util/concurrent/ConcurrentMap.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import java.util.Map;
import java.util.Objects;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Function;

/**
 * A {@link java.util.Map} providing thread safety and atomicity
 * guarantees.
 *
 * <p>To maintain the specified guarantees, default implementations of
 * methods including {@link #putIfAbsent} inherited from {@link Map}
 * must be overridden by implementations of this interface. Similarly,
 * implementations of the collections returned by methods {@link
 * #keySet}, {@link #values}, and {@link #entrySet} must override
 * methods such as {@code removeIf} when necessary to
 * preserve atomicity guarantees.
 *
 * <p>Memory consistency effects: As with other concurrent
 * collections, actions in a thread prior to placing an object into a
 * {@code ConcurrentMap} as a key or value
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions subsequent to the access or removal of that object from
 * the {@code ConcurrentMap} in another thread.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <K> the type of keys maintained by this map
 * @param <V> the type of mapped values
 */
public interface ConcurrentMap<K,V> extends Map<K,V> {

    /**
     * {@inheritDoc}
     *
     * @implNote This implementation assumes that the ConcurrentMap cannot
     * contain null values and {@code get()} returning null unambiguously means
     * the key is absent. Implementations which support null values
     * <strong>must</strong> override this default implementation.
     *
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     * @since 1.8
     */
    @Override
    default V getOrDefault(Object key, V defaultValue) {
        V v;
        return ((v = get(key)) != null) ? v : defaultValue;
    }

    /**
     * {@inheritDoc}
     *
     * @implSpec The default implementation is equivalent to, for this
     * {@code map}:
     * <pre> {@code
     * for (Map.Entry<K,V> entry : map.entrySet()) {
     *   action.accept(entry.getKey(), entry.getValue());
     * }}</pre>
     *
     * @implNote The default implementation assumes that
     * {@code IllegalStateException} thrown by {@code getKey()} or
     * {@code getValue()} indicates that the entry has been removed and cannot
     * be processed. Operation continues for subsequent entries.
     *
     * @throws NullPointerException {@inheritDoc}
     * @since 1.8
     */
    @Override
    default void forEach(BiConsumer<? super K, ? super V> action) {
        Objects.requireNonNull(action);
        for (Map.Entry<K,V> entry : entrySet()) {
            K k;
            V v;
            try {
                k = entry.getKey();
                v = entry.getValue();
            } catch (IllegalStateException ise) {
                // this usually means the entry is no longer in the map.
                continue;
            }
            action.accept(k, v);
        }
    }

    /**
     * If the specified key is not already associated
     * with a value, associates it with the given value.
     * This is equivalent to, for this {@code map}:
     * <pre> {@code
     * if (!map.containsKey(key))
     *   return map.put(key, value);
     * else
     *   return map.get(key);}</pre>
     *
     * except that the action is performed atomically.
     *
     * @implNote This implementation intentionally re-abstracts the
     * inappropriate default provided in {@code Map}.
     *
     * @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 the specified key, or
     *         {@code null} if there was no mapping for the key.
     *         (A {@code null} return can also indicate that the map
     *         previously associated {@code null} with the key,
     *         if the implementation supports null values.)
     * @throws UnsupportedOperationException if the {@code put} operation
     *         is not supported by this map
     * @throws ClassCastException if the class of the specified key or value
     *         prevents it from being stored in this map
     * @throws NullPointerException if the specified key or value is null,
     *         and this map does not permit null keys or values
     * @throws IllegalArgumentException if some property of the specified key
     *         or value prevents it from being stored in this map
     */
    V putIfAbsent(K key, V value);

    /**
     * Removes the entry for a key only if currently mapped to a given value.
     * This is equivalent to, for this {@code map}:
     * <pre> {@code
     * if (map.containsKey(key)
     *     && Objects.equals(map.get(key), value)) {
     *   map.remove(key);
     *   return true;
     * } else {
     *   return false;
     * }}</pre>
     *
     * except that the action is performed atomically.
     *
     * @implNote This implementation intentionally re-abstracts the
     * inappropriate default provided in {@code Map}.
