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 support atomic usages, ConcurrentMaps are expected not to
 * allow {@code null} as a legal value (and to throw exceptions upon
 * attempted insertions). This enables a return value of {@code null}
 * to unambiguously indicate the absence of a mapping. This interface
 * does not strictly forbid implementations that may hold {@code null}
 * values. However, in any that do so, a {@code null} value must bear
 * the same interpretation as the absence of a mapping in order to
 * conform to method atomicity requirements.  Further, any that do so
 * must override all default method implementations.
 *
 * <p>Several methods (for example {@link #putIfAbsent}) inherited
 * from {@link Map} do not have default implementations, and so must
 * be provided by implementations of this interface, even though they
 * have (non-atomic) default implementations in the {@link Map}
 * interface.
 *
 * <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 The default implementation returns the result of
     * {@code get(key)} unless {@code null}, in which case it returns
     * the given defaultValue.
     *
     * @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 no longer exists.
     * 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
     *  <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 There is no default implementation.
     *
     * @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
     *  <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 There is no default implementation.
     *
     * @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
     *  <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 There is no default implementation.
     *
     * @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
     *  <pre> {@code
     * if (map.containsKey(key)) {
     *   return map.put(key, value);
     * } else
     *   return null;
     * }</pre>
     *
     * except that the action is performed atomically.
     *
     * @implNote There is no default implementation.
     *
     * @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, and may call the function multiple
     * times.
     *
     * @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, and may call the mapping function
     * multiple times.
     *
     * @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, and may call the remapping function
     * multiple times.
     *
     * @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, and may call the remapping function
     * multiple times.
     *
     * @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>
     *
     * The default implementation may retry these steps when multiple
     * threads attempt updates, and may call the remapping function
     * multiple times.
     *
     * @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:	1.47
Committed:	Sat Dec 7 15:58:13 2013 UTC (10 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.46:	+11 -11 lines
Log Message:	coding style
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.17	* Expert Group and released to the public domain, as explained at
4	jsr166	1.31	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.2	*/
6
7	tim	1.1	package java.util.concurrent;
8			import java.util.Map;
9	dl	1.46	import java.util.Objects;
10			import java.util.function.BiConsumer;
11	dl	1.44	import java.util.function.BiFunction;
12	dl	1.46	import java.util.function.Function;
13	tim	1.1
14			/**
15	jsr166	1.43	* A {@link java.util.Map} providing thread safety and atomicity
16	dl	1.42	* guarantees.
17	dl	1.19	*
18	dl	1.46	* <p>To support atomic usages, ConcurrentMaps are expected not to
19			* allow {@code null} as a legal value (and to throw exceptions upon
20			* attempted insertions). This enables a return value of {@code null}
21			* to unambiguously indicate the absence of a mapping. This interface
22			* does not strictly forbid implementations that may hold {@code null}
23			* values. However, in any that do so, a {@code null} value must bear
24			* the same interpretation as the absence of a mapping in order to
25			* conform to method atomicity requirements. Further, any that do so
26			* must override all default method implementations.
27			*
28			* <p>Several methods (for example {@link #putIfAbsent}) inherited
29			* from {@link Map} do not have default implementations, and so must
30			* be provided by implementations of this interface, even though they
31			* have (non-atomic) default implementations in the {@link Map}
32			* interface.
33			*
34	jsr166	1.29	* <p>Memory consistency effects: As with other concurrent
35			* collections, actions in a thread prior to placing an object into a
36			* {@code ConcurrentMap} as a key or value
37			* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
38			* actions subsequent to the access or removal of that object from
39			* the {@code ConcurrentMap} in another thread.
40			*
41	dl	1.19	* <p>This interface is a member of the
42	jsr166	1.30	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
43	jsr166	1.47	* Java Collections Framework</a>.
