/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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/*
*
*
*
*
*
* 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>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, 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.
*
* @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
* <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="../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.
*
* @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
* <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())
* do {
* K k = entry.getKey();
* V v = entry.getValue();
* } while(!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}, 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 including potentially calling the mapping
* function 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}
* @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 including potentially calling the remapping function
* 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}
* @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 including potentially calling the remapping
* function 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}
* @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>
*
* <p>The default implementation may retry these steps when multiple
* threads attempt updates including potentially calling the remapping
* function 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}
* @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;
}
}
}
}
}