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    /*
 * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * The Universal Permissive License (UPL), Version 1.0
 *
 * Subject to the condition set forth below, permission is hereby granted to any
 * person obtaining a copy of this software, associated documentation and/or
 * data (collectively the "Software"), free of charge and under any and all
 * copyright rights in the Software, and any and all patent rights owned or
 * freely licensable by each licensor hereunder covering either (i) the
 * unmodified Software as contributed to or provided by such licensor, or (ii)
 * the Larger Works (as defined below), to deal in both
 *
 * (a) the Software, and
 *
 * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
 * one is included with the Software each a "Larger Work" to which the Software
 * is contributed by such licensors),
 *
 * without restriction, including without limitation the rights to copy, create
 * derivative works of, display, perform, and distribute the Software and make,
 * use, sell, offer for sale, import, export, have made, and have sold the
 * Software and the Larger Work(s), and to sublicense the foregoing rights on
 * either these or other terms.
 *
 * This license is subject to the following condition:
 *
 * The above copyright notice and either this complete permission notice or at a
 * minimum a reference to the UPL must be included in all copies or substantial
 * portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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 * SOFTWARE.
 */
/* @formatter:off for the whole file. */
/* Checkstyle: stop for the whole file. */
package com.oracle.graal.python.util;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Set;
import java.util.Spliterator;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Consumer;


/**
 * Hash table based implementation of the Map interface, with
 * weak keys.
 * An entry in a WeakHashMap will automatically be removed when
 * its key is no longer in ordinary use.  More precisely, the presence of a
 * mapping for a given key will not prevent the key from being discarded by the
 * garbage collector, that is, made finalizable, finalized, and then reclaimed.
 * When a key has been discarded its entry is effectively removed from the map,
 * so this class behaves somewhat differently from other Map
 * implementations.
 *
 * 
     Both null values and the null key are supported. This class has
 * performance characteristics similar to those of the HashMap
 * class, and has the same efficiency parameters of initial capacity
 * and load factor.
 *
 * 
     Like most collection classes, this class is not synchronized.
 * A synchronized WeakHashMap may be constructed using the
 * {@link Collections#synchronizedMap Collections.synchronizedMap}
 * method.
 *
 * 
     This class is intended primarily for use with key objects whose
 * equals methods test for object identity using the
 * == operator.  Once such a key is discarded it can never be
 * recreated, so it is impossible to do a lookup of that key in a
 * WeakHashMap at some later time and be surprised that its entry
 * has been removed.  This class will work perfectly well with key objects
 * whose equals methods are not based upon object identity, such
 * as String instances.  With such recreatable key objects,
 * however, the automatic removal of WeakHashMap entries whose
 * keys have been discarded may prove to be confusing.
 *
 * 
     The behavior of the WeakHashMap class depends in part upon
 * the actions of the garbage collector, so several familiar (though not
 * required) Map invariants do not hold for this class.  Because
 * the garbage collector may discard keys at any time, a
 * WeakHashMap may behave as though an unknown thread is silently
 * removing entries.  In particular, even if you synchronize on a
 * WeakHashMap instance and invoke none of its mutator methods, it
 * is possible for the size method to return smaller values over
 * time, for the isEmpty method to return false and
 * then true, for the containsKey method to return
 * true and later false for a given key, for the
 * get method to return a value for a given key but later return
 * null, for the put method to return
 * null and the remove method to return
 * false for a key that previously appeared to be in the map, and
 * for successive examinations of the key set, the value collection, and
 * the entry set to yield successively smaller numbers of elements.
 *
 * 
     Each key object in a WeakHashMap is stored indirectly as
 * the referent of a weak reference.  Therefore a key will automatically be
 * removed only after the weak references to it, both inside and outside of the
 * map, have been cleared by the garbage collector.
 *
 * 
     Implementation note: The value objects in a
 * WeakHashMap are held by ordinary strong references.  Thus care
 * should be taken to ensure that value objects do not strongly refer to their
 * own keys, either directly or indirectly, since that will prevent the keys
 * from being discarded.  Note that a value object may refer indirectly to its
 * key via the WeakHashMap itself; that is, a value object may
 * strongly refer to some other key object whose associated value object, in
 * turn, strongly refers to the key of the first value object.  If the values
 * in the map do not rely on the map holding strong references to them, one way
 * to deal with this is to wrap values themselves within
 * WeakReferences before
 * inserting, as in: m.put(key, new WeakReference(value)),
 * and then unwrapping upon each get.
 *
 * 
    The iterators returned by the iterator method of the collections
 * returned by all of this class's "collection view methods" are
 * fail-fast: if the map is structurally modified at any time after the
 * iterator is created, in any way except through the iterator's own
 * remove method, the iterator will throw a {@link
 * ConcurrentModificationException}.  Thus, in the face of concurrent
 * modification, the iterator fails quickly and cleanly, rather than risking
 * arbitrary, non-deterministic behavior at an undetermined time in the future.
 *
 * 
    Note that the fail-fast behavior of an iterator cannot be guaranteed
 * as it is, generally speaking, impossible to make any hard guarantees in the
 * presence of unsynchronized concurrent modification.  Fail-fast iterators
 * throw ConcurrentModificationException on a best-effort basis.
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness:  the fail-fast behavior of iterators
 * should be used only to detect bugs.
 *
 * 
    This class is a member of the
 * 
 * Java Collections Framework.
 *
 * @param  the type of keys maintained by this map
 * @param  the type of mapped values
 *
 * @author      Doug Lea
 * @author      Josh Bloch
 * @author      Mark Reinhold
 * @since       1.2
 * @see         java.util.HashMap
 * @see         java.lang.ref.WeakReference
 */
/**
 * This file is a copy (sigh) of  OpenJDK / jdk8u / jdk8u-dev / jdk
 * src/share/classes/java/util/WeakHashMap.java @ 13329:c35f231af17a 
 * with the following changes:
 * 
      