44	jsr166	1.21	*
45	dl	1.4	* @since 1.5
46			* @author Doug Lea
47	dl	1.13	* @param <K> the type of keys maintained by this map
48	jsr166	1.21	* @param <V> the type of mapped values
49	dl	1.4	*/
50	jsr166	1.47	public interface ConcurrentMap<K,V> extends Map<K,V> {
51	dl	1.41
52			/**
53			* {@inheritDoc}
54			*
55	dl	1.46	* @implNote The default implementation returns the result of
56			* {@code get(key)} unless {@code null}, in which case it returns
57			* the given defaultValue.
58			*
59			* @throws ClassCastException {@inheritDoc}
60			* @throws NullPointerException {@inheritDoc}
61			* @since 1.8
62	dl	1.41	*/
63			@Override
64			default V getOrDefault(Object key, V defaultValue) {
65			V v;
66			return ((v = get(key)) != null) ? v : defaultValue;
67			}
68
69	dl	1.46	/**
70			* {@inheritDoc}
71			*
72			* @implSpec The default implementation is equivalent to, for this
73			* {@code map}:
74			* <pre> {@code
75	jsr166	1.47	* for ((Map.Entry<K,V> entry : map.entrySet())
76	dl	1.46	* action.accept(entry.getKey(), entry.getValue());
77			* }</pre>
78			*
79			* @implNote The default implementation assumes that {@code
80			* IllegalStateException} thrown by {@code getKey()} or {@code
81			* getValue()} indicates that the entry no longer exists.
82			* Operation continues for subsequent entries.
83			*
84			* @throws NullPointerException {@inheritDoc}
85			* @since 1.8
86			*/
87			@Override
88			default void forEach(BiConsumer<? super K, ? super V> action) {
89			Objects.requireNonNull(action);
90	jsr166	1.47	for (Map.Entry<K,V> entry : entrySet()) {
91	dl	1.46	K k;
92			V v;
93			try {
94			k = entry.getKey();
95			v = entry.getValue();
96	jsr166	1.47	} catch (IllegalStateException ise) {
97	dl	1.46	// this usually means the entry is no longer in the map.
98			continue;
99			}
100			action.accept(k, v);
101			}
102			}
103
104	tim	1.1	/**
105			* If the specified key is not already associated
106	dl	1.46	* with a value, associates it with the given value.
107	tim	1.1	* This is equivalent to
108	jsr166	1.36	* <pre> {@code
109			* if (!map.containsKey(key))
110			* return map.put(key, value);
111			* else
112	dl	1.46	* return map.get(key);
113			* }</pre>
114	jsr166	1.36	*
115	jsr166	1.21	* except that the action is performed atomically.
116			*
117	dl	1.46	* @implNote There is no default implementation.
118			*
119	jsr166	1.24	* @param key key with which the specified value is to be associated
120			* @param value value to be associated with the specified key
121	jsr166	1.25	* @return the previous value associated with the specified key, or
122	jsr166	1.38	* {@code null} if there was no mapping for the key.
123			* (A {@code null} return can also indicate that the map
124			* previously associated {@code null} with the key,
125	jsr166	1.25	* if the implementation supports null values.)
126	jsr166	1.38	* @throws UnsupportedOperationException if the {@code put} operation
127	jsr166	1.24	* is not supported by this map
128	tim	1.1	* @throws ClassCastException if the class of the specified key or value
129	jsr166	1.24	* prevents it from being stored in this map
130			* @throws NullPointerException if the specified key or value is null,
131			* and this map does not permit null keys or values
132			* @throws IllegalArgumentException if some property of the specified key
133			* or value prevents it from being stored in this map
134	dl	1.18	*/
135	jsr166	1.47	V putIfAbsent(K key, V value);
136	dl	1.6
137			/**
138	jsr166	1.21	* Removes the entry for a key only if currently mapped to a given value.
139			* This is equivalent to
140	jsr166	1.36	* <pre> {@code
141	dl	1.40	* if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
142	jsr166	1.36	* map.remove(key);
143			* return true;
144			* } else
145	dl	1.46	* return false;
146			* }</pre>
147	jsr166	1.36	*
148	dl	1.6	* except that the action is performed atomically.
