein processed. 
Note: locked reads should use recordLockedRead. /**
     * Records the relative order in which this read was performed by adding {@code entry} to the
     * recency queue. At write-time, or when the queue is full past the threshold, the queue will be
     * drained and the entries therein processed.
     *
     * <p>Note: locked reads should use {@link #recordLockedRead}.
     */
    void recordRead(ReferenceEntry<K, V> entry, long now) {
      if (map.recordsAccess()) {
        entry.setAccessTime(now);
      }
      recencyQueue.add(entry);
    }

    
Updates the eviction metadata that entry was just read. This currently amounts to adding entry to relevant eviction lists. 
Note: this method should only be called under lock, as it directly manipulates the eviction queues. Unlocked reads should use recordRead. /**
     * Updates the eviction metadata that {@code entry} was just read. This currently amounts to
     * adding {@code entry} to relevant eviction lists.
     *
     * <p>Note: this method should only be called under lock, as it directly manipulates the
     * eviction queues. Unlocked reads should use {@link #recordRead}.
     */
    @GuardedBy("this")
    void recordLockedRead(ReferenceEntry<K, V> entry, long now) {
      if (map.recordsAccess()) {
        entry.setAccessTime(now);
      }
      accessQueue.add(entry);
    }

    
Updates eviction metadata that entry was just written. This currently amounts to adding entry to relevant eviction lists. /**
     * Updates eviction metadata that {@code entry} was just written. This currently amounts to
     * adding {@code entry} to relevant eviction lists.
     */
    @GuardedBy("this")
    void recordWrite(ReferenceEntry<K, V> entry, int weight, long now) {
      // we are already under lock, so drain the recency queue immediately
      drainRecencyQueue();
      totalWeight += weight;

      if (map.recordsAccess()) {
        entry.setAccessTime(now);
      }
      if (map.recordsWrite()) {
        entry.setWriteTime(now);
      }
      accessQueue.add(entry);
      writeQueue.add(entry);
    }

    
Drains the recency queue, updating eviction metadata that the entries therein were read in
the specified relative order. This currently amounts to adding them to relevant eviction
lists (accounting for the fact that they could have been removed from the map since being
added to the recency queue).
/**
     * Drains the recency queue, updating eviction metadata that the entries therein were read in
     * the specified relative order. This currently amounts to adding them to relevant eviction
     * lists (accounting for the fact that they could have been removed from the map since being
     * added to the recency queue).
     */
    @GuardedBy("this")
    void drainRecencyQueue() {
      ReferenceEntry<K, V> e;
      while ((e = recencyQueue.poll()) != null) {
        // An entry may be in the recency queue despite it being removed from
        // the map . This can occur when the entry was concurrently read while a
        // writer is removing it from the segment or after a clear has removed
        // all of the segment's entries.
        if (accessQueue.contains(e)) {
          accessQueue.add(e);
        }
      }
    }

    // expiration

    
Cleanup expired entries when the lock is available. /** Cleanup expired entries when the lock is available. */
    void tryExpireEntries(long now) {
      if (tryLock()) {
        try {
          expireEntries(now);
        } finally {
          unlock();
          // don't call postWriteCleanup as we're in a read
        }
      }
    }

    @GuardedBy("this")
    void expireEntries(long now) {
      drainRecencyQueue();

      ReferenceEntry<K, V> e;
      while ((e = writeQueue.peek()) != null && map.isExpired(e, now)) {
        if (!removeEntry(e, e.getHash(), RemovalCause.EXPIRED)) {
          throw new AssertionError();
        }
      }
      while ((e = accessQueue.peek()) != null && map.isExpired(e, now)) {
        if (!removeEntry(e, e.getHash(), RemovalCause.EXPIRED)) {
          throw new AssertionError();
        }
      }
    }

    // eviction

    @GuardedBy("this")
    void enqueueNotification(
        @Nullable K key, int hash, @Nullable V value, int weight, RemovalCause cause) {
      totalWeight -= weight;
      if (cause.wasEvicted()) {
        statsCounter.recordEviction();
      }
      if (map.removalNotificationQueue != DISCARDING_QUEUE) {
        RemovalNotification<K, V> notification = RemovalNotification.create(key, value, cause);
        map.removalNotificationQueue.offer(notification);
      }
    }

    
Performs eviction if the segment is over capacity. Avoids flushing the entire cache if the
newest entry exceeds the maximum weight all on its own.
Params:
newest – the most recently added entry/**
     * Performs eviction if the segment is over capacity. Avoids flushing the entire cache if the
     * newest entry exceeds the maximum weight all on its own.
     *
     * @param newest the most recently added entry
     */
    @GuardedBy("this")
    void evictEntries(ReferenceEntry<K, V> newest) {
      if (!map.evictsBySize()) {
        return;
      }

      drainRecencyQueue();

      // If the newest entry by itself is too heavy for the segment, don't bother evicting
      // anything else, just that
      if (newest.getValueReference().getWeight() > maxSegmentWeight) {
        if (!removeEntry(newest, newest.getHash(), RemovalCause.SIZE)) {
          throw new AssertionError();
        }
      }

      while (totalWeight > maxSegmentWeight) {
        ReferenceEntry<K, V> e = getNextEvictable();
        if (!removeEntry(e, e.getHash(), RemovalCause.SIZE)) {
          throw new AssertionError();
        }
      }
    }

    // TODO(fry): instead implement this with an eviction head
    @GuardedBy("this")
    ReferenceEntry<K, V> getNextEvictable() {
      for (ReferenceEntry<K, V> e : accessQueue) {
        int weight = e.getValueReference().getWeight();
        if (weight > 0) {
          return e;
        }
      }
      throw new AssertionError();
    }

    
Returns first entry of bin for given hash. /** Returns first entry of bin for given hash. */
    ReferenceEntry<K, V> getFirst(int hash) {
      // read this volatile field only once
      AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
      return table.get(hash & (table.length() - 1));
    }

    // Specialized implementations of map methods

    @Nullable
    ReferenceEntry<K, V> getEntry(Object key, int hash) {
      for (ReferenceEntry<K, V> e = getFirst(hash); e != null; e = e.getNext()) {
        if (e.getHash() != hash) {
          continue;
        }

        K entryKey = e.getKey();
        if (entryKey == null) {
          tryDrainReferenceQueues();
          continue;
        }

        if (map.keyEquivalence.equivalent(key, entryKey)) {
          return e;
        }
      }

      return null;
    }

    @Nullable
    ReferenceEntry<K, V> getLiveEntry(Object key, int hash, long now) {
      ReferenceEntry<K, V> e = getEntry(key, hash);
      if (e == null) {
        return null;
      } else if (map.isExpired(e, now)) {
        tryExpireEntries(now);
        return null;
      }
      return e;
    }

    
Gets the value from an entry. Returns null if the entry is invalid, partially-collected,
loading, or expired.
/**
     * Gets the value from an entry. Returns null if the entry is invalid, partially-collected,
     * loading, or expired.
     */
    V getLiveValue(ReferenceEntry<K, V> entry, long now) {
      if (entry.getKey() == null) {
        tryDrainReferenceQueues();
        return null;
      }
      V value = entry.getValueReference().get();
      if (value == null) {
        tryDrainReferenceQueues();
        return null;
      }

      if (map.isExpired(entry, now)) {
        tryExpireEntries(now);
        return null;
      }
      return value;
    }

    boolean containsKey(Object key, int hash) {
      try {
        if (count != 0) { // read-volatile
          long now = map.ticker.read();
          ReferenceEntry<K, V> e = getLiveEntry(key, hash, now);
          if (e == null) {
            return false;
          }
          return e.getValueReference().get() != null;
        }

        return false;
      } finally {
        postReadCleanup();
      }
    }

    
This method is a convenience for testing. Code should call LocalCache.containsValue directly. /**
     * This method is a convenience for testing. Code should call {@link LocalCache#containsValue}
     * directly.
     */
    @VisibleForTesting
    boolean containsValue(Object value) {
      try {
        if (count != 0) { // read-volatile
          long now = map.ticker.read();
          AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
          int length = table.length();
          for (int i = 0; i < length; ++i) {
            for (ReferenceEntry<K, V> e = table.get(i); e != null; e = e.getNext()) {
              V entryValue = getLiveValue(e, now);
              if (entryValue == null) {
                continue;
              }
              if (map.valueEquivalence.equivalent(value, entryValue)) {
                return true;
              }
            }
          }
        }

        return false;
      } finally {
        postReadCleanup();
      }
    }

    @Nullable
    V put(K key, int hash, V value, boolean onlyIfAbsent) {
      lock();
      try {
        long now = map.ticker.read();
        preWriteCleanup(now);

        int newCount = this.count + 1;
        if (newCount > this.threshold) { // ensure capacity
          expand();
          newCount = this.count + 1;
        }

        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        // Look for an existing entry.
        for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            // We found an existing entry.

