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/*
 * Copyright (C) 2007 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.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.j2objc.annotations.RetainedWith;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Collection;
import java.util.Comparator;
import java.util.Deque;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NavigableMap;
import java.util.NavigableSet;
import java.util.Queue;
import java.util.RandomAccess;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import org.checkerframework.checker.nullness.compatqual.MonotonicNonNullDecl;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;

/**
 * Synchronized collection views. The returned synchronized collection views are serializable if the
 * backing collection and the mutex are serializable.
 *
 * If {@code null} is passed as the {@code mutex} parameter to any of this class's top-level
 * methods or inner class constructors, the created object uses itself as the synchronization mutex.
 *
 * This class should be used by other collection classes only.
 *
 * @author Mike Bostock
 * @author Jared Levy
 */
@GwtCompatible(emulated = true)
final class Synchronized {
  private Synchronized() {}

  static class SynchronizedObject implements Serializable {
    final Object delegate;
    final Object mutex;

    SynchronizedObject(Object delegate, @NullableDecl Object mutex) {
      this.delegate = checkNotNull(delegate);
      this.mutex = (mutex == null) ? this : mutex;
    }

    Object delegate() {
      return delegate;
    }

    // No equals and hashCode; see ForwardingObject for details.

    @Override
    public String toString() {
      synchronized (mutex) {
        return delegate.toString();
      }
    }

    // Serialization invokes writeObject only when it's private.
    // The SynchronizedObject subclasses don't need a writeObject method since
    // they don't contain any non-transient member variables, while the
    // following writeObject() handles the SynchronizedObject members.

    @GwtIncompatible // java.io.ObjectOutputStream
    private void writeObject(ObjectOutputStream stream) throws IOException {
      synchronized (mutex) {
        stream.defaultWriteObject();
      }
    }

    @GwtIncompatible // not needed in emulated source
    private static final long serialVersionUID = 0;
  }

  private static  Collection collection(
      Collection collection, @NullableDecl Object mutex) {
    return new SynchronizedCollection(collection, mutex);
  }

  @VisibleForTesting
  static class SynchronizedCollection extends SynchronizedObject implements Collection {
    private SynchronizedCollection(Collection delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @SuppressWarnings("unchecked")
    @Override
    Collection delegate() {
      return (Collection) super.delegate();
    }

    @Override
    public boolean add(E e) {
      synchronized (mutex) {
        return delegate().add(e);
      }
    }

    @Override
    public boolean addAll(Collection c) {
      synchronized (mutex) {
        return delegate().addAll(c);
      }
    }

    @Override
    public void clear() {
      synchronized (mutex) {
        delegate().clear();
      }
    }

    @Override
    public boolean contains(Object o) {
      synchronized (mutex) {
        return delegate().contains(o);
      }
    }

    @Override
    public boolean containsAll(Collection c) {
      synchronized (mutex) {
        return delegate().containsAll(c);
      }
    }

    @Override
    public boolean isEmpty() {
      synchronized (mutex) {
        return delegate().isEmpty();
      }
    }

    @Override
    public Iterator iterator() {
      return delegate().iterator(); // manually synchronized
    }

    @Override
    public boolean remove(Object o) {
      synchronized (mutex) {
        return delegate().remove(o);
      }
    }

    @Override
    public boolean removeAll(Collection c) {
      synchronized (mutex) {
        return delegate().removeAll(c);
      }
    }

    @Override
    public boolean retainAll(Collection c) {
      synchronized (mutex) {
        return delegate().retainAll(c);
      }
    }

    @Override
    public int size() {
      synchronized (mutex) {
        return delegate().size();
      }
    }

    @Override
    public Object[] toArray() {
      synchronized (mutex) {
        return delegate().toArray();
      }
    }

    @Override
    public  T[] toArray(T[] a) {
      synchronized (mutex) {
        return delegate().toArray(a);
      }
    }

    private static final long serialVersionUID = 0;
  }

  @VisibleForTesting
  static  Set set(Set set, @NullableDecl Object mutex) {
    return new SynchronizedSet(set, mutex);
  }

  static class SynchronizedSet extends SynchronizedCollection implements Set {

    SynchronizedSet(Set delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    Set delegate() {
      return (Set) super.delegate();
    }

    @Override
    public boolean equals(Object o) {
      if (o == this) {
        return true;
      }
      synchronized (mutex) {
        return delegate().equals(o);
      }
    }

    @Override
    public int hashCode() {
      synchronized (mutex) {
        return delegate().hashCode();
      }
    }

    private static final long serialVersionUID = 0;
  }

  private static  SortedSet sortedSet(SortedSet set, @NullableDecl Object mutex) {
    return new SynchronizedSortedSet(set, mutex);
  }

  static class SynchronizedSortedSet extends SynchronizedSet implements SortedSet {
    SynchronizedSortedSet(SortedSet delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    SortedSet delegate() {
      return (SortedSet) super.delegate();
    }

    @Override
    public Comparator comparator() {
      synchronized (mutex) {
        return delegate().comparator();
      }
    }

    @Override
    public SortedSet subSet(E fromElement, E toElement) {
      synchronized (mutex) {
        return sortedSet(delegate().subSet(fromElement, toElement), mutex);
      }
    }

    @Override
    public SortedSet headSet(E toElement) {
      synchronized (mutex) {
        return sortedSet(delegate().headSet(toElement), mutex);
      }
    }