 * 
    1. Turning off the formatter for the whole file so that comments stay the same.
      2. 
 * 
    2. Disabling checkstyle for the whole file.
      3. 
 * 
    3. Changing the copyright date.
      4. 
 * 
    4. Changing the package name.
      5. 
 * 
    5. Disabling warnings for the whole class.
      6. 
 * 
    6. Uniformly changing WeakHashMap to WeakIdentityHashMap
 *     in the code (but not the JavaDoc! So the diff is easier to read.).
      7. 
 * 
    7. Updating the import statements.
      8. 
 * 
    8. Copying in the declarations of {@link #keySet} and {@link #values}
 *     from {@link AbstractMap}, which are otherwise package-private.
      9. 
 * 
    9. Changing {@link #hash(Object)} to use {@link System#identityHashCode(Object)}.
      10. 
 * 
    10. Changing {@link #eq(Object, Object)} to compare objects with reference equality.
      11. 
 * 
    11. Changing {@link Entry#hashCode()} to use {@link System#identityHashCode(Object)}
 *     to contribute to the hash code of an {@link Entry}.
      12. 
 * 
    12. Changing {@link Entry#equals(Object)} to compare keys using reference equality
 *     (after which the values are compared with {@link Object#equals(Object)}).
      13. 
 * 
    
 */
@SuppressWarnings("all")
public class WeakIdentityHashMap
        extends AbstractMap
        implements Map {

    /**
     * The default initial capacity -- MUST be a power of two.
     */
    private static final int DEFAULT_INITIAL_CAPACITY = 16;

    /**
     * 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.
     */
    private static final int MAXIMUM_CAPACITY = 1 << 30;

    /**
     * The load factor used when none specified in constructor.
     */
    private static final float DEFAULT_LOAD_FACTOR = 0.75f;

    /**
     * The table, resized as necessary. Length MUST Always be a power of two.
     */
    Entry[] table;

    /**
     * The number of key-value mappings contained in this weak hash map.
     */
    private int size;

    /**
     * The next size value at which to resize (capacity * load factor).
     */
    private int threshold;

    /**
     * The load factor for the hash table.
     */
    private final float loadFactor;

    /**
     * Reference queue for cleared WeakEntries
     */
    private final ReferenceQueue queue = new ReferenceQueue<>();

    /**
     * The number of times this WeakHashMap has been structurally modified.
     * Structural modifications are those that change the number of
     * mappings in the map or otherwise modify its internal structure
     * (e.g., rehash).  This field is used to make iterators on
     * Collection-views of the map fail-fast.
     *
     * @see ConcurrentModificationException
     */
    int modCount;

    /** "Inherited" from {@link AbstractMap}. */
    transient Set keySet;
    /** "Inherited" from {@link AbstractMap}. */
    transient Collection values;

    @SuppressWarnings("unchecked")
    private Entry[] newTable(int n) {
        return (Entry[]) new Entry[n];
    }

    /**
     * Constructs a new, empty WeakHashMap with the given initial
     * capacity and the given load factor.
     *
     * @param  initialCapacity The initial capacity of the WeakHashMap
     * @param  loadFactor      The load factor of the WeakHashMap
     * @throws IllegalArgumentException if the initial capacity is negative,
     *         or if the load factor is nonpositive.
     */
    public WeakIdentityHashMap(int initialCapacity, float loadFactor) {
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Initial Capacity: "+
                    initialCapacity);
        if (initialCapacity > MAXIMUM_CAPACITY)
            initialCapacity = MAXIMUM_CAPACITY;

        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new IllegalArgumentException("Illegal Load factor: "+
                    loadFactor);
        int capacity = 1;
        while (capacity < initialCapacity)
            capacity <<= 1;
        table = newTable(capacity);
        this.loadFactor = loadFactor;
        threshold = (int)(capacity * loadFactor);
    }

