groovyx.gpars.extra166y
[Java] Class CustomConcurrentHashMap

java.lang.Object
  java.util.AbstractMap
      groovyx.gpars.extra166y.CustomConcurrentHashMap

All Implemented Interfaces:

java.util.concurrent.ConcurrentMap, java.io.Serializable

public class CustomConcurrentHashMap
extends java.util.AbstractMap

A java.util.ConcurrentMap supporting user-defined equivalence comparisons, soft, weak, or strong keys and values, and user-supplied computational methods for setting and updating values. In particular:

• Identity-based, Equality-based or User-definable Equivalence-based comparisons controlling membership.
• {

  linkplain:

  SoftReference Soft}, {@linkplain WeakReference weak} or strong (regular) keys and values.

  User-definable MappingFunctions that may be used in method CustomConcurrentHashMap#computeIfAbsent#computeIfAbsent to atomically establish a computed value, along with RemappingFunctions that can be used in method CustomConcurrentHashMap#compute#compute to atomically replace values.

  Factory methods returning specialized forms for int keys and/or values, that may be more space-efficient

 identityMap = new CustomConcurrentHashMap
     (STRONG, IDENTITY, STRONG, EQUALS, 0);
 weakKeyMap = new CustomConcurrentHashMap
     (WEAK, IDENTITY, STRONG, EQUALS, 0);
     .weakKeys());
 byNameMap = new CustomConcurrentHashMap
     (STRONG,
      new Equivalence() {
          public boolean equal(Person k, Object x) {
            return x instanceof Person && k.name.equals(((Person)x).name);
          
          public int hash(Object x) {
             return (x instanceof Person) ? ((Person)x).name.hashCode() : 0;
          }
        },
      STRONG, EQUALS, 0);
 }
 

This class also includes nested class KeySet that provides space-efficient Set views of maps, also supporting method intern, which may be of use in canonicalizing elements.

When used with (Weak or Soft) Reference keys and/or values, elements that have asynchronously become null are treated as absent from the map and (eventually) removed from maps via a background thread common across all maps. Because of the potential for asynchronous clearing of References, methods such as containsValue have weaker guarantees than you might expect even in the absence of other explicitly concurrent operations. For example containsValue(value) may return true even if value is no longer available upon return from the method.

When Equivalences other than equality are used, the returned collections may violate the specifications of Map and/or Set interfaces, which mandate the use of the equals method when comparing objects. The methods of this class otherwise have properties similar to those of java.util.ConcurrentHashMap under its default settings. To adaptively maintain semantics and performance under varying conditions, this class does not support load factor or concurrency level parameters. This class does not permit null keys or values. This class is serializable; however, serializing a map that uses soft or weak references can give unpredictable results. This class supports all optional operations of the ConcurrentMap interface. It supports have weakly consistent iteration: an iterator over one of the map's view collections may reflect some, all or none of the changes made to the collection after the iterator was created.

This class is a member of the Java Collections Framework.

Parameters:

- the type of keys maintained by this map

- the type of mapped values

EQUALS

public static final CustomConcurrentHashMap.Equivalence EQUALS

An Equivalence object performing java.lang.Object#equals based comparisons and using java.lang.Object#hashCode hashing

IDENTITY

public static final CustomConcurrentHashMap.Equivalence IDENTITY

An Equivalence object performing identity-based comparisons and using java.lang.System#identityHashCode for hashing