    @Override
    public SortedSet tailSet(E fromElement) {
      synchronized (mutex) {
        return sortedSet(delegate().tailSet(fromElement), mutex);
      }
    }

    @Override
    public E first() {
      synchronized (mutex) {
        return delegate().first();
      }
    }

    @Override
    public E last() {
      synchronized (mutex) {
        return delegate().last();
      }
    }

    private static final long serialVersionUID = 0;
  }

  private static  List list(List list, @NullableDecl Object mutex) {
    return (list instanceof RandomAccess)
        ? new SynchronizedRandomAccessList(list, mutex)
        : new SynchronizedList(list, mutex);
  }

  private static class SynchronizedList extends SynchronizedCollection implements List {
    SynchronizedList(List delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    List delegate() {
      return (List) super.delegate();
    }

    @Override
    public void add(int index, E element) {
      synchronized (mutex) {
        delegate().add(index, element);
      }
    }

    @Override
    public boolean addAll(int index, Collection c) {
      synchronized (mutex) {
        return delegate().addAll(index, c);
      }
    }

    @Override
    public E get(int index) {
      synchronized (mutex) {
        return delegate().get(index);
      }
    }

    @Override
    public int indexOf(Object o) {
      synchronized (mutex) {
        return delegate().indexOf(o);
      }
    }

    @Override
    public int lastIndexOf(Object o) {
      synchronized (mutex) {
        return delegate().lastIndexOf(o);
      }
    }

    @Override
    public ListIterator listIterator() {
      return delegate().listIterator(); // manually synchronized
    }

    @Override
    public ListIterator listIterator(int index) {
      return delegate().listIterator(index); // manually synchronized
    }

    @Override
    public E remove(int index) {
      synchronized (mutex) {
        return delegate().remove(index);
      }
    }

    @Override
    public E set(int index, E element) {
      synchronized (mutex) {
        return delegate().set(index, element);
      }
    }

    @Override
    public List subList(int fromIndex, int toIndex) {
      synchronized (mutex) {
        return list(delegate().subList(fromIndex, toIndex), mutex);
      }
    }

    @Override
    public boolean equals(Object o) {
      if (o == this) {
        return true;
      }
      synchronized (mutex) {
        return delegate().equals(o);
      }
    }

    @Override
    public int hashCode() {
      synchronized (mutex) {
        return delegate().hashCode();
      }
    }

    private static final long serialVersionUID = 0;
  }

  private static class SynchronizedRandomAccessList extends SynchronizedList
      implements RandomAccess {
    SynchronizedRandomAccessList(List list, @NullableDecl Object mutex) {
      super(list, mutex);
    }

    private static final long serialVersionUID = 0;
  }

  static  Multiset multiset(Multiset multiset, @NullableDecl Object mutex) {
    if (multiset instanceof SynchronizedMultiset || multiset instanceof ImmutableMultiset) {
      return multiset;
    }
    return new SynchronizedMultiset(multiset, mutex);
  }

  private static class SynchronizedMultiset extends SynchronizedCollection
      implements Multiset {
    @MonotonicNonNullDecl transient Set elementSet;
    @MonotonicNonNullDecl transient Set> entrySet;

    SynchronizedMultiset(Multiset delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    Multiset delegate() {
      return (Multiset) super.delegate();
    }

    @Override
    public int count(Object o) {
      synchronized (mutex) {
        return delegate().count(o);
      }
    }

    @Override
    public int add(E e, int n) {
      synchronized (mutex) {
        return delegate().add(e, n);
      }
    }

    @Override
    public int remove(Object o, int n) {
      synchronized (mutex) {
        return delegate().remove(o, n);
      }
    }

    @Override
    public int setCount(E element, int count) {
      synchronized (mutex) {
        return delegate().setCount(element, count);
      }
    }

    @Override
    public boolean setCount(E element, int oldCount, int newCount) {
      synchronized (mutex) {
        return delegate().setCount(element, oldCount, newCount);
      }
    }

    @Override
    public Set elementSet() {
      synchronized (mutex) {
        if (elementSet == null) {
          elementSet = typePreservingSet(delegate().elementSet(), mutex);
        }
        return elementSet;
      }
    }

    @Override
    public Set> entrySet() {
      synchronized (mutex) {
        if (entrySet == null) {
          entrySet = typePreservingSet(delegate().entrySet(), mutex);
        }
        return entrySet;
      }
    }

    @Override
    public boolean equals(Object o) {
      if (o == this) {
        return true;
      }
      synchronized (mutex) {
        return delegate().equals(o);
      }
    }

    @Override
    public int hashCode() {
      synchronized (mutex) {
        return delegate().hashCode();
      }
    }

    private static final long serialVersionUID = 0;
  }

  static  Multimap multimap(Multimap multimap, @NullableDecl Object mutex) {
    if (multimap instanceof SynchronizedMultimap || multimap instanceof BaseImmutableMultimap) {
      return multimap;
    }
    return new SynchronizedMultimap<>(multimap, mutex);
  }

  private static class SynchronizedMultimap extends SynchronizedObject
      implements Multimap {
    @MonotonicNonNullDecl transient Set keySet;
    @MonotonicNonNullDecl transient Collection valuesCollection;
    @MonotonicNonNullDecl transient Collection> entries;
    @MonotonicNonNullDecl transient Map> asMap;
    @MonotonicNonNullDecl transient Multiset keys;