    /**
     * Constructs a new, empty WeakHashMap with the given initial
     * capacity and the default load factor (0.75).
     *
     * @param  initialCapacity The initial capacity of the WeakHashMap
     * @throws IllegalArgumentException if the initial capacity is negative
     */
    public WeakIdentityHashMap(int initialCapacity) {
        this(initialCapacity, DEFAULT_LOAD_FACTOR);
    }

    /**
     * Constructs a new, empty WeakHashMap with the default initial
     * capacity (16) and load factor (0.75).
     */
    public WeakIdentityHashMap() {
        this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
    }

    /**
     * Constructs a new WeakHashMap with the same mappings as the
     * specified map.  The WeakHashMap is created with the default
     * load factor (0.75) and an initial capacity sufficient to hold the
     * mappings in the specified map.
     *
     * @param   m the map whose mappings are to be placed in this map
     * @throws  NullPointerException if the specified map is null
     * @since   1.3
     */
    @SuppressWarnings("this-escape")
    public WeakIdentityHashMap(Map m) {
        this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
                DEFAULT_INITIAL_CAPACITY),
                DEFAULT_LOAD_FACTOR);
        putAll(m);
    }

    // internal utilities

    /**
     * Value representing null keys inside tables.
     */
    private static final Object NULL_KEY = new Object();

    /**
     * Use NULL_KEY for key if it is null.
     */
    private static Object maskNull(Object key) {
        return (key == null) ? NULL_KEY : key;
    }

    /**
     * Returns internal representation of null key back to caller as null.
     */
    static Object unmaskNull(Object key) {
        return (key == NULL_KEY) ? null : key;
    }

    /**
     * Checks for equality of non-null reference x and possibly-null y.  By
     * default uses Object.equals.
     */
    private static boolean eq(Object x, Object y) {
        return x == y;
    }

    /**
     * Retrieve object hash code and applies a supplemental hash function to the
     * result hash, which defends against poor quality hash functions.  This is
     * critical because HashMap uses power-of-two length hash tables, that
     * otherwise encounter collisions for hashCodes that do not differ
     * in lower bits.
     */
    final int hash(Object k) {
        int h = System.identityHashCode(k);

        // This function ensures that hashCodes that differ only by
        // constant multiples at each bit position have a bounded
        // number of collisions (approximately 8 at default load factor).
        h ^= (h >>> 20) ^ (h >>> 12);
        return h ^ (h >>> 7) ^ (h >>> 4);
    }

    /**
     * Returns index for hash code h.
     */
    private static int indexFor(int h, int length) {
        return h & (length-1);
    }

    /**
     * Expunges stale entries from the table.
     */
    @SuppressFBWarnings(value = "SA_FIELD_SELF_ASSIGNMENT")
    private void expungeStaleEntries() {
        for (Object x; (x = queue.poll()) != null; ) {
            synchronized (queue) {
                @SuppressWarnings("unchecked")
                Entry e = (Entry) x;
                int i = indexFor(e.hash, table.length);

                Entry prev = table[i];
                Entry p = prev;
                while (p != null) {
                    Entry next = p.next;
                    if (p == e) {
                        if (prev == e)
                            table[i] = next;
                        else
                            prev.next = next;
                        // Must not null out e.next;
                        // stale entries may be in use by a HashIterator
                        e.value = null; // Help GC
                        size--;
                        break;
                    }
                    prev = p;
                    p = next;
                }
            }
        }
    }

    /**
     * Returns the table after first expunging stale entries.
     */
    private Entry[] getTable() {
        expungeStaleEntries();
        return table;
    }

    /**
     * Returns the number of key-value mappings in this map.
     * This result is a snapshot, and may not reflect unprocessed
     * entries that will be removed before next attempted access
     * because they are no longer referenced.
     */
    public int size() {
        if (size == 0)
            return 0;
        expungeStaleEntries();
        return size;
    }

    /**
     * Returns true if this map contains no key-value mappings.
     * This result is a snapshot, and may not reflect unprocessed
     * entries that will be removed before next attempted access
     * because they are no longer referenced.
     */
    public boolean isEmpty() {
        return size() == 0;
    }

    /**
     * Returns the value to which the specified key is mapped,
     * or {@code null} if this map contains no mapping for the key.
     *
     * 
    More formally, if this map contains a mapping from a key
     * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
     * key.equals(k))}, then this method returns {@code v}; otherwise
     * it returns {@code null}.  (There can be at most one such mapping.)
     *
     * 
    A return value of {@code null} does not necessarily
     * indicate that the map contains no mapping for the key; it's also
     * possible that the map explicitly maps the key to {@code null}.
     * The {@link #containsKey containsKey} operation may be used to
     * distinguish these two cases.
     *
     * @see #put(Object, Object)
     */
    public V get(Object key) {
        Object k = maskNull(key);
        int h = hash(k);
        Entry[] tab = getTable();
        int index = indexFor(h, tab.length);
        Entry e = tab[index];
        while (e != null) {
            if (e.hash == h && eq(k, e.get()))
                return e.value;
            e = e.next;
        }
        return null;
    }

