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="../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="../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()) {
     *   do {
     *     K k = entry.getKey();
     *     V v = entry.getValue();
     *   } while (!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}, then returning the current value or {@code null} if now
     * absent:
     *
     * <pre> {@code
     * if (map.get(key) == null) {
     *   V newValue = mappingFunction.apply(key);
     *   if (newValue != null)
     *     return map.putIfAbsent(key, newValue);
     * }}</pre>
     *
     * The default implementation may retry these steps when multiple
     * threads attempt updates including potentially calling the mapping
     * function 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}
     * @since 1.8
     */
    @Override
    default V computeIfAbsent(K key,
            Function<? super K, ? extends V> mappingFunction) {
        Objects.requireNonNull(mappingFunction);
        V v, newValue;
        return ((v = get(key)) == null &&
                (newValue = mappingFunction.apply(key)) != null &&
                (v = putIfAbsent(key, newValue)) == null) ? newValue : v;
    }

    /**
     * {@inheritDoc}
     *
     * @implSpec
     * The default implementation is equivalent to performing the following
     * steps for this {@code map}, then returning the current value or
     * {@code null} if now absent:
     *
     * <pre> {@code
     * if (map.get(key) != null) {
     *   V oldValue = map.get(key);
     *   V newValue = remappingFunction.apply(key, oldValue);
     *   if (newValue != null)
     *     map.replace(key, oldValue, newValue);
     *   else
     *     map.remove(key, oldValue);
     * }}</pre>
     *
     * The default implementation may retry these steps when multiple threads
     * attempt updates including potentially calling the remapping function
     * 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}
     * @since 1.8
     */
    @Override
    default V computeIfPresent(K key,
            BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
        V oldValue;
        while ((oldValue = get(key)) != null) {
            V newValue = remappingFunction.apply(key, oldValue);
            if (newValue != null) {
                if (replace(key, oldValue, newValue))
                    return newValue;
            } else if (remove(key, oldValue))
                return null;
        }
        return oldValue;
    }

    /**
     * {@inheritDoc}
     *
     * @implSpec
     * The default implementation is equivalent to performing the following
     * steps for this {@code map}, then returning the current value or
     * {@code null} if absent:
     *
     * <pre> {@code
     * V oldValue = map.get(key);
     * V newValue = remappingFunction.apply(key, oldValue);
     * if (oldValue != null ) {
     *   if (newValue != null)
     *     map.replace(key, oldValue, newValue);
     *   else
     *     map.remove(key, oldValue);
     * } else {
     *   if (newValue != null)
     *     map.putIfAbsent(key, newValue);
     *   else
     *     return null;
     * }}</pre>
     *
     * The default implementation may retry these steps when multiple
     * threads attempt updates including potentially calling the remapping
     * function 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}
     * @since 1.8
     */
    @Override
    default V compute(K key,
            BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
        V oldValue = get(key);
        for (;;) {
            V newValue = remappingFunction.apply(key, oldValue);
            if (newValue == null) {
                // delete mapping
                if (oldValue != null || containsKey(key)) {
                    // something to remove
                    if (remove(key, oldValue)) {
                        // removed the old value as expected
                        return null;
                    }

                    // some other value replaced old value. try again.
                    oldValue = get(key);
                } else {
                    // nothing to do. Leave things as they were.
                    return null;
                }
            } else {
                // add or replace old mapping
                if (oldValue != null) {
                    // replace
                    if (replace(key, oldValue, newValue)) {
                        // replaced as expected.
                        return newValue;
                    }

                    // some other value replaced old value. try again.
                    oldValue = get(key);
                } else {
                    // add (replace if oldValue was null)
                    if ((oldValue = putIfAbsent(key, newValue)) == null) {
                        // replaced
                        return newValue;
                    }

                    // some other value replaced old value. try again.
                }
            }
        }
    }