INT_STRING

private static final java.lang.String INT_STRING

Config string for int maps

MAX_SEGMENT_CAPACITY

static final int MAX_SEGMENT_CAPACITY

MIN_SEGMENT_CAPACITY

static final int MIN_SEGMENT_CAPACITY

NSEGMENTS

static final int NSEGMENTS

SEGMENT_BITS

static final int SEGMENT_BITS

SEGMENT_MASK

static final int SEGMENT_MASK

SEGMENT_SHIFT

static final int SEGMENT_SHIFT

SELF_STRING

private static final java.lang.String SELF_STRING

Config string for self-map (Set view) refs

SOFT

public static final CustomConcurrentHashMap.Strength SOFT

The strength of soft references

STRONG

public static final CustomConcurrentHashMap.Strength STRONG

The strength of ordinary references

UNSAFE

static final sun.misc.Unsafe UNSAFE

WEAK

public static final CustomConcurrentHashMap.Strength WEAK

The strength of weak references

entrySet

java.util.Set entrySet

factory

final CustomConcurrentHashMap.NodeFactory factory

The factory for this map

initialSegmentCapacity

final int initialSegmentCapacity

The initial size of Segment tables when they are first constructed

keyEquivalence

final CustomConcurrentHashMap.Equivalence keyEquivalence

Equivalence object for keys

keySet

java.util.Set keySet

refQueue

static java.lang.ref.ReferenceQueue refQueue

segments

CustomConcurrentHashMap.Segment[] segments

The segments, each of which acts as a hash table

segmentsBase

static final long segmentsBase

segmentsShift

static final int segmentsShift

serialVersionUID

private static final long serialVersionUID

tableBase

static final long tableBase

tableShift

static final int tableShift

valueEquivalence

final CustomConcurrentHashMap.Equivalence valueEquivalence

Equivalence object for values

values

java.util.Collection values

CustomConcurrentHashMap

CustomConcurrentHashMap()

CustomConcurrentHashMap

java.lang.Object CustomConcurrentHashMap(java.lang.String ks, CustomConcurrentHashMap.Equivalence keq, java.lang.String vs, CustomConcurrentHashMap.Equivalence veq, int expectedSize)

Internal constructor to set factory, equivalences and segment capacities, and to create segments array.

CustomConcurrentHashMap

public java.lang.Object CustomConcurrentHashMap(CustomConcurrentHashMap.Strength keyStrength, CustomConcurrentHashMap.Equivalence keyEquivalence, CustomConcurrentHashMap.Strength valueStrength, CustomConcurrentHashMap.Equivalence valueEquivalence, int expectedSize)

Creates a new CustomConcurrentHashMap with the given parameters

Parameters:

keyStrength - the strength for keys

keyEquivalence - the Equivalence to use for keys

valueStrength - the strength for values

valueEquivalence - the Equivalence to use for values

expectedSize - an estimate of the number of elements that will be held in the map. If no estimate is known, zero is an acceptable value.

CustomConcurrentHashMap

public java.lang.Object CustomConcurrentHashMap()

Creates a new CustomConcurrentHashMap with strong keys and values, and equality-based equivalence.

clear

public final void clear()

Removes all of the mappings from this map.

compute

public java.lang.Object compute(java.lang.Object key, CustomConcurrentHashMap.RemappingFunction remappingFunction)

Updates the mapping for the given key with the result of the given remappingFunction. This is equivalent to

   value = remappingFunction.remap(key, get(key));
   if (value != null)
     return put(key, value):
   else
     return remove(key);
 

except that the action is performed atomically. Some attempted operations on this map by other threads may be blocked while computation is in progress.

Sample Usage. A remapping function can be used to perform frequency counting of words using code such as:

 map.compute(word, new RemappingFunction<String,Integer>() {
   public Integer remap(String k, Integer v) {
     return (v == null) ? 1 : v + 1;
   }});
 

throws:

NullPointerException if the specified key or remappingFunction is null,

throws:

RuntimeException or Error if the remappingFunction does so, in which case the mapping is left in its previous state

Parameters:

key - key with which the specified value is to be associated

remappingFunction - the function to compute a value

Returns:

the updated value or null if the computation returned null

computeIfAbsent

public java.lang.Object computeIfAbsent(java.lang.Object key, CustomConcurrentHashMap.MappingFunction mappingFunction)

If the specified key is not already associated with a value, computes its value using the given mappingFunction, and if non-null, enters it into the map. This is equivalent to

   if (map.containsKey(key))
       return map.get(key);
   value = mappingFunction.map(key);
   if (value != null)
      return map.put(key, value);
   else
      return null;
 

except that the action is performed atomically. Some attempted operations on this map by other threads may be blocked while computation is in progress. Because this function is invoked within atomicity control, the computation should be short and simple. The most common usage is to construct a new object serving as an initial mapped value, or memoized result.

throws:

NullPointerException if the specified key or mappingFunction is null,

throws:

RuntimeException or Error if the mappingFunction does so, in which case the mapping is left unestablished.