    /**
     * Returns true if this map contains a mapping for the
     * specified key.
     *
     * @param  key   The key whose presence in this map is to be tested
     * @return true if there is a mapping for key;
     *         false otherwise
     */
    public boolean containsKey(Object key) {
        return getEntry(key) != null;
    }

    /**
     * Returns the entry associated with the specified key in this map.
     * Returns null if the map contains no mapping for this key.
     */
    Entry getEntry(Object key) {
        Object k = maskNull(key);
        int h = hash(k);
        Entry[] tab = getTable();
        int index = indexFor(h, tab.length);
        Entry e = tab[index];
        while (e != null && !(e.hash == h && eq(k, e.get())))
            e = e.next;
        return e;
    }

    /**
     * Associates the specified value with the specified key in this map.
     * If the map previously contained a mapping for this key, the old
     * value is replaced.
     *
     * @param key key with which the specified value is to be associated.
     * @param value value to be associated with the specified key.
     * @return the previous value associated with key, or
     *         null if there was no mapping for key.
     *         (A null return can also indicate that the map
     *         previously associated null with key.)
     */
    public V put(K key, V value) {
        Object k = maskNull(key);
        int h = hash(k);
        Entry[] tab = getTable();
        int i = indexFor(h, tab.length);

        for (Entry e = tab[i]; e != null; e = e.next) {
            if (h == e.hash && eq(k, e.get())) {
                V oldValue = e.value;
                if (value != oldValue)
                    e.value = value;
                return oldValue;
            }
        }

        modCount++;
        Entry e = tab[i];
        tab[i] = new Entry<>(k, value, queue, h, e);
        if (++size >= threshold)
            resize(tab.length * 2);
        return null;
    }

    /**
     * Rehashes the contents of this map into a new array with a
     * larger capacity.  This method is called automatically when the
     * number of keys in this map reaches its threshold.
     *
     * If current capacity is MAXIMUM_CAPACITY, this method does not
     * resize the map, but sets threshold to Integer.MAX_VALUE.
     * This has the effect of preventing future calls.
     *
     * @param newCapacity the new capacity, MUST be a power of two;
     *        must be greater than current capacity unless current
     *        capacity is MAXIMUM_CAPACITY (in which case value
     *        is irrelevant).
     */
    void resize(int newCapacity) {
        Entry[] oldTable = getTable();
        int oldCapacity = oldTable.length;
        if (oldCapacity == MAXIMUM_CAPACITY) {
            threshold = Integer.MAX_VALUE;
            return;
        }

        Entry[] newTable = newTable(newCapacity);
        transfer(oldTable, newTable);
        table = newTable;

        /*
         * If ignoring null elements and processing ref queue caused massive
         * shrinkage, then restore old table.  This should be rare, but avoids
         * unbounded expansion of garbage-filled tables.
         */
        if (size >= threshold / 2) {
            threshold = (int)(newCapacity * loadFactor);
        } else {
            expungeStaleEntries();
            transfer(newTable, oldTable);
            table = oldTable;
        }
    }

    /** Transfers all entries from src to dest tables */
    private void transfer(Entry[] src, Entry[] dest) {
        for (int j = 0; j < src.length; ++j) {
            Entry e = src[j];
            src[j] = null;
            while (e != null) {
                Entry next = e.next;
                Object key = e.get();
                if (key == null) {
                    e.next = null;  // Help GC
                    e.value = null; //  "   "
                    size--;
                } else {
                    int i = indexFor(e.hash, dest.length);
                    e.next = dest[i];
                    dest[i] = e;
                }
                e = next;
            }
        }
    }

    /**
     * Copies all of the mappings from the specified map to this map.
     * These mappings will replace any mappings that this map had for any
     * of the keys currently in the specified map.
     *
     * @param m mappings to be stored in this map.
     * @throws  NullPointerException if the specified map is null.
     */
    public void putAll(Map m) {
        int numKeysToBeAdded = m.size();
        if (numKeysToBeAdded == 0)
            return;

        /*
         * Expand the map if the map if the number of mappings to be added
         * is greater than or equal to threshold.  This is conservative; the
         * obvious condition is (m.size() + size) >= threshold, but this
         * condition could result in a map with twice the appropriate capacity,
         * if the keys to be added overlap with the keys already in this map.
         * By using the conservative calculation, we subject ourself
         * to at most one extra resize.
         */
        if (numKeysToBeAdded > threshold) {
            int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
            if (targetCapacity > MAXIMUM_CAPACITY)
                targetCapacity = MAXIMUM_CAPACITY;
            int newCapacity = table.length;
            while (newCapacity < targetCapacity)
                newCapacity <<= 1;
            if (newCapacity > table.length)
                resize(newCapacity);
        }

        for (Map.Entry e : m.entrySet())
            put(e.getKey(), e.getValue());
    }