    @SuppressWarnings("unchecked")
    @Override
    Multimap delegate() {
      return (Multimap) super.delegate();
    }

    SynchronizedMultimap(Multimap delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    public int size() {
      synchronized (mutex) {
        return delegate().size();
      }
    }

    @Override
    public boolean isEmpty() {
      synchronized (mutex) {
        return delegate().isEmpty();
      }
    }

    @Override
    public boolean containsKey(Object key) {
      synchronized (mutex) {
        return delegate().containsKey(key);
      }
    }

    @Override
    public boolean containsValue(Object value) {
      synchronized (mutex) {
        return delegate().containsValue(value);
      }
    }

    @Override
    public boolean containsEntry(Object key, Object value) {
      synchronized (mutex) {
        return delegate().containsEntry(key, value);
      }
    }

    @Override
    public Collection get(K key) {
      synchronized (mutex) {
        return typePreservingCollection(delegate().get(key), mutex);
      }
    }

    @Override
    public boolean put(K key, V value) {
      synchronized (mutex) {
        return delegate().put(key, value);
      }
    }

    @Override
    public boolean putAll(K key, Iterable values) {
      synchronized (mutex) {
        return delegate().putAll(key, values);
      }
    }

    @Override
    public boolean putAll(Multimap multimap) {
      synchronized (mutex) {
        return delegate().putAll(multimap);
      }
    }

    @Override
    public Collection replaceValues(K key, Iterable values) {
      synchronized (mutex) {
        return delegate().replaceValues(key, values); // copy not synchronized
      }
    }

    @Override
    public boolean remove(Object key, Object value) {
      synchronized (mutex) {
        return delegate().remove(key, value);
      }
    }

    @Override
    public Collection removeAll(Object key) {
      synchronized (mutex) {
        return delegate().removeAll(key); // copy not synchronized
      }
    }

    @Override
    public void clear() {
      synchronized (mutex) {
        delegate().clear();
      }
    }

    @Override
    public Set keySet() {
      synchronized (mutex) {
        if (keySet == null) {
          keySet = typePreservingSet(delegate().keySet(), mutex);
        }
        return keySet;
      }
    }

    @Override
    public Collection values() {
      synchronized (mutex) {
        if (valuesCollection == null) {
          valuesCollection = collection(delegate().values(), mutex);
        }
        return valuesCollection;
      }
    }

    @Override
    public Collection> entries() {
      synchronized (mutex) {
        if (entries == null) {
          entries = typePreservingCollection(delegate().entries(), mutex);
        }
        return entries;
      }
    }

    @Override
    public Map> asMap() {
      synchronized (mutex) {
        if (asMap == null) {
          asMap = new SynchronizedAsMap<>(delegate().asMap(), mutex);
        }
        return asMap;
      }
    }

    @Override
    public Multiset keys() {
      synchronized (mutex) {
        if (keys == null) {
          keys = multiset(delegate().keys(), mutex);
        }
        return keys;
      }
    }

    @Override
    public boolean equals(Object o) {
      if (o == this) {
        return true;
      }
      synchronized (mutex) {
        return delegate().equals(o);
      }
    }

    @Override
    public int hashCode() {
      synchronized (mutex) {
        return delegate().hashCode();
      }
    }

    private static final long serialVersionUID = 0;
  }

  static  ListMultimap listMultimap(
      ListMultimap multimap, @NullableDecl Object mutex) {
    if (multimap instanceof SynchronizedListMultimap || multimap instanceof BaseImmutableMultimap) {
      return multimap;
    }
    return new SynchronizedListMultimap<>(multimap, mutex);
  }

  private static class SynchronizedListMultimap extends SynchronizedMultimap
      implements ListMultimap {
    SynchronizedListMultimap(ListMultimap delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    ListMultimap delegate() {
      return (ListMultimap) super.delegate();
    }

    @Override
    public List get(K key) {
      synchronized (mutex) {
        return list(delegate().get(key), mutex);
      }
    }

    @Override
    public List removeAll(Object key) {
      synchronized (mutex) {
        return delegate().removeAll(key); // copy not synchronized
      }
    }

    @Override
    public List replaceValues(K key, Iterable values) {
      synchronized (mutex) {
        return delegate().replaceValues(key, values); // copy not synchronized
      }
    }

    private static final long serialVersionUID = 0;
  }

  static  SetMultimap setMultimap(
      SetMultimap multimap, @NullableDecl Object mutex) {
    if (multimap instanceof SynchronizedSetMultimap || multimap instanceof BaseImmutableMultimap) {
      return multimap;
    }
    return new SynchronizedSetMultimap<>(multimap, mutex);
  }

  private static class SynchronizedSetMultimap extends SynchronizedMultimap
      implements SetMultimap {
    @MonotonicNonNullDecl transient Set> entrySet;

    SynchronizedSetMultimap(SetMultimap delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    SetMultimap delegate() {
      return (SetMultimap) super.delegate();
    }

    @Override
    public Set get(K key) {
      synchronized (mutex) {
        return set(delegate().get(key), mutex);
      }
    }

    @Override
    public Set removeAll(Object key) {
      synchronized (mutex) {
        return delegate().removeAll(key); // copy not synchronized
      }
    }

    @Override
    public Set replaceValues(K key, Iterable values) {
      synchronized (mutex) {
        return delegate().replaceValues(key, values); // copy not synchronized
      }
    }

