/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* 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.BiFunction;
/**
* A {@link java.util.Map} providing thread safety and 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 get() returning null unambiguously means the key
* is absent. Implementations which support null values must override this
* default implementation.
*/
@Override
default V getOrDefault(Object key, V defaultValue) {
V v;
return ((v = get(key)) != null) ? v : defaultValue;
}
/**
* If the specified key is not already associated
* with a value, associate it with the given value.
* This is equivalent to
* <pre> {@code
* if (!map.containsKey(key))
* return map.put(key, value);
* else
* return map.get(key);}</pre>
*
* except that the action is performed atomically.
*
* @param key key with which the specified value is to be associated
* @param value value to be associated with the specified key
* @return the previous value associated with the specified key, or
* {@code null} if there was no mapping for the key.
* (A {@code null} return can also indicate that the map
* previously associated {@code null} with the key,
* if the implementation supports null values.)
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by this map
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in this map
* @throws NullPointerException if the specified key or value is null,
* and this map does not permit null keys or values
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in this map
*/
V putIfAbsent(K key, V value);
/**
* Removes the entry for a key only if currently mapped to a given value.
* This is equivalent to
* <pre> {@code
* if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
* map.remove(key);
* return true;
* } else
* return false;}</pre>
*
* except that the action is performed atomically.
*
* @param key key with which the specified value is associated
* @param value value expected to be associated with the specified key
* @return {@code true} if the value was removed
* @throws UnsupportedOperationException if the {@code remove} operation
* is not supported by this map
* @throws ClassCastException if the key or value is of an inappropriate
* type for this map
* (<a href="../Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified key or value is null,
* and this map does not permit null keys or values
* (<a href="../Collection.html#optional-restrictions">optional</a>)
*/
boolean remove(Object key, Object value);
/**
* Replaces the entry for a key only if currently mapped to a given value.
* This is equivalent to
* <pre> {@code
* if (map.containsKey(key) && Objects.equals(map.get(key), oldValue)) {
* map.put(key, newValue);
* return true;
* } else
* return false;}</pre>
*
* except that the action is performed atomically.
*
* @param key key with which the specified value is associated
* @param oldValue value expected to be associated with the specified key
* @param newValue value to be associated with the specified key
* @return {@code true} if the value was replaced
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by this map
* @throws ClassCastException if the class of a specified key or value
* prevents it from being stored in this map
* @throws NullPointerException if a specified key or value is null,
* and this map does not permit null keys or values
* @throws IllegalArgumentException if some property of a specified key
* or value prevents it from being stored in this map
*/
boolean replace(K key, V oldValue, V newValue);
/**
* Replaces the entry for a key only if currently mapped to some value.
* This is equivalent to
* <pre> {@code
* if (map.containsKey(key)) {
* return map.put(key, value);
* } else
* return null;}</pre>
*
* except that the action is performed atomically.
*
* @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}
*
* @implNote This implementation assumes that the ConcurrentMap cannot
* contain null values and get() returning null unambiguously means the key
* is absent. Implementations which support null values
* <strong>must</strong> override this default implementation.
*/
@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;
}
}
});
}
}