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, for this {@code map}:
     * <pre> {@code
     * if (map.containsKey(key))
     *   return map.get(key);
     * else
     *   return map.put(key, value);}</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, 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 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, 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 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, 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 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()) {
     *   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, 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:	1.52
Committed:	Mon Dec 9 17:00:23 2013 UTC (10 years, 6 months ago) by jsr166
Branch:	MAIN
Changes since 1.51:	+20 -24 lines
Log Message:	use the one true code snippet 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	jsr166	1.52	* <pre> {@code
75	jsr166	1.49	* for (Map.Entry<K,V> entry : map.entrySet())
76	jsr166	1.52	* action.accept(entry.getKey(), entry.getValue());}</pre>
77	dl	1.46	*
78			* @implNote The default implementation assumes that {@code
79			* IllegalStateException} thrown by {@code getKey()} or {@code
80			* getValue()} indicates that the entry no longer exists.
81			* Operation continues for subsequent entries.
82			*
83			* @throws NullPointerException {@inheritDoc}
84			* @since 1.8
85			*/
86			@Override
87			default void forEach(BiConsumer<? super K, ? super V> action) {
88			Objects.requireNonNull(action);
89	jsr166	1.47	for (Map.Entry<K,V> entry : entrySet()) {
90	dl	1.46	K k;
91			V v;
92			try {
93			k = entry.getKey();
94			v = entry.getValue();
95	jsr166	1.47	} catch (IllegalStateException ise) {
96	dl	1.46	// this usually means the entry is no longer in the map.
97			continue;
98			}
99			action.accept(k, v);
100			}
101			}
102
103	tim	1.1	/**
104			* If the specified key is not already associated
105	dl	1.46	* with a value, associates it with the given value.
106	jsr166	1.51	* This is equivalent to, for this {@code map}:
107	jsr166	1.52	* <pre> {@code
108	jsr166	1.48	* if (map.containsKey(key))
109			* return map.get(key);
110			* else
111	jsr166	1.52	* return map.put(key, value);}</pre>
112	jsr166	1.36	*
113	jsr166	1.21	* except that the action is performed atomically.
114			*
115	dl	1.46	* @implNote There is no default implementation.
116			*
117	jsr166	1.24	* @param key key with which the specified value is to be associated
118			* @param value value to be associated with the specified key
119	jsr166	1.25	* @return the previous value associated with the specified key, or
120	jsr166	1.38	* {@code null} if there was no mapping for the key.
121			* (A {@code null} return can also indicate that the map
122			* previously associated {@code null} with the key,
123	jsr166	1.25	* if the implementation supports null values.)
124	jsr166	1.38	* @throws UnsupportedOperationException if the {@code put} operation
125	jsr166	1.24	* is not supported by this map
126	tim	1.1	* @throws ClassCastException if the class of the specified key or value
127	jsr166	1.24	* prevents it from being stored in this map
128			* @throws NullPointerException if the specified key or value is null,
129			* and this map does not permit null keys or values
130			* @throws IllegalArgumentException if some property of the specified key
131			* or value prevents it from being stored in this map
132	dl	1.18	*/
133	jsr166	1.47	V putIfAbsent(K key, V value);
134	dl	1.6
135			/**
136	jsr166	1.21	* Removes the entry for a key only if currently mapped to a given value.
137	jsr166	1.51	* This is equivalent to, for this {@code map}:
138	jsr166	1.52	* <pre> {@code
139			* if (map.containsKey(key)
140			* && Objects.equals(map.get(key), value)) {
141	jsr166	1.36	* map.remove(key);
142			* return true;
143			* } else
144	jsr166	1.52	* return false;}</pre>
145	jsr166	1.36	*
146	dl	1.6	* except that the action is performed atomically.
147	jsr166	1.21	*
148	dl	1.46	* @implNote There is no default implementation.
