util/concurrent/ConcurrentMap.java

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

package java.util.concurrent;

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

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

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

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

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

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

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

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

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

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

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

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

    /**
     * {@inheritDoc}
     *
     * @implSpec
     * The default implementation is equivalent to performing the following
     * steps for this {@code map}:
     *
     * <pre> {@code
     * for (;;) {
     *   V oldValue = map.get(key);
     *   if (oldValue != null) {
     *     V newValue = remappingFunction.apply(oldValue, value);
     *     if (newValue != null) {
     *       if (map.replace(key, oldValue, newValue))
     *         return newValue;
     *     } else if (map.remove(key, oldValue)) {
     *       return null;
     *     }
     *   } else if (map.putIfAbsent(key, value) == null) {
     *     return value;
     *   }
     * }}</pre>
     * When multiple threads attempt updates, map operations and the
     * remapping function may be called multiple times.
     *
     * <p>This implementation assumes that the ConcurrentMap cannot contain null
     * values and {@code get()} returning null unambiguously means the key is
     * absent. Implementations which support null values <strong>must</strong>
     * override this default implementation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.8
     */
    @Override
    default V merge(K key, V value,
            BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
        Objects.requireNonNull(value);
        retry: for (;;) {
            V oldValue = get(key);
            // if putIfAbsent fails, opportunistically use its return value
            haveOldValue: for (;;) {
                if (oldValue != null) {
                    V newValue = remappingFunction.apply(oldValue, value);
                    if (newValue != null) {
                        if (replace(key, oldValue, newValue))
                            return newValue;
                    } else if (remove(key, oldValue)) {
                        return null;
                    }
                    continue retry;
                } else {
                    if ((oldValue = putIfAbsent(key, value)) == null)
                        return value;
                    continue haveOldValue;
                }
            }
        }
    }
}
Revision:	1.67
Committed:	Mon Dec 14 21:15:46 2015 UTC (8 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.66:	+95 -117 lines
Log Message:	improve Map default method implementations, docs and tests
#	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	jsr166	1.53
9	tim	1.1	import java.util.Map;
10	dl	1.46	import java.util.Objects;
11			import java.util.function.BiConsumer;
12	dl	1.44	import java.util.function.BiFunction;
13	dl	1.46	import java.util.function.Function;
14	tim	1.1
15			/**
16	jsr166	1.43	* A {@link java.util.Map} providing thread safety and atomicity
17	dl	1.42	* guarantees.
18	dl	1.19	*
19	dl	1.55	* <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	dl	1.46	*
27	jsr166	1.29	* <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	dl	1.19	* <p>This interface is a member of the
35	jsr166	1.30	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
36	jsr166	1.47	* Java Collections Framework</a>.
37	jsr166	1.21	*
38	dl	1.4	* @since 1.5
39			* @author Doug Lea