    @Override
    public Set> entries() {
      synchronized (mutex) {
        if (entrySet == null) {
          entrySet = set(delegate().entries(), mutex);
        }
        return entrySet;
      }
    }

    private static final long serialVersionUID = 0;
  }

  static  SortedSetMultimap sortedSetMultimap(
      SortedSetMultimap multimap, @NullableDecl Object mutex) {
    if (multimap instanceof SynchronizedSortedSetMultimap) {
      return multimap;
    }
    return new SynchronizedSortedSetMultimap<>(multimap, mutex);
  }

  private static class SynchronizedSortedSetMultimap extends SynchronizedSetMultimap
      implements SortedSetMultimap {
    SynchronizedSortedSetMultimap(SortedSetMultimap delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    SortedSetMultimap delegate() {
      return (SortedSetMultimap) super.delegate();
    }

    @Override
    public SortedSet get(K key) {
      synchronized (mutex) {
        return sortedSet(delegate().get(key), mutex);
      }
    }

    @Override
    public SortedSet removeAll(Object key) {
      synchronized (mutex) {
        return delegate().removeAll(key); // copy not synchronized
      }
    }

    @Override
    public SortedSet replaceValues(K key, Iterable values) {
      synchronized (mutex) {
        return delegate().replaceValues(key, values); // copy not synchronized
      }
    }

    @Override
    public Comparator valueComparator() {
      synchronized (mutex) {
        return delegate().valueComparator();
      }
    }

    private static final long serialVersionUID = 0;
  }

  private static  Collection typePreservingCollection(
      Collection collection, @NullableDecl Object mutex) {
    if (collection instanceof SortedSet) {
      return sortedSet((SortedSet) collection, mutex);
    }
    if (collection instanceof Set) {
      return set((Set) collection, mutex);
    }
    if (collection instanceof List) {
      return list((List) collection, mutex);
    }
    return collection(collection, mutex);
  }

  private static  Set typePreservingSet(Set set, @NullableDecl Object mutex) {
    if (set instanceof SortedSet) {
      return sortedSet((SortedSet) set, mutex);
    } else {
      return set(set, mutex);
    }
  }

  private static class SynchronizedAsMapEntries
      extends SynchronizedSet>> {
    SynchronizedAsMapEntries(Set>> delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    public Iterator>> iterator() {
      // Must be manually synchronized.
      return new TransformedIterator>, Entry>>(
          super.iterator()) {
        @Override
        Entry> transform(final Entry> entry) {
          return new ForwardingMapEntry>() {
            @Override
            protected Entry> delegate() {
              return entry;
            }

            @Override
            public Collection getValue() {
              return typePreservingCollection(entry.getValue(), mutex);
            }
          };
        }
      };
    }

    // See Collections.CheckedMap.CheckedEntrySet for details on attacks.

    @Override
    public Object[] toArray() {
      synchronized (mutex) {
        return ObjectArrays.toArrayImpl(delegate());
      }
    }

    @Override
    public  T[] toArray(T[] array) {
      synchronized (mutex) {
        return ObjectArrays.toArrayImpl(delegate(), array);
      }
    }

    @Override
    public boolean contains(Object o) {
      synchronized (mutex) {
        return Maps.containsEntryImpl(delegate(), o);
      }
    }

    @Override
    public boolean containsAll(Collection c) {
      synchronized (mutex) {
        return Collections2.containsAllImpl(delegate(), c);
      }
    }

    @Override
    public boolean equals(Object o) {
      if (o == this) {
        return true;
      }
      synchronized (mutex) {
        return Sets.equalsImpl(delegate(), o);
      }
    }

    @Override
    public boolean remove(Object o) {
      synchronized (mutex) {
        return Maps.removeEntryImpl(delegate(), o);
      }
    }

    @Override
    public boolean removeAll(Collection c) {
      synchronized (mutex) {
        return Iterators.removeAll(delegate().iterator(), c);
      }
    }

    @Override
    public boolean retainAll(Collection c) {
      synchronized (mutex) {
        return Iterators.retainAll(delegate().iterator(), c);
      }
    }

    private static final long serialVersionUID = 0;
  }

  @VisibleForTesting
  static  Map map(Map map, @NullableDecl Object mutex) {
    return new SynchronizedMap<>(map, mutex);
  }

  private static class SynchronizedMap extends SynchronizedObject implements Map {
    @MonotonicNonNullDecl transient Set keySet;
    @MonotonicNonNullDecl transient Collection values;
    @MonotonicNonNullDecl transient Set> entrySet;

    SynchronizedMap(Map delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @SuppressWarnings("unchecked")
    @Override
    Map delegate() {
      return (Map) super.delegate();
    }

    @Override
    public void clear() {
      synchronized (mutex) {
        delegate().clear();
      }
    }

    @Override
    public boolean containsKey(Object key) {
      synchronized (mutex) {
        return delegate().containsKey(key);
      }
    }

    @Override
    public boolean containsValue(Object value) {
      synchronized (mutex) {
        return delegate().containsValue(value);
      }
    }

    @Override
    public Set> entrySet() {
      synchronized (mutex) {
        if (entrySet == null) {
          entrySet = set(delegate().entrySet(), mutex);
        }
        return entrySet;
      }
    }