149			*
150	jsr166	1.24	* @param key key with which the specified value is associated
151	jsr166	1.25	* @param value value expected to be associated with the specified key
152	jsr166	1.38	* @return {@code true} if the value was removed
153			* @throws UnsupportedOperationException if the {@code remove} operation
154	jsr166	1.24	* is not supported by this map
155	jsr166	1.25	* @throws ClassCastException if the key or value is of an inappropriate
156	jsr166	1.35	* type for this map
157	dl	1.33	* (<a href="../Collection.html#optional-restrictions">optional</a>)
158	jsr166	1.24	* @throws NullPointerException if the specified key or value is null,
159	dl	1.32	* and this map does not permit null keys or values
160	dl	1.33	* (<a href="../Collection.html#optional-restrictions">optional</a>)
161	dl	1.6	*/
162	dl	1.7	boolean remove(Object key, Object value);
163	dl	1.14
164			/**
165	jsr166	1.21	* Replaces the entry for a key only if currently mapped to a given value.
166	jsr166	1.51	* This is equivalent to, for this {@code map}:
167	jsr166	1.52	* <pre> {@code
168			* if (map.containsKey(key)
169			* && Objects.equals(map.get(key), oldValue)) {
170	jsr166	1.36	* map.put(key, newValue);
171			* return true;
172			* } else
173	jsr166	1.52	* return false;}</pre>
174	jsr166	1.36	*
175	dl	1.14	* except that the action is performed atomically.
176	jsr166	1.21	*
177	dl	1.46	* @implNote There is no default implementation.
178			*
179	jsr166	1.24	* @param key key with which the specified value is associated
180			* @param oldValue value expected to be associated with the specified key
181			* @param newValue value to be associated with the specified key
182	jsr166	1.38	* @return {@code true} if the value was replaced
183			* @throws UnsupportedOperationException if the {@code put} operation
184	jsr166	1.24	* is not supported by this map
185	jsr166	1.25	* @throws ClassCastException if the class of a specified key or value
186			* prevents it from being stored in this map
187	jsr166	1.24	* @throws NullPointerException if a specified key or value is null,
188			* and this map does not permit null keys or values
189	jsr166	1.25	* @throws IllegalArgumentException if some property of a specified key
190			* or value prevents it from being stored in this map
191	dl	1.14	*/
192			boolean replace(K key, V oldValue, V newValue);
193	dl	1.6
194	dl	1.15	/**
195	jsr166	1.21	* Replaces the entry for a key only if currently mapped to some value.
196	jsr166	1.51	* This is equivalent to, for this {@code map}:
197	jsr166	1.52	* <pre> {@code
198	jsr166	1.51	* if (map.containsKey(key))
199	jsr166	1.36	* return map.put(key, value);
200	jsr166	1.51	* else
201	jsr166	1.52	* return null;}</pre>
202	jsr166	1.36	*
203	dl	1.15	* except that the action is performed atomically.
204	jsr166	1.21	*
205	dl	1.46	* @implNote There is no default implementation.
206			*
207	jsr166	1.24	* @param key key with which the specified value is associated
208			* @param value value to be associated with the specified key
209	jsr166	1.25	* @return the previous value associated with the specified key, or
210	jsr166	1.38	* {@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	jsr166	1.25	* if the implementation supports null values.)
214	jsr166	1.38	* @throws UnsupportedOperationException if the {@code put} operation
215	jsr166	1.24	* is not supported by this map
216	jsr166	1.25	* @throws ClassCastException if the class of the specified key or value
217			* prevents it from being stored in this map
218	jsr166	1.24	* @throws NullPointerException if the specified key or value is null,
219			* and this map does not permit null keys or values
220	jsr166	1.25	* @throws IllegalArgumentException if some property of the specified key
221			* or value prevents it from being stored in this map
222	dl	1.15	*/
223	dl	1.16	V replace(K key, V value);
224	dl	1.44
225			/**
226			* {@inheritDoc}
227			*
228	dl	1.46	* @implSpec
229			* <p>The default implementation is equivalent to, for this {@code map}:
230	jsr166	1.52	* <pre> {@code
231	jsr166	1.50	* 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	jsr166	1.51	* }}</pre>
239	dl	1.46	*
240			* The default implementation may retry these steps when multiple
241			* threads attempt updates, and may call the function multiple
242			* times.
