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:	1.53
Committed:	Wed Dec 31 07:54:13 2014 UTC (9 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.52:	+1 -0 lines
Log Message:	standardize import statement order
#	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	1.46	* <p>To support atomic usages, ConcurrentMaps are expected not to
20			* allow {@code null} as a legal value (and to throw exceptions upon
21			* attempted insertions). This enables a return value of {@code null}
22			* to unambiguously indicate the absence of a mapping. This interface
23			* does not strictly forbid implementations that may hold {@code null}
24			* values. However, in any that do so, a {@code null} value must bear
25			* the same interpretation as the absence of a mapping in order to
26			* conform to method atomicity requirements. Further, any that do so
27			* must override all default method implementations.
28			*
29			* <p>Several methods (for example {@link #putIfAbsent}) inherited
30			* from {@link Map} do not have default implementations, and so must
31			* be provided by implementations of this interface, even though they
32			* have (non-atomic) default implementations in the {@link Map}
33			* interface.
34			*
35	jsr166	1.29	* <p>Memory consistency effects: As with other concurrent
36			* collections, actions in a thread prior to placing an object into a
37			* {@code ConcurrentMap} as a key or value
38			* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
39			* actions subsequent to the access or removal of that object from
40			* the {@code ConcurrentMap} in another thread.
41			*
42	dl	1.19	* <p>This interface is a member of the
43	jsr166	1.30	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
44	jsr166	1.47	* Java Collections Framework</a>.
45	jsr166	1.21	*
46	dl	1.4	* @since 1.5
47			* @author Doug Lea
48	dl	1.13	* @param <K> the type of keys maintained by this map
49	jsr166	1.21	* @param <V> the type of mapped values
50	dl	1.4	*/
51	jsr166	1.47	public interface ConcurrentMap<K,V> extends Map<K,V> {
52	dl	1.41
53			/**
54			* {@inheritDoc}
55			*
56	dl	1.46	* @implNote The default implementation returns the result of
57			* {@code get(key)} unless {@code null}, in which case it returns
58			* the given defaultValue.
59			*
60			* @throws ClassCastException {@inheritDoc}
61			* @throws NullPointerException {@inheritDoc}
62			* @since 1.8
63	dl	1.41	*/
64			@Override
65			default V getOrDefault(Object key, V defaultValue) {
66			V v;
67			return ((v = get(key)) != null) ? v : defaultValue;
68			}
69
70	dl	1.46	/**
71			* {@inheritDoc}
72			*
73			* @implSpec The default implementation is equivalent to, for this
74			* {@code map}:
75	jsr166	1.52	* <pre> {@code
76	jsr166	1.49	* for (Map.Entry<K,V> entry : map.entrySet())
77	jsr166	1.52	* action.accept(entry.getKey(), entry.getValue());}</pre>
78	dl	1.46	*
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	jsr166	1.51	* This is equivalent to, for this {@code map}:
108	jsr166	1.52	* <pre> {@code
109	jsr166	1.48	* if (map.containsKey(key))
110			* return map.get(key);
111			* else
112	jsr166	1.52	* return map.put(key, value);}</pre>
113	jsr166	1.36	*
114	jsr166	1.21	* except that the action is performed atomically.
115			*
116	dl	1.46	* @implNote There is no default implementation.
117			*
118	jsr166	1.24	* @param key key with which the specified value is to be associated
119			* @param value value to be associated with the specified key
120	jsr166	1.25	* @return the previous value associated with the specified key, or
121	jsr166	1.38	* {@code null} if there was no mapping for the key.
122			* (A {@code null} return can also indicate that the map
123			* previously associated {@code null} with the key,
124	jsr166	1.25	* if the implementation supports null values.)
125	jsr166	1.38	* @throws UnsupportedOperationException if the {@code put} operation
126	jsr166	1.24	* is not supported by this map
127	tim	1.1	* @throws ClassCastException if the class of the specified key or value
128	jsr166	1.24	* prevents it from being stored in this map
129			* @throws NullPointerException if the specified key or value is null,
130			* and this map does not permit null keys or values
131			* @throws IllegalArgumentException if some property of the specified key
132			* or value prevents it from being stored in this map
133	dl	1.18	*/
134	jsr166	1.47	V putIfAbsent(K key, V value);
135	dl	1.6
136			/**
137	jsr166	1.21	* Removes the entry for a key only if currently mapped to a given value.
138	jsr166	1.51	* This is equivalent to, for this {@code map}:
139	jsr166	1.52	* <pre> {@code
140			* if (map.containsKey(key)
141			* && Objects.equals(map.get(key), value)) {
142	jsr166	1.36	* map.remove(key);
143			* return true;
144			* } else
145	jsr166	1.52	* return false;}</pre>
146	jsr166	1.36	*
147	dl	1.6	* except that the action is performed atomically.
148	jsr166	1.21	*
149	dl	1.46	* @implNote There is no default implementation.