    @Override
    public V get(Object key) {
      synchronized (mutex) {
        return delegate().get(key);
      }
    }

    @Override
    public boolean isEmpty() {
      synchronized (mutex) {
        return delegate().isEmpty();
      }
    }

    @Override
    public Set keySet() {
      synchronized (mutex) {
        if (keySet == null) {
          keySet = set(delegate().keySet(), mutex);
        }
        return keySet;
      }
    }

    @Override
    public V put(K key, V value) {
      synchronized (mutex) {
        return delegate().put(key, value);
      }
    }

    @Override
    public void putAll(Map map) {
      synchronized (mutex) {
        delegate().putAll(map);
      }
    }

    @Override
    public V remove(Object key) {
      synchronized (mutex) {
        return delegate().remove(key);
      }
    }

    @Override
    public int size() {
      synchronized (mutex) {
        return delegate().size();
      }
    }

    @Override
    public Collection values() {
      synchronized (mutex) {
        if (values == null) {
          values = collection(delegate().values(), mutex);
        }
        return values;
      }
    }

    @Override
    public boolean equals(Object o) {
      if (o == this) {
        return true;
      }
      synchronized (mutex) {
        return delegate().equals(o);
      }
    }

    @Override
    public int hashCode() {
      synchronized (mutex) {
        return delegate().hashCode();
      }
    }

    private static final long serialVersionUID = 0;
  }

  static  SortedMap sortedMap(SortedMap sortedMap, @NullableDecl Object mutex) {
    return new SynchronizedSortedMap<>(sortedMap, mutex);
  }

  static class SynchronizedSortedMap extends SynchronizedMap
      implements SortedMap {

    SynchronizedSortedMap(SortedMap delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    SortedMap delegate() {
      return (SortedMap) super.delegate();
    }

    @Override
    public Comparator comparator() {
      synchronized (mutex) {
        return delegate().comparator();
      }
    }

    @Override
    public K firstKey() {
      synchronized (mutex) {
        return delegate().firstKey();
      }
    }

    @Override
    public SortedMap headMap(K toKey) {
      synchronized (mutex) {
        return sortedMap(delegate().headMap(toKey), mutex);
      }
    }

    @Override
    public K lastKey() {
      synchronized (mutex) {
        return delegate().lastKey();
      }
    }

    @Override
    public SortedMap subMap(K fromKey, K toKey) {
      synchronized (mutex) {
        return sortedMap(delegate().subMap(fromKey, toKey), mutex);
      }
    }

    @Override
    public SortedMap tailMap(K fromKey) {
      synchronized (mutex) {
        return sortedMap(delegate().tailMap(fromKey), mutex);
      }
    }

    private static final long serialVersionUID = 0;
  }

  static  BiMap biMap(BiMap bimap, @NullableDecl Object mutex) {
    if (bimap instanceof SynchronizedBiMap || bimap instanceof ImmutableBiMap) {
      return bimap;
    }
    return new SynchronizedBiMap<>(bimap, mutex, null);
  }

  @VisibleForTesting
  static class SynchronizedBiMap extends SynchronizedMap
      implements BiMap, Serializable {
    @MonotonicNonNullDecl private transient Set valueSet;
    @MonotonicNonNullDecl @RetainedWith private transient BiMap inverse;

    private SynchronizedBiMap(
        BiMap delegate, @NullableDecl Object mutex, @NullableDecl BiMap inverse) {
      super(delegate, mutex);
      this.inverse = inverse;
    }

    @Override
    BiMap delegate() {
      return (BiMap) super.delegate();
    }

    @Override
    public Set values() {
      synchronized (mutex) {
        if (valueSet == null) {
          valueSet = set(delegate().values(), mutex);
        }
        return valueSet;
      }
    }

    @Override
    public V forcePut(K key, V value) {
      synchronized (mutex) {
        return delegate().forcePut(key, value);
      }
    }

    @Override
    public BiMap inverse() {
      synchronized (mutex) {
        if (inverse == null) {
          inverse = new SynchronizedBiMap<>(delegate().inverse(), mutex, this);
        }
        return inverse;
      }
    }

    private static final long serialVersionUID = 0;
  }

  private static class SynchronizedAsMap extends SynchronizedMap> {
    @MonotonicNonNullDecl transient Set>> asMapEntrySet;
    @MonotonicNonNullDecl transient Collection> asMapValues;

    SynchronizedAsMap(Map> delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    public Collection get(Object key) {
      synchronized (mutex) {
        Collection collection = super.get(key);
        return (collection == null) ? null : typePreservingCollection(collection, mutex);
      }
    }

    @Override
    public Set>> entrySet() {
      synchronized (mutex) {
        if (asMapEntrySet == null) {
          asMapEntrySet = new SynchronizedAsMapEntries<>(delegate().entrySet(), mutex);
        }
        return asMapEntrySet;
      }
    }

    @Override
    public Collection> values() {
      synchronized (mutex) {
        if (asMapValues == null) {
          asMapValues = new SynchronizedAsMapValues(delegate().values(), mutex);
        }
        return asMapValues;
      }
    }