149	jsr166	1.21	*
150	dl	1.46	* @implNote There is no default implementation.
151			*
152	jsr166	1.24	* @param key key with which the specified value is associated
153	jsr166	1.25	* @param value value expected to be associated with the specified key
154	jsr166	1.38	* @return {@code true} if the value was removed
155			* @throws UnsupportedOperationException if the {@code remove} operation
156	jsr166	1.24	* is not supported by this map
157	jsr166	1.25	* @throws ClassCastException if the key or value is of an inappropriate
158	jsr166	1.35	* type for this map
159	dl	1.33	* (<a href="../Collection.html#optional-restrictions">optional</a>)
160	jsr166	1.24	* @throws NullPointerException if the specified key or value is null,
161	dl	1.32	* and this map does not permit null keys or values
162	dl	1.33	* (<a href="../Collection.html#optional-restrictions">optional</a>)
163	dl	1.6	*/
164	dl	1.7	boolean remove(Object key, Object value);
165	dl	1.14
166			/**
167	jsr166	1.21	* Replaces the entry for a key only if currently mapped to a given value.
168			* This is equivalent to
169	jsr166	1.36	* <pre> {@code
170	dl	1.40	* if (map.containsKey(key) && Objects.equals(map.get(key), oldValue)) {
171	jsr166	1.36	* map.put(key, newValue);
172			* return true;
173			* } else
174	dl	1.46	* return false;
175			* }</pre>
176	jsr166	1.36	*
177	dl	1.14	* except that the action is performed atomically.
178	jsr166	1.21	*
179	dl	1.46	* @implNote There is no default implementation.
180			*
181	jsr166	1.24	* @param key key with which the specified value is associated
182			* @param oldValue value expected to be associated with the specified key
183			* @param newValue value to be associated with the specified key
184	jsr166	1.38	* @return {@code true} if the value was replaced
185			* @throws UnsupportedOperationException if the {@code put} operation
186	jsr166	1.24	* is not supported by this map
187	jsr166	1.25	* @throws ClassCastException if the class of a specified key or value
188			* prevents it from being stored in this map
189	jsr166	1.24	* @throws NullPointerException if a specified key or value is null,
190			* and this map does not permit null keys or values
191	jsr166	1.25	* @throws IllegalArgumentException if some property of a specified key
192			* or value prevents it from being stored in this map
193	dl	1.14	*/
194			boolean replace(K key, V oldValue, V newValue);
195	dl	1.6
196	dl	1.15	/**
197	jsr166	1.21	* Replaces the entry for a key only if currently mapped to some value.
198			* This is equivalent to
199	jsr166	1.36	* <pre> {@code
200			* if (map.containsKey(key)) {
201			* return map.put(key, value);
202			* } else
203	dl	1.46	* return null;
204			* }</pre>
205	jsr166	1.36	*
206	dl	1.15	* except that the action is performed atomically.
207	jsr166	1.21	*
208	dl	1.46	* @implNote There is no default implementation.
209			*
210	jsr166	1.24	* @param key key with which the specified value is associated
211			* @param value value to be associated with the specified key
212	jsr166	1.25	* @return the previous value associated with the specified key, or
213	jsr166	1.38	* {@code null} if there was no mapping for the key.
214			* (A {@code null} return can also indicate that the map
215			* previously associated {@code null} with the key,
216	jsr166	1.25	* if the implementation supports null values.)
