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package java8.util.concurrent;
import java.util.ConcurrentModificationException;
import java.util.Map;
import java.util.concurrent.ConcurrentMap;
import java8.util.Objects;
import java8.util.function.BiConsumer;
import java8.util.function.BiFunction;
import java8.util.function.Function;
/**
* A place for static default implementations of the new Java 8
* default interface methods and static interface methods in the
* {@link ConcurrentMap} interface.
*/
public final class ConcurrentMaps {
/**
* If the specified key is not already associated with a value or is
* associated with null, associates it with the given non-null value.
* Otherwise, replaces the associated value with the results of the given
* remapping function, or removes if the result is {@code null}. This
* method may be of use when combining multiple mapped values for a key.
* For example, to either create or append a {@code String msg} to a
* value mapping:
*
* {@code
* map.merge(key, msg, String::concat)
* }
*
* If the remapping function returns {@code null} the mapping is removed.
* If the remapping function itself throws an (unchecked) exception, the
* exception is rethrown, and the current mapping is left unchanged.
*
*
The remapping function itself should not modify the passed map during computation.
*
*
Implementation Requirements:
* The default implementation is equivalent to performing the following
* steps for the {@code map}:
*
*
{@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.
*
* 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 the default implementation.
*
*
The default implementation makes no guarantees about detecting if the
* remapping function modifies the passed map during computation and, if
* appropriate, reporting an error. Concurrent implementations should override
* this method and, on a best-effort basis, throw an {@code IllegalStateException}
* if it is detected that the remapping function modifies the map during computation
* and as a result computation would never complete.
*
* @param the type of keys maintained by the passed map
* @param the type of mapped values in the passed map
* @param map the {@code ConcurrentMap} on which to execute the {@code merge}
* operation.
* @param key key with which the resulting value is to be associated
* @param value the non-null value to be merged with the existing value
* associated with the key or, if no existing value or a null value
* is associated with the key, to be associated with the key
* @param remappingFunction the function to recompute a value if present
* @return the new value associated with the specified key, or null if no
* value is associated with the key
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by the map (optional)
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in the map (optional)
* @throws NullPointerException if the specified key is null and the map
* does not support null keys or the value or remappingFunction is
* null
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in the map (optional)
* @since 1.8
*/
public static V merge(ConcurrentMap map, K key, V value,
BiFunction remappingFunction) {
Objects.requireNonNull(map);
Objects.requireNonNull(remappingFunction);
Objects.requireNonNull(value);
retry: for (;;) {
V oldValue = map.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 (map.replace(key, oldValue, newValue))
return newValue;
} else if (map.remove(key, oldValue)) {
return null;
}
continue retry;
} else {
if ((oldValue = map.putIfAbsent(key, value)) == null)
return value;
continue haveOldValue;
}
}
}
}
/**
* If the specified key is not already associated with a value (or is mapped
* to {@code null}), attempts to compute its value using the given mapping
* function and enters it into the passed {@code map} unless {@code null}.
*
* If the mapping function returns {@code null} no mapping is recorded.
* If the mapping function itself throws an (unchecked) exception, the
* exception is rethrown, and no mapping is recorded. The most
* common usage is to construct a new object serving as an initial
* mapped value or memoized result, as in:
*
*
{@code
* map.computeIfAbsent(key, k -> new Value(f(k)));
* }
*
* Or to implement a multi-value map, {@code Map>},
* supporting multiple values per key:
*
* {@code
* map.computeIfAbsent(key, k -> new HashSet()).add(v);
* }
*
* The mapping function itself should not modify the passed map during computation.
*
*
Implementation Requirements:
* The default implementation is equivalent to the following steps for the
* {@code map}:
*
*
{@code
* V oldValue, newValue;
* return ((oldValue = map.get(key)) == null
* && (newValue = mappingFunction.apply(key)) != null
* && (oldValue = map.putIfAbsent(key, newValue)) == null)
* ? newValue
* : oldValue;}
*
* 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 the default implementation.