    @Override
    public boolean containsValue(Object o) {
      // values() and its contains() method are both synchronized.
      return values().contains(o);
    }

    private static final long serialVersionUID = 0;
  }

  private static class SynchronizedAsMapValues extends SynchronizedCollection> {
    SynchronizedAsMapValues(Collection> delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    public Iterator> iterator() {
      // Must be manually synchronized.
      return new TransformedIterator, Collection>(super.iterator()) {
        @Override
        Collection transform(Collection from) {
          return typePreservingCollection(from, mutex);
        }
      };
    }

    private static final long serialVersionUID = 0;
  }

  @GwtIncompatible // NavigableSet
  @VisibleForTesting
  static class SynchronizedNavigableSet extends SynchronizedSortedSet
      implements NavigableSet {
    SynchronizedNavigableSet(NavigableSet delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    NavigableSet delegate() {
      return (NavigableSet) super.delegate();
    }

    @Override
    public E ceiling(E e) {
      synchronized (mutex) {
        return delegate().ceiling(e);
      }
    }

    @Override
    public Iterator descendingIterator() {
      return delegate().descendingIterator(); // manually synchronized
    }

    @MonotonicNonNullDecl transient NavigableSet descendingSet;

    @Override
    public NavigableSet descendingSet() {
      synchronized (mutex) {
        if (descendingSet == null) {
          NavigableSet dS = Synchronized.navigableSet(delegate().descendingSet(), mutex);
          descendingSet = dS;
          return dS;
        }
        return descendingSet;
      }
    }

    @Override
    public E floor(E e) {
      synchronized (mutex) {
        return delegate().floor(e);
      }
    }

    @Override
    public NavigableSet headSet(E toElement, boolean inclusive) {
      synchronized (mutex) {
        return Synchronized.navigableSet(delegate().headSet(toElement, inclusive), mutex);
      }
    }

    @Override
    public SortedSet headSet(E toElement) {
      return headSet(toElement, false);
    }

    @Override
    public E higher(E e) {
      synchronized (mutex) {
        return delegate().higher(e);
      }
    }

    @Override
    public E lower(E e) {
      synchronized (mutex) {
        return delegate().lower(e);
      }
    }

    @Override
    public E pollFirst() {
      synchronized (mutex) {
        return delegate().pollFirst();
      }
    }

    @Override
    public E pollLast() {
      synchronized (mutex) {
        return delegate().pollLast();
      }
    }

    @Override
    public NavigableSet subSet(
        E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
      synchronized (mutex) {
        return Synchronized.navigableSet(
            delegate().subSet(fromElement, fromInclusive, toElement, toInclusive), mutex);
      }
    }

    @Override
    public SortedSet subSet(E fromElement, E toElement) {
      return subSet(fromElement, true, toElement, false);
    }

    @Override
    public NavigableSet tailSet(E fromElement, boolean inclusive) {
      synchronized (mutex) {
        return Synchronized.navigableSet(delegate().tailSet(fromElement, inclusive), mutex);
      }
    }

    @Override
    public SortedSet tailSet(E fromElement) {
      return tailSet(fromElement, true);
    }

    private static final long serialVersionUID = 0;
  }

  @GwtIncompatible // NavigableSet
  static  NavigableSet navigableSet(
      NavigableSet navigableSet, @NullableDecl Object mutex) {
    return new SynchronizedNavigableSet(navigableSet, mutex);
  }

  @GwtIncompatible // NavigableSet
  static  NavigableSet navigableSet(NavigableSet navigableSet) {
    return navigableSet(navigableSet, null);
  }

  @GwtIncompatible // NavigableMap
  static  NavigableMap navigableMap(NavigableMap navigableMap) {
    return navigableMap(navigableMap, null);
  }

  @GwtIncompatible // NavigableMap
  static  NavigableMap navigableMap(
      NavigableMap navigableMap, @NullableDecl Object mutex) {
    return new SynchronizedNavigableMap<>(navigableMap, mutex);
  }

  @GwtIncompatible // NavigableMap
  @VisibleForTesting
  static class SynchronizedNavigableMap extends SynchronizedSortedMap
      implements NavigableMap {

    SynchronizedNavigableMap(NavigableMap delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    NavigableMap delegate() {
      return (NavigableMap) super.delegate();
    }

    @Override
    public Entry ceilingEntry(K key) {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().ceilingEntry(key), mutex);
      }
    }

    @Override
    public K ceilingKey(K key) {
      synchronized (mutex) {
        return delegate().ceilingKey(key);
      }
    }

    @MonotonicNonNullDecl transient NavigableSet descendingKeySet;

    @Override
    public NavigableSet descendingKeySet() {
      synchronized (mutex) {
        if (descendingKeySet == null) {
          return descendingKeySet = Synchronized.navigableSet(delegate().descendingKeySet(), mutex);
        }
        return descendingKeySet;
      }
    }

    @MonotonicNonNullDecl transient NavigableMap descendingMap;

    @Override
    public NavigableMap descendingMap() {
      synchronized (mutex) {
        if (descendingMap == null) {
          return descendingMap = navigableMap(delegate().descendingMap(), mutex);
        }
        return descendingMap;
      }
    }

    @Override
    public Entry firstEntry() {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().firstEntry(), mutex);
      }
    }

    @Override
    public Entry floorEntry(K key) {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().floorEntry(key), mutex);
      }
    }

    @Override
    public K floorKey(K key) {
      synchronized (mutex) {
        return delegate().floorKey(key);
      }
    }

    @Override
    public NavigableMap headMap(K toKey, boolean inclusive) {
      synchronized (mutex) {
        return navigableMap(delegate().headMap(toKey, inclusive), mutex);
      }
    }