            ValueReference<K, V> valueReference = e.getValueReference();
            V entryValue = valueReference.get();

            if (entryValue == null) {
              ++modCount;
              if (valueReference.isActive()) {
                enqueueNotification(
                    key, hash, entryValue, valueReference.getWeight(), RemovalCause.COLLECTED);
                setValue(e, key, value, now);
                newCount = this.count; // count remains unchanged
              } else {
                setValue(e, key, value, now);
                newCount = this.count + 1;
              }
              this.count = newCount; // write-volatile
              evictEntries(e);
              return null;
            } else if (onlyIfAbsent) {
              // Mimic
              // "if (!map.containsKey(key)) ...
              // else return map.get(key);
              recordLockedRead(e, now);
              return entryValue;
            } else {
              // clobber existing entry, count remains unchanged
              ++modCount;
              enqueueNotification(
                  key, hash, entryValue, valueReference.getWeight(), RemovalCause.REPLACED);
              setValue(e, key, value, now);
              evictEntries(e);
              return entryValue;
            }
          }
        }

        // Create a new entry.
        ++modCount;
        ReferenceEntry<K, V> newEntry = newEntry(key, hash, first);
        setValue(newEntry, key, value, now);
        table.set(index, newEntry);
        newCount = this.count + 1;
        this.count = newCount; // write-volatile
        evictEntries(newEntry);
        return null;
      } finally {
        unlock();
        postWriteCleanup();
      }
    }

    
Expands the table if possible. /** Expands the table if possible. */
    @GuardedBy("this")
    void expand() {
      AtomicReferenceArray<ReferenceEntry<K, V>> oldTable = table;
      int oldCapacity = oldTable.length();
      if (oldCapacity >= MAXIMUM_CAPACITY) {
        return;
      }

      /*
       * Reclassify nodes in each list to new Map. Because we are using power-of-two expansion, the
       * elements from each bin must either stay at same index, or move with a power of two offset.
       * We eliminate unnecessary node creation by catching cases where old nodes can be reused
       * because their next fields won't change. Statistically, at the default threshold, only about
       * one-sixth of them need cloning when a table doubles. The nodes they replace will be garbage
       * collectable as soon as they are no longer referenced by any reader thread that may be in
       * the midst of traversing table right now.
       */

      int newCount = count;
      AtomicReferenceArray<ReferenceEntry<K, V>> newTable = newEntryArray(oldCapacity << 1);
      threshold = newTable.length() * 3 / 4;
      int newMask = newTable.length() - 1;
      for (int oldIndex = 0; oldIndex < oldCapacity; ++oldIndex) {
        // We need to guarantee that any existing reads of old Map can
        // proceed. So we cannot yet null out each bin.
        ReferenceEntry<K, V> head = oldTable.get(oldIndex);

        if (head != null) {
          ReferenceEntry<K, V> next = head.getNext();
          int headIndex = head.getHash() & newMask;

          // Single node on list
          if (next == null) {
            newTable.set(headIndex, head);
          } else {
            // Reuse the consecutive sequence of nodes with the same target
            // index from the end of the list. tail points to the first
            // entry in the reusable list.
            ReferenceEntry<K, V> tail = head;
            int tailIndex = headIndex;
            for (ReferenceEntry<K, V> e = next; e != null; e = e.getNext()) {
              int newIndex = e.getHash() & newMask;
              if (newIndex != tailIndex) {
                // The index changed. We'll need to copy the previous entry.
                tailIndex = newIndex;
                tail = e;
              }
            }
            newTable.set(tailIndex, tail);

            // Clone nodes leading up to the tail.
            for (ReferenceEntry<K, V> e = head; e != tail; e = e.getNext()) {
              int newIndex = e.getHash() & newMask;
              ReferenceEntry<K, V> newNext = newTable.get(newIndex);
              ReferenceEntry<K, V> newFirst = copyEntry(e, newNext);
              if (newFirst != null) {
                newTable.set(newIndex, newFirst);
              } else {
                removeCollectedEntry(e);
                newCount--;
              }
            }
          }
        }
      }
      table = newTable;
      this.count = newCount;
    }

    boolean replace(K key, int hash, V oldValue, V newValue) {
      lock();
      try {
        long now = map.ticker.read();
        preWriteCleanup(now);

        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            ValueReference<K, V> valueReference = e.getValueReference();
            V entryValue = valueReference.get();
            if (entryValue == null) {
              if (valueReference.isActive()) {
                // If the value disappeared, this entry is partially collected.
                int newCount = this.count - 1;
                ++modCount;
                ReferenceEntry<K, V> newFirst =
                    removeValueFromChain(
                        first,
                        e,
                        entryKey,
                        hash,
                        entryValue,
                        valueReference,
                        RemovalCause.COLLECTED);
                newCount = this.count - 1;
                table.set(index, newFirst);
                this.count = newCount; // write-volatile
              }
              return false;
            }

            if (map.valueEquivalence.equivalent(oldValue, entryValue)) {
              ++modCount;
              enqueueNotification(
                  key, hash, entryValue, valueReference.getWeight(), RemovalCause.REPLACED);
              setValue(e, key, newValue, now);
              evictEntries(e);
              return true;
            } else {
              // Mimic
              // "if (map.containsKey(key) && map.get(key).equals(oldValue))..."
              recordLockedRead(e, now);
              return false;
            }
          }
        }

        return false;
      } finally {
        unlock();
        postWriteCleanup();
      }
    }

    @Nullable
    V replace(K key, int hash, V newValue) {
      lock();
      try {
        long now = map.ticker.read();
        preWriteCleanup(now);

        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            ValueReference<K, V> valueReference = e.getValueReference();
            V entryValue = valueReference.get();
            if (entryValue == null) {
              if (valueReference.isActive()) {
                // If the value disappeared, this entry is partially collected.
                int newCount = this.count - 1;
                ++modCount;
                ReferenceEntry<K, V> newFirst =
                    removeValueFromChain(
                        first,
                        e,
                        entryKey,
                        hash,
                        entryValue,
                        valueReference,
                        RemovalCause.COLLECTED);
                newCount = this.count - 1;
                table.set(index, newFirst);
                this.count = newCount; // write-volatile
              }
              return null;
            }

            ++modCount;
            enqueueNotification(
                key, hash, entryValue, valueReference.getWeight(), RemovalCause.REPLACED);
            setValue(e, key, newValue, now);
            evictEntries(e);
            return entryValue;
          }
        }

        return null;
      } finally {
        unlock();
        postWriteCleanup();
      }
    }

    @Nullable
    V remove(Object key, int hash) {
      lock();
      try {
        long now = map.ticker.read();
        preWriteCleanup(now);

        int newCount = this.count - 1;
        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            ValueReference<K, V> valueReference = e.getValueReference();
            V entryValue = valueReference.get();

            RemovalCause cause;
            if (entryValue != null) {
              cause = RemovalCause.EXPLICIT;
            } else if (valueReference.isActive()) {
              cause = RemovalCause.COLLECTED;
            } else {
              // currently loading
              return null;
            }

            ++modCount;
            ReferenceEntry<K, V> newFirst =
                removeValueFromChain(first, e, entryKey, hash, entryValue, valueReference, cause);
            newCount = this.count - 1;
            table.set(index, newFirst);
            this.count = newCount; // write-volatile
            return entryValue;
          }
        }

        return null;
      } finally {
        unlock();
        postWriteCleanup();
      }
    }

    boolean remove(Object key, int hash, Object value) {
      lock();
      try {
        long now = map.ticker.read();
        preWriteCleanup(now);

        int newCount = this.count - 1;
        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            ValueReference<K, V> valueReference = e.getValueReference();
            V entryValue = valueReference.get();

            RemovalCause cause;
            if (map.valueEquivalence.equivalent(value, entryValue)) {
              cause = RemovalCause.EXPLICIT;
            } else if (entryValue == null && valueReference.isActive()) {
              cause = RemovalCause.COLLECTED;
            } else {
              // currently loading
              return false;
            }

            ++modCount;
            ReferenceEntry<K, V> newFirst =
                removeValueFromChain(first, e, entryKey, hash, entryValue, valueReference, cause);
            newCount = this.count - 1;
            table.set(index, newFirst);
            this.count = newCount; // write-volatile
            return (cause == RemovalCause.EXPLICIT);
          }
        }

        return false;
      } finally {
        unlock();
        postWriteCleanup();
      }
    }

    boolean storeLoadedValue(
        K key, int hash, LoadingValueReference<K, V> oldValueReference, V newValue) {
      lock();
      try {
        long now = map.ticker.read();
        preWriteCleanup(now);

        int newCount = this.count + 1;
        if (newCount > this.threshold) { // ensure capacity
          expand();
          newCount = this.count + 1;
        }