217	jsr166	1.38	* @throws UnsupportedOperationException if the {@code put} operation
218	jsr166	1.24	* is not supported by this map
219	jsr166	1.25	* @throws ClassCastException if the class of the specified key or value
220			* prevents it from being stored in this map
221	jsr166	1.24	* @throws NullPointerException if the specified key or value is null,
222			* and this map does not permit null keys or values
223	jsr166	1.25	* @throws IllegalArgumentException if some property of the specified key
224			* or value prevents it from being stored in this map
225	dl	1.15	*/
226	dl	1.16	V replace(K key, V value);
227	dl	1.44
228			/**
229			* {@inheritDoc}
230			*
231	dl	1.46	* @implSpec
232			* <p>The default implementation is equivalent to, for this {@code map}:
233			* <pre> {@code
234	jsr166	1.47	* for ((Map.Entry<K,V> entry : map.entrySet())
235	dl	1.46	* do {
236			* K k = entry.getKey();
237			* V v = entry.getValue();
238	jsr166	1.47	* } while (!replace(k, v, function.apply(k, v)));
239	dl	1.46	* }</pre>
240			*
241			* The default implementation may retry these steps when multiple
242			* threads attempt updates, and may call the function multiple
243			* times.
244			*
245			* @throws UnsupportedOperationException {@inheritDoc}
246			* @throws NullPointerException {@inheritDoc}
247			* @throws ClassCastException {@inheritDoc}
248			* @throws IllegalArgumentException {@inheritDoc}
249			* @since 1.8
250	dl	1.44	*/
251			@Override
252			default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
253	dl	1.46	Objects.requireNonNull(function);
254			forEach((k,v) -> {
255	jsr166	1.47	while (!replace(k, v, function.apply(k, v))) {
256	dl	1.46	// v changed or k is gone
257			if ( (v = get(k)) == null) {
258			// k is no longer in the map.
259			break;
260			}
261	dl	1.44	}
262	dl	1.46	});
263			}
264
265			/**
266			* {@inheritDoc}
267			*
268			* @implSpec
269			* The default implementation is equivalent to the following steps for this
270			* {@code map}, then returning the current value or {@code null} if now
271			* absent:
272			*
273			* <pre> {@code
274			* if (map.get(key) == null) {
275			* V newValue = mappingFunction.apply(key);
276			* if (newValue != null)
277			* return map.putIfAbsent(key, newValue);
278			* }
279			* }</pre>
280			*
281			* The default implementation may retry these steps when multiple
282			* threads attempt updates, and may call the mapping function
283			* multiple times.
284			*
285			* @throws UnsupportedOperationException {@inheritDoc}
286			* @throws ClassCastException {@inheritDoc}
287			* @throws NullPointerException {@inheritDoc}
288			* @since 1.8
289			*/
290			@Override
291			default V computeIfAbsent(K key,
292			Function<? super K, ? extends V> mappingFunction) {
293			Objects.requireNonNull(mappingFunction);
294			V v, newValue;
295			return ((v = get(key)) == null &&
296			(newValue = mappingFunction.apply(key)) != null &&
297			(v = putIfAbsent(key, newValue)) == null) ? newValue : v;
298			}
299	dl	1.44
300	dl	1.46	/**
301			* {@inheritDoc}
302			*
303			* @implSpec
304			* The default implementation is equivalent to performing the following
305			* steps for this {@code map}, then returning the current value or
306			* {@code null} if now absent. :
307			*
308			* <pre> {@code
309			* if (map.get(key) != null) {
310			* V oldValue = map.get(key);
311			* V newValue = remappingFunction.apply(key, oldValue);
312			* if (newValue != null)
313			* map.replace(key, oldValue, newValue);
314			* else
315			* map.remove(key, oldValue);
316			* }
317			* }</pre>
318			*
319			* The default implementation may retry these steps when multiple
320			* threads attempt updates, and may call the remapping function
321			* multiple times.
