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 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}/java.base/java/util/package-summary.html#CollectionsFramework">
 * 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}/java.base/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}/java.base/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:	1.70
Committed:	Mon Oct 1 00:10:53 2018 UTC (5 years, 7 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.69:	+3 -3 lines
Log Message:	update to using jdk11 by default, except link to jdk10 javadocs; sync @docRoot references in javadoc with upstream
#	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 Map} providing thread safety and atomicity guarantees.
17	*
18	* <p>To maintain the specified guarantees, default implementations of
19	* methods including {@link #putIfAbsent} inherited from {@link Map}
20	* must be overridden by implementations of this interface. Similarly,
21	* implementations of the collections returned by methods {@link
22	* #keySet}, {@link #values}, and {@link #entrySet} must override
23	* methods such as {@code removeIf} when necessary to
24	* preserve atomicity guarantees.
25	*
26	* <p>Memory consistency effects: As with other concurrent
27	* collections, actions in a thread prior to placing an object into a
28	* {@code ConcurrentMap} as a key or value
29	* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
30	* actions subsequent to the access or removal of that object from
31	* the {@code ConcurrentMap} in another thread.
32	*
33	* <p>This interface is a member of the
34	* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
35	* Java Collections Framework</a>.
36	*
37	* @since 1.5
38	* @author Doug Lea
39	* @param <K> the type of keys maintained by this map
40	* @param <V> the type of mapped values
41	*/
42	public interface ConcurrentMap<K,V> extends Map<K,V> {
43
44	/**
45	* {@inheritDoc}
46	*
47	* @implNote This implementation assumes that the ConcurrentMap cannot
48	* contain null values and {@code get()} returning null unambiguously means
49	* the key is absent. Implementations which support null values
50	* <strong>must</strong> override this default implementation.
51	*
52	* @throws ClassCastException {@inheritDoc}
53	* @throws NullPointerException {@inheritDoc}
54	* @since 1.8
55	*/
56	@Override
57	default V getOrDefault(Object key, V defaultValue) {
58	V v;
59	return ((v = get(key)) != null) ? v : defaultValue;
60	}
61
62	/**
63	* {@inheritDoc}
64	*
65	* @implSpec The default implementation is equivalent to, for this
66	* {@code map}:
67	* <pre> {@code
68	* for (Map.Entry<K,V> entry : map.entrySet()) {
69	* action.accept(entry.getKey(), entry.getValue());
70	* }}</pre>
71	*
72	* @implNote The default implementation assumes that
73	* {@code IllegalStateException} thrown by {@code getKey()} or
74	* {@code getValue()} indicates that the entry has been removed and cannot
75	* be processed. Operation continues for subsequent entries.
76	*
77	* @throws NullPointerException {@inheritDoc}
78	* @since 1.8
79	*/
80	@Override
81	default void forEach(BiConsumer<? super K, ? super V> action) {
82	Objects.requireNonNull(action);
83	for (Map.Entry<K,V> entry : entrySet()) {
84	K k;
85	V v;
86	try {
87	k = entry.getKey();
88	v = entry.getValue();
89	} catch (IllegalStateException ise) {
90	// this usually means the entry is no longer in the map.
91	continue;
92	}
93	action.accept(k, v);
94	}
95	}
96
97	/**
98	* If the specified key is not already associated
99	* with a value, associates it with the given value.
100	* This is equivalent to, for this {@code map}:
101	* <pre> {@code
102	* if (!map.containsKey(key))
103	* return map.put(key, value);
104	* else
105	* return map.get(key);}</pre>
106	*
107	* except that the action is performed atomically.
108	*
109	* @implNote This implementation intentionally re-abstracts the
110	* inappropriate default provided in {@code Map}.
111	*
112	* @param key key with which the specified value is to be associated
113	* @param value value to be associated with the specified key
114	* @return the previous value associated with the specified key, or
115	* {@code null} if there was no mapping for the key.
116	* (A {@code null} return can also indicate that the map
117	* previously associated {@code null} with the key,
118	* if the implementation supports null values.)