243			*
244			* @throws UnsupportedOperationException {@inheritDoc}
245			* @throws NullPointerException {@inheritDoc}
246			* @throws ClassCastException {@inheritDoc}
247			* @throws IllegalArgumentException {@inheritDoc}
248			* @since 1.8
249	dl	1.44	*/
250			@Override
251			default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
252	dl	1.46	Objects.requireNonNull(function);
253			forEach((k,v) -> {
254	jsr166	1.47	while (!replace(k, v, function.apply(k, v))) {
255	dl	1.46	// v changed or k is gone
256			if ( (v = get(k)) == null) {
257			// k is no longer in the map.
258			break;
259			}
260	dl	1.44	}
261	dl	1.46	});
262			}
263
264			/**
265			* {@inheritDoc}
266			*
267			* @implSpec
268			* The default implementation is equivalent to the following steps for this
269			* {@code map}, then returning the current value or {@code null} if now
270			* absent:
271			*
272	jsr166	1.52	* <pre> {@code
273	dl	1.46	* if (map.get(key) == null) {
274	jsr166	1.51	* V newValue = mappingFunction.apply(key);
275			* if (newValue != null)
276			* return map.putIfAbsent(key, newValue);
277			* }}</pre>
278	dl	1.46	*
279			* The default implementation may retry these steps when multiple
280			* threads attempt updates, and may call the mapping function
281			* multiple times.
282			*
283			* @throws UnsupportedOperationException {@inheritDoc}
284			* @throws ClassCastException {@inheritDoc}
285			* @throws NullPointerException {@inheritDoc}
286			* @since 1.8
287			*/
288			@Override
289			default V computeIfAbsent(K key,
290			Function<? super K, ? extends V> mappingFunction) {
291			Objects.requireNonNull(mappingFunction);
292			V v, newValue;
293			return ((v = get(key)) == null &&
294			(newValue = mappingFunction.apply(key)) != null &&
295			(v = putIfAbsent(key, newValue)) == null) ? newValue : v;
296			}
297	dl	1.44
298	dl	1.46	/**
299			* {@inheritDoc}
300			*
301			* @implSpec
302			* The default implementation is equivalent to performing the following
303			* steps for this {@code map}, then returning the current value or
304	jsr166	1.51	* {@code null} if now absent:
305	dl	1.46	*
306	jsr166	1.52	* <pre> {@code
307	dl	1.46	* if (map.get(key) != null) {
308	jsr166	1.51	* V oldValue = map.get(key);
309			* V newValue = remappingFunction.apply(key, oldValue);
310			* if (newValue != null)
311			* map.replace(key, oldValue, newValue);
312			* else
313			* map.remove(key, oldValue);
314			* }}</pre>
315	dl	1.46	*
316			* The default implementation may retry these steps when multiple
317			* threads attempt updates, and may call the remapping function
318			* multiple times.