322			*
323			* @throws UnsupportedOperationException {@inheritDoc}
324			* @throws ClassCastException {@inheritDoc}
325			* @throws NullPointerException {@inheritDoc}
326			* @since 1.8
327			*/
328			@Override
329			default V computeIfPresent(K key,
330			BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
331			Objects.requireNonNull(remappingFunction);
332			V oldValue;
333	jsr166	1.47	while ((oldValue = get(key)) != null) {
334	dl	1.46	V newValue = remappingFunction.apply(key, oldValue);
335			if (newValue != null) {
336			if (replace(key, oldValue, newValue))
337			return newValue;
338			} else if (remove(key, oldValue))
339			return null;
340			}
341			return oldValue;
342			}
343
344			/**
345			* {@inheritDoc}
346			*
347			* @implSpec
348			* The default implementation is equivalent to performing the following
349			* steps for this {@code map}, then returning the current value or
350			* {@code null} if absent:
351			*
352			* <pre> {@code
353			* V oldValue = map.get(key);
354			* V newValue = remappingFunction.apply(key, oldValue);
355			* if (oldValue != null ) {
356			* if (newValue != null)
357			* map.replace(key, oldValue, newValue);
358			* else
359			* map.remove(key, oldValue);
360			* } else {
361			* if (newValue != null)
362			* map.putIfAbsent(key, newValue);
363			* else
364			* return null;
365			* }
366			* }</pre>
367			*
368			* The default implementation may retry these steps when multiple
369			* threads attempt updates, and may call the remapping function
370			* multiple times.
371			*
372			* @throws UnsupportedOperationException {@inheritDoc}
373			* @throws ClassCastException {@inheritDoc}
374			* @throws NullPointerException {@inheritDoc}
375			* @since 1.8
376			*/
377			@Override
378			default V compute(K key,
379			BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
380			Objects.requireNonNull(remappingFunction);
381			V oldValue = get(key);
382	jsr166	1.47	for (;;) {
383	dl	1.46	V newValue = remappingFunction.apply(key, oldValue);
384			if (newValue == null) {
385			// delete mapping
386			if (oldValue != null \|\| containsKey(key)) {
387			// something to remove
388			if (remove(key, oldValue)) {
389			// removed the old value as expected
390			return null;
391			}
392
393			// some other value replaced old value. try again.
394			oldValue = get(key);
395			} else {
396			// nothing to do. Leave things as they were.
397			return null;
398			}
399			} else {
400			// add or replace old mapping
401			if (oldValue != null) {
402			// replace
403			if (replace(key, oldValue, newValue)) {
404			// replaced as expected.
405			return newValue;
406			}
407
408			// some other value replaced old value. try again.
409			oldValue = get(key);
410			} else {
411			// add (replace if oldValue was null)
412			if ((oldValue = putIfAbsent(key, newValue)) == null) {
413			// replaced
414			return newValue;
415			}
416
417			// some other value replaced old value. try again.
418			}
419	dl	1.44	}
420			}
421			}
422
423	dl	1.46
424			/**
425			* {@inheritDoc}
426			*
427			* @implSpec
428			* The default implementation is equivalent to performing the following
429			* steps for this {@code map}, then returning the current value or
430			* {@code null} if absent:
431			*
432			* <pre> {@code
433			* V oldValue = map.get(key);
434			* V newValue = (oldValue == null) ? value :
435			* remappingFunction.apply(oldValue, value);
436			* if (newValue == null)
437			* map.remove(key);
438			* else
439			* map.put(key, newValue);
440			* }</pre>
441			*
442			* The default implementation may retry these steps when multiple
443			* threads attempt updates, and may call the remapping function
444			* multiple times.
445			*
446			* @throws UnsupportedOperationException {@inheritDoc}
447			* @throws ClassCastException {@inheritDoc}
448			* @throws NullPointerException {@inheritDoc}
449			* @since 1.8
450			*/
451			@Override
452			default V merge(K key, V value,
453			BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
454			Objects.requireNonNull(remappingFunction);
455			Objects.requireNonNull(value);
456			V oldValue = get(key);
457			for (;;) {
458			if (oldValue != null) {
459			V newValue = remappingFunction.apply(oldValue, value);
460			if (newValue != null) {
461			if (replace(key, oldValue, newValue))
462			return newValue;
463			} else if (remove(key, oldValue)) {
464			return null;
465			}
466			oldValue = get(key);
467			} else {
468			if ((oldValue = putIfAbsent(key, value)) == null) {
469			return value;
470			}
471			}
472			}
473			}
474	tim	1.1	}