    /**
     * {@inheritDoc}
     *
     * @implSpec
     * The default implementation is equivalent to performing the following
     * steps for this {@code map}, then returning the current value or
     * {@code null} if absent:
     *
     * <pre> {@code
     * V oldValue = map.get(key);
     * V newValue = (oldValue == null) ? value :
     *     remappingFunction.apply(oldValue, value);
     * if (newValue == null)
     *   map.remove(key);
     * else
     *   map.put(key, newValue);}</pre>
     *
     * <p>The default implementation may retry these steps when multiple
     * threads attempt updates including potentially calling the remapping
     * function 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}
     * @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);
        V oldValue = get(key);
        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;
                }
                oldValue = get(key);
            } else {
                if ((oldValue = putIfAbsent(key, value)) == null) {
                    return value;
                }
            }
        }
    }
}
Revision:	1.60
Committed:	Thu Apr 30 18:47:12 2015 UTC (9 years, 1 month ago) by jsr166
Branch:	MAIN
Changes since 1.59:	+5 -5 lines
Log Message:	add "for this map"
#	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) && 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="../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="../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) && Objects.equals(map.get(key), oldValue)) {
166	* map.put(key, newValue);
167	* return true;
168	* } else {
169	* return false;
170	* }}</pre>
171	*
172	* except that the action is performed atomically.
173	*
174	* @implNote This implementation intentionally re-abstracts the
175	* inappropriate default provided in {@code Map}.
176	*
177	* @param key key with which the specified value is associated
178	* @param oldValue value expected to be associated with the specified key
179	* @param newValue value to be associated with the specified key
180	* @return {@code true} if the value was replaced
181	* @throws UnsupportedOperationException if the {@code put} operation
182	* is not supported by this map
183	* @throws ClassCastException if the class of a specified key or value
184	* prevents it from being stored in this map
185	* @throws NullPointerException if a specified key or value is null,
186	* and this map does not permit null keys or values
187	* @throws IllegalArgumentException if some property of a specified key
188	* or value prevents it from being stored in this map
189	*/
190	boolean replace(K key, V oldValue, V newValue);
191
192	/**
193	* Replaces the entry for a key only if currently mapped to some value.
194	* This is equivalent to, for this {@code map}:
195	* <pre> {@code
196	* if (map.containsKey(key)) {
197	* return map.put(key, value);
198	* } else {
199	* return null;
200	* }}</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	* do {
233	* K k = entry.getKey();
234	* V v = entry.getValue();
235	* } while (!replace(k, v, function.apply(k, v)));
236	* }}</pre>
237	*
238	* The default implementation may retry these steps when multiple
239	* threads attempt updates including potentially calling the function
240	* repeatedly for a given key.
241	*
242	* <p>This implementation assumes that the ConcurrentMap cannot contain null
243	* values and {@code get()} returning null unambiguously means the key is
244	* absent. Implementations which support null values <strong>must</strong>
245	* override this default implementation.
246	*
247	* @throws UnsupportedOperationException {@inheritDoc}
248	* @throws NullPointerException {@inheritDoc}
249	* @throws ClassCastException {@inheritDoc}
250	* @throws IllegalArgumentException {@inheritDoc}
251	* @since 1.8
252	*/
253	@Override
254	default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
255	Objects.requireNonNull(function);
256	forEach((k,v) -> {
257	while (!replace(k, v, function.apply(k, v))) {
258	// v changed or k is gone
259	if ( (v = get(k)) == null) {
260	// k is no longer in the map.
261	break;
262	}
263	}
264	});
265	}
266
267	/**
268	* {@inheritDoc}
269	*
270	* @implSpec
271	* The default implementation is equivalent to the following steps for this
272	* {@code map}, then returning the current value or {@code null} if now
273	* absent:
274	*
275	* <pre> {@code
276	* if (map.get(key) == null) {
277	* V newValue = mappingFunction.apply(key);
278	* if (newValue != null)
279	* return map.putIfAbsent(key, newValue);
280	* }}</pre>
281	*
282	* The default implementation may retry these steps when multiple
283	* threads attempt updates including potentially calling the mapping
284	* function multiple times.
285	*
286	* <p>This implementation assumes that the ConcurrentMap cannot contain null
287	* values and {@code get()} returning null unambiguously means the key is
288	* absent. Implementations which support null values <strong>must</strong>
289	* override this default implementation.
290	*
291	* @throws UnsupportedOperationException {@inheritDoc}
292	* @throws ClassCastException {@inheritDoc}
293	* @throws NullPointerException {@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 v, newValue;
301	return ((v = get(key)) == null &&
302	(newValue = mappingFunction.apply(key)) != null &&
303	(v = putIfAbsent(key, newValue)) == null) ? newValue : v;
304	}
305
306	/**
307	* {@inheritDoc}
308	*
309	* @implSpec
310	* The default implementation is equivalent to performing the following