    /**
     * Removes the mapping for a key from this weak hash map if it is present.
     * More formally, if this map contains a mapping from key k to
     * value v such that (key==null ?  k==null :
     * key.equals(k)), that mapping is removed.  (The map can contain
     * at most one such mapping.)
     *
     * 
    Returns the value to which this map previously associated the key,
     * or null if the map contained no mapping for the key.  A
     * return value of null does not necessarily indicate
     * that the map contained no mapping for the key; it's also possible
     * that the map explicitly mapped the key to null.
     *
     * 
    The map will not contain a mapping for the specified key once the
     * call returns.
     *
     * @param key key whose mapping is to be removed from the map
     * @return the previous value associated with key, or
     *         null if there was no mapping for key
     */
    public V remove(Object key) {
        Object k = maskNull(key);
        int h = hash(k);
        Entry[] tab = getTable();
        int i = indexFor(h, tab.length);
        Entry prev = tab[i];
        Entry e = prev;

        while (e != null) {
            Entry next = e.next;
            if (h == e.hash && eq(k, e.get())) {
                modCount++;
                size--;
                if (prev == e)
                    tab[i] = next;
                else
                    prev.next = next;
                return e.value;
            }
            prev = e;
            e = next;
        }

        return null;
    }

    /** Special version of remove needed by Entry set */
    boolean removeMapping(Object o) {
        if (!(o instanceof Map.Entry))
            return false;
        Entry[] tab = getTable();
        Map.Entry entry = (Map.Entry)o;
        Object k = maskNull(entry.getKey());
        int h = hash(k);
        int i = indexFor(h, tab.length);
        Entry prev = tab[i];
        Entry e = prev;

        while (e != null) {
            Entry next = e.next;
            if (h == e.hash && e.equals(entry)) {
                modCount++;
                size--;
                if (prev == e)
                    tab[i] = next;
                else
                    prev.next = next;
                return true;
            }
            prev = e;
            e = next;
        }

        return false;
    }

    /**
     * Removes all of the mappings from this map.
     * The map will be empty after this call returns.
     */
    public void clear() {
        // clear out ref queue. We don't need to expunge entries
        // since table is getting cleared.
        while (queue.poll() != null)
            ;

        modCount++;
        Arrays.fill(table, null);
        size = 0;

        // Allocation of array may have caused GC, which may have caused
        // additional entries to go stale.  Removing these entries from the
        // reference queue will make them eligible for reclamation.
        while (queue.poll() != null)
            ;
    }

    /**
     * Returns true if this map maps one or more keys to the
     * specified value.
     *
     * @param value value whose presence in this map is to be tested
     * @return true if this map maps one or more keys to the
     *         specified value
     */
    public boolean containsValue(Object value) {
        if (value==null)
            return containsNullValue();

        Entry[] tab = getTable();
        for (int i = tab.length; i-- > 0;)
            for (Entry e = tab[i]; e != null; e = e.next)
                if (value.equals(e.value))
                    return true;
        return false;
    }

    /**
     * Special-case code for containsValue with null argument
     */
    private boolean containsNullValue() {
        Entry[] tab = getTable();
        for (int i = tab.length; i-- > 0;)
            for (Entry e = tab[i]; e != null; e = e.next)
                if (e.value==null)
                    return true;
        return false;
    }

    /**
     * The entries in this hash table extend WeakReference, using its main ref
     * field as the key.
     */
    private static class Entry extends WeakReference implements Map.Entry {
        V value;
        final int hash;
        Entry next;

        /**
         * Creates new entry.
         */
        Entry(Object key, V value,
              ReferenceQueue queue,
              int hash, Entry next) {
            super(key, queue);
            this.value = value;
            this.hash  = hash;
            this.next  = next;
        }

        @SuppressWarnings("unchecked")
        public K getKey() {
            return (K) WeakIdentityHashMap.unmaskNull(get());
        }

        public V getValue() {
            return value;
        }

        public V setValue(V newValue) {
            V oldValue = value;
            value = newValue;
            return oldValue;
        }

        public boolean equals(Object o) {
            if (!(o instanceof Map.Entry))
                return false;
            Map.Entry e = (Map.Entry)o;
            K k1 = getKey();
            Object k2 = e.getKey();
            if (k1 == k2) {
                V v1 = getValue();
                Object v2 = e.getValue();
                if (v1 == v2 || (v1 != null && v1.equals(v2)))
                    return true;
            }
            return false;
        }

        public int hashCode() {
            K k = getKey();
            V v = getValue();
            return System.identityHashCode(k) ^ Objects.hashCode(v);
        }

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

    private abstract class HashIterator implements Iterator {
        private int index;
        private Entry entry;
        private Entry lastReturned;
        private int expectedModCount = modCount;

        /**
         * Strong reference needed to avoid disappearance of key
         * between hasNext and next
         */
        private Object nextKey;

        /**
         * Strong reference needed to avoid disappearance of key
         * between nextEntry() and any use of the entry
         */
        private Object currentKey;