     *
     * @param key key with which the specified value is associated
     * @param value value expected to be associated with the specified key
     * @return {@code true} if the value was removed
     * @throws UnsupportedOperationException if the {@code remove} operation
     *         is not supported by this map
     * @throws ClassCastException if the key or value is of an inappropriate
     *         type for this map
     * (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified key or value is null,
     *         and this map does not permit null keys or values
     * (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>)
     */
    boolean remove(Object key, Object value);

    /**
     * Replaces the entry for a key only if currently mapped to a given value.
     * This is equivalent to, for this {@code map}:
     * <pre> {@code
     * if (map.containsKey(key)
     *     && Objects.equals(map.get(key), oldValue)) {
     *   map.put(key, newValue);
     *   return true;
     * } else {
     *   return false;
     * }}</pre>
     *
     * except that the action is performed atomically.
     *
     * @implNote This implementation intentionally re-abstracts the
     * inappropriate default provided in {@code Map}.
     *
     * @param key key with which the specified value is associated
     * @param oldValue value expected to be associated with the specified key
     * @param newValue value to be associated with the specified key
     * @return {@code true} if the value was replaced
     * @throws UnsupportedOperationException if the {@code put} operation
     *         is not supported by this map
     * @throws ClassCastException if the class of a specified key or value
     *         prevents it from being stored in this map
     * @throws NullPointerException if a specified key or value is null,
     *         and this map does not permit null keys or values
     * @throws IllegalArgumentException if some property of a specified key
     *         or value prevents it from being stored in this map
     */
    boolean replace(K key, V oldValue, V newValue);

    /**
     * Replaces the entry for a key only if currently mapped to some value.
     * This is equivalent to, for this {@code map}:
     * <pre> {@code
     * if (map.containsKey(key))
     *   return map.put(key, value);
     * else
     *   return null;}</pre>
     *
     * except that the action is performed atomically.
     *
     * @implNote This implementation intentionally re-abstracts the
     * inappropriate default provided in {@code Map}.
     *
     * @param key key with which the specified value is associated
     * @param value value to be associated with the specified key
     * @return the previous value associated with the specified key, or
     *         {@code null} if there was no mapping for the key.
     *         (A {@code null} return can also indicate that the map
     *         previously associated {@code null} with the key,
     *         if the implementation supports null values.)
     * @throws UnsupportedOperationException if the {@code put} operation
     *         is not supported by this map
     * @throws ClassCastException if the class of the specified key or value
     *         prevents it from being stored in this map
     * @throws NullPointerException if the specified key or value is null,
     *         and this map does not permit null keys or values
     * @throws IllegalArgumentException if some property of the specified key
     *         or value prevents it from being stored in this map
     */
    V replace(K key, V value);

    /**
     * {@inheritDoc}
     *
     * @implSpec
     * <p>The default implementation is equivalent to, for this {@code map}:
     * <pre> {@code
     * for (Map.Entry<K,V> entry : map.entrySet()) {
     *   K k;
     *   V v;
     *   do {
     *     k = entry.getKey();
     *     v = entry.getValue();
     *   } while (!map.replace(k, v, function.apply(k, v)));
     * }}</pre>
     *
     * The default implementation may retry these steps when multiple
     * threads attempt updates including potentially calling the function
     * repeatedly for a given key.
     *
     * <p>This implementation assumes that the ConcurrentMap cannot contain null
     * values and {@code get()} returning null unambiguously means the key is
     * absent. Implementations which support null values <strong>must</strong>
     * override this default implementation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     * @throws ClassCastException {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.8
     */
    @Override
    default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
        Objects.requireNonNull(function);
        forEach((k,v) -> {
            while (!replace(k, v, function.apply(k, v))) {
                // v changed or k is gone
                if ( (v = get(k)) == null) {
                    // k is no longer in the map.