    @Override
    public SortedMap headMap(K toKey) {
      return headMap(toKey, false);
    }

    @Override
    public Entry higherEntry(K key) {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().higherEntry(key), mutex);
      }
    }

    @Override
    public K higherKey(K key) {
      synchronized (mutex) {
        return delegate().higherKey(key);
      }
    }

    @Override
    public Entry lastEntry() {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().lastEntry(), mutex);
      }
    }

    @Override
    public Entry lowerEntry(K key) {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().lowerEntry(key), mutex);
      }
    }

    @Override
    public K lowerKey(K key) {
      synchronized (mutex) {
        return delegate().lowerKey(key);
      }
    }

    @Override
    public Set keySet() {
      return navigableKeySet();
    }

    @MonotonicNonNullDecl transient NavigableSet navigableKeySet;

    @Override
    public NavigableSet navigableKeySet() {
      synchronized (mutex) {
        if (navigableKeySet == null) {
          return navigableKeySet = Synchronized.navigableSet(delegate().navigableKeySet(), mutex);
        }
        return navigableKeySet;
      }
    }

    @Override
    public Entry pollFirstEntry() {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().pollFirstEntry(), mutex);
      }
    }

    @Override
    public Entry pollLastEntry() {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().pollLastEntry(), mutex);
      }
    }

    @Override
    public NavigableMap subMap(
        K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
      synchronized (mutex) {
        return navigableMap(delegate().subMap(fromKey, fromInclusive, toKey, toInclusive), mutex);
      }
    }

    @Override
    public SortedMap subMap(K fromKey, K toKey) {
      return subMap(fromKey, true, toKey, false);
    }

    @Override
    public NavigableMap tailMap(K fromKey, boolean inclusive) {
      synchronized (mutex) {
        return navigableMap(delegate().tailMap(fromKey, inclusive), mutex);
      }
    }

    @Override
    public SortedMap tailMap(K fromKey) {
      return tailMap(fromKey, true);
    }

    private static final long serialVersionUID = 0;
  }

  @GwtIncompatible // works but is needed only for NavigableMap
  private static  Entry nullableSynchronizedEntry(
      @NullableDecl Entry entry, @NullableDecl Object mutex) {
    if (entry == null) {
      return null;
    }
    return new SynchronizedEntry<>(entry, mutex);
  }

  @GwtIncompatible // works but is needed only for NavigableMap
  private static class SynchronizedEntry extends SynchronizedObject implements Entry {

    SynchronizedEntry(Entry delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @SuppressWarnings("unchecked") // guaranteed by the constructor
    @Override
    Entry delegate() {
      return (Entry) super.delegate();
    }

    @Override
    public boolean equals(Object obj) {
      synchronized (mutex) {
        return delegate().equals(obj);
      }
    }

    @Override
    public int hashCode() {
      synchronized (mutex) {
        return delegate().hashCode();
      }
    }

    @Override
    public K getKey() {
      synchronized (mutex) {
        return delegate().getKey();
      }
    }

    @Override
    public V getValue() {
      synchronized (mutex) {
        return delegate().getValue();
      }
    }

    @Override
    public V setValue(V value) {
      synchronized (mutex) {
        return delegate().setValue(value);
      }
    }

    private static final long serialVersionUID = 0;
  }

  static  Queue queue(Queue queue, @NullableDecl Object mutex) {
    return (queue instanceof SynchronizedQueue) ? queue : new SynchronizedQueue(queue, mutex);
  }

  private static class SynchronizedQueue extends SynchronizedCollection implements Queue {

    SynchronizedQueue(Queue delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    Queue delegate() {
      return (Queue) super.delegate();
    }

    @Override
    public E element() {
      synchronized (mutex) {
        return delegate().element();
      }
    }

    @Override
    public boolean offer(E e) {
      synchronized (mutex) {
        return delegate().offer(e);
      }
    }

    @Override
    public E peek() {
      synchronized (mutex) {
        return delegate().peek();
      }
    }

    @Override
    public E poll() {
      synchronized (mutex) {
        return delegate().poll();
      }
    }

    @Override
    public E remove() {
      synchronized (mutex) {
        return delegate().remove();
      }
    }

    private static final long serialVersionUID = 0;
  }

  static  Deque deque(Deque deque, @NullableDecl Object mutex) {
    return new SynchronizedDeque(deque, mutex);
  }

  private static final class SynchronizedDeque extends SynchronizedQueue implements Deque {

    SynchronizedDeque(Deque delegate, @NullableDecl Object mutex) {
      super(delegate, mutex);
    }

    @Override
    Deque delegate() {
      return (Deque) super.delegate();
    }

    @Override
    public void addFirst(E e) {
      synchronized (mutex) {
        delegate().addFirst(e);
      }
    }

    @Override
    public void addLast(E e) {
      synchronized (mutex) {
        delegate().addLast(e);
      }
    }

    @Override
    public boolean offerFirst(E e) {
      synchronized (mutex) {
        return delegate().offerFirst(e);
      }
    }

    @Override
    public boolean offerLast(E e) {
      synchronized (mutex) {
        return delegate().offerLast(e);
      }
    }

    @Override
    public E removeFirst() {
      synchronized (mutex) {
        return delegate().removeFirst();
      }
    }

    @Override
    public E removeLast() {
      synchronized (mutex) {
        return delegate().removeLast();
      }
    }