        HashIterator() {
            index = isEmpty() ? 0 : table.length;
        }

        @SuppressFBWarnings(value = "SA_FIELD_SELF_ASSIGNMENT")
        public boolean hasNext() {
            Entry[] t = table;

            while (nextKey == null) {
                Entry e = entry;
                int i = index;
                while (e == null && i > 0)
                    e = t[--i];
                entry = e;
                index = i;
                if (e == null) {
                    currentKey = null;
                    return false;
                }
                nextKey = e.get(); // hold on to key in strong ref
                if (nextKey == null)
                    entry = entry.next;
            }
            return true;
        }

        /** The common parts of next() across different types of iterators */
        protected Entry nextEntry() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            if (nextKey == null && !hasNext())
                throw new NoSuchElementException();

            lastReturned = entry;
            entry = entry.next;
            currentKey = nextKey;
            nextKey = null;
            return lastReturned;
        }

        public void remove() {
            if (lastReturned == null)
                throw new IllegalStateException();
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();

            WeakIdentityHashMap.this.remove(currentKey);
            expectedModCount = modCount;
            lastReturned = null;
            currentKey = null;
        }

    }

    private class ValueIterator extends HashIterator {
        public V next() {
            return nextEntry().value;
        }
    }

    private class KeyIterator extends HashIterator {
        public K next() {
            return nextEntry().getKey();
        }
    }

    private class EntryIterator extends HashIterator> {
        public Map.Entry next() {
            return nextEntry();
        }
    }

    // Views

    private transient Set> entrySet;

    /**
     * Returns a {@link Set} view of the keys contained in this map.
     * The set is backed by the map, so changes to the map are
     * reflected in the set, and vice-versa.  If the map is modified
     * while an iteration over the set is in progress (except through
     * the iterator's own remove operation), the results of
     * the iteration are undefined.  The set supports element removal,
     * which removes the corresponding mapping from the map, via the
     * Iterator.remove, Set.remove,
     * removeAll, retainAll, and clear
     * operations.  It does not support the add or addAll
     * operations.
     */
    public Set keySet() {
        Set ks = keySet;
        if (ks == null) {
            ks = new KeySet();
            keySet = ks;
        }
        return ks;
    }

    private class KeySet extends AbstractSet {
        public Iterator iterator() {
            return new KeyIterator();
        }

        public int size() {
            return WeakIdentityHashMap.this.size();
        }

        public boolean contains(Object o) {
            return containsKey(o);
        }

        public boolean remove(Object o) {
            if (containsKey(o)) {
                WeakIdentityHashMap.this.remove(o);
                return true;
            }
            else
                return false;
        }

        public void clear() {
            WeakIdentityHashMap.this.clear();
        }

        public Spliterator spliterator() {
            return new KeySpliterator<>(WeakIdentityHashMap.this, 0, -1, 0, 0);
        }
    }

    /**
     * Returns a {@link Collection} view of the values contained in this map.
     * The collection is backed by the map, so changes to the map are
     * reflected in the collection, and vice-versa.  If the map is
     * modified while an iteration over the collection is in progress
     * (except through the iterator's own remove operation),
     * the results of the iteration are undefined.  The collection
     * supports element removal, which removes the corresponding
     * mapping from the map, via the Iterator.remove,
     * Collection.remove, removeAll,
     * retainAll and clear operations.  It does not
     * support the add or addAll operations.
     */
    public Collection values() {
        Collection vs = values;
        if (vs == null) {
            vs = new Values();
            values = vs;
        }
        return vs;
    }

    private class Values extends AbstractCollection {
        public Iterator iterator() {
            return new ValueIterator();
        }

        public int size() {
            return WeakIdentityHashMap.this.size();
        }

        public boolean contains(Object o) {
            return containsValue(o);
        }

        public void clear() {
            WeakIdentityHashMap.this.clear();
        }

        public Spliterator spliterator() {
            return new ValueSpliterator<>(WeakIdentityHashMap.this, 0, -1, 0, 0);
        }
    }

    /**
     * Returns a {@link Set} view of the mappings contained in this map.
     * The set is backed by the map, so changes to the map are
     * reflected in the set, and vice-versa.  If the map is modified
     * while an iteration over the set is in progress (except through
     * the iterator's own remove operation, or through the
     * setValue operation on a map entry returned by the
     * iterator) the results of the iteration are undefined.  The set
     * supports element removal, which removes the corresponding
     * mapping from the map, via the Iterator.remove,
     * Set.remove, removeAll, retainAll and
     * clear operations.  It does not support the
     * add or addAll operations.
     */
    public Set> entrySet() {
        Set> es = entrySet;
        return es != null ? es : (entrySet = new EntrySet());
    }

    private class EntrySet extends AbstractSet> {
        public Iterator> iterator() {
            return new EntryIterator();
        }