        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            ValueReference<K, V> valueReference = e.getValueReference();
            V entryValue = valueReference.get();
            // replace the old LoadingValueReference if it's live, otherwise
            // perform a putIfAbsent
            if (oldValueReference == valueReference
                || (entryValue == null && valueReference != UNSET)) {
              ++modCount;
              if (oldValueReference.isActive()) {
                RemovalCause cause =
                    (entryValue == null) ? RemovalCause.COLLECTED : RemovalCause.REPLACED;
                enqueueNotification(key, hash, entryValue, oldValueReference.getWeight(), cause);
                newCount--;
              }
              setValue(e, key, newValue, now);
              this.count = newCount; // write-volatile
              evictEntries(e);
              return true;
            }

            // the loaded value was already clobbered
            enqueueNotification(key, hash, newValue, 0, RemovalCause.REPLACED);
            return false;
          }
        }

        ++modCount;
        ReferenceEntry<K, V> newEntry = newEntry(key, hash, first);
        setValue(newEntry, key, newValue, now);
        table.set(index, newEntry);
        this.count = newCount; // write-volatile
        evictEntries(newEntry);
        return true;
      } finally {
        unlock();
        postWriteCleanup();
      }
    }

    void clear() {
      if (count != 0) { // read-volatile
        lock();
        try {
          long now = map.ticker.read();
          preWriteCleanup(now);

          AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
          for (int i = 0; i < table.length(); ++i) {
            for (ReferenceEntry<K, V> e = table.get(i); e != null; e = e.getNext()) {
              // Loading references aren't actually in the map yet.
              if (e.getValueReference().isActive()) {
                K key = e.getKey();
                V value = e.getValueReference().get();
                RemovalCause cause =
                    (key == null || value == null) ? RemovalCause.COLLECTED : RemovalCause.EXPLICIT;
                enqueueNotification(
                    key, e.getHash(), value, e.getValueReference().getWeight(), cause);
              }
            }
          }
          for (int i = 0; i < table.length(); ++i) {
            table.set(i, null);
          }
          clearReferenceQueues();
          writeQueue.clear();
          accessQueue.clear();
          readCount.set(0);

          ++modCount;
          count = 0; // write-volatile
        } finally {
          unlock();
          postWriteCleanup();
        }
      }
    }

    @GuardedBy("this")
    @Nullable
    ReferenceEntry<K, V> removeValueFromChain(
        ReferenceEntry<K, V> first,
        ReferenceEntry<K, V> entry,
        @Nullable K key,
        int hash,
        V value,
        ValueReference<K, V> valueReference,
        RemovalCause cause) {
      enqueueNotification(key, hash, value, valueReference.getWeight(), cause);
      writeQueue.remove(entry);
      accessQueue.remove(entry);

      if (valueReference.isLoading()) {
        valueReference.notifyNewValue(null);
        return first;
      } else {
        return removeEntryFromChain(first, entry);
      }
    }

    @GuardedBy("this")
    @Nullable
    ReferenceEntry<K, V> removeEntryFromChain(
        ReferenceEntry<K, V> first, ReferenceEntry<K, V> entry) {
      int newCount = count;
      ReferenceEntry<K, V> newFirst = entry.getNext();
      for (ReferenceEntry<K, V> e = first; e != entry; e = e.getNext()) {
        ReferenceEntry<K, V> next = copyEntry(e, newFirst);
        if (next != null) {
          newFirst = next;
        } else {
          removeCollectedEntry(e);
          newCount--;
        }
      }
      this.count = newCount;
      return newFirst;
    }

    @GuardedBy("this")
    void removeCollectedEntry(ReferenceEntry<K, V> entry) {
      enqueueNotification(
          entry.getKey(),
          entry.getHash(),
          entry.getValueReference().get(),
          entry.getValueReference().getWeight(),
          RemovalCause.COLLECTED);
      writeQueue.remove(entry);
      accessQueue.remove(entry);
    }

    
Removes an entry whose key has been garbage collected. /** Removes an entry whose key has been garbage collected. */
    boolean reclaimKey(ReferenceEntry<K, V> entry, int hash) {
      lock();
      try {
        int newCount = count - 1;
        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) {
          if (e == entry) {
            ++modCount;
            ReferenceEntry<K, V> newFirst =
                removeValueFromChain(
                    first,
                    e,
                    e.getKey(),
                    hash,
                    e.getValueReference().get(),
                    e.getValueReference(),
                    RemovalCause.COLLECTED);
            newCount = this.count - 1;
            table.set(index, newFirst);
            this.count = newCount; // write-volatile
            return true;
          }
        }

        return false;
      } finally {
        unlock();
        postWriteCleanup();
      }
    }

    
Removes an entry whose value has been garbage collected. /** Removes an entry whose value has been garbage collected. */
    boolean reclaimValue(K key, int hash, ValueReference<K, V> valueReference) {
      lock();
      try {
        int newCount = this.count - 1;
        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            ValueReference<K, V> v = e.getValueReference();
            if (v == valueReference) {
              ++modCount;
              ReferenceEntry<K, V> newFirst =
                  removeValueFromChain(
                      first,
                      e,
                      entryKey,
                      hash,
                      valueReference.get(),
                      valueReference,
                      RemovalCause.COLLECTED);
              newCount = this.count - 1;
              table.set(index, newFirst);
              this.count = newCount; // write-volatile
              return true;
            }
            return false;
          }
        }

        return false;
      } finally {
        unlock();
        if (!isHeldByCurrentThread()) { // don't cleanup inside of put
          postWriteCleanup();
        }
      }
    }

    boolean removeLoadingValue(K key, int hash, LoadingValueReference<K, V> valueReference) {
      lock();
      try {
        AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
        int index = hash & (table.length() - 1);
        ReferenceEntry<K, V> first = table.get(index);

        for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) {
          K entryKey = e.getKey();
          if (e.getHash() == hash
              && entryKey != null
              && map.keyEquivalence.equivalent(key, entryKey)) {
            ValueReference<K, V> v = e.getValueReference();
            if (v == valueReference) {
              if (valueReference.isActive()) {
                e.setValueReference(valueReference.getOldValue());
              } else {
                ReferenceEntry<K, V> newFirst = removeEntryFromChain(first, e);
                table.set(index, newFirst);
              }
              return true;
            }
            return false;
          }
        }

        return false;
      } finally {
        unlock();
        postWriteCleanup();
      }
    }

    @VisibleForTesting
    @GuardedBy("this")
    boolean removeEntry(ReferenceEntry<K, V> entry, int hash, RemovalCause cause) {
      int newCount = this.count - 1;
      AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table;
      int index = hash & (table.length() - 1);
      ReferenceEntry<K, V> first = table.get(index);

      for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) {
        if (e == entry) {
          ++modCount;
          ReferenceEntry<K, V> newFirst =
              removeValueFromChain(
                  first,
                  e,
                  e.getKey(),
                  hash,
                  e.getValueReference().get(),
                  e.getValueReference(),
                  cause);
          newCount = this.count - 1;
          table.set(index, newFirst);
          this.count = newCount; // write-volatile
          return true;
        }
      }

      return false;
    }

    
Performs routine cleanup following a read. Normally cleanup happens during writes. If cleanup
is not observed after a sufficient number of reads, try cleaning up from the read thread.
/**
     * Performs routine cleanup following a read. Normally cleanup happens during writes. If cleanup
     * is not observed after a sufficient number of reads, try cleaning up from the read thread.
     */
    void postReadCleanup() {
      if ((readCount.incrementAndGet() & DRAIN_THRESHOLD) == 0) {
        cleanUp();
      }
    }

    
Performs routine cleanup prior to executing a write. This should be called every time a write
thread acquires the segment lock, immediately after acquiring the lock.
Post-condition: expireEntries has been run.
/**
     * Performs routine cleanup prior to executing a write. This should be called every time a write
     * thread acquires the segment lock, immediately after acquiring the lock.
     *
     * <p>Post-condition: expireEntries has been run.
     */
    @GuardedBy("this")
    void preWriteCleanup(long now) {
      runLockedCleanup(now);
    }