40	dl	1.13	* @param <K> the type of keys maintained by this map
41	jsr166	1.21	* @param <V> the type of mapped values
42	dl	1.4	*/
43	jsr166	1.56	public interface ConcurrentMap<K,V> extends Map<K,V> {
44	dl	1.41
45			/**
46			* {@inheritDoc}
47			*
48	dl	1.55	* @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	dl	1.46	*
53			* @throws ClassCastException {@inheritDoc}
54			* @throws NullPointerException {@inheritDoc}
55			* @since 1.8
56	dl	1.41	*/
57			@Override
58			default V getOrDefault(Object key, V defaultValue) {
59			V v;
60			return ((v = get(key)) != null) ? v : defaultValue;
61			}
62
63	jsr166	1.64	/**
64	dl	1.46	* {@inheritDoc}
65			*
66			* @implSpec The default implementation is equivalent to, for this
67			* {@code map}:
68	jsr166	1.52	* <pre> {@code
69	jsr166	1.57	* for (Map.Entry<K,V> entry : map.entrySet()) {
70	jsr166	1.56	* action.accept(entry.getKey(), entry.getValue());
71	jsr166	1.57	* }}</pre>
72	dl	1.55	*
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	dl	1.46	*
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	jsr166	1.56	for (Map.Entry<K,V> entry : entrySet()) {
85	dl	1.46	K k;
86			V v;
87			try {
88			k = entry.getKey();
89			v = entry.getValue();
90	jsr166	1.56	} catch (IllegalStateException ise) {
91	dl	1.46	// this usually means the entry is no longer in the map.
92			continue;
93			}
94			action.accept(k, v);
95			}
96			}
97
98	tim	1.1	/**
99			* If the specified key is not already associated
100	jsr166	1.60	* with a value, associates it with the given value.
101			* This is equivalent to, for this {@code map}:
102	jsr166	1.59	* <pre> {@code
103	dl	1.55	* if (!map.containsKey(key))
104			* return map.put(key, value);
105			* else
106	jsr166	1.59	* return map.get(key);}</pre>
107	jsr166	1.36	*
108	jsr166	1.21	* except that the action is performed atomically.
109			*
110	dl	1.55	* @implNote This implementation intentionally re-abstracts the
111			* inappropriate default provided in {@code Map}.
112	dl	1.46	*
113	jsr166	1.24	* @param key key with which the specified value is to be associated
114			* @param value value to be associated with the specified key
115	jsr166	1.25	* @return the previous value associated with the specified key, or
116	jsr166	1.38	* {@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	jsr166	1.25	* if the implementation supports null values.)
120	jsr166	1.38	* @throws UnsupportedOperationException if the {@code put} operation
121	jsr166	1.24	* is not supported by this map
122	tim	1.1	* @throws ClassCastException if the class of the specified key or value
123	jsr166	1.24	* 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	dl	1.18	*/
129	jsr166	1.57	V putIfAbsent(K key, V value);
130	dl	1.6
131			/**
132	jsr166	1.21	* Removes the entry for a key only if currently mapped to a given value.
133	jsr166	1.60	* This is equivalent to, for this {@code map}:
134	jsr166	1.59	* <pre> {@code
135	jsr166	1.61	* if (map.containsKey(key)
136			* && Objects.equals(map.get(key), value)) {
137	jsr166	1.36	* map.remove(key);
138			* return true;
139	jsr166	1.59	* } else {
140	dl	1.55	* return false;
141	jsr166	1.59	* }}</pre>
142	jsr166	1.36	*
143	dl	1.6	* except that the action is performed atomically.
144	jsr166	1.21	*
145	dl	1.55	* @implNote This implementation intentionally re-abstracts the
146			* inappropriate default provided in {@code Map}.
147	dl	1.46	*
148	jsr166	1.24	* @param key key with which the specified value is associated
149	jsr166	1.25	* @param value value expected to be associated with the specified key
150	jsr166	1.38	* @return {@code true} if the value was removed
151			* @throws UnsupportedOperationException if the {@code remove} operation
152	jsr166	1.24	* is not supported by this map
153	jsr166	1.25	* @throws ClassCastException if the key or value is of an inappropriate
154	jsr166	1.35	* type for this map
155	jsr166	1.65	* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>)