        public boolean contains(Object o) {
            if (!(o instanceof Map.Entry))
                return false;
            Map.Entry e = (Map.Entry)o;
            Entry candidate = getEntry(e.getKey());
            return candidate != null && candidate.equals(e);
        }

        public boolean remove(Object o) {
            return removeMapping(o);
        }

        public int size() {
            return WeakIdentityHashMap.this.size();
        }

        public void clear() {
            WeakIdentityHashMap.this.clear();
        }

        private List> deepCopy() {
            List> list = new ArrayList<>(size());
            for (Map.Entry e : this)
                list.add(new AbstractMap.SimpleEntry<>(e));
            return list;
        }

        public Object[] toArray() {
            return deepCopy().toArray();
        }

        public  T[] toArray(T[] a) {
            return deepCopy().toArray(a);
        }

        public Spliterator> spliterator() {
            return new EntrySpliterator<>(WeakIdentityHashMap.this, 0, -1, 0, 0);
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public void forEach(BiConsumer action) {
        Objects.requireNonNull(action);
        int expectedModCount = modCount;

        Entry[] tab = getTable();
        for (Entry entry : tab) {
            while (entry != null) {
                Object key = entry.get();
                if (key != null) {
                    action.accept((K)WeakIdentityHashMap.unmaskNull(key), entry.value);
                }
                entry = entry.next;

                if (expectedModCount != modCount) {
                    throw new ConcurrentModificationException();
                }
            }
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public void replaceAll(BiFunction function) {
        Objects.requireNonNull(function);
        int expectedModCount = modCount;

        Entry[] tab = getTable();;
        for (Entry entry : tab) {
            while (entry != null) {
                Object key = entry.get();
                if (key != null) {
                    entry.value = function.apply((K)WeakIdentityHashMap.unmaskNull(key), entry.value);
                }
                entry = entry.next;

                if (expectedModCount != modCount) {
                    throw new ConcurrentModificationException();
                }
            }
        }
    }

    /**
     * Similar form as other hash Spliterators, but skips dead
     * elements.
     */
    static class WeakIdentityHashMapSpliterator {
        final WeakIdentityHashMap map;
        WeakIdentityHashMap.Entry current; // current node
        int index;             // current index, modified on advance/split
        int fence;             // -1 until first use; then one past last index
        int est;               // size estimate
        int expectedModCount;  // for comodification checks

        WeakIdentityHashMapSpliterator(WeakIdentityHashMap m, int origin,
                                       int fence, int est,
                                       int expectedModCount) {
            this.map = m;
            this.index = origin;
            this.fence = fence;
            this.est = est;
            this.expectedModCount = expectedModCount;
        }

        final int getFence() { // initialize fence and size on first use
            int hi;
            if ((hi = fence) < 0) {
                WeakIdentityHashMap m = map;
                est = m.size();
                expectedModCount = m.modCount;
                hi = fence = m.table.length;
            }
            return hi;
        }

        public final long estimateSize() {
            getFence(); // force init
            return (long) est;
        }
    }

    static final class KeySpliterator
            extends WeakIdentityHashMapSpliterator
            implements Spliterator {
        KeySpliterator(WeakIdentityHashMap m, int origin, int fence, int est,
                       int expectedModCount) {
            super(m, origin, fence, est, expectedModCount);
        }

        public KeySpliterator trySplit() {
            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
            return (lo >= mid) ? null :
                    new KeySpliterator(map, lo, index = mid, est >>>= 1,
                            expectedModCount);
        }

        public void forEachRemaining(Consumer action) {
            int i, hi, mc;
            if (action == null)
                throw new NullPointerException();
            WeakIdentityHashMap m = map;
            WeakIdentityHashMap.Entry[] tab = m.table;
            if ((hi = fence) < 0) {
                mc = expectedModCount = m.modCount;
                hi = fence = tab.length;
            }
            else
                mc = expectedModCount;
            if (tab.length >= hi && (i = index) >= 0 &&
                    (i < (index = hi) || current != null)) {
                WeakIdentityHashMap.Entry p = current;
                current = null; // exhaust
                do {
                    if (p == null)
                        p = tab[i++];
                    else {
                        Object x = p.get();
                        p = p.next;
                        if (x != null) {
                            @SuppressWarnings("unchecked") K k =
                                    (K) WeakIdentityHashMap.unmaskNull(x);
                            action.accept(k);
                        }
                    }
                } while (p != null || i < hi);
            }
            if (m.modCount != mc)
                throw new ConcurrentModificationException();
        }

        public boolean tryAdvance(Consumer action) {
            int hi;
            if (action == null)
                throw new NullPointerException();
            WeakIdentityHashMap.Entry[] tab = map.table;
            if (tab.length >= (hi = getFence()) && index >= 0) {
                while (current != null || index < hi) {
                    if (current == null)
                        current = tab[index++];
                    else {
                        Object x = current.get();
                        current = current.next;
                        if (x != null) {
                            @SuppressWarnings("unchecked") K k =
                                    (K) WeakIdentityHashMap.unmaskNull(x);
                            action.accept(k);
                            if (map.modCount != expectedModCount)
                                throw new ConcurrentModificationException();
                            return true;
                        }
                    }
                }
            }
            return false;
        }