                    break;
                }
            }
        });
    }

    /**
     * {@inheritDoc}
     *
     * @implSpec
     * The default implementation is equivalent to the following steps for this
     * {@code map}:
     *
     * <pre> {@code
     * V oldValue, newValue;
     * return ((oldValue = map.get(key)) == null
     *         && (newValue = mappingFunction.apply(key)) != null
     *         && (oldValue = map.putIfAbsent(key, newValue)) == null)
     *   ? newValue
     *   : oldValue;}</pre>
     *
     * <p>This implementation assumes that the ConcurrentMap cannot contain null
     * values and {@code get()} returning null unambiguously means the key is
     * absent. Implementations which support null values <strong>must</strong>
     * override this default implementation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.8
     */
    @Override
    default V computeIfAbsent(K key,
            Function<? super K, ? extends V> mappingFunction) {
        Objects.requireNonNull(mappingFunction);
        V oldValue, newValue;
        return ((oldValue = get(key)) == null
                && (newValue = mappingFunction.apply(key)) != null
                && (oldValue = putIfAbsent(key, newValue)) == null)
            ? newValue
            : oldValue;
    }

    /**
     * {@inheritDoc}
     *
     * @implSpec
     * The default implementation is equivalent to performing the following
     * steps for this {@code map}:
     *
     * <pre> {@code
     * for (V oldValue; (oldValue = map.get(key)) != null; ) {
     *   V newValue = remappingFunction.apply(key, oldValue);
     *   if ((newValue == null)
     *       ? map.remove(key, oldValue)
     *       : map.replace(key, oldValue, newValue))
     *     return newValue;
     * }
     * return null;}</pre>
     * When multiple threads attempt updates, map operations and the
     * remapping function may be called multiple times.
     *
     * <p>This implementation assumes that the ConcurrentMap cannot contain null
     * values and {@code get()} returning null unambiguously means the key is
     * absent. Implementations which support null values <strong>must</strong>
     * override this default implementation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.8
     */
    @Override
    default V computeIfPresent(K key,
            BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
        for (V oldValue; (oldValue = get(key)) != null; ) {
            V newValue = remappingFunction.apply(key, oldValue);
            if ((newValue == null)
                ? remove(key, oldValue)
                : replace(key, oldValue, newValue))
                return newValue;
        }
        return null;
    }

    /**
     * {@inheritDoc}
     *
     * @implSpec
     * The default implementation is equivalent to performing the following
     * steps for this {@code map}:
     *
     * <pre> {@code
     * for (;;) {
     *   V oldValue = map.get(key);
     *   V newValue = remappingFunction.apply(key, oldValue);
     *   if (newValue != null) {
     *     if ((oldValue != null)
     *       ? map.replace(key, oldValue, newValue)
     *       : map.putIfAbsent(key, newValue) == null)
     *       return newValue;
     *   } else if (oldValue == null || map.remove(key, oldValue)) {
     *     return null;
     *   }
     * }}</pre>
     * When multiple threads attempt updates, map operations and the
     * remapping function may be called multiple times.
     *
     * <p>This implementation assumes that the ConcurrentMap cannot contain null
     * values and {@code get()} returning null unambiguously means the key is
     * absent. Implementations which support null values <strong>must</strong>
     * override this default implementation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.8
     */
    @Override
    default V compute(K key,
                      BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        retry: for (;;) {
            V oldValue = get(key);
            // if putIfAbsent fails, opportunistically use its return value
            haveOldValue: for (;;) {
                V newValue = remappingFunction.apply(key, oldValue);
                if (newValue != null) {
                    if (oldValue != null) {
                        if (replace(key, oldValue, newValue))
                            return newValue;
                    }
                    else if ((oldValue = putIfAbsent(key, newValue)) == null)
                        return newValue;
                    else continue haveOldValue;
                } else if (oldValue == null || remove(key, oldValue)) {
                    return null;
                }
                continue retry;
            }
        }
    }

    /**
     * {@inheritDoc}
     *
     * @implSpec
     * The default implementation is equivalent to performing the following
     * steps for this {@code map}:
     *
     * <pre> {@code
     * for (;;) {
     *   V oldValue = map.get(key);
     *   if (oldValue != null) {
     *     V newValue = remappingFunction.apply(oldValue, value);
     *     if (newValue != null) {
     *       if (map.replace(key, oldValue, newValue))
     *         return newValue;
     *     } else if (map.remove(key, oldValue)) {
     *       return null;
     *     }
     *   } else if (map.putIfAbsent(key, value) == null) {
     *     return value;
     *   }
     * }}</pre>
     * When multiple threads attempt updates, map operations and the
     * remapping function may be called multiple times.