119	* @throws UnsupportedOperationException if the {@code put} operation
120	* is not supported by this map
121	* @throws ClassCastException if the class of the specified key or value
122	* prevents it from being stored in this map
123	* @throws NullPointerException if the specified key or value is null,
124	* and this map does not permit null keys or values
125	* @throws IllegalArgumentException if some property of the specified key
126	* or value prevents it from being stored in this map
127	*/
128	V putIfAbsent(K key, V value);
129
130	/**
131	* Removes the entry for a key only if currently mapped to a given value.
132	* This is equivalent to, for this {@code map}:
133	* <pre> {@code
134	* if (map.containsKey(key)
135	* && Objects.equals(map.get(key), value)) {
136	* map.remove(key);
137	* return true;
138	* } else {
139	* return false;
140	* }}</pre>
141	*
142	* except that the action is performed atomically.
143	*
144	* @implNote This implementation intentionally re-abstracts the
145	* inappropriate default provided in {@code Map}.
146	*
147	* @param key key with which the specified value is associated
148	* @param value value expected to be associated with the specified key
149	* @return {@code true} if the value was removed
150	* @throws UnsupportedOperationException if the {@code remove} operation
151	* is not supported by this map
152	* @throws ClassCastException if the key or value is of an inappropriate
153	* type for this map
154	* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
155	* @throws NullPointerException if the specified key or value is null,
156	* and this map does not permit null keys or values
157	* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
158	*/
159	boolean remove(Object key, Object value);
160
161	/**
162	* Replaces the entry for a key only if currently mapped to a given value.
163	* This is equivalent to, for this {@code map}:
164	* <pre> {@code
165	* if (map.containsKey(key)
166	* && Objects.equals(map.get(key), oldValue)) {
167	* map.put(key, newValue);
168	* return true;
169	* } else {
170	* return false;
171	* }}</pre>
172	*
173	* except that the action is performed atomically.
174	*
175	* @implNote This implementation intentionally re-abstracts the
176	* inappropriate default provided in {@code Map}.
177	*
178	* @param key key with which the specified value is associated
179	* @param oldValue value expected to be associated with the specified key
180	* @param newValue value to be associated with the specified key
181	* @return {@code true} if the value was replaced
182	* @throws UnsupportedOperationException if the {@code put} operation
183	* is not supported by this map
184	* @throws ClassCastException if the class of a specified key or value
185	* prevents it from being stored in this map
186	* @throws NullPointerException if a specified key or value is null,
187	* and this map does not permit null keys or values
188	* @throws IllegalArgumentException if some property of a specified key
189	* or value prevents it from being stored in this map
190	*/
191	boolean replace(K key, V oldValue, V newValue);
192
193	/**
194	* Replaces the entry for a key only if currently mapped to some value.
195	* This is equivalent to, for this {@code map}:
196	* <pre> {@code
197	* if (map.containsKey(key))
198	* return map.put(key, value);
199	* else
200	* return null;}</pre>
201	*
202	* except that the action is performed atomically.
203	*
204	* @implNote This implementation intentionally re-abstracts the
205	* inappropriate default provided in {@code Map}.
206	*
207	* @param key key with which the specified value is associated
208	* @param value value to be associated with the specified key
209	* @return the previous value associated with the specified key, or
210	* {@code null} if there was no mapping for the key.
211	* (A {@code null} return can also indicate that the map
212	* previously associated {@code null} with the key,
213	* if the implementation supports null values.)
214	* @throws UnsupportedOperationException if the {@code put} operation
215	* is not supported by this map
216	* @throws ClassCastException if the class of the specified key or value
217	* prevents it from being stored in this map
218	* @throws NullPointerException if the specified key or value is null,
219	* and this map does not permit null keys or values
220	* @throws IllegalArgumentException if some property of the specified key
221	* or value prevents it from being stored in this map
222	*/
223	V replace(K key, V value);
224
225	/**
226	* {@inheritDoc}
227	*
228	* @implSpec
229	* <p>The default implementation is equivalent to, for this {@code map}:
230	* <pre> {@code
231	* for (Map.Entry<K,V> entry : map.entrySet()) {
232	* K k;
233	* V v;
234	* do {
235	* k = entry.getKey();
236	* v = entry.getValue();
237	* } while (!map.replace(k, v, function.apply(k, v)));
238	* }}</pre>
239	*
240	* The default implementation may retry these steps when multiple
241	* threads attempt updates including potentially calling the function
242	* repeatedly for a given key.