156	jsr166	1.24	* @throws NullPointerException if the specified key or value is null,
157	dl	1.32	* and this map does not permit null keys or values
158	jsr166	1.65	* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>)
159	dl	1.6	*/
160	dl	1.7	boolean remove(Object key, Object value);
161	dl	1.14
162			/**
163	jsr166	1.21	* Replaces the entry for a key only if currently mapped to a given value.
164	jsr166	1.60	* This is equivalent to, for this {@code map}:
165	jsr166	1.59	* <pre> {@code
166	jsr166	1.61	* if (map.containsKey(key)
167			* && Objects.equals(map.get(key), oldValue)) {
168	jsr166	1.36	* map.put(key, newValue);
169			* return true;
170	jsr166	1.59	* } else {
171	dl	1.55	* return false;
172	jsr166	1.59	* }}</pre>
173	jsr166	1.36	*
174	dl	1.14	* except that the action is performed atomically.
175	jsr166	1.21	*
176	dl	1.55	* @implNote This implementation intentionally re-abstracts the
177			* inappropriate default provided in {@code Map}.
178	dl	1.46	*
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	1.60	* This is equivalent to, for this {@code map}:
197	jsr166	1.59	* <pre> {@code
198	jsr166	1.63	* if (map.containsKey(key))
199	jsr166	1.36	* return map.put(key, value);
200	jsr166	1.63	* else
201			* return null;}</pre>
202	jsr166	1.36	*
203	dl	1.15	* except that the action is performed atomically.
204	jsr166	1.21	*
205	dl	1.55	* @implNote This implementation intentionally re-abstracts the
206			* inappropriate default provided in {@code Map}.
207	dl	1.46	*
208	jsr166	1.24	* @param key key with which the specified value is associated
209			* @param value value to be associated with the specified key
210	jsr166	1.25	* @return the previous value associated with the specified key, or
211	jsr166	1.38	* {@code null} if there was no mapping for the key.
212			* (A {@code null} return can also indicate that the map
213			* previously associated {@code null} with the key,
214	jsr166	1.25	* if the implementation supports null values.)
215	jsr166	1.38	* @throws UnsupportedOperationException if the {@code put} operation
216	jsr166	1.24	* is not supported by this map
217	jsr166	1.25	* @throws ClassCastException if the class of the specified key or value
218			* prevents it from being stored in this map
219	jsr166	1.24	* @throws NullPointerException if the specified key or value is null,
220			* and this map does not permit null keys or values
221	jsr166	1.25	* @throws IllegalArgumentException if some property of the specified key
222			* or value prevents it from being stored in this map
223	dl	1.15	*/
224	dl	1.16	V replace(K key, V value);
225	dl	1.44
226			/**
227			* {@inheritDoc}
228			*
229	dl	1.46	* @implSpec
230			* <p>The default implementation is equivalent to, for this {@code map}:
231	jsr166	1.52	* <pre> {@code
232	jsr166	1.57	* for (Map.Entry<K,V> entry : map.entrySet()) {
233	jsr166	1.62	* K k;
234			* V v;
235	jsr166	1.56	* do {
236	jsr166	1.62	* k = entry.getKey();
237			* v = entry.getValue();
238			* } while (!map.replace(k, v, function.apply(k, v)));
239	jsr166	1.57	* }}</pre>
240	dl	1.46	*
241			* The default implementation may retry these steps when multiple
242	dl	1.55	* threads attempt updates including potentially calling the function
243			* repeatedly for a given key.
244			*
245			* <p>This implementation assumes that the ConcurrentMap cannot contain null
246			* values and {@code get()} returning null unambiguously means the key is
247			* absent. Implementations which support null values <strong>must</strong>
248			* override this default implementation.
249	dl	1.46	*
250			* @throws UnsupportedOperationException {@inheritDoc}
251			* @throws NullPointerException {@inheritDoc}
252			* @throws ClassCastException {@inheritDoc}
253			* @throws IllegalArgumentException {@inheritDoc}
254			* @since 1.8
255	dl	1.44	*/
256			@Override
257			default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