*
*
The default implementation makes no guarantees about detecting if the
* mapping function modifies the passed map during computation and, if
* appropriate, reporting an error. Concurrent implementations should override
* this method and, on a best-effort basis, throw an {@code IllegalStateException}
* if it is detected that the mapping function modifies the map during computation
* and as a result computation would never complete.
*
* @param the type of keys maintained by the passed map
* @param the type of mapped values in the passed map
* @param map the {@code ConcurrentMap} on which to execute the {@code computeIfAbsent}
* operation.
* @param key key with which the specified value is to be associated
* @param mappingFunction the mapping function to compute a value
* @return the current (existing or computed) value associated with
* the specified key, or null if the computed value is null
* @throws NullPointerException if the specified key is null and
* the map does not support null keys, or the mappingFunction
* is null
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by the map (optional)
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in the map (optional)
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in the map (optional)
* @since 1.8
*/
public static V computeIfAbsent(ConcurrentMap map, K key,
Function mappingFunction) {
Objects.requireNonNull(map);
Objects.requireNonNull(mappingFunction);
V oldValue, newValue;
return ((oldValue = map.get(key)) == null
&& (newValue = mappingFunction.apply(key)) != null
&& (oldValue = map.putIfAbsent(key, newValue)) == null)
? newValue
: oldValue;
}
/**
* If the value for the specified key is present and non-null, attempts to
* compute a new mapping given the key and its current mapped value.
*
* If the remapping function returns {@code null}, the mapping is removed.
* If the remapping function itself throws an (unchecked) exception, the
* exception is rethrown, and the current mapping is left unchanged.
*
*
The remapping function itself should not modify the passed map during
* computation.
*
*
Implementation Requirements:
* The default implementation is equivalent to performing the following
* steps for the {@code map}:
*
*
{@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.
*
* 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.
*
* @param the type of keys maintained by the passed map
* @param the type of mapped values in the passed map
* @param map the {@code ConcurrentMap} on which to execute the
* {@code computeIfPresent} operation.
* @param key key with which the specified value is to be associated
* @param remappingFunction the remapping function to compute a value
* @return the new value associated with the specified key, or null if none
* @throws NullPointerException if the specified key is null and
* the map does not support null keys, or the
* remappingFunction is null
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by the map (optional)
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in the map (optional)
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in this map (optional)
* @since 1.8
*/
public static V computeIfPresent(ConcurrentMap map, K key,
BiFunction remappingFunction) {
Objects.requireNonNull(map);
Objects.requireNonNull(remappingFunction);
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;
}
/**
* Attempts to compute a mapping for the specified key and its current
* mapped value (or {@code null} if there is no current mapping). For
* example, to either create or append a {@code String} msg to a value
* mapping:
*
* {@code
* map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}
* (Method {@link #merge merge()} is often simpler to use for such purposes.)
*
* If the remapping function returns {@code null}, the mapping is removed
* (or remains absent if initially absent). If the remapping function itself
* throws an (unchecked) exception, the exception is rethrown, and the current
* mapping is left unchanged.
*
*
The remapping function itself should not modify the passed map during
* computation.
*
*
Implementation Requirements:
* The default implementation is equivalent to performing the following
* steps for the {@code map}:
*
*
{@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.
*
* 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.
*
* @param the type of keys maintained by the passed map
* @param the type of mapped values in the passed map
* @param map the {@code ConcurrentMap} on which to execute the {@code compute}
* operation.
* @param key key with which the specified value is to be associated
* @param remappingFunction the remapping function to compute a value
* @return the new value associated with the specified key, or null if none
* @throws NullPointerException if the specified key is null and
* the map does not support null keys, or the
* remappingFunction is null
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by the map (optional)
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in the map (optional)
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in this map (optional)
* @since 1.8
*/
public static V compute(ConcurrentMap map, K key,
BiFunction remappingFunction) {
Objects.requireNonNull(map);
retry: for (;;) {
V oldValue = map.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 (map.replace(key, oldValue, newValue))
return newValue;
}
else if ((oldValue = map.putIfAbsent(key, newValue)) == null)
return newValue;
else continue haveOldValue;
} else if (oldValue == null || map.remove(key, oldValue)) {
return null;
}
continue retry;
}
}
}
/**
* Replaces each entry's value with the result of invoking the given
* function on that entry until all entries have been processed or the
* function throws an exception. Exceptions thrown by the function are
* relayed to the caller.