     *
     * <p>This implementation assumes that the ConcurrentMap cannot contain null
     * values and {@code get()} returning null unambiguously means the key is
     * absent. Implementations which support null values <strong>must</strong>
     * override this default implementation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.8
     */
    @Override
    default V merge(K key, V value,
            BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
        Objects.requireNonNull(value);
        retry: for (;;) {
            V oldValue = get(key);
            // if putIfAbsent fails, opportunistically use its return value
            haveOldValue: for (;;) {
                if (oldValue != null) {
                    V newValue = remappingFunction.apply(oldValue, value);
                    if (newValue != null) {
                        if (replace(key, oldValue, newValue))
                            return newValue;
                    } else if (remove(key, oldValue)) {
                        return null;
                    }
                    continue retry;
                } else {
                    if ((oldValue = putIfAbsent(key, value)) == null)
                        return value;
                    continue haveOldValue;
                }
            }
        }
    }
}
Revision:	1.1
Committed:	Sat Mar 26 06:22:49 2016 UTC (8 years, 2 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	fork jdk8 maintenance branch for source and jtreg tests
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/publicdomain/zero/1.0/
5	*/
6
7	package java.util.concurrent;
8
9	import java.util.Map;
10	import java.util.Objects;
11	import java.util.function.BiConsumer;
12	import java.util.function.BiFunction;
13	import java.util.function.Function;
14
15	/**
16	* A {@link java.util.Map} providing thread safety and atomicity
17	* guarantees.
18	*
19	* <p>To maintain the specified guarantees, default implementations of
20	* methods including {@link #putIfAbsent} inherited from {@link Map}
21	* must be overridden by implementations of this interface. Similarly,
22	* implementations of the collections returned by methods {@link
23	* #keySet}, {@link #values}, and {@link #entrySet} must override
24	* methods such as {@code removeIf} when necessary to
25	* preserve atomicity guarantees.
26	*
27	* <p>Memory consistency effects: As with other concurrent
28	* collections, actions in a thread prior to placing an object into a
29	* {@code ConcurrentMap} as a key or value
30	* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
31	* actions subsequent to the access or removal of that object from
32	* the {@code ConcurrentMap} in another thread.
33	*
34	* <p>This interface is a member of the
35	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
36	* Java Collections Framework</a>.
37	*
38	* @since 1.5
39	* @author Doug Lea
40	* @param <K> the type of keys maintained by this map
41	* @param <V> the type of mapped values
42	*/
43	public interface ConcurrentMap<K,V> extends Map<K,V> {
44
45	/**
46	* {@inheritDoc}
47	*
48	* @implNote This implementation assumes that the ConcurrentMap cannot
49	* contain null values and {@code get()} returning null unambiguously means
50	* the key is absent. Implementations which support null values
51	* <strong>must</strong> override this default implementation.
52	*
53	* @throws ClassCastException {@inheritDoc}
54	* @throws NullPointerException {@inheritDoc}
55	* @since 1.8
56	*/
57	@Override
58	default V getOrDefault(Object key, V defaultValue) {
59	V v;
60	return ((v = get(key)) != null) ? v : defaultValue;
61	}
62
63	/**
64	* {@inheritDoc}
65	*
66	* @implSpec The default implementation is equivalent to, for this
67	* {@code map}:
68	* <pre> {@code
69	* for (Map.Entry<K,V> entry : map.entrySet()) {
70	* action.accept(entry.getKey(), entry.getValue());
71	* }}</pre>
72	*
73	* @implNote The default implementation assumes that
74	* {@code IllegalStateException} thrown by {@code getKey()} or
75	* {@code getValue()} indicates that the entry has been removed and cannot
76	* be processed. Operation continues for subsequent entries.
77	*
78	* @throws NullPointerException {@inheritDoc}
79	* @since 1.8
80	*/
81	@Override
82	default void forEach(BiConsumer<? super K, ? super V> action) {
83	Objects.requireNonNull(action);
84	for (Map.Entry<K,V> entry : entrySet()) {
85	K k;
86	V v;
87	try {
88	k = entry.getKey();
89	v = entry.getValue();
90	} catch (IllegalStateException ise) {
91	// this usually means the entry is no longer in the map.
92	continue;
93	}
94	action.accept(k, v);
95	}
96	}
97
98	/**
99	* If the specified key is not already associated
100	* with a value, associates it with the given value.
101	* This is equivalent to, for this {@code map}:
102	* <pre> {@code
103	* if (!map.containsKey(key))
104	* return map.put(key, value);
105	* else
106	* return map.get(key);}</pre>
107	*
108	* except that the action is performed atomically.