311	* steps for this {@code map}, then returning the current value or
312	* {@code null} if now absent:
313	*
314	* <pre> {@code
315	* if (map.get(key) != null) {
316	* V oldValue = map.get(key);
317	* V newValue = remappingFunction.apply(key, oldValue);
318	* if (newValue != null)
319	* map.replace(key, oldValue, newValue);
320	* else
321	* map.remove(key, oldValue);
322	* }}</pre>
323	*
324	* The default implementation may retry these steps when multiple threads
325	* attempt updates including potentially calling the remapping function
326	* multiple times.
327	*
328	* <p>This implementation assumes that the ConcurrentMap cannot contain null
329	* values and {@code get()} returning null unambiguously means the key is
330	* absent. Implementations which support null values <strong>must</strong>
331	* override this default implementation.
332	*
333	* @throws UnsupportedOperationException {@inheritDoc}
334	* @throws ClassCastException {@inheritDoc}
335	* @throws NullPointerException {@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	V oldValue;
343	while ((oldValue = get(key)) != null) {
344	V newValue = remappingFunction.apply(key, oldValue);
345	if (newValue != null) {
346	if (replace(key, oldValue, newValue))
347	return newValue;
348	} else if (remove(key, oldValue))
349	return null;
350	}
351	return oldValue;
352	}
353
354	/**
355	* {@inheritDoc}
356	*
357	* @implSpec
358	* The default implementation is equivalent to performing the following
359	* steps for this {@code map}, then returning the current value or
360	* {@code null} if absent:
361	*
362	* <pre> {@code
363	* V oldValue = map.get(key);
364	* V newValue = remappingFunction.apply(key, oldValue);
365	* if (oldValue != null ) {
366	* if (newValue != null)
367	* map.replace(key, oldValue, newValue);
368	* else
369	* map.remove(key, oldValue);
370	* } else {
371	* if (newValue != null)
372	* map.putIfAbsent(key, newValue);
373	* else
374	* return null;
375	* }}</pre>
376	*
377	* The default implementation may retry these steps when multiple
378	* threads attempt updates including potentially calling the remapping
379	* function multiple times.
380	*
381	* <p>This implementation assumes that the ConcurrentMap cannot contain null
382	* values and {@code get()} returning null unambiguously means the key is
383	* absent. Implementations which support null values <strong>must</strong>
384	* override this default implementation.
385	*
386	* @throws UnsupportedOperationException {@inheritDoc}
387	* @throws ClassCastException {@inheritDoc}
388	* @throws NullPointerException {@inheritDoc}
389	* @since 1.8
390	*/
391	@Override
392	default V compute(K key,
393	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
394	Objects.requireNonNull(remappingFunction);
395	V oldValue = get(key);
396	for (;;) {
397	V newValue = remappingFunction.apply(key, oldValue);
398	if (newValue == null) {
399	// delete mapping
400	if (oldValue != null \|\| containsKey(key)) {
401	// something to remove
402	if (remove(key, oldValue)) {
403	// removed the old value as expected
404	return null;
405	}
406
407	// some other value replaced old value. try again.
408	oldValue = get(key);
409	} else {
410	// nothing to do. Leave things as they were.
411	return null;
412	}
413	} else {
414	// add or replace old mapping
415	if (oldValue != null) {
416	// replace
417	if (replace(key, oldValue, newValue)) {
418	// replaced as expected.
419	return newValue;
420	}
421
422	// some other value replaced old value. try again.
423	oldValue = get(key);
424	} else {
425	// add (replace if oldValue was null)
426	if ((oldValue = putIfAbsent(key, newValue)) == null) {
427	// replaced
428	return newValue;
429	}
430
431	// some other value replaced old value. try again.
432	}
433	}
434	}
435	}
436
437	/**
438	* {@inheritDoc}
439	*
440	* @implSpec
441	* The default implementation is equivalent to performing the following
442	* steps for this {@code map}, then returning the current value or
443	* {@code null} if absent:
444	*
445	* <pre> {@code
446	* V oldValue = map.get(key);
447	* V newValue = (oldValue == null) ? value :
448	* remappingFunction.apply(oldValue, value);
449	* if (newValue == null)
450	* map.remove(key);
451	* else
452	* map.put(key, newValue);}</pre>
453	*
454	* <p>The default implementation may retry these steps when multiple
455	* threads attempt updates including potentially calling the remapping
456	* function multiple times.
457	*
458	* <p>This implementation assumes that the ConcurrentMap cannot contain null
459	* values and {@code get()} returning null unambiguously means the key is
460	* absent. Implementations which support null values <strong>must</strong>
461	* override this default implementation.
462	*
463	* @throws UnsupportedOperationException {@inheritDoc}
464	* @throws ClassCastException {@inheritDoc}
465	* @throws NullPointerException {@inheritDoc}
466	* @since 1.8
467	*/
468	@Override
469	default V merge(K key, V value,
470	BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
471	Objects.requireNonNull(remappingFunction);
472	Objects.requireNonNull(value);
473	V oldValue = get(key);
474	for (;;) {
475	if (oldValue != null) {
476	V newValue = remappingFunction.apply(oldValue, value);
477	if (newValue != null) {
478	if (replace(key, oldValue, newValue))
479	return newValue;
480	} else if (remove(key, oldValue)) {
481	return null;
482	}
483	oldValue = get(key);
484	} else {
485	if ((oldValue = putIfAbsent(key, value)) == null) {
486	return value;
487	}
488	}
489	}
490	}
491	}