    
Performs routine cleanup following a write. /** Performs routine cleanup following a write. */
    void postWriteCleanup() {
      runUnlockedCleanup();
    }

    void cleanUp() {
      long now = map.ticker.read();
      runLockedCleanup(now);
      runUnlockedCleanup();
    }

    void runLockedCleanup(long now) {
      if (tryLock()) {
        try {
          drainReferenceQueues();
          expireEntries(now); // calls drainRecencyQueue
          readCount.set(0);
        } finally {
          unlock();
        }
      }
    }

    void runUnlockedCleanup() {
      // locked cleanup may generate notifications we can send unlocked
      if (!isHeldByCurrentThread()) {
        map.processPendingNotifications();
      }
    }
  }

  static class LoadingValueReference<K, V> implements ValueReference<K, V> {
    volatile ValueReference<K, V> oldValue;

    // TODO(fry): rename get, then extend AbstractFuture instead of containing SettableFuture
    final SettableFuture<V> futureValue = SettableFuture.create();
    final Stopwatch stopwatch = Stopwatch.createUnstarted();

    public LoadingValueReference() {
      this(null);
    }

    public LoadingValueReference(ValueReference<K, V> oldValue) {
      this.oldValue = (oldValue == null) ? LocalCache.<K, V>unset() : oldValue;
    }

    @Override
    public boolean isLoading() {
      return true;
    }

    @Override
    public boolean isActive() {
      return oldValue.isActive();
    }

    @Override
    public int getWeight() {
      return oldValue.getWeight();
    }

    public boolean set(@Nullable V newValue) {
      return futureValue.set(newValue);
    }

    public boolean setException(Throwable t) {
      return futureValue.setException(t);
    }

    private ListenableFuture<V> fullyFailedFuture(Throwable t) {
      return Futures.immediateFailedFuture(t);
    }

    @Override
    public void notifyNewValue(@Nullable V newValue) {
      if (newValue != null) {
        // The pending load was clobbered by a manual write.
        // Unblock all pending gets, and have them return the new value.
        set(newValue);
      } else {
        // The pending load was removed. Delay notifications until loading completes.
        oldValue = unset();
      }

      // TODO(fry): could also cancel loading if we had a handle on its future
    }

    public ListenableFuture<V> loadFuture(K key, CacheLoader<? super K, V> loader) {
      try {
        stopwatch.start();
        V previousValue = oldValue.get();
        if (previousValue == null) {
          V newValue = loader.load(key);
          return set(newValue) ? futureValue : Futures.immediateFuture(newValue);
        }
        ListenableFuture<V> newValue = loader.reload(key, previousValue);
        if (newValue == null) {
          return Futures.immediateFuture(null);
        }
        // To avoid a race, make sure the refreshed value is set into loadingValueReference
        // *before* returning newValue from the cache query.
        return transform(
            newValue,
            new com.google.common.base.Function<V, V>() {
              @Override
              public V apply(V newValue) {
                LoadingValueReference.this.set(newValue);
                return newValue;
              }
            },
            directExecutor());
      } catch (Throwable t) {
        ListenableFuture<V> result = setException(t) ? futureValue : fullyFailedFuture(t);
        if (t instanceof InterruptedException) {
          Thread.currentThread().interrupt();
        }
        return result;
      }
    }

    public V compute(K key, BiFunction<? super K, ? super V, ? extends V> function) {
      stopwatch.start();
      V previousValue;
      try {
        previousValue = oldValue.waitForValue();
      } catch (ExecutionException e) {
        previousValue = null;
      }
      V newValue;
      try {
         newValue = function.apply(key, previousValue);
      } catch (Throwable th) {
         this.setException(th);
         throw th;
      }
      this.set(newValue);
      return newValue;
    }

    public long elapsedNanos() {
      return stopwatch.elapsed(NANOSECONDS);
    }

    @Override
    public V waitForValue() throws ExecutionException {
      return getUninterruptibly(futureValue);
    }

    @Override
    public V get() {
      return oldValue.get();
    }

    public ValueReference<K, V> getOldValue() {
      return oldValue;
    }

    @Override
    public ReferenceEntry<K, V> getEntry() {
      return null;
    }

    @Override
    public ValueReference<K, V> copyFor(
        ReferenceQueue<V> queue, @Nullable V value, ReferenceEntry<K, V> entry) {
      return this;
    }
  }

  // Queues

  
A custom queue for managing eviction order. Note that this is tightly integrated with 
ReferenceEntry, upon which it relies to perform its linking. 
Note that this entire implementation makes the assumption that all elements which are in the
map are also in this queue, and that all elements not in the queue are not in the map.
The benefits of creating our own queue are that (1) we can replace elements in the middle of
the queue as part of copyWriteEntry, and (2) the contains method is highly optimized for the
current model.
/**
   * A custom queue for managing eviction order. Note that this is tightly integrated with {@code
   * ReferenceEntry}, upon which it relies to perform its linking.
   *
   * <p>Note that this entire implementation makes the assumption that all elements which are in the
   * map are also in this queue, and that all elements not in the queue are not in the map.
   *
   * <p>The benefits of creating our own queue are that (1) we can replace elements in the middle of
   * the queue as part of copyWriteEntry, and (2) the contains method is highly optimized for the
   * current model.
   */
  static final class WriteQueue<K, V> extends AbstractQueue<ReferenceEntry<K, V>> {
    final ReferenceEntry<K, V> head =
        new AbstractReferenceEntry<K, V>() {

          @Override
          public long getWriteTime() {
            return Long.MAX_VALUE;
          }

          @Override
          public void setWriteTime(long time) {}

          ReferenceEntry<K, V> nextWrite = this;

          @Override
          public ReferenceEntry<K, V> getNextInWriteQueue() {
            return nextWrite;
          }

          @Override
          public void setNextInWriteQueue(ReferenceEntry<K, V> next) {
            this.nextWrite = next;
          }

          ReferenceEntry<K, V> previousWrite = this;

          @Override
          public ReferenceEntry<K, V> getPreviousInWriteQueue() {
            return previousWrite;
          }

          @Override
          public void setPreviousInWriteQueue(ReferenceEntry<K, V> previous) {
            this.previousWrite = previous;
          }
        };

    // implements Queue

    @Override
    public boolean offer(ReferenceEntry<K, V> entry) {
      // unlink
      connectWriteOrder(entry.getPreviousInWriteQueue(), entry.getNextInWriteQueue());

      // add to tail
      connectWriteOrder(head.getPreviousInWriteQueue(), entry);
      connectWriteOrder(entry, head);

      return true;
    }

    @Override
    public ReferenceEntry<K, V> peek() {
      ReferenceEntry<K, V> next = head.getNextInWriteQueue();
      return (next == head) ? null : next;
    }

    @Override
    public ReferenceEntry<K, V> poll() {
      ReferenceEntry<K, V> next = head.getNextInWriteQueue();
      if (next == head) {
        return null;
      }

      remove(next);
      return next;
    }

    @Override
    @SuppressWarnings("unchecked")
    public boolean remove(Object o) {
      ReferenceEntry<K, V> e = (ReferenceEntry) o;
      ReferenceEntry<K, V> previous = e.getPreviousInWriteQueue();
      ReferenceEntry<K, V> next = e.getNextInWriteQueue();
      connectWriteOrder(previous, next);
      nullifyWriteOrder(e);

      return next != NullEntry.INSTANCE;
    }

    @Override
    @SuppressWarnings("unchecked")
    public boolean contains(Object o) {
      ReferenceEntry<K, V> e = (ReferenceEntry) o;
      return e.getNextInWriteQueue() != NullEntry.INSTANCE;
    }

    @Override
    public boolean isEmpty() {
      return head.getNextInWriteQueue() == head;
    }

    @Override
    public int size() {
      int size = 0;
      for (ReferenceEntry<K, V> e = head.getNextInWriteQueue();
          e != head;
          e = e.getNextInWriteQueue()) {
        size++;
      }
      return size;
    }

    @Override
    public void clear() {
      ReferenceEntry<K, V> e = head.getNextInWriteQueue();
      while (e != head) {
        ReferenceEntry<K, V> next = e.getNextInWriteQueue();
        nullifyWriteOrder(e);
        e = next;
      }

      head.setNextInWriteQueue(head);
      head.setPreviousInWriteQueue(head);
    }

    @Override
    public Iterator<ReferenceEntry<K, V>> iterator() {
      return new AbstractSequentialIterator<ReferenceEntry<K, V>>(peek()) {
        @Override
        protected ReferenceEntry<K, V> computeNext(ReferenceEntry<K, V> previous) {
          ReferenceEntry<K, V> next = previous.getNextInWriteQueue();
          return (next == head) ? null : next;
        }
      };
    }
  }