258	dl	1.46	Objects.requireNonNull(function);
259			forEach((k,v) -> {
260	jsr166	1.56	while (!replace(k, v, function.apply(k, v))) {
261	dl	1.46	// v changed or k is gone
262			if ( (v = get(k)) == null) {
263			// k is no longer in the map.
264			break;
265			}
266	dl	1.44	}
267	dl	1.46	});
268			}
269
270			/**
271			* {@inheritDoc}
272			*
273			* @implSpec
274			* The default implementation is equivalent to the following steps for this
275	jsr166	1.67	* {@code map}:
276	dl	1.46	*
277	jsr166	1.52	* <pre> {@code
278	jsr166	1.67	* V oldValue, newValue;
279			* return ((oldValue = map.get(key)) == null
280			* && (newValue = mappingFunction.apply(key)) != null
281			* && (oldValue = map.putIfAbsent(key, newValue)) == null)
282			* ? newValue
283			* : oldValue;}</pre>
284	dl	1.55	*
285			* <p>This implementation assumes that the ConcurrentMap cannot contain null
286			* values and {@code get()} returning null unambiguously means the key is
287			* absent. Implementations which support null values <strong>must</strong>
288			* override this default implementation.
289	dl	1.46	*
290			* @throws UnsupportedOperationException {@inheritDoc}
291			* @throws ClassCastException {@inheritDoc}
292			* @throws NullPointerException {@inheritDoc}
293	jsr166	1.67	* @throws IllegalArgumentException {@inheritDoc}
294	dl	1.46	* @since 1.8
295			*/
296			@Override
297			default V computeIfAbsent(K key,
298			Function<? super K, ? extends V> mappingFunction) {
299			Objects.requireNonNull(mappingFunction);
300	jsr166	1.67	V oldValue, newValue;
301			return ((oldValue = get(key)) == null
302			&& (newValue = mappingFunction.apply(key)) != null
303			&& (oldValue = putIfAbsent(key, newValue)) == null)
304			? newValue
305			: oldValue;
306	dl	1.46	}
307	dl	1.44
308	dl	1.46	/**
309			* {@inheritDoc}
310			*
311			* @implSpec
312			* The default implementation is equivalent to performing the following
313	jsr166	1.67	* steps for this {@code map}:
314	dl	1.46	*
315	jsr166	1.52	* <pre> {@code
316	jsr166	1.67	* for (V oldValue; (oldValue = map.get(key)) != null; ) {
317	jsr166	1.59	* V newValue = remappingFunction.apply(key, oldValue);
318	jsr166	1.67	* if ((newValue == null)
319			* ? map.remove(key, oldValue)
320			* : map.replace(key, oldValue, newValue))
321			* return newValue;
322			* }
323			* return null;}</pre>
324			* When multiple threads attempt updates, map operations and the
325			* remapping function may be called multiple times.
326	dl	1.46	*
327	dl	1.55	* <p>This implementation assumes that the ConcurrentMap cannot contain null
328			* values and {@code get()} returning null unambiguously means the key is
329			* absent. Implementations which support null values <strong>must</strong>
330			* override this default implementation.
331			*
332	dl	1.46	* @throws UnsupportedOperationException {@inheritDoc}
333			* @throws ClassCastException {@inheritDoc}
334			* @throws NullPointerException {@inheritDoc}
335	jsr166	1.67	* @throws IllegalArgumentException {@inheritDoc}
336	dl	1.46	* @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	jsr166	1.67	for (V oldValue; (oldValue = get(key)) != null; ) {
343	dl	1.46	V newValue = remappingFunction.apply(key, oldValue);
344	jsr166	1.67	if ((newValue == null)
345			? remove(key, oldValue)
346			: replace(key, oldValue, newValue))
347			return newValue;
348	dl	1.46	}
349	jsr166	1.67	return null;
350	dl	1.46	}
351
352			/**
353			* {@inheritDoc}
354			*
355			* @implSpec
356			* The default implementation is equivalent to performing the following
357	jsr166	1.67	* steps for this {@code map}:
358	dl	1.46	*
359	jsr166	1.52	* <pre> {@code
360	jsr166	1.67	* for (;;) {
361			* V oldValue = map.get(key);
362			* V newValue = remappingFunction.apply(key, oldValue);
363			* if (newValue != null) {
364			* if ((oldValue != null)
365			* ? map.replace(key, oldValue, newValue)
