/*
* 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.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}/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}/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;
}
}
}
}
}