Parameters:

key - key with which the specified value is to be associated

mappingFunction - the function to compute a value

Returns:

the current (existing or computed) value associated with the specified key, or null if the computation returned null.

containsKey

public boolean containsKey(java.lang.Object key)

Returns true if this map contains a key equivalent to the given key with respect to this map's key Equivalence.

throws:

NullPointerException if the specified key is null

Parameters:

key - possible key

Returns:

true if this map contains the specified key

containsValue

public final boolean containsValue(java.lang.Object value)

Returns true if this map maps one or more keys to a value equivalent to the given value with respect to this map's value Equivalence. Note: This method requires a full internal traversal of the hash table, and so is much slower than method containsKey.

throws:

NullPointerException if the specified value is null

Parameters:

value - value whose presence in this map is to be tested

Returns:

true if this map maps one or more keys to the specified value

doPut

final java.lang.Object doPut(java.lang.Object key, java.lang.Object value, boolean onlyIfNull)

Shared implementation for put, putIfAbsent

entrySet

public java.util.Set entrySet()

Returns a java.util.Set view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

The view's iterator is a "weakly consistent" iterator that will never throw java.util.ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

equals

public boolean equals(java.lang.Object o)

Compares the specified object with this map for equality. Returns true if the given object is also a map of the same size, holding keys that are equal using this Map's key Equivalence, and which map to values that are equal according to this Map's value equivalence.

Parameters:

o - object to be compared for equality with this map

Returns:

true if the specified object is equal to this map

findNode

final CustomConcurrentHashMap.Node findNode(java.lang.Object key, int hash, CustomConcurrentHashMap.Segment seg)

Returns node for key, or null if none

get

public java.lang.Object get(java.lang.Object key)

Returns the value associated with a key equivalent to the given key with respect to this map's key Equivalence, or null if no such mapping exists.

throws:

NullPointerException if the specified key is null

Parameters:

key - possible key

Returns:

the value associated with the key or null if there is no mapping.

getReclamationQueue

static java.lang.ref.ReferenceQueue getReclamationQueue()

Returns a queue that may be used as the ReferenceQueue argument to java.lang.ref.Reference constructors to arrange removal of reclaimed nodes from maps via a background thread.

Returns:

the reference queue associated with the background cleanup thread.

getSegmentForAdd

final CustomConcurrentHashMap.Segment getSegmentForAdd(int hash)

Returns the segment for possibly inserting into the table associated with given hash, constructing it if necessary.

Parameters:

hash - the hash code for the key

Returns:

the segment

getSegmentForTraversal

final CustomConcurrentHashMap.Segment getSegmentForTraversal(int hash)

Returns the segment for traversing table for key with given hash

Parameters:

hash - the hash code for the key

Returns:

the segment, or null if not yet initialized

getUnsafe

private static sun.misc.Unsafe getUnsafe()

getUnsafePrivileged

private static sun.misc.Unsafe getUnsafePrivileged()

hashCode

public int hashCode()

Returns the sum of the hash codes of each entry in this map's entrySet() view, which in turn are the hash codes computed using key and value Equivalences for this Map.

Returns:

the hash code

isEmpty

public final boolean isEmpty()

Returns true if this map contains no key-value mappings.

Returns:

true if this map contains no key-value mappings

keyIterator

final CustomConcurrentHashMap.KeyIterator keyIterator()

keySet

public java.util.Set keySet()

Returns a java.util.Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

The view's iterator is a "weakly consistent" iterator that will never throw java.util.ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

newIntKeyIntValueMap

public static CustomConcurrentHashMap newIntKeyIntValueMap(int expectedSize)

Returns a new map using Integer keys and values

Parameters:

expectedSize - an estimate of the number of elements that will be held in the map. If no estimate is known, zero is an acceptable value.