109	*
110	* @implNote This implementation intentionally re-abstracts the
111	* inappropriate default provided in {@code Map}.
112	*
113	* @param key key with which the specified value is to be associated
114	* @param value value to be associated with the specified key
115	* @return the previous value associated with the specified key, or
116	* {@code null} if there was no mapping for the key.
117	* (A {@code null} return can also indicate that the map
118	* previously associated {@code null} with the key,
119	* if the implementation supports null values.)
120	* @throws UnsupportedOperationException if the {@code put} operation
121	* is not supported by this map
122	* @throws ClassCastException if the class of the specified key or value
123	* prevents it from being stored in this map
124	* @throws NullPointerException if the specified key or value is null,
125	* and this map does not permit null keys or values
126	* @throws IllegalArgumentException if some property of the specified key
127	* or value prevents it from being stored in this map
128	*/
129	V putIfAbsent(K key, V value);
130
131	/**
132	* Removes the entry for a key only if currently mapped to a given value.
133	* This is equivalent to, for this {@code map}:
134	* <pre> {@code
135	* if (map.containsKey(key)
136	* && Objects.equals(map.get(key), value)) {
137	* map.remove(key);
138	* return true;
139	* } else {
140	* return false;
141	* }}</pre>
142	*
143	* except that the action is performed atomically.
144	*
145	* @implNote This implementation intentionally re-abstracts the
146	* inappropriate default provided in {@code Map}.
147	*
148	* @param key key with which the specified value is associated
149	* @param value value expected to be associated with the specified key
150	* @return {@code true} if the value was removed
151	* @throws UnsupportedOperationException if the {@code remove} operation
152	* is not supported by this map
153	* @throws ClassCastException if the key or value is of an inappropriate
154	* type for this map
155	* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>)
156	* @throws NullPointerException if the specified key or value is null,
157	* and this map does not permit null keys or values
158	* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>)
159	*/
160	boolean remove(Object key, Object value);
161
162	/**
163	* Replaces the entry for a key only if currently mapped to a given value.
164	* This is equivalent to, for this {@code map}:
165	* <pre> {@code
166	* if (map.containsKey(key)
167	* && Objects.equals(map.get(key), oldValue)) {
168	* map.put(key, newValue);
169	* return true;
170	* } else {
171	* return false;
172	* }}</pre>
173	*
174	* except that the action is performed atomically.
175	*
176	* @implNote This implementation intentionally re-abstracts the
177	* inappropriate default provided in {@code Map}.
178	*
179	* @param key key with which the specified value is associated
180	* @param oldValue value expected to be associated with the specified key
181	* @param newValue value to be associated with the specified key
182	* @return {@code true} if the value was replaced
183	* @throws UnsupportedOperationException if the {@code put} operation
184	* is not supported by this map
185	* @throws ClassCastException if the class of a specified key or value
186	* prevents it from being stored in this map
187	* @throws NullPointerException if a specified key or value is null,
188	* and this map does not permit null keys or values
189	* @throws IllegalArgumentException if some property of a specified key
190	* or value prevents it from being stored in this map
191	*/
192	boolean replace(K key, V oldValue, V newValue);
193
194	/**
195	* Replaces the entry for a key only if currently mapped to some value.
196	* This is equivalent to, for this {@code map}:
197	* <pre> {@code
198	* if (map.containsKey(key))
199	* return map.put(key, value);
200	* else
201	* return null;}</pre>
202	*
203	* except that the action is performed atomically.
204	*
205	* @implNote This implementation intentionally re-abstracts the
206	* inappropriate default provided in {@code Map}.
207	*
208	* @param key key with which the specified value is associated
209	* @param value value to be associated with the specified key
210	* @return the previous value associated with the specified key, or
211	* {@code null} if there was no mapping for the key.
212	* (A {@code null} return can also indicate that the map
213	* previously associated {@code null} with the key,
214	* if the implementation supports null values.)