150			*
151	jsr166	1.24	* @param key key with which the specified value is associated
152	jsr166	1.25	* @param value value expected to be associated with the specified key
153	jsr166	1.38	* @return {@code true} if the value was removed
154			* @throws UnsupportedOperationException if the {@code remove} operation
155	jsr166	1.24	* is not supported by this map
156	jsr166	1.25	* @throws ClassCastException if the key or value is of an inappropriate
157	jsr166	1.35	* type for this map
158	dl	1.33	* (<a href="../Collection.html#optional-restrictions">optional</a>)
159	jsr166	1.24	* @throws NullPointerException if the specified key or value is null,
160	dl	1.32	* and this map does not permit null keys or values
161	dl	1.33	* (<a href="../Collection.html#optional-restrictions">optional</a>)
162	dl	1.6	*/
163	dl	1.7	boolean remove(Object key, Object value);
164	dl	1.14
165			/**
166	jsr166	1.21	* Replaces the entry for a key only if currently mapped to a given value.
167	jsr166	1.51	* This is equivalent to, for this {@code map}:
168	jsr166	1.52	* <pre> {@code
169			* if (map.containsKey(key)
170			* && Objects.equals(map.get(key), oldValue)) {
171	jsr166	1.36	* map.put(key, newValue);
172			* return true;
173			* } else
174	jsr166	1.52	* return false;}</pre>
175	jsr166	1.36	*
176	dl	1.14	* except that the action is performed atomically.
177	jsr166	1.21	*
178	dl	1.46	* @implNote There is no default implementation.
179			*
180	jsr166	1.24	* @param key key with which the specified value is associated
181			* @param oldValue value expected to be associated with the specified key
182			* @param newValue value to be associated with the specified key
183	jsr166	1.38	* @return {@code true} if the value was replaced
184			* @throws UnsupportedOperationException if the {@code put} operation
185	jsr166	1.24	* is not supported by this map
186	jsr166	1.25	* @throws ClassCastException if the class of a specified key or value
187			* prevents it from being stored in this map
188	jsr166	1.24	* @throws NullPointerException if a specified key or value is null,
189			* and this map does not permit null keys or values
190	jsr166	1.25	* @throws IllegalArgumentException if some property of a specified key
191			* or value prevents it from being stored in this map
192	dl	1.14	*/
193			boolean replace(K key, V oldValue, V newValue);
194	dl	1.6
195	dl	1.15	/**
196	jsr166	1.21	* Replaces the entry for a key only if currently mapped to some value.
197	jsr166	1.51	* This is equivalent to, for this {@code map}:
198	jsr166	1.52	* <pre> {@code
199	jsr166	1.51	* if (map.containsKey(key))
200	jsr166	1.36	* return map.put(key, value);
201	jsr166	1.51	* else
202	jsr166	1.52	* return null;}</pre>
203	jsr166	1.36	*
204	dl	1.15	* except that the action is performed atomically.
205	jsr166	1.21	*
206	dl	1.46	* @implNote There is no default implementation.
207			*
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	1.50	* for (Map.Entry<K,V> entry : map.entrySet()) {
233			* K k;
234			* V v;
235			* do {
236			* k = entry.getKey();
237			* v = entry.getValue();
238			* } while (!map.replace(k, v, function.apply(k, v)));
239	jsr166	1.51	* }}</pre>
240	dl	1.46	*
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	jsr166	1.52	* <pre> {@code
274	dl	1.46	* if (map.get(key) == null) {
275	jsr166	1.51	* V newValue = mappingFunction.apply(key);
276			* if (newValue != null)
277			* return map.putIfAbsent(key, newValue);
278			* }}</pre>
279	dl	1.46	*
280			* The default implementation may retry these steps when multiple
281			* threads attempt updates, and may call the mapping function
282			* multiple times.
283			*
284			* @throws UnsupportedOperationException {@inheritDoc}
285			* @throws ClassCastException {@inheritDoc}
286			* @throws NullPointerException {@inheritDoc}
287			* @since 1.8
288			*/
289			@Override
290			default V computeIfAbsent(K key,
291			Function<? super K, ? extends V> mappingFunction) {
292			Objects.requireNonNull(mappingFunction);
293			V v, newValue;
294			return ((v = get(key)) == null &&
295			(newValue = mappingFunction.apply(key)) != null &&
296			(v = putIfAbsent(key, newValue)) == null) ? newValue : v;
297			}
298	dl	1.44
299	dl	1.46	/**
300			* {@inheritDoc}
301			*
302			* @implSpec
303			* The default implementation is equivalent to performing the following
304			* steps for this {@code map}, then returning the current value or
305	jsr166	1.51	* {@code null} if now absent:
306	dl	1.46	*
307	jsr166	1.52	* <pre> {@code
308	dl	1.46	* if (map.get(key) != null) {
309	jsr166	1.51	* V oldValue = map.get(key);
310			* V newValue = remappingFunction.apply(key, oldValue);
311			* if (newValue != null)
312			* map.replace(key, oldValue, newValue);
313			* else
314			* map.remove(key, oldValue);
315			* }}</pre>
316	dl	1.46	*
317			* The default implementation may retry these steps when multiple
318			* threads attempt updates, and may call the remapping function
319			* multiple times.