319			*
320			* @throws UnsupportedOperationException {@inheritDoc}
321			* @throws ClassCastException {@inheritDoc}
322			* @throws NullPointerException {@inheritDoc}
323			* @since 1.8
324			*/
325			@Override
326			default V computeIfPresent(K key,
327			BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
328			Objects.requireNonNull(remappingFunction);
329			V oldValue;
330	jsr166	1.47	while ((oldValue = get(key)) != null) {
331	dl	1.46	V newValue = remappingFunction.apply(key, oldValue);
332			if (newValue != null) {
333			if (replace(key, oldValue, newValue))
334			return newValue;
335			} else if (remove(key, oldValue))
336			return null;
337			}
338			return oldValue;
339			}
340
341			/**
342			* {@inheritDoc}
343			*
344			* @implSpec
345			* The default implementation is equivalent to performing the following
346			* steps for this {@code map}, then returning the current value or
347			* {@code null} if absent:
348			*
349	jsr166	1.52	* <pre> {@code
350	dl	1.46	* V oldValue = map.get(key);
351			* V newValue = remappingFunction.apply(key, oldValue);
352			* if (oldValue != null ) {
353	jsr166	1.51	* if (newValue != null)
354			* map.replace(key, oldValue, newValue);
355			* else
356			* map.remove(key, oldValue);
357	dl	1.46	* } else {
358	jsr166	1.51	* if (newValue != null)
359			* map.putIfAbsent(key, newValue);
360			* else
361			* return null;
362			* }}</pre>
363	dl	1.46	*
364			* The default implementation may retry these steps when multiple
365			* threads attempt updates, and may call the remapping function
366			* multiple times.
367			*
368			* @throws UnsupportedOperationException {@inheritDoc}
369			* @throws ClassCastException {@inheritDoc}
370			* @throws NullPointerException {@inheritDoc}
371			* @since 1.8
372			*/
373			@Override
374			default V compute(K key,
375			BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
376			Objects.requireNonNull(remappingFunction);
377			V oldValue = get(key);
378	jsr166	1.47	for (;;) {
379	dl	1.46	V newValue = remappingFunction.apply(key, oldValue);
380			if (newValue == null) {
381			// delete mapping
382			if (oldValue != null \|\| containsKey(key)) {
383			// something to remove
384			if (remove(key, oldValue)) {
385			// removed the old value as expected
386			return null;
387			}
388
389			// some other value replaced old value. try again.
390			oldValue = get(key);
391			} else {
392			// nothing to do. Leave things as they were.
393			return null;
394			}
395			} else {
396			// add or replace old mapping
397			if (oldValue != null) {
398			// replace
399			if (replace(key, oldValue, newValue)) {
400			// replaced as expected.
401			return newValue;
402			}
403
404			// some other value replaced old value. try again.
405			oldValue = get(key);
406			} else {
407			// add (replace if oldValue was null)
408			if ((oldValue = putIfAbsent(key, newValue)) == null) {
409			// replaced
410			return newValue;
411			}
412
413			// some other value replaced old value. try again.
414			}
415	dl	1.44	}
416			}
417			}
418
419	dl	1.46	/**
420			* {@inheritDoc}
421			*
422			* @implSpec
423			* The default implementation is equivalent to performing the following
424			* steps for this {@code map}, then returning the current value or
425			* {@code null} if absent:
426			*
427	jsr166	1.52	* <pre> {@code
428	dl	1.46	* V oldValue = map.get(key);
429			* V newValue = (oldValue == null) ? value :
430	jsr166	1.51	* remappingFunction.apply(oldValue, value);
431	dl	1.46	* if (newValue == null)
432	jsr166	1.51	* map.remove(key);
433	dl	1.46	* else
434	jsr166	1.52	* map.put(key, newValue);}</pre>
435	dl	1.46	*
436			* The default implementation may retry these steps when multiple
437			* threads attempt updates, and may call the remapping function
438			* multiple times.
439			*
440			* @throws UnsupportedOperationException {@inheritDoc}
441			* @throws ClassCastException {@inheritDoc}
442			* @throws NullPointerException {@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			V oldValue = get(key);
451			for (;;) {
452			if (oldValue != null) {
453			V newValue = remappingFunction.apply(oldValue, value);
454			if (newValue != null) {
455			if (replace(key, oldValue, newValue))
456			return newValue;
457			} else if (remove(key, oldValue)) {
458			return null;
459			}
460			oldValue = get(key);
461			} else {
462			if ((oldValue = putIfAbsent(key, value)) == null) {
463			return value;
464			}
465			}
466			}
467			}
468	tim	1.1	}