    @Override
    public E pollFirst() {
      synchronized (mutex) {
        return delegate().pollFirst();
      }
    }

    @Override
    public E pollLast() {
      synchronized (mutex) {
        return delegate().pollLast();
      }
    }

    @Override
    public E getFirst() {
      synchronized (mutex) {
        return delegate().getFirst();
      }
    }

    @Override
    public E getLast() {
      synchronized (mutex) {
        return delegate().getLast();
      }
    }

    @Override
    public E peekFirst() {
      synchronized (mutex) {
        return delegate().peekFirst();
      }
    }

    @Override
    public E peekLast() {
      synchronized (mutex) {
        return delegate().peekLast();
      }
    }

    @Override
    public boolean removeFirstOccurrence(Object o) {
      synchronized (mutex) {
        return delegate().removeFirstOccurrence(o);
      }
    }

    @Override
    public boolean removeLastOccurrence(Object o) {
      synchronized (mutex) {
        return delegate().removeLastOccurrence(o);
      }
    }

    @Override
    public void push(E e) {
      synchronized (mutex) {
        delegate().push(e);
      }
    }

    @Override
    public E pop() {
      synchronized (mutex) {
        return delegate().pop();
      }
    }

    @Override
    public Iterator descendingIterator() {
      synchronized (mutex) {
        return delegate().descendingIterator();
      }
    }

    private static final long serialVersionUID = 0;
  }

  static  Table table(Table table, Object mutex) {
    return new SynchronizedTable<>(table, mutex);
  }

  private static final class SynchronizedTable extends SynchronizedObject
      implements Table {

    SynchronizedTable(Table delegate, Object mutex) {
      super(delegate, mutex);
    }

    @SuppressWarnings("unchecked")
    @Override
    Table delegate() {
      return (Table) super.delegate();
    }

    @Override
    public boolean contains(@NullableDecl Object rowKey, @NullableDecl Object columnKey) {
      synchronized (mutex) {
        return delegate().contains(rowKey, columnKey);
      }
    }

    @Override
    public boolean containsRow(@NullableDecl Object rowKey) {
      synchronized (mutex) {
        return delegate().containsRow(rowKey);
      }
    }

    @Override
    public boolean containsColumn(@NullableDecl Object columnKey) {
      synchronized (mutex) {
        return delegate().containsColumn(columnKey);
      }
    }

    @Override
    public boolean containsValue(@NullableDecl Object value) {
      synchronized (mutex) {
        return delegate().containsValue(value);
      }
    }

    @Override
    public V get(@NullableDecl Object rowKey, @NullableDecl Object columnKey) {
      synchronized (mutex) {
        return delegate().get(rowKey, columnKey);
      }
    }

    @Override
    public boolean isEmpty() {
      synchronized (mutex) {
        return delegate().isEmpty();
      }
    }

    @Override
    public int size() {
      synchronized (mutex) {
        return delegate().size();
      }
    }

    @Override
    public void clear() {
      synchronized (mutex) {
        delegate().clear();
      }
    }

    @Override
    public V put(@NullableDecl R rowKey, @NullableDecl C columnKey, @NullableDecl V value) {
      synchronized (mutex) {
        return delegate().put(rowKey, columnKey, value);
      }
    }

    @Override
    public void putAll(Table table) {
      synchronized (mutex) {
        delegate().putAll(table);
      }
    }

    @Override
    public V remove(@NullableDecl Object rowKey, @NullableDecl Object columnKey) {
      synchronized (mutex) {
        return delegate().remove(rowKey, columnKey);
      }
    }

    @Override
    public Map row(@NullableDecl R rowKey) {
      synchronized (mutex) {
        return map(delegate().row(rowKey), mutex);
      }
    }

    @Override
    public Map column(@NullableDecl C columnKey) {
      synchronized (mutex) {
        return map(delegate().column(columnKey), mutex);
      }
    }

    @Override
    public Set> cellSet() {
      synchronized (mutex) {
        return set(delegate().cellSet(), mutex);
      }
    }

    @Override
    public Set rowKeySet() {
      synchronized (mutex) {
        return set(delegate().rowKeySet(), mutex);
      }
    }

    @Override
    public Set columnKeySet() {
      synchronized (mutex) {
        return set(delegate().columnKeySet(), mutex);
      }
    }

    @Override
    public Collection values() {
      synchronized (mutex) {
        return collection(delegate().values(), mutex);
      }
    }

    @Override
    public Map> rowMap() {
      synchronized (mutex) {
        return map(
            Maps.transformValues(
                delegate().rowMap(),
                new com.google.common.base.Function, Map>() {
                  @Override
                  public Map apply(Map t) {
                    return map(t, mutex);
                  }
                }),
            mutex);
      }
    }

    @Override
    public Map> columnMap() {
      synchronized (mutex) {
        return map(
            Maps.transformValues(
                delegate().columnMap(),
                new com.google.common.base.Function, Map>() {
                  @Override
                  public Map apply(Map t) {
                    return map(t, mutex);
                  }
                }),
            mutex);
      }
    }

    @Override
    public int hashCode() {
      synchronized (mutex) {
        return delegate().hashCode();
      }
    }

    @Override
    public boolean equals(@NullableDecl Object obj) {
      if (this == obj) {
        return true;
      }
      synchronized (mutex) {
        return delegate().equals(obj);
      }
    }
  }
}