243	*
244	* <p>This implementation assumes that the ConcurrentMap cannot contain null
245	* values and {@code get()} returning null unambiguously means the key is
246	* absent. Implementations which support null values <strong>must</strong>
247	* override this default implementation.
248	*
249	* @throws UnsupportedOperationException {@inheritDoc}
250	* @throws NullPointerException {@inheritDoc}
251	* @throws ClassCastException {@inheritDoc}
252	* @throws IllegalArgumentException {@inheritDoc}
253	* @since 1.8
254	*/
255	@Override
256	default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
257	Objects.requireNonNull(function);
258	forEach((k,v) -> {
259	while (!replace(k, v, function.apply(k, v))) {
260	// v changed or k is gone
261	if ( (v = get(k)) == null) {
262	// k is no longer in the map.
263	break;
264	}
265	}
266	});
267	}
268
269	/**
270	* {@inheritDoc}
271	*
272	* @implSpec
273	* The default implementation is equivalent to the following steps for this
274	* {@code map}:
275	*
276	* <pre> {@code
277	* V oldValue, newValue;
278	* return ((oldValue = map.get(key)) == null
279	* && (newValue = mappingFunction.apply(key)) != null
280	* && (oldValue = map.putIfAbsent(key, newValue)) == null)
281	* ? newValue
282	* : oldValue;}</pre>
283	*
284	* <p>This implementation assumes that the ConcurrentMap cannot contain null
285	* values and {@code get()} returning null unambiguously means the key is
286	* absent. Implementations which support null values <strong>must</strong>
287	* override this default implementation.
288	*
289	* @throws UnsupportedOperationException {@inheritDoc}
290	* @throws ClassCastException {@inheritDoc}
291	* @throws NullPointerException {@inheritDoc}
292	* @throws IllegalArgumentException {@inheritDoc}
293	* @since 1.8
294	*/
295	@Override
296	default V computeIfAbsent(K key,
297	Function<? super K, ? extends V> mappingFunction) {
298	Objects.requireNonNull(mappingFunction);
299	V oldValue, newValue;
300	return ((oldValue = get(key)) == null
301	&& (newValue = mappingFunction.apply(key)) != null
302	&& (oldValue = putIfAbsent(key, newValue)) == null)
303	? newValue
304	: oldValue;
305	}
306
307	/**
308	* {@inheritDoc}
309	*
310	* @implSpec
311	* The default implementation is equivalent to performing the following
312	* steps for this {@code map}:
313	*
314	* <pre> {@code
315	* for (V oldValue; (oldValue = map.get(key)) != null; ) {
316	* V newValue = remappingFunction.apply(key, oldValue);
317	* if ((newValue == null)
318	* ? map.remove(key, oldValue)
319	* : map.replace(key, oldValue, newValue))
320	* return newValue;
321	* }
322	* return null;}</pre>
323	* When multiple threads attempt updates, map operations and the
324	* remapping function may be called multiple times.
325	*
326	* <p>This implementation assumes that the ConcurrentMap cannot contain null
327	* values and {@code get()} returning null unambiguously means the key is
328	* absent. Implementations which support null values <strong>must</strong>
329	* override this default implementation.