215	* @throws UnsupportedOperationException if the {@code put} operation
216	* is not supported by this map
217	* @throws ClassCastException if the class of the specified key or value
218	* prevents it from being stored in this map
219	* @throws NullPointerException if the specified key or value is null,
220	* and this map does not permit null keys or values
221	* @throws IllegalArgumentException if some property of the specified key
222	* or value prevents it from being stored in this map
223	*/
224	V replace(K key, V value);
225
226	/**
227	* {@inheritDoc}
228	*
229	* @implSpec
230	* <p>The default implementation is equivalent to, for this {@code map}:
231	* <pre> {@code
232	* for (Map.Entry<K,V> entry : map.entrySet()) {
233	* K k;
234	* V v;
235	* do {
236	* k = entry.getKey();
237	* v = entry.getValue();
238	* } while (!map.replace(k, v, function.apply(k, v)));
239	* }}</pre>
240	*
241	* The default implementation may retry these steps when multiple
242	* threads attempt updates including potentially calling the function
243	* repeatedly for a given key.
244	*
245	* <p>This implementation assumes that the ConcurrentMap cannot contain null
246	* values and {@code get()} returning null unambiguously means the key is
247	* absent. Implementations which support null values <strong>must</strong>
248	* override this default implementation.
249	*
250	* @throws UnsupportedOperationException {@inheritDoc}
251	* @throws NullPointerException {@inheritDoc}
252	* @throws ClassCastException {@inheritDoc}
253	* @throws IllegalArgumentException {@inheritDoc}
254	* @since 1.8
255	*/
256	@Override
257	default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
258	Objects.requireNonNull(function);
259	forEach((k,v) -> {
260	while (!replace(k, v, function.apply(k, v))) {
261	// v changed or k is gone
262	if ( (v = get(k)) == null) {
263	// k is no longer in the map.
264	break;
265	}
266	}
267	});
268	}
269
270	/**
271	* {@inheritDoc}
272	*
273	* @implSpec
274	* The default implementation is equivalent to the following steps for this
275	* {@code map}:
276	*
277	* <pre> {@code
278	* V oldValue, newValue;
279	* return ((oldValue = map.get(key)) == null
280	* && (newValue = mappingFunction.apply(key)) != null
281	* && (oldValue = map.putIfAbsent(key, newValue)) == null)
282	* ? newValue
283	* : oldValue;}</pre>
284	*
285	* <p>This implementation assumes that the ConcurrentMap cannot contain null
286	* values and {@code get()} returning null unambiguously means the key is
287	* absent. Implementations which support null values <strong>must</strong>
288	* override this default implementation.
289	*
290	* @throws UnsupportedOperationException {@inheritDoc}
291	* @throws ClassCastException {@inheritDoc}
292	* @throws NullPointerException {@inheritDoc}
293	* @throws IllegalArgumentException {@inheritDoc}
294	* @since 1.8
295	*/
296	@Override
297	default V computeIfAbsent(K key,
298	Function<? super K, ? extends V> mappingFunction) {
299	Objects.requireNonNull(mappingFunction);
300	V oldValue, newValue;
301	return ((oldValue = get(key)) == null
302	&& (newValue = mappingFunction.apply(key)) != null
303	&& (oldValue = putIfAbsent(key, newValue)) == null)
304	? newValue
305	: oldValue;
306	}
307
308	/**
309	* {@inheritDoc}
310	*
311	* @implSpec
312	* The default implementation is equivalent to performing the following
313	* steps for this {@code map}:
314	*
315	* <pre> {@code
316	* for (V oldValue; (oldValue = map.get(key)) != null; ) {
317	* V newValue = remappingFunction.apply(key, oldValue);
318	* if ((newValue == null)
319	* ? map.remove(key, oldValue)
320	* : map.replace(key, oldValue, newValue))
321	* return newValue;
322	* }
323	* return null;}</pre>
324	* When multiple threads attempt updates, map operations and the
325	* remapping function may be called multiple times.
326	*
327	* <p>This implementation assumes that the ConcurrentMap cannot contain null
328	* values and {@code get()} returning null unambiguously means the key is
329	* absent. Implementations which support null values <strong>must</strong>
330	* override this default implementation.
