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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 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 javax.annotation.Nullable;

/**
 * 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, @Nullable 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, @Nullable Object mutex) {
    return new SynchronizedCollection(collection, mutex);
  }

  @VisibleForTesting static class SynchronizedCollection
      extends SynchronizedObject implements Collection {
    private SynchronizedCollection(
        Collection delegate, @Nullable 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, @Nullable Object mutex) {
    return new SynchronizedSet(set, mutex);
  }

  static class SynchronizedSet
      extends SynchronizedCollection implements Set {

    SynchronizedSet(Set delegate, @Nullable 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, @Nullable Object mutex) {
    return new SynchronizedSortedSet(set, mutex);
  }

  static class SynchronizedSortedSet extends SynchronizedSet
      implements SortedSet {
    SynchronizedSortedSet(SortedSet delegate, @Nullable 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, @Nullable 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, @Nullable 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, @Nullable Object mutex) {
      super(list, mutex);
    }
    private static final long serialVersionUID = 0;
  }

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

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

    SynchronizedMultiset(Multiset delegate, @Nullable 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, @Nullable Object mutex) {
    if (multimap instanceof SynchronizedMultimap ||
        multimap instanceof ImmutableMultimap) {
      return multimap;
    }
    return new SynchronizedMultimap(multimap, mutex);
  }

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

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

    SynchronizedMultimap(Multimap delegate, @Nullable 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, @Nullable Object mutex) {
    if (multimap instanceof SynchronizedListMultimap ||
        multimap instanceof ImmutableListMultimap) {
      return multimap;
    }
    return new SynchronizedListMultimap(multimap, mutex);
  }

  private static class SynchronizedListMultimap
      extends SynchronizedMultimap implements ListMultimap {
    SynchronizedListMultimap(
        ListMultimap delegate, @Nullable 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, @Nullable Object mutex) {
    if (multimap instanceof SynchronizedSetMultimap ||
        multimap instanceof ImmutableSetMultimap) {
      return multimap;
    }
    return new SynchronizedSetMultimap(multimap, mutex);
  }

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

    SynchronizedSetMultimap(
        SetMultimap delegate, @Nullable 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, @Nullable Object mutex) {
    if (multimap instanceof SynchronizedSortedSetMultimap) {
      return multimap;
    }
    return new SynchronizedSortedSetMultimap(multimap, mutex);
  }

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

    @Override public Iterator>> iterator() {
      // Must be manually synchronized.
      final Iterator>> iterator = super.iterator();
      return new ForwardingIterator>>() {
        @Override protected Iterator>> delegate() {
          return iterator;
        }

        @Override public Map.Entry> next() {
          final Map.Entry> entry = super.next();
          return new ForwardingMapEntry>() {
            @Override protected Map.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, @Nullable Object mutex) {
    return new SynchronizedMap(map, mutex);
  }

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

    SynchronizedMap(Map delegate, @Nullable 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, @Nullable Object mutex) {
    return new SynchronizedSortedMap(sortedMap, mutex);
  }

  static class SynchronizedSortedMap extends SynchronizedMap
      implements SortedMap {

    SynchronizedSortedMap(SortedMap delegate, @Nullable 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, @Nullable 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 {
    private transient Set valueSet;
    private transient BiMap inverse;

    private SynchronizedBiMap(BiMap delegate, @Nullable Object mutex,
        @Nullable 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> {
    transient Set>> asMapEntrySet;
    transient Collection> asMapValues;

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

    @Override public Iterator> iterator() {
      // Must be manually synchronized.
      final Iterator> iterator = super.iterator();
      return new ForwardingIterator>() {
        @Override protected Iterator> delegate() {
          return iterator;
        }
        @Override public Collection next() {
          return typePreservingCollection(super.next(), mutex);
        }
      };
    }

    private static final long serialVersionUID = 0;
  }

  @GwtIncompatible("NavigableSet")
  @VisibleForTesting
  static class SynchronizedNavigableSet extends SynchronizedSortedSet
      implements NavigableSet {
    SynchronizedNavigableSet(NavigableSet delegate, @Nullable 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
    }

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

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

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

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

    private static final long serialVersionUID = 0;
  }

  @GwtIncompatible("NavigableSet")
  static  NavigableSet navigableSet(
      NavigableSet navigableSet, @Nullable 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, @Nullable Object mutex) {
    return new SynchronizedNavigableMap(navigableMap, mutex);
  }

  @GwtIncompatible("NavigableMap")
  @VisibleForTesting static class SynchronizedNavigableMap
      extends SynchronizedSortedMap implements NavigableMap {

    SynchronizedNavigableMap(
        NavigableMap delegate, @Nullable 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);
      }
    }

    transient NavigableSet descendingKeySet;

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

    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 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();
    }

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

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

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

    @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(
      @Nullable Entry entry, @Nullable 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, @Nullable 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, @Nullable Object mutex) {
    return (queue instanceof SynchronizedQueue)
        ? queue
        : new SynchronizedQueue(queue, mutex);
  }

  private static class SynchronizedQueue extends SynchronizedCollection
      implements Queue {

    SynchronizedQueue(Queue delegate, @Nullable 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;
  }

  @GwtIncompatible("Deque")
  static  Deque deque(Deque deque, @Nullable Object mutex) {
    return new SynchronizedDeque(deque, mutex);
  }

  @GwtIncompatible("Deque")
  private static final class SynchronizedDeque
      extends SynchronizedQueue implements Deque {

    SynchronizedDeque(Deque delegate, @Nullable 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;
  }
}