330	*
331	* @throws UnsupportedOperationException {@inheritDoc}
332	* @throws ClassCastException {@inheritDoc}
333	* @throws NullPointerException {@inheritDoc}
334	* @throws IllegalArgumentException {@inheritDoc}
335	* @since 1.8
336	*/
337	@Override
338	default V computeIfPresent(K key,
339	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
340	Objects.requireNonNull(remappingFunction);
341	for (V oldValue; (oldValue = get(key)) != null; ) {
342	V newValue = remappingFunction.apply(key, oldValue);
343	if ((newValue == null)
344	? remove(key, oldValue)
345	: replace(key, oldValue, newValue))
346	return newValue;
347	}
348	return null;
349	}
350
351	/**
352	* {@inheritDoc}
353	*
354	* @implSpec
355	* The default implementation is equivalent to performing the following
356	* steps for this {@code map}:
357	*
358	* <pre> {@code
359	* for (;;) {
360	* V oldValue = map.get(key);
361	* V newValue = remappingFunction.apply(key, oldValue);
362	* if (newValue != null) {
363	* if ((oldValue != null)
364	* ? map.replace(key, oldValue, newValue)
365	* : map.putIfAbsent(key, newValue) == null)
366	* return newValue;
367	* } else if (oldValue == null \|\| map.remove(key, oldValue)) {
368	* return null;
369	* }
370	* }}</pre>
371	* When multiple threads attempt updates, map operations and the
372	* remapping function may be called multiple times.
373	*
374	* <p>This implementation assumes that the ConcurrentMap cannot contain null
375	* values and {@code get()} returning null unambiguously means the key is
376	* absent. Implementations which support null values <strong>must</strong>
377	* override this default implementation.
378	*
379	* @throws UnsupportedOperationException {@inheritDoc}
380	* @throws ClassCastException {@inheritDoc}
381	* @throws NullPointerException {@inheritDoc}
382	* @throws IllegalArgumentException {@inheritDoc}
383	* @since 1.8
384	*/
385	@Override
386	default V compute(K key,
387	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
388	retry: for (;;) {
389	V oldValue = get(key);
390	// if putIfAbsent fails, opportunistically use its return value
391	haveOldValue: for (;;) {
392	V newValue = remappingFunction.apply(key, oldValue);
393	if (newValue != null) {
394	if (oldValue != null) {
395	if (replace(key, oldValue, newValue))
396	return newValue;
397	}
398	else if ((oldValue = putIfAbsent(key, newValue)) == null)
399	return newValue;
400	else continue haveOldValue;
401	} else if (oldValue == null \|\| remove(key, oldValue)) {
402	return null;
403	}
404	continue retry;
405	}
406	}
407	}
408
409	/**
410	* {@inheritDoc}
411	*
412	* @implSpec
413	* The default implementation is equivalent to performing the following
414	* steps for this {@code map}:
415	*
416	* <pre> {@code
417	* for (;;) {
418	* V oldValue = map.get(key);
419	* if (oldValue != null) {
420	* V newValue = remappingFunction.apply(oldValue, value);
421	* if (newValue != null) {
422	* if (map.replace(key, oldValue, newValue))
423	* return newValue;
424	* } else if (map.remove(key, oldValue)) {
425	* return null;
426	* }
427	* } else if (map.putIfAbsent(key, value) == null) {
428	* return value;
429	* }
430	* }}</pre>
431	* When multiple threads attempt updates, map operations and the
432	* remapping function may be called multiple times.
433	*
434	* <p>This implementation assumes that the ConcurrentMap cannot contain null
435	* values and {@code get()} returning null unambiguously means the key is
436	* absent. Implementations which support null values <strong>must</strong>
437	* override this default implementation.
438	*
439	* @throws UnsupportedOperationException {@inheritDoc}
440	* @throws ClassCastException {@inheritDoc}
441	* @throws NullPointerException {@inheritDoc}
442	* @throws IllegalArgumentException {@inheritDoc}
443	* @since 1.8
444	*/
445	@Override
446	default V merge(K key, V value,
447	BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
448	Objects.requireNonNull(remappingFunction);
449	Objects.requireNonNull(value);
450	retry: for (;;) {
451	V oldValue = get(key);
452	// if putIfAbsent fails, opportunistically use its return value
453	haveOldValue: for (;;) {
454	if (oldValue != null) {
455	V newValue = remappingFunction.apply(oldValue, value);
456	if (newValue != null) {
457	if (replace(key, oldValue, newValue))
458	return newValue;
459	} else if (remove(key, oldValue)) {
460	return null;
461	}
462	continue retry;
463	} else {
464	if ((oldValue = putIfAbsent(key, value)) == null)
465	return value;
466	continue haveOldValue;
467	}
468	}
469	}
470	}
471	}