  
A custom queue for managing access order. Note that this is tightly integrated with 
ReferenceEntry, upon which it relies to perform its linking. 
Note that this entire implementation makes the assumption that all elements which are in the
map are also in this queue, and that all elements not in the queue are not in the map.
The benefits of creating our own queue are that (1) we can replace elements in the middle of
the queue as part of copyWriteEntry, and (2) the contains method is highly optimized for the
current model.
/**
   * A custom queue for managing access order. Note that this is tightly integrated with {@code
   * ReferenceEntry}, upon which it relies to perform its linking.
   *
   * <p>Note that this entire implementation makes the assumption that all elements which are in the
   * map are also in this queue, and that all elements not in the queue are not in the map.
   *
   * <p>The benefits of creating our own queue are that (1) we can replace elements in the middle of
   * the queue as part of copyWriteEntry, and (2) the contains method is highly optimized for the
   * current model.
   */
  static final class AccessQueue<K, V> extends AbstractQueue<ReferenceEntry<K, V>> {
    final ReferenceEntry<K, V> head =
        new AbstractReferenceEntry<K, V>() {

          @Override
          public long getAccessTime() {
            return Long.MAX_VALUE;
          }

          @Override
          public void setAccessTime(long time) {}

          ReferenceEntry<K, V> nextAccess = this;

          @Override
          public ReferenceEntry<K, V> getNextInAccessQueue() {
            return nextAccess;
          }

          @Override
          public void setNextInAccessQueue(ReferenceEntry<K, V> next) {
            this.nextAccess = next;
          }

          ReferenceEntry<K, V> previousAccess = this;

          @Override
          public ReferenceEntry<K, V> getPreviousInAccessQueue() {
            return previousAccess;
          }

          @Override
          public void setPreviousInAccessQueue(ReferenceEntry<K, V> previous) {
            this.previousAccess = previous;
          }
        };

    // implements Queue

    @Override
    public boolean offer(ReferenceEntry<K, V> entry) {
      // unlink
      connectAccessOrder(entry.getPreviousInAccessQueue(), entry.getNextInAccessQueue());

      // add to tail
      connectAccessOrder(head.getPreviousInAccessQueue(), entry);
      connectAccessOrder(entry, head);

      return true;
    }

    @Override
    public ReferenceEntry<K, V> peek() {
      ReferenceEntry<K, V> next = head.getNextInAccessQueue();
      return (next == head) ? null : next;
    }

    @Override
    public ReferenceEntry<K, V> poll() {
      ReferenceEntry<K, V> next = head.getNextInAccessQueue();
      if (next == head) {
        return null;
      }

      remove(next);
      return next;
    }

    @Override
    @SuppressWarnings("unchecked")
    public boolean remove(Object o) {
      ReferenceEntry<K, V> e = (ReferenceEntry) o;
      ReferenceEntry<K, V> previous = e.getPreviousInAccessQueue();
      ReferenceEntry<K, V> next = e.getNextInAccessQueue();
      connectAccessOrder(previous, next);
      nullifyAccessOrder(e);

      return next != NullEntry.INSTANCE;
    }

    @Override
    @SuppressWarnings("unchecked")
    public boolean contains(Object o) {
      ReferenceEntry<K, V> e = (ReferenceEntry) o;
      return e.getNextInAccessQueue() != NullEntry.INSTANCE;
    }

    @Override
    public boolean isEmpty() {
      return head.getNextInAccessQueue() == head;
    }

    @Override
    public int size() {
      int size = 0;
      for (ReferenceEntry<K, V> e = head.getNextInAccessQueue();
          e != head;
          e = e.getNextInAccessQueue()) {
        size++;
      }
      return size;
    }

    @Override
    public void clear() {
      ReferenceEntry<K, V> e = head.getNextInAccessQueue();
      while (e != head) {
        ReferenceEntry<K, V> next = e.getNextInAccessQueue();
        nullifyAccessOrder(e);
        e = next;
      }

      head.setNextInAccessQueue(head);
      head.setPreviousInAccessQueue(head);
    }

    @Override
    public Iterator<ReferenceEntry<K, V>> iterator() {
      return new AbstractSequentialIterator<ReferenceEntry<K, V>>(peek()) {
        @Override
        protected ReferenceEntry<K, V> computeNext(ReferenceEntry<K, V> previous) {
          ReferenceEntry<K, V> next = previous.getNextInAccessQueue();
          return (next == head) ? null : next;
        }
      };
    }
  }

  // Cache support

  public void cleanUp() {
    for (Segment<?, ?> segment : segments) {
      segment.cleanUp();
    }
  }

  // ConcurrentMap methods

  @Override
  public boolean isEmpty() {
    /*
     * Sum per-segment modCounts to avoid mis-reporting when elements are concurrently added and
     * removed in one segment while checking another, in which case the table was never actually
     * empty at any point. (The sum ensures accuracy up through at least 1<<31 per-segment
     * modifications before recheck.) Method containsValue() uses similar constructions for
     * stability checks.
     */
    long sum = 0L;
    Segment<K, V>[] segments = this.segments;
    for (int i = 0; i < segments.length; ++i) {
      if (segments[i].count != 0) {
        return false;
      }
      sum += segments[i].modCount;
    }

    if (sum != 0L) { // recheck unless no modifications
      for (int i = 0; i < segments.length; ++i) {
        if (segments[i].count != 0) {
          return false;
        }
        sum -= segments[i].modCount;
      }
      if (sum != 0L) {
        return false;
      }
    }
    return true;
  }

  long longSize() {
    Segment<K, V>[] segments = this.segments;
    long sum = 0;
    for (int i = 0; i < segments.length; ++i) {
      sum += Math.max(0, segments[i].count); // see https://github.com/google/guava/issues/2108
    }
    return sum;
  }

  @Override
  public int size() {
    return Ints.saturatedCast(longSize());
  }

  @Override
  public @Nullable V get(@Nullable Object key) {
    if (key == null) {
      return null;
    }
    int hash = hash(key);
    return segmentFor(hash).get(key, hash);
  }

  V get(K key, CacheLoader<? super K, V> loader) throws ExecutionException {
    int hash = hash(checkNotNull(key));
    return segmentFor(hash).get(key, hash, loader);
  }

  public @Nullable V getIfPresent(Object key) {
    int hash = hash(checkNotNull(key));
    V value = segmentFor(hash).get(key, hash);
    if (value == null) {
      globalStatsCounter.recordMisses(1);
    } else {
      globalStatsCounter.recordHits(1);
    }
    return value;
  }

  // Only becomes available in Java 8 when it's on the interface.
  // @Override
  public @Nullable V getOrDefault(@Nullable Object key, @Nullable V defaultValue) {
    V result = get(key);
    return (result != null) ? result : defaultValue;
  }

  V getOrLoad(K key) throws ExecutionException {
    return get(key, defaultLoader);
  }

  ImmutableMap<K, V> getAllPresent(Iterable<?> keys) {
    int hits = 0;
    int misses = 0;

    Map<K, V> result = Maps.newLinkedHashMap();
    for (Object key : keys) {
      V value = get(key);
      if (value == null) {
        misses++;
      } else {
        // TODO(fry): store entry key instead of query key
        @SuppressWarnings("unchecked")
        K castKey = (K) key;
        result.put(castKey, value);
        hits++;
      }
    }
    globalStatsCounter.recordHits(hits);
    globalStatsCounter.recordMisses(misses);
    return ImmutableMap.copyOf(result);
  }

  ImmutableMap<K, V> getAll(Iterable<? extends K> keys) throws ExecutionException {
    int hits = 0;
    int misses = 0;

    Map<K, V> result = Maps.newLinkedHashMap();
    Set<K> keysToLoad = Sets.newLinkedHashSet();
    for (K key : keys) {
      V value = get(key);
      if (!result.containsKey(key)) {
        result.put(key, value);
        if (value == null) {
          misses++;
          keysToLoad.add(key);
        } else {
          hits++;
        }
      }
    }

    try {
      if (!keysToLoad.isEmpty()) {
        try {
          Map<K, V> newEntries = loadAll(keysToLoad, defaultLoader);
          for (K key : keysToLoad) {
            V value = newEntries.get(key);
            if (value == null) {
              throw new InvalidCacheLoadException("loadAll failed to return a value for " + key);
            }
            result.put(key, value);
          }
        } catch (UnsupportedLoadingOperationException e) {
          // loadAll not implemented, fallback to load
          for (K key : keysToLoad) {
            misses--; // get will count this miss
            result.put(key, get(key, defaultLoader));
          }
        }
      }
      return ImmutableMap.copyOf(result);
    } finally {
      globalStatsCounter.recordHits(hits);
      globalStatsCounter.recordMisses(misses);
    }
  }