331	*
332	* @throws UnsupportedOperationException {@inheritDoc}
333	* @throws ClassCastException {@inheritDoc}
334	* @throws NullPointerException {@inheritDoc}
335	* @throws IllegalArgumentException {@inheritDoc}
336	* @since 1.8
337	*/
338	@Override
339	default V computeIfPresent(K key,
340	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
341	Objects.requireNonNull(remappingFunction);
342	for (V oldValue; (oldValue = get(key)) != null; ) {
343	V newValue = remappingFunction.apply(key, oldValue);
344	if ((newValue == null)
345	? remove(key, oldValue)
346	: replace(key, oldValue, newValue))
347	return newValue;
348	}
349	return null;
350	}
351
352	/**
353	* {@inheritDoc}
354	*
355	* @implSpec
356	* The default implementation is equivalent to performing the following
357	* steps for this {@code map}:
358	*
359	* <pre> {@code
360	* for (;;) {
361	* V oldValue = map.get(key);
362	* V newValue = remappingFunction.apply(key, oldValue);
363	* if (newValue != null) {
364	* if ((oldValue != null)
365	* ? map.replace(key, oldValue, newValue)
366	* : map.putIfAbsent(key, newValue) == null)
367	* return newValue;
368	* } else if (oldValue == null \|\| map.remove(key, oldValue)) {
369	* return null;
370	* }
371	* }}</pre>
372	* When multiple threads attempt updates, map operations and the
373	* remapping function may be called multiple times.
374	*
375	* <p>This implementation assumes that the ConcurrentMap cannot contain null
376	* values and {@code get()} returning null unambiguously means the key is
377	* absent. Implementations which support null values <strong>must</strong>
378	* override this default implementation.
379	*
380	* @throws UnsupportedOperationException {@inheritDoc}
381	* @throws ClassCastException {@inheritDoc}
382	* @throws NullPointerException {@inheritDoc}
383	* @throws IllegalArgumentException {@inheritDoc}
384	* @since 1.8
385	*/
386	@Override
387	default V compute(K key,
388	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
389	retry: for (;;) {
390	V oldValue = get(key);
391	// if putIfAbsent fails, opportunistically use its return value
392	haveOldValue: for (;;) {
393	V newValue = remappingFunction.apply(key, oldValue);
394	if (newValue != null) {
395	if (oldValue != null) {
396	if (replace(key, oldValue, newValue))
397	return newValue;
398	}
399	else if ((oldValue = putIfAbsent(key, newValue)) == null)
400	return newValue;
401	else continue haveOldValue;
402	} else if (oldValue == null \|\| remove(key, oldValue)) {
403	return null;
404	}
405	continue retry;
406	}
407	}
408	}
409
410	/**
411	* {@inheritDoc}
412	*
413	* @implSpec
414	* The default implementation is equivalent to performing the following
415	* steps for this {@code map}:
416	*
417	* <pre> {@code
418	* for (;;) {
419	* V oldValue = map.get(key);
420	* if (oldValue != null) {
421	* V newValue = remappingFunction.apply(oldValue, value);
422	* if (newValue != null) {
423	* if (map.replace(key, oldValue, newValue))
424	* return newValue;
425	* } else if (map.remove(key, oldValue)) {
426	* return null;
427	* }
428	* } else if (map.putIfAbsent(key, value) == null) {
429	* return value;
430	* }
431	* }}</pre>
432	* When multiple threads attempt updates, map operations and the
433	* remapping function may be called multiple times.
434	*
435	* <p>This implementation assumes that the ConcurrentMap cannot contain null
436	* values and {@code get()} returning null unambiguously means the key is
437	* absent. Implementations which support null values <strong>must</strong>
438	* override this default implementation.
439	*
440	* @throws UnsupportedOperationException {@inheritDoc}
441	* @throws ClassCastException {@inheritDoc}
442	* @throws NullPointerException {@inheritDoc}
443	* @throws IllegalArgumentException {@inheritDoc}
444	* @since 1.8
445	*/
446	@Override
447	default V merge(K key, V value,
448	BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
449	Objects.requireNonNull(remappingFunction);
450	Objects.requireNonNull(value);
451	retry: for (;;) {
452	V oldValue = get(key);
453	// if putIfAbsent fails, opportunistically use its return value
454	haveOldValue: for (;;) {
455	if (oldValue != null) {
456	V newValue = remappingFunction.apply(oldValue, value);
457	if (newValue != null) {
458	if (replace(key, oldValue, newValue))
459	return newValue;
460	} else if (remove(key, oldValue)) {
461	return null;
462	}
463	continue retry;
464	} else {
465	if ((oldValue = putIfAbsent(key, value)) == null)
466	return value;
467	continue haveOldValue;
468	}
469	}
470	}
471	}
472	}