320			*
321			* @throws UnsupportedOperationException {@inheritDoc}
322			* @throws ClassCastException {@inheritDoc}
323			* @throws NullPointerException {@inheritDoc}
324			* @since 1.8
325			*/
326			@Override
327			default V computeIfPresent(K key,
328			BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
329			Objects.requireNonNull(remappingFunction);
330			V oldValue;
331	jsr166	1.47	while ((oldValue = get(key)) != null) {
332	dl	1.46	V newValue = remappingFunction.apply(key, oldValue);
333			if (newValue != null) {
334			if (replace(key, oldValue, newValue))
335			return newValue;
336			} else if (remove(key, oldValue))
337			return null;
338			}
339			return oldValue;
340			}
341
342			/**
343			* {@inheritDoc}
344			*
345			* @implSpec
346			* The default implementation is equivalent to performing the following
347			* steps for this {@code map}, then returning the current value or
348			* {@code null} if absent:
349			*
350	jsr166	1.52	* <pre> {@code
351	dl	1.46	* V oldValue = map.get(key);
352			* V newValue = remappingFunction.apply(key, oldValue);
353			* if (oldValue != null ) {
354	jsr166	1.51	* if (newValue != null)
355			* map.replace(key, oldValue, newValue);
356			* else
357			* map.remove(key, oldValue);
358	dl	1.46	* } else {
359	jsr166	1.51	* if (newValue != null)
360			* map.putIfAbsent(key, newValue);
361			* else
362			* return null;
363			* }}</pre>
364	dl	1.46	*
365			* The default implementation may retry these steps when multiple
366			* threads attempt updates, and may call the remapping function
367			* multiple times.
368			*
369			* @throws UnsupportedOperationException {@inheritDoc}
370			* @throws ClassCastException {@inheritDoc}
371			* @throws NullPointerException {@inheritDoc}
372			* @since 1.8
373			*/
374			@Override
375			default V compute(K key,
376			BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
377			Objects.requireNonNull(remappingFunction);
378			V oldValue = get(key);
379	jsr166	1.47	for (;;) {
380	dl	1.46	V newValue = remappingFunction.apply(key, oldValue);
381			if (newValue == null) {
382			// delete mapping
383			if (oldValue != null \|\| containsKey(key)) {
384			// something to remove
385			if (remove(key, oldValue)) {
386			// removed the old value as expected
387			return null;
388			}
389
390			// some other value replaced old value. try again.
391			oldValue = get(key);
392			} else {
393			// nothing to do. Leave things as they were.
394			return null;
395			}
396			} else {
397			// add or replace old mapping
398			if (oldValue != null) {
399			// replace
400			if (replace(key, oldValue, newValue)) {
401			// replaced as expected.
402			return newValue;
403			}
404
405			// some other value replaced old value. try again.
406			oldValue = get(key);
407			} else {
408			// add (replace if oldValue was null)
409			if ((oldValue = putIfAbsent(key, newValue)) == null) {
410			// replaced
411			return newValue;
412			}
413
414			// some other value replaced old value. try again.
415			}
416	dl	1.44	}
417			}
418			}
419
420	dl	1.46	/**
421			* {@inheritDoc}
422			*
423			* @implSpec
424			* The default implementation is equivalent to performing the following
425			* steps for this {@code map}, then returning the current value or
426			* {@code null} if absent:
427			*
428	jsr166	1.52	* <pre> {@code
429	dl	1.46	* V oldValue = map.get(key);
430			* V newValue = (oldValue == null) ? value :
431	jsr166	1.51	* remappingFunction.apply(oldValue, value);
432	dl	1.46	* if (newValue == null)
433	jsr166	1.51	* map.remove(key);
434	dl	1.46	* else
435	jsr166	1.52	* map.put(key, newValue);}</pre>
436	dl	1.46	*
437			* The default implementation may retry these steps when multiple
438			* threads attempt updates, and may call the remapping function
439			* multiple times.
440			*
441			* @throws UnsupportedOperationException {@inheritDoc}
442			* @throws ClassCastException {@inheritDoc}
443			* @throws NullPointerException {@inheritDoc}
444			* @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			V oldValue = get(key);
452			for (;;) {
453			if (oldValue != null) {
454			V newValue = remappingFunction.apply(oldValue, value);
455			if (newValue != null) {
456			if (replace(key, oldValue, newValue))
457			return newValue;
458			} else if (remove(key, oldValue)) {
459			return null;
460			}
461			oldValue = get(key);
462			} else {
463			if ((oldValue = putIfAbsent(key, value)) == null) {
464			return value;
465			}
466			}
467			}
468			}
469	tim	1.1	}