  
Returns the result of calling CacheLoader.loadAll, or null if loader doesn't implement loadAll. /**
   * Returns the result of calling {@link CacheLoader#loadAll}, or null if {@code loader} doesn't
   * implement {@code loadAll}.
   */
  @Nullable
  Map<K, V> loadAll(Set<? extends K> keys, CacheLoader<? super K, V> loader)
      throws ExecutionException {
    checkNotNull(loader);
    checkNotNull(keys);
    Stopwatch stopwatch = Stopwatch.createStarted();
    Map<K, V> result;
    boolean success = false;
    try {
      @SuppressWarnings("unchecked") // safe since all keys extend K
      Map<K, V> map = (Map<K, V>) loader.loadAll(keys);
      result = map;
      success = true;
    } catch (UnsupportedLoadingOperationException e) {
      success = true;
      throw e;
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
      throw new ExecutionException(e);
    } catch (RuntimeException e) {
      throw new UncheckedExecutionException(e);
    } catch (Exception e) {
      throw new ExecutionException(e);
    } catch (Error e) {
      throw new ExecutionError(e);
    } finally {
      if (!success) {
        globalStatsCounter.recordLoadException(stopwatch.elapsed(NANOSECONDS));
      }
    }

    if (result == null) {
      globalStatsCounter.recordLoadException(stopwatch.elapsed(NANOSECONDS));
      throw new InvalidCacheLoadException(loader + " returned null map from loadAll");
    }

    stopwatch.stop();
    // TODO(fry): batch by segment
    boolean nullsPresent = false;
    for (Entry<K, V> entry : result.entrySet()) {
      K key = entry.getKey();
      V value = entry.getValue();
      if (key == null || value == null) {
        // delay failure until non-null entries are stored
        nullsPresent = true;
      } else {
        put(key, value);
      }
    }

    if (nullsPresent) {
      globalStatsCounter.recordLoadException(stopwatch.elapsed(NANOSECONDS));
      throw new InvalidCacheLoadException(loader + " returned null keys or values from loadAll");
    }

    // TODO(fry): record count of loaded entries
    globalStatsCounter.recordLoadSuccess(stopwatch.elapsed(NANOSECONDS));
    return result;
  }

  
Returns the internal entry for the specified key. The entry may be loading, expired, or
partially collected.
/**
   * Returns the internal entry for the specified key. The entry may be loading, expired, or
   * partially collected.
   */
  ReferenceEntry<K, V> getEntry(@Nullable Object key) {
    // does not impact recency ordering
    if (key == null) {
      return null;
    }
    int hash = hash(key);
    return segmentFor(hash).getEntry(key, hash);
  }

  void refresh(K key) {
    int hash = hash(checkNotNull(key));
    segmentFor(hash).refresh(key, hash, defaultLoader, false);
  }

  @Override
  public boolean containsKey(@Nullable Object key) {
    // does not impact recency ordering
    if (key == null) {
      return false;
    }
    int hash = hash(key);
    return segmentFor(hash).containsKey(key, hash);
  }

  @Override
  public boolean containsValue(@Nullable Object value) {
    // does not impact recency ordering
    if (value == null) {
      return false;
    }

    // This implementation is patterned after ConcurrentHashMap, but without the locking. The only
    // way for it to return a false negative would be for the target value to jump around in the map
    // such that none of the subsequent iterations observed it, despite the fact that at every point
    // in time it was present somewhere int the map. This becomes increasingly unlikely as
    // CONTAINS_VALUE_RETRIES increases, though without locking it is theoretically possible.
    long now = ticker.read();
    final Segment<K, V>[] segments = this.segments;
    long last = -1L;
    for (int i = 0; i < CONTAINS_VALUE_RETRIES; i++) {
      long sum = 0L;
      for (Segment<K, V> segment : segments) {
        // ensure visibility of most recent completed write
        int unused = segment.count; // read-volatile

        AtomicReferenceArray<ReferenceEntry<K, V>> table = segment.table;
        for (int j = 0; j < table.length(); j++) {
          for (ReferenceEntry<K, V> e = table.get(j); e != null; e = e.getNext()) {
            V v = segment.getLiveValue(e, now);
            if (v != null && valueEquivalence.equivalent(value, v)) {
              return true;
            }
          }
        }
        sum += segment.modCount;
      }
      if (sum == last) {
        break;
      }
      last = sum;
    }
    return false;
  }

  @Override
  public V put(K key, V value) {
    checkNotNull(key);
    checkNotNull(value);
    int hash = hash(key);
    return segmentFor(hash).put(key, hash, value, false);
  }

  @Override
  public V putIfAbsent(K key, V value) {
    checkNotNull(key);
    checkNotNull(value);
    int hash = hash(key);
    return segmentFor(hash).put(key, hash, value, true);
  }

  @Override
  public V compute(K key, BiFunction<? super K, ? super V, ? extends V> function) {
    checkNotNull(key);
    checkNotNull(function);
    int hash = hash(key);
    return segmentFor(hash).compute(key, hash, function);
  }

  @Override
  public V computeIfAbsent(K key, Function<? super K, ? extends V> function) {
    checkNotNull(key);
    checkNotNull(function);
    return compute(key, (k, oldValue) -> (oldValue == null) ? function.apply(key) : oldValue);
  }

  @Override
  public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> function) {
    checkNotNull(key);
    checkNotNull(function);
    return compute(key, (k, oldValue) -> (oldValue == null) ? null : function.apply(k, oldValue));
  }

  @Override
  public V merge(K key, V newValue, BiFunction<? super V, ? super V, ? extends V> function) {
    checkNotNull(key);
    checkNotNull(newValue);
    checkNotNull(function);
    return compute(
        key, (k, oldValue) -> (oldValue == null) ? newValue : function.apply(oldValue, newValue));
  }

  @Override
  public void putAll(Map<? extends K, ? extends V> m) {
    for (Entry<? extends K, ? extends V> e : m.entrySet()) {
      put(e.getKey(), e.getValue());
    }
  }

  @Override
  public V remove(@Nullable Object key) {
    if (key == null) {
      return null;
    }
    int hash = hash(key);
    return segmentFor(hash).remove(key, hash);
  }

  @Override
  public boolean remove(@Nullable Object key, @Nullable Object value) {
    if (key == null || value == null) {
      return false;
    }
    int hash = hash(key);
    return segmentFor(hash).remove(key, hash, value);
  }

  @Override
  public boolean replace(K key, @Nullable V oldValue, V newValue) {
    checkNotNull(key);
    checkNotNull(newValue);
    if (oldValue == null) {
      return false;
    }
    int hash = hash(key);
    return segmentFor(hash).replace(key, hash, oldValue, newValue);
  }

  @Override
  public V replace(K key, V value) {
    checkNotNull(key);
    checkNotNull(value);
    int hash = hash(key);
    return segmentFor(hash).replace(key, hash, value);
  }

  @Override
  public void clear() {
    for (Segment<K, V> segment : segments) {
      segment.clear();
    }
  }

  void invalidateAll(Iterable<?> keys) {
    // TODO(fry): batch by segment
    for (Object key : keys) {
      remove(key);
    }
  }

  @MonotonicNonNull Set<K> keySet;

  @Override
  public Set<K> keySet() {
    // does not impact recency ordering
    Set<K> ks = keySet;
    return (ks != null) ? ks : (keySet = new KeySet(this));
  }

  @MonotonicNonNull Collection<V> values;

  @Override
  public Collection<V> values() {
    // does not impact recency ordering
    Collection<V> vs = values;
    return (vs != null) ? vs : (values = new Values(this));
  }

  @MonotonicNonNull Set<Entry<K, V>> entrySet;

  @Override
  @GwtIncompatible // Not supported.
  public Set<Entry<K, V>> entrySet() {
    // does not impact recency ordering
    Set<Entry<K, V>> es = entrySet;
    return (es != null) ? es : (entrySet = new EntrySet(this));
  }

  // Iterator Support

  abstract class HashIterator<T> implements Iterator<T> {

    int nextSegmentIndex;
    int nextTableIndex;
    @MonotonicNonNull Segment<K, V> currentSegment;
    @MonotonicNonNull AtomicReferenceArray<ReferenceEntry<K, V>> currentTable;
    @Nullable ReferenceEntry<K, V> nextEntry;
    @Nullable WriteThroughEntry nextExternal;
    @Nullable WriteThroughEntry lastReturned;

    HashIterator() {
      nextSegmentIndex = segments.length - 1;
      nextTableIndex = -1;
      advance();
    }

    @Override
    public abstract T next();

    final void advance() {
      nextExternal = null;

      if (nextInChain()) {
        return;
      }

      if (nextInTable()) {
        return;
      }

      while (nextSegmentIndex >= 0) {
        currentSegment = segments[nextSegmentIndex--];
        if (currentSegment.count != 0) {
          currentTable = currentSegment.table;
          nextTableIndex = currentTable.length() - 1;
          if (nextInTable()) {
            return;
          }
        }
      }
    }

