/* * 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; // BEGIN android-note // removed link to collections framework docs // fixed framework docs link to "Collection#optional" // END android-note /** * A {@link java.util.Map} providing thread safety and atomicity * guarantees. * *
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. * *
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
* happen-before
* actions subsequent to the access or removal of that object from
* the {@code ConcurrentMap} in another thread.
*
* @since 1.5
* @author Doug Lea
* @param The default implementation is equivalent to, for this {@code map}:
* 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 must
* 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}:
*
* 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 must
* 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}:
*
* 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 must
* 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}:
*
* 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 must
* 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}:
*
* 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 must
* 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;
}
}
}
}
}
{@code
* for (Map.Entry
*
* @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 {@code
* if (!map.containsKey(key))
* return map.put(key, value);
* else
* return map.get(key);}
*
* 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}:
* {@code
* if (map.containsKey(key)
* && Objects.equals(map.get(key), value)) {
* map.remove(key);
* return true;
* } else {
* return false;
* }}
*
* 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
* (optional)
* @throws NullPointerException if the specified key or value is null,
* and this map does not permit null keys or values
* (optional)
*/
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}:
* {@code
* if (map.containsKey(key)
* && Objects.equals(map.get(key), oldValue)) {
* map.put(key, newValue);
* return true;
* } else {
* return false;
* }}
*
* 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}:
* {@code
* if (map.containsKey(key))
* return map.put(key, value);
* else
* return null;}
*
* 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
* {@code
* for (Map.Entry
*
* The default implementation may retry these steps when multiple
* threads attempt updates including potentially calling the function
* repeatedly for a given key.
*
* {@code
* V oldValue, newValue;
* return ((oldValue = map.get(key)) == null
* && (newValue = mappingFunction.apply(key)) != null
* && (oldValue = map.putIfAbsent(key, newValue)) == null)
* ? newValue
* : oldValue;}
*
* {@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;}
* When multiple threads attempt updates, map operations and the
* remapping function may be called multiple times.
*
* {@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;
* }
* }}
* When multiple threads attempt updates, map operations and the
* remapping function may be called multiple times.
*
* {@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;
* }
* }}
* When multiple threads attempt updates, map operations and the
* remapping function may be called multiple times.
*
*