Returns:

the map

newIntKeyMap

public static CustomConcurrentHashMap newIntKeyMap(CustomConcurrentHashMap.Strength valueStrength, CustomConcurrentHashMap.Equivalence valueEquivalence, int expectedSize)

Returns a new map using Integer keys and the given value parameters

Parameters:

valueStrength - the strength for values

valueEquivalence - the Equivalence to use for values

expectedSize - an estimate of the number of elements that will be held in the map. If no estimate is known, zero is an acceptable value.

Returns:

the map

newIntValueMap

public static CustomConcurrentHashMap newIntValueMap(CustomConcurrentHashMap.Strength keyStrength, CustomConcurrentHashMap.Equivalence keyEquivalence, int expectedSize)

Returns a new map using the given key parameters and Integer values

Parameters:

keyStrength - the strength for keys

keyEquivalence - the Equivalence to use for keys

expectedSize - an estimate of the number of elements that will be held in the map. If no estimate is known, zero is an acceptable value.

Returns:

the map

put

public java.lang.Object put(java.lang.Object key, java.lang.Object value)

Maps the specified key to the specified value in this map.

throws:

NullPointerException if the specified key or value is null

Parameters:

key - key with which the specified value is to be associated

value - value to be associated with the specified key

Returns:

the previous value associated with key, or null if there was no mapping for key

putAll

public void putAll(java.util.Map m)

Copies all of the mappings from the specified map to this one. These mappings replace any mappings that this map had for any of the keys currently in the specified map.

Parameters:

m - mappings to be stored in this map

putIfAbsent

public java.lang.Object putIfAbsent(java.lang.Object key, java.lang.Object value)

{@inheritDoc}

throws:

NullPointerException if the specified key or value is null

Returns:

the previous value associated with the specified key, or null if there was no mapping for the key

readObject

private void readObject(java.io.ObjectInputStream s)

Reconstitutes the instance from a stream (that is, deserializes it).

Parameters:

s - the stream

remove

public java.lang.Object remove(java.lang.Object key)

Removes the mapping for the specified key.

throws:

NullPointerException if the specified key is null

Parameters:

key - the key to remove

Returns:

the previous value associated with key, or null if there was no mapping for key

remove

public boolean remove(java.lang.Object key, java.lang.Object value)

{@inheritDoc}

throws:

NullPointerException if the specified key is null

removeIfReclaimed

final void removeIfReclaimed(CustomConcurrentHashMap.Node r)

Removes node if its key or value are null.

replace

public java.lang.Object replace(java.lang.Object key, java.lang.Object value)

{@inheritDoc}

throws:

NullPointerException if any of the arguments are null

replace

public boolean replace(java.lang.Object key, java.lang.Object oldValue, java.lang.Object newValue)

{@inheritDoc}

throws:

NullPointerException if the specified key or value is null

Returns:

the previous value associated with the specified key, or null if there was no mapping for the key

size

public final int size()

Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Returns:

the number of key-value mappings in this map

spreadHash

static int spreadHash(int h)

Applies a supplemental hash function to a given hashCode, which defends against poor quality hash functions. This is critical because we use power-of-two length hash tables, that otherwise encounter collisions for hashCodes that do not differ in lower or upper bits.

startReclamation

static java.lang.ref.ReferenceQueue startReclamation()

storeNode

static final void storeNode(CustomConcurrentHashMap.Node[] table, int i, CustomConcurrentHashMap.Node r)

storeSegment

static final void storeSegment(CustomConcurrentHashMap.Segment[] segs, int i, CustomConcurrentHashMap.Segment s)

valueOf

CustomConcurrentHashMap valueOf(java.lang.String name)

Returns the enum constant of this type with the specified name.

values

CustomConcurrentHashMap[] values()

Returns an array containing the constants of this enum type, in the order they are declared.

values

public java.util.Collection values()

Returns a java.util.Collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

The view's iterator is a "weakly consistent" iterator that will never throw java.util.ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

writeObject

private void writeObject(java.io.ObjectOutputStream s)

Saves the state of the instance to a stream (i.e., serializes it).

serialData:

the key (Object) and value (Object) for each key-value mapping, followed by a null pair. The key-value mappings are emitted in no particular order.

Parameters:

s - the stream

Copyright © 2008–2012 Václav Pech. All Rights Reserved.