    
Finds the next entry in the current chain. Returns true if an entry was found. /** Finds the next entry in the current chain. Returns true if an entry was found. */
    boolean nextInChain() {
      if (nextEntry != null) {
        for (nextEntry = nextEntry.getNext(); nextEntry != null; nextEntry = nextEntry.getNext()) {
          if (advanceTo(nextEntry)) {
            return true;
          }
        }
      }
      return false;
    }

    
Finds the next entry in the current table. Returns true if an entry was found. /** Finds the next entry in the current table. Returns true if an entry was found. */
    boolean nextInTable() {
      while (nextTableIndex >= 0) {
        if ((nextEntry = currentTable.get(nextTableIndex--)) != null) {
          if (advanceTo(nextEntry) || nextInChain()) {
            return true;
          }
        }
      }
      return false;
    }

    
Advances to the given entry. Returns true if the entry was valid, false if it should be
skipped.
/**
     * Advances to the given entry. Returns true if the entry was valid, false if it should be
     * skipped.
     */
    boolean advanceTo(ReferenceEntry<K, V> entry) {
      try {
        long now = ticker.read();
        K key = entry.getKey();
        V value = getLiveValue(entry, now);
        if (value != null) {
          nextExternal = new WriteThroughEntry(key, value);
          return true;
        } else {
          // Skip stale entry.
          return false;
        }
      } finally {
        currentSegment.postReadCleanup();
      }
    }

    @Override
    public boolean hasNext() {
      return nextExternal != null;
    }

    WriteThroughEntry nextEntry() {
      if (nextExternal == null) {
        throw new NoSuchElementException();
      }
      lastReturned = nextExternal;
      advance();
      return lastReturned;
    }

    @Override
    public void remove() {
      checkState(lastReturned != null);
      LocalCache.this.remove(lastReturned.getKey());
      lastReturned = null;
    }
  }

  final class KeyIterator extends HashIterator<K> {

    @Override
    public K next() {
      return nextEntry().getKey();
    }
  }

  final class ValueIterator extends HashIterator<V> {

    @Override
    public V next() {
      return nextEntry().getValue();
    }
  }

  
Custom Entry class used by EntryIterator.next(), that relays setValue changes to the underlying
map.
/**
   * Custom Entry class used by EntryIterator.next(), that relays setValue changes to the underlying
   * map.
   */
  final class WriteThroughEntry implements Entry<K, V> {
    final K key; // non-null
    V value; // non-null

    WriteThroughEntry(K key, V value) {
      this.key = key;
      this.value = value;
    }

    @Override
    public K getKey() {
      return key;
    }

    @Override
    public V getValue() {
      return value;
    }

    @Override
    public boolean equals(@Nullable Object object) {
      // Cannot use key and value equivalence
      if (object instanceof Entry) {
        Entry<?, ?> that = (Entry<?, ?>) object;
        return key.equals(that.getKey()) && value.equals(that.getValue());
      }
      return false;
    }

    @Override
    public int hashCode() {
      // Cannot use key and value equivalence
      return key.hashCode() ^ value.hashCode();
    }

    @Override
    public V setValue(V newValue) {
      V oldValue = put(key, newValue);
      value = newValue; // only if put succeeds
      return oldValue;
    }

    @Override
    public String toString() {
      return getKey() + "=" + getValue();
    }
  }

  final class EntryIterator extends HashIterator<Entry<K, V>> {

    @Override
    public Entry<K, V> next() {
      return nextEntry();
    }
  }

  abstract class AbstractCacheSet<T> extends AbstractSet<T> {
    @Weak final ConcurrentMap<?, ?> map;

    AbstractCacheSet(ConcurrentMap<?, ?> map) {
      this.map = map;
    }

    @Override
    public int size() {
      return map.size();
    }

    @Override
    public boolean isEmpty() {
      return map.isEmpty();
    }

    @Override
    public void clear() {
      map.clear();
    }

    // super.toArray() may misbehave if size() is inaccurate, at least on old versions of Android.
    // https://code.google.com/p/android/issues/detail?id=36519 / http://r.android.com/47508

    @Override
    public Object[] toArray() {
      return toArrayList(this).toArray();
    }

    @Override
    public <E> E[] toArray(E[] a) {
      return toArrayList(this).toArray(a);
    }
  }

  private static <E> ArrayList<E> toArrayList(Collection<E> c) {
    // Avoid calling ArrayList(Collection), which may call back into toArray.
    ArrayList<E> result = new ArrayList<E>(c.size());
    Iterators.addAll(result, c.iterator());
    return result;
  }

  boolean removeIf(BiPredicate<? super K, ? super V> filter) {
    checkNotNull(filter);
    boolean changed = false;
    for (K key : keySet()) {
      while (true) {
        V value = get(key);
        if (value == null || !filter.test(key, value)) {
          break;
        } else if (LocalCache.this.remove(key, value)) {
          changed = true;
          break;
        }
      }
    }
    return changed;
  }

  @WeakOuter
  final class KeySet extends AbstractCacheSet<K> {

    KeySet(ConcurrentMap<?, ?> map) {
      super(map);
    }

    @Override
    public Iterator<K> iterator() {
      return new KeyIterator();
    }

    @Override
    public boolean contains(Object o) {
      return map.containsKey(o);
    }

    @Override
    public boolean remove(Object o) {
      return map.remove(o) != null;
    }
  }

  @WeakOuter
  final class Values extends AbstractCollection<V> {
    private final ConcurrentMap<?, ?> map;

    Values(ConcurrentMap<?, ?> map) {
      this.map = map;
    }

    @Override
    public int size() {
      return map.size();
    }

    @Override
    public boolean isEmpty() {
      return map.isEmpty();
    }

    @Override
    public void clear() {
      map.clear();
    }

    @Override
    public Iterator<V> iterator() {
      return new ValueIterator();
    }

    @Override
    public boolean removeIf(Predicate<? super V> filter) {
      checkNotNull(filter);
      return LocalCache.this.removeIf((k, v) -> filter.test(v));
    }

    @Override
    public boolean contains(Object o) {
      return map.containsValue(o);
    }

    // super.toArray() may misbehave if size() is inaccurate, at least on old versions of Android.
    // https://code.google.com/p/android/issues/detail?id=36519 / http://r.android.com/47508

    @Override
    public Object[] toArray() {
      return toArrayList(this).toArray();
    }

    @Override
    public <E> E[] toArray(E[] a) {
      return toArrayList(this).toArray(a);
    }
  }

  @WeakOuter
  final class EntrySet extends AbstractCacheSet<Entry<K, V>> {

    EntrySet(ConcurrentMap<?, ?> map) {
      super(map);
    }

    @Override
    public Iterator<Entry<K, V>> iterator() {
      return new EntryIterator();
    }

    @Override
    public boolean removeIf(Predicate<? super Entry<K, V>> filter) {
      checkNotNull(filter);
      return LocalCache.this.removeIf((k, v) -> filter.test(Maps.immutableEntry(k, v)));
    }

    @Override
    public boolean contains(Object o) {
      if (!(o instanceof Entry)) {
        return false;
      }
      Entry<?, ?> e = (Entry<?, ?>) o;
      Object key = e.getKey();
      if (key == null) {
        return false;
      }
      V v = LocalCache.this.get(key);

      return v != null && valueEquivalence.equivalent(e.getValue(), v);
    }

    @Override
    public boolean remove(Object o) {
      if (!(o instanceof Entry)) {
        return false;
      }
      Entry<?, ?> e = (Entry<?, ?>) o;
      Object key = e.getKey();
      return key != null && LocalCache.this.remove(key, e.getValue());
    }
  }

  // Serialization Support

  
Serializes the configuration of a LocalCache, reconstituting it as a Cache using CacheBuilder
upon deserialization. An instance of this class is fit for use by the writeReplace of
LocalManualCache.
Unfortunately, readResolve() doesn't get called when a circular dependency is present, so
the proxy must be able to behave as the cache itself.
/**
   * Serializes the configuration of a LocalCache, reconstituting it as a Cache using CacheBuilder
   * upon deserialization. An instance of this class is fit for use by the writeReplace of
   * LocalManualCache.
   *
   * <p>Unfortunately, readResolve() doesn't get called when a circular dependency is present, so
   * the proxy must be able to behave as the cache itself.
   */
  static class ManualSerializationProxy<K, V> extends ForwardingCache<K, V>
      implements Serializable {
    private static final long serialVersionUID = 1;

    final Strength keyStrength;
    final Strength valueStrength;
    final Equivalence<Object> keyEquivalence;
    final Equivalence<Object> valueEquivalence;
    final long expireAfterWriteNanos;
    final long expireAfterAccessNanos;
    final long maxWeight;
    final Weigher<K, V> weigher;
    final int concurrencyLevel;
    final RemovalListener<? super K, ? super V> removalListener;
    final @Nullable Ticker ticker;
    final CacheLoader<? super K, V> loader;

    transient @MonotonicNonNull Cache<K, V> delegate;