366			* : map.putIfAbsent(key, newValue) == null)
367			* return newValue;
368			* } else if (oldValue == null \|\| map.remove(key, oldValue)) {
369	jsr166	1.59	* return null;
370	jsr166	1.67	* }
371	jsr166	1.59	* }}</pre>
372	jsr166	1.67	* When multiple threads attempt updates, map operations and the
373			* remapping function may be called multiple times.
374	dl	1.55	*
375			* <p>This implementation assumes that the ConcurrentMap cannot contain null
376			* values and {@code get()} returning null unambiguously means the key is
377			* absent. Implementations which support null values <strong>must</strong>
378			* override this default implementation.
379	dl	1.46	*
380			* @throws UnsupportedOperationException {@inheritDoc}
381			* @throws ClassCastException {@inheritDoc}
382			* @throws NullPointerException {@inheritDoc}
383	jsr166	1.67	* @throws IllegalArgumentException {@inheritDoc}
384	dl	1.46	* @since 1.8
385			*/
386			@Override
387			default V compute(K key,
388	jsr166	1.67	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
389			retry: for (;;) {
390			V oldValue = get(key);
391			// if putIfAbsent fails, opportunistically use its return value
392			haveOldValue: for (;;) {
393			V newValue = remappingFunction.apply(key, oldValue);
394			if (newValue != null) {
395			if (oldValue != null) {
396			if (replace(key, oldValue, newValue))
397			return newValue;
398	dl	1.46	}
399	jsr166	1.67	else if ((oldValue = putIfAbsent(key, newValue)) == null)
400			return newValue;
401			else continue haveOldValue;
402			} else if (oldValue == null \|\| remove(key, oldValue)) {
403	dl	1.46	return null;
404			}
405	jsr166	1.67	continue retry;
406	dl	1.44	}
407			}
408			}
409
410	dl	1.46	/**
411			* {@inheritDoc}
412			*
413			* @implSpec
414			* The default implementation is equivalent to performing the following
415	jsr166	1.67	* steps for this {@code map}:
416	dl	1.46	*
417	jsr166	1.52	* <pre> {@code
418	jsr166	1.67	* for (;;) {
419			* V oldValue = map.get(key);
420			* if (oldValue != null) {
421			* V newValue = remappingFunction.apply(oldValue, value);
422			* if (newValue != null) {
423			* if (map.replace(key, oldValue, newValue))
424			* return newValue;
425			* } else if (map.remove(key, oldValue)) {
426			* return null;
427			* }
428			* } else if (map.putIfAbsent(key, value) == null) {
429			* return value;
430			* }
431			* }}</pre>
432			* When multiple threads attempt updates, map operations and the
433			* remapping function may be called multiple times.
434	dl	1.55	*
435			* <p>This implementation assumes that the ConcurrentMap cannot contain null
436			* values and {@code get()} returning null unambiguously means the key is
437			* absent. Implementations which support null values <strong>must</strong>
438			* override this default implementation.
439	dl	1.46	*
440			* @throws UnsupportedOperationException {@inheritDoc}
441			* @throws ClassCastException {@inheritDoc}
442			* @throws NullPointerException {@inheritDoc}
443	jsr166	1.67	* @throws IllegalArgumentException {@inheritDoc}
444	dl	1.46	* @since 1.8
445			*/
446			@Override
447			default V merge(K key, V value,
448			BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
449			Objects.requireNonNull(remappingFunction);
450			Objects.requireNonNull(value);
451	jsr166	1.67	retry: for (;;) {
452			V oldValue = get(key);
453			// if putIfAbsent fails, opportunistically use its return value
454			haveOldValue: for (;;) {
455			if (oldValue != null) {
456			V newValue = remappingFunction.apply(oldValue, value);
457			if (newValue != null) {
458			if (replace(key, oldValue, newValue))
459			return newValue;
460			} else if (remove(key, oldValue)) {
461			return null;
462			}
463			continue retry;
464			} else {
465			if ((oldValue = putIfAbsent(key, value)) == null)
466			return value;
467			continue haveOldValue;
468	dl	1.46	}
469			}
470			}
471			}
472	tim	1.1	}