*
* Implementation Requirements:
*
The default implementation is equivalent to, for the {@code map}:
*
{@code
* for ((Map.Entry entry : map.entrySet())
* do {
* K k = entry.getKey();
* V v = entry.getValue();
* } while(!replace(k, v, function.apply(k, v)));
* }
*
* The default implementation may retry these steps when multiple
* threads attempt updates including potentially calling the function
* repeatedly for a given key.
*
* 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 the default implementation.
*
* @param the type of keys maintained by the passed map
* @param the type of mapped values in the passed map
* @param map the {@code ConcurrentMap} on which to execute the {@code replaceAll}
* operation.
* @param function the function to apply to each entry
* @throws UnsupportedOperationException if the {@code set} operation
* is not supported by the map's entry set iterator.
* @throws ClassCastException if the class of a replacement value
* prevents it from being stored in the map
* @throws NullPointerException if the specified function is null, or the
* specified replacement value is null, and the map does not permit null
* values
* @throws ClassCastException if a replacement value is of an inappropriate
* type for the map (optional)
* @throws NullPointerException if function or a replacement value is null,
* and the map does not permit null keys or values (optional)
* @throws IllegalArgumentException if some property of a replacement value
* prevents it from being stored in the map (optional)
* @throws ConcurrentModificationException if an entry is found to be
* removed during iteration
* @since 1.8
*/
public static void replaceAll(ConcurrentMap map, BiFunction function) {
Objects.requireNonNull(map);
Objects.requireNonNull(function);
forEach(map, (k,v) -> {
while (!map.replace(k, v, function.apply(k, v))) {
// v changed or k is gone
if ( (v = map.get(k)) == null) {
// k is no longer in the map.
break;
}
}
});
}
/**
* Returns the value to which the specified key is mapped, or
* {@code defaultValue} if the map contains no mapping for the key.
*
* Implementation Note:
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.
*
* @param the type of keys maintained by the passed map
* @param the type of mapped values in the passed map
* @param map the {@code ConcurrentMap} on which to execute the {@code getOrDefault}
* operation.
* @param key the key whose associated value is to be returned
* @param defaultValue the default mapping of the key
* @return the value to which the specified key is mapped, or
* {@code defaultValue} if the map contains no mapping for the key
* @throws ClassCastException if the key is of an inappropriate type for
* the map (optional)
* @throws NullPointerException if the specified key is null and the map
* does not permit null keys (optional)
* @since 1.8
*/
public static V getOrDefault(ConcurrentMap map, Object key, V defaultValue) {
Objects.requireNonNull(map);
V v;
return ((v = map.get(key)) != null) ? v : defaultValue;
}
/**
* Performs the given action for each entry in the map until all entries
* have been processed or the action throws an exception. Unless
* otherwise specified by the implementing class, actions are performed in
* the order of entry set iteration (if an iteration order is specified.)
* Exceptions thrown by the action are relayed to the caller.
*
* Implementation Requirements:
The default implementation
* is equivalent to, for the
* {@code map}:
*
{@code
* for ((Map.Entry entry : map.entrySet())
* action.accept(entry.getKey(), entry.getValue());
* }
*
* Implementation Note:
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.
*
* @param the type of keys maintained by the passed map
* @param the type of mapped values in the passed map
* @param map the {@code ConcurrentMap} on which to execute the {@code forEach}
* operation.
* @param action The action to be performed for each entry
* @throws NullPointerException if the specified map or action is null
* @throws ConcurrentModificationException if an entry is found to be
* removed during iteration
* @since 1.8
*/
public static void forEach(ConcurrentMap map, BiConsumer action) {
Objects.requireNonNull(map);
Objects.requireNonNull(action);
for (Map.Entry entry : map.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);
}
}
private ConcurrentMaps() {
}
}