    ManualSerializationProxy(LocalCache<K, V> cache) {
      this(
          cache.keyStrength,
          cache.valueStrength,
          cache.keyEquivalence,
          cache.valueEquivalence,
          cache.expireAfterWriteNanos,
          cache.expireAfterAccessNanos,
          cache.maxWeight,
          cache.weigher,
          cache.concurrencyLevel,
          cache.removalListener,
          cache.ticker,
          cache.defaultLoader);
    }

    private ManualSerializationProxy(
        Strength keyStrength,
        Strength valueStrength,
        Equivalence<Object> keyEquivalence,
        Equivalence<Object> valueEquivalence,
        long expireAfterWriteNanos,
        long expireAfterAccessNanos,
        long maxWeight,
        Weigher<K, V> weigher,
        int concurrencyLevel,
        RemovalListener<? super K, ? super V> removalListener,
        Ticker ticker,
        CacheLoader<? super K, V> loader) {
      this.keyStrength = keyStrength;
      this.valueStrength = valueStrength;
      this.keyEquivalence = keyEquivalence;
      this.valueEquivalence = valueEquivalence;
      this.expireAfterWriteNanos = expireAfterWriteNanos;
      this.expireAfterAccessNanos = expireAfterAccessNanos;
      this.maxWeight = maxWeight;
      this.weigher = weigher;
      this.concurrencyLevel = concurrencyLevel;
      this.removalListener = removalListener;
      this.ticker = (ticker == Ticker.systemTicker() || ticker == NULL_TICKER) ? null : ticker;
      this.loader = loader;
    }

    CacheBuilder<K, V> recreateCacheBuilder() {
      CacheBuilder<K, V> builder =
          CacheBuilder.newBuilder()
              .setKeyStrength(keyStrength)
              .setValueStrength(valueStrength)
              .keyEquivalence(keyEquivalence)
              .valueEquivalence(valueEquivalence)
              .concurrencyLevel(concurrencyLevel)
              .removalListener(removalListener);
      builder.strictParsing = false;
      if (expireAfterWriteNanos > 0) {
        builder.expireAfterWrite(expireAfterWriteNanos, TimeUnit.NANOSECONDS);
      }
      if (expireAfterAccessNanos > 0) {
        builder.expireAfterAccess(expireAfterAccessNanos, TimeUnit.NANOSECONDS);
      }
      if (weigher != OneWeigher.INSTANCE) {
        builder.weigher(weigher);
        if (maxWeight != UNSET_INT) {
          builder.maximumWeight(maxWeight);
        }
      } else {
        if (maxWeight != UNSET_INT) {
          builder.maximumSize(maxWeight);
        }
      }
      if (ticker != null) {
        builder.ticker(ticker);
      }
      return builder;
    }

    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
      in.defaultReadObject();
      CacheBuilder<K, V> builder = recreateCacheBuilder();
      this.delegate = builder.build();
    }

    private Object readResolve() {
      return delegate;
    }

    @Override
    protected Cache<K, V> delegate() {
      return delegate;
    }
  }

  
Serializes the configuration of a LocalCache, reconstituting it as an LoadingCache using
CacheBuilder upon deserialization. An instance of this class is fit for use by the writeReplace
of LocalLoadingCache.
Unfortunately, readResolve() doesn't get called when a circular dependency is present, so
the proxy must be able to behave as the cache itself.
/**
   * Serializes the configuration of a LocalCache, reconstituting it as an LoadingCache using
   * CacheBuilder upon deserialization. An instance of this class is fit for use by the writeReplace
   * of LocalLoadingCache.
   *
   * <p>Unfortunately, readResolve() doesn't get called when a circular dependency is present, so
   * the proxy must be able to behave as the cache itself.
   */
  static final class LoadingSerializationProxy<K, V> extends ManualSerializationProxy<K, V>
      implements LoadingCache<K, V>, Serializable {
    private static final long serialVersionUID = 1;

    transient @MonotonicNonNull LoadingCache<K, V> autoDelegate;

    LoadingSerializationProxy(LocalCache<K, V> cache) {
      super(cache);
    }

    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
      in.defaultReadObject();
      CacheBuilder<K, V> builder = recreateCacheBuilder();
      this.autoDelegate = builder.build(loader);
    }

    @Override
    public V get(K key) throws ExecutionException {
      return autoDelegate.get(key);
    }

    @Override
    public V getUnchecked(K key) {
      return autoDelegate.getUnchecked(key);
    }

    @Override
    public ImmutableMap<K, V> getAll(Iterable<? extends K> keys) throws ExecutionException {
      return autoDelegate.getAll(keys);
    }

    @Override
    public final V apply(K key) {
      return autoDelegate.apply(key);
    }

    @Override
    public void refresh(K key) {
      autoDelegate.refresh(key);
    }

    private Object readResolve() {
      return autoDelegate;
    }
  }

  static class LocalManualCache<K, V> implements Cache<K, V>, Serializable {
    final LocalCache<K, V> localCache;

    LocalManualCache(CacheBuilder<? super K, ? super V> builder) {
      this(new LocalCache<K, V>(builder, null));
    }

    private LocalManualCache(LocalCache<K, V> localCache) {
      this.localCache = localCache;
    }

    // Cache methods

    @Override
    public @Nullable V getIfPresent(Object key) {
      return localCache.getIfPresent(key);
    }

    @Override
    public V get(K key, final Callable<? extends V> valueLoader) throws ExecutionException {
      checkNotNull(valueLoader);
      return localCache.get(
          key,
          new CacheLoader<Object, V>() {
            @Override
            public V load(Object key) throws Exception {
              return valueLoader.call();
            }
          });
    }

    @Override
    public ImmutableMap<K, V> getAllPresent(Iterable<?> keys) {
      return localCache.getAllPresent(keys);
    }

    @Override
    public void put(K key, V value) {
      localCache.put(key, value);
    }

    @Override
    public void putAll(Map<? extends K, ? extends V> m) {
      localCache.putAll(m);
    }

    @Override
    public void invalidate(Object key) {
      checkNotNull(key);
      localCache.remove(key);
    }

    @Override
    public void invalidateAll(Iterable<?> keys) {
      localCache.invalidateAll(keys);
    }

    @Override
    public void invalidateAll() {
      localCache.clear();
    }

    @Override
    public long size() {
      return localCache.longSize();
    }

    @Override
    public ConcurrentMap<K, V> asMap() {
      return localCache;
    }

    @Override
    public CacheStats stats() {
      SimpleStatsCounter aggregator = new SimpleStatsCounter();
      aggregator.incrementBy(localCache.globalStatsCounter);
      for (Segment<K, V> segment : localCache.segments) {
        aggregator.incrementBy(segment.statsCounter);
      }
      return aggregator.snapshot();
    }

    @Override
    public void cleanUp() {
      localCache.cleanUp();
    }

    // Serialization Support

    private static final long serialVersionUID = 1;

    Object writeReplace() {
      return new ManualSerializationProxy<>(localCache);
    }
  }

  static class LocalLoadingCache<K, V> extends LocalManualCache<K, V>
      implements LoadingCache<K, V> {

    LocalLoadingCache(
        CacheBuilder<? super K, ? super V> builder, CacheLoader<? super K, V> loader) {
      super(new LocalCache<K, V>(builder, checkNotNull(loader)));
    }

    // LoadingCache methods

    @Override
    public V get(K key) throws ExecutionException {
      return localCache.getOrLoad(key);
    }

    @Override
    public V getUnchecked(K key) {
      try {
        return get(key);
      } catch (ExecutionException e) {
        throw new UncheckedExecutionException(e.getCause());
      }
    }

    @Override
    public ImmutableMap<K, V> getAll(Iterable<? extends K> keys) throws ExecutionException {
      return localCache.getAll(keys);
    }

    @Override
    public void refresh(K key) {
      localCache.refresh(key);
    }

    @Override
    public final V apply(K key) {
      return getUnchecked(key);
    }

    // Serialization Support

    private static final long serialVersionUID = 1;

    @Override
    Object writeReplace() {
      return new LoadingSerializationProxy<>(localCache);
    }
  }
}