        public int characteristics() {
            return Spliterator.DISTINCT;
        }
    }

    static final class ValueSpliterator
            extends WeakIdentityHashMapSpliterator
            implements Spliterator {
        ValueSpliterator(WeakIdentityHashMap m, int origin, int fence, int est,
                         int expectedModCount) {
            super(m, origin, fence, est, expectedModCount);
        }

        public ValueSpliterator trySplit() {
            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
            return (lo >= mid) ? null :
                    new ValueSpliterator(map, lo, index = mid, est >>>= 1,
                            expectedModCount);
        }

        public void forEachRemaining(Consumer action) {
            int i, hi, mc;
            if (action == null)
                throw new NullPointerException();
            WeakIdentityHashMap m = map;
            WeakIdentityHashMap.Entry[] tab = m.table;
            if ((hi = fence) < 0) {
                mc = expectedModCount = m.modCount;
                hi = fence = tab.length;
            }
            else
                mc = expectedModCount;
            if (tab.length >= hi && (i = index) >= 0 &&
                    (i < (index = hi) || current != null)) {
                WeakIdentityHashMap.Entry p = current;
                current = null; // exhaust
                do {
                    if (p == null)
                        p = tab[i++];
                    else {
                        Object x = p.get();
                        V v = p.value;
                        p = p.next;
                        if (x != null)
                            action.accept(v);
                    }
                } while (p != null || i < hi);
            }
            if (m.modCount != mc)
                throw new ConcurrentModificationException();
        }

        public boolean tryAdvance(Consumer action) {
            int hi;
            if (action == null)
                throw new NullPointerException();
            WeakIdentityHashMap.Entry[] tab = map.table;
            if (tab.length >= (hi = getFence()) && index >= 0) {
                while (current != null || index < hi) {
                    if (current == null)
                        current = tab[index++];
                    else {
                        Object x = current.get();
                        V v = current.value;
                        current = current.next;
                        if (x != null) {
                            action.accept(v);
                            if (map.modCount != expectedModCount)
                                throw new ConcurrentModificationException();
                            return true;
                        }
                    }
                }
            }
            return false;
        }

        public int characteristics() {
            return 0;
        }
    }

    static final class EntrySpliterator
            extends WeakIdentityHashMapSpliterator
            implements Spliterator> {
        EntrySpliterator(WeakIdentityHashMap m, int origin, int fence, int est,
                         int expectedModCount) {
            super(m, origin, fence, est, expectedModCount);
        }

        public EntrySpliterator trySplit() {
            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
            return (lo >= mid) ? null :
                    new EntrySpliterator(map, lo, index = mid, est >>>= 1,
                            expectedModCount);
        }


        public void forEachRemaining(Consumer> action) {
            int i, hi, mc;
            if (action == null)
                throw new NullPointerException();
            WeakIdentityHashMap m = map;
            WeakIdentityHashMap.Entry[] tab = m.table;
            if ((hi = fence) < 0) {
                mc = expectedModCount = m.modCount;
                hi = fence = tab.length;
            }
            else
                mc = expectedModCount;
            if (tab.length >= hi && (i = index) >= 0 &&
                    (i < (index = hi) || current != null)) {
                WeakIdentityHashMap.Entry p = current;
                current = null; // exhaust
                do {
                    if (p == null)
                        p = tab[i++];
                    else {
                        Object x = p.get();
                        V v = p.value;
                        p = p.next;
                        if (x != null) {
                            @SuppressWarnings("unchecked") K k =
                                    (K) WeakIdentityHashMap.unmaskNull(x);
                            action.accept
                                    (new AbstractMap.SimpleImmutableEntry(k, v));
                        }
                    }
                } while (p != null || i < hi);
            }
            if (m.modCount != mc)
                throw new ConcurrentModificationException();
        }

        public boolean tryAdvance(Consumer> action) {
            int hi;
            if (action == null)
                throw new NullPointerException();
            WeakIdentityHashMap.Entry[] tab = map.table;
            if (tab.length >= (hi = getFence()) && index >= 0) {
                while (current != null || index < hi) {
                    if (current == null)
                        current = tab[index++];
                    else {
                        Object x = current.get();
                        V v = current.value;
                        current = current.next;
                        if (x != null) {
                            @SuppressWarnings("unchecked") K k =
                                    (K) WeakIdentityHashMap.unmaskNull(x);
                            action.accept
                                    (new AbstractMap.SimpleImmutableEntry(k, v));
                            if (map.modCount != expectedModCount)
                                throw new ConcurrentModificationException();
                            return true;
                        }
                    }
                }
            }
            return false;
        }

        public int characteristics() {
            return Spliterator.DISTINCT;
        }
    }

}
    
    
    
    

    




    
    
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