Package org.apache.openjpa.lib.util.concurrent

Class ConcurrentReferenceHashMap

java.lang.Object
java.util.AbstractMap
org.apache.openjpa.lib.util.concurrent.ConcurrentReferenceHashMap
All Implemented Interfaces:
Cloneable, Map, ConcurrentMap, ReferenceMap, SizedMap
public class ConcurrentReferenceHashMap extends AbstractMap implements ConcurrentMap, ReferenceMap, SizedMap, Cloneable
This class implements a HashMap which has limited synchronization and reference keys or values(but not both). In particular mutators are generally synchronized while accessors are generally not. Additionally the Iterators returned by this class are not "fail-fast", but instead try to continue to iterate over the data structure after changes have been made. Finally purging of the reference queue is only done inside mutators. Null keys are not supported if keys use references. Null values are not supported if values use references. This class is based heavily on the WeakHashMap class in the Java collections package.

  • Constructor Details

    • ConcurrentReferenceHashMap

      public ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType, int initialCapacity, float loadFactor)
      Constructs a new, empty HashMap with the specified initial capacity and the specified load factor.
      Parameters:
      keyType - the reference type of map keys
      valueType - the reference type of map values
      initialCapacity - the initial capacity of the HashMap.
      loadFactor - a number between 0.0 and 1.0.
      Throws:
      IllegalArgumentException - if neither keys nor values use hard references, if the initial capacity is less than or equal to zero, or if the load factor is less than or equal to zero

    • ConcurrentReferenceHashMap

      public ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType, int initialCapacity)
      Constructs a new, empty HashMap with the specified initial capacity and default load factor.
      Parameters:
      keyType - the reference type of map keys
      valueType - the reference type of map values
      initialCapacity - the initial capacity of the HashMap.

    • ConcurrentReferenceHashMap

      public ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType)
      Constructs a new, empty HashMap with a default capacity and load factor.
      Parameters:
      keyType - the reference type of map keys
      valueType - the reference type of map values

    • ConcurrentReferenceHashMap

      public ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType, Map t)
      Constructs a new HashMap with the same mappings as the given Map. The HashMap is created with a capacity of thrice the number of entries in the given Map or 11 (whichever is greater), and a default load factor.
      Parameters:
      keyType - the reference type of map keys
      valueType - the reference type of map values

  • Method Details

    • eq

      protected boolean eq(Object x, Object y)
      Compare two objects. These might be keys, values, or Entry instances. This implementation uses a normal null-safe object equality algorithm.
      Since:
      1.0.0

    • hc

      protected int hc(Object o)
      Obtain the hashcode of an object. The object might be a key, a value, or an Entry. This implementation just delegates to Object.hashCode()
      Since:
      1.0.0

    • getMaxSize

      public int getMaxSize()
      Description copied from interface: SizedMap
      The maximum number of entries, or Integer.MAX_VALUE for no limit.
      Specified by:
      getMaxSize in interface SizedMap

    • setMaxSize

      public void setMaxSize(int maxSize)
      Description copied from interface: SizedMap
      The maximum number of entries, or Integer.MAX_VALUE for no limit.
      Specified by:
      setMaxSize in interface SizedMap

    • isFull

      public boolean isFull()
      Description copied from interface: SizedMap
      Whether the map is full.
      Specified by:
      isFull in interface SizedMap

    • overflowRemoved

      public void overflowRemoved(Object key, Object value)
      Description copied from interface: SizedMap
      Overridable callback for when an overflow entry is automatically removed.
      Specified by:
      overflowRemoved in interface SizedMap

    • size

      public int size()
      Returns the number of key-value mappings in this Map. This result is a snapshot, and may not reflect unprocessed entries that will be removed before next attempted access because they are no longer referenced.
      Specified by:
      size in interface Map
      Overrides:
      size in class AbstractMap

    • isEmpty

      public boolean isEmpty()
      Returns true if this Map contains no key-value mappings. This result is a snapshot, and may not reflect unprocessed entries that will be removed before next attempted access because they are no longer referenced.
      Specified by:
      isEmpty in interface Map
      Overrides:
      isEmpty in class AbstractMap

    • containsValue

      public boolean containsValue(Object value)
      Returns true if this HashMap maps one or more keys to the specified value.
      Specified by:
      containsValue in interface Map
      Overrides:
      containsValue in class AbstractMap
      Parameters:
      value - value whose presence in this Map is to be tested.

    • containsKey

      public boolean containsKey(Object key)
      Returns true if this HashMap contains a mapping for the specified key.
      Specified by:
      containsKey in interface Map
      Overrides:
      containsKey in class AbstractMap
      Parameters:
      key - key whose presence in this Map is to be tested.

    • get

      public Object get(Object key)
      Returns the value to which this HashMap maps the specified key. Returns null if the HashMap contains no mapping for this key.
      Specified by:
      get in interface Map
      Overrides:
      get in class AbstractMap
      Parameters:
      key - key whose associated value is to be returned.

    • put

      public Object put(Object key, Object value)
      Associates the specified value with the specified key in this HashMap. If the HashMap previously contained a mapping for this key, the old value is replaced.
      Specified by:
      put in interface Map
      Overrides:
      put in class AbstractMap
      Parameters:
      key - key with which the specified value is to be associated.
      value - value to be associated with the specified key.
      Returns:
      previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the HashMap previously associated null with the specified key.

    • remove

      public Object remove(Object key)
      Removes the mapping for this key from this HashMap if present.
      Specified by:
      remove in interface Map
      Overrides:
      remove in class AbstractMap
      Parameters:
      key - key whose mapping is to be removed from the Map.
      Returns:
      previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the HashMap previously associated null with the specified key.

    • removeExpired

      public void removeExpired()
      Description copied from interface: ReferenceMap
      Purge stale entries.
      Specified by:
      removeExpired in interface ReferenceMap

    • keyExpired

      public void keyExpired(Object value)
      Description copied from interface: ReferenceMap
      Overridable callback for when a key reference expires.
      Specified by:
      keyExpired in interface ReferenceMap
      Parameters:
      value - the value for the expired key

    • valueExpired

      public void valueExpired(Object key)
      Description copied from interface: ReferenceMap
      Overridable callback for when a value reference expires.
      Specified by:
      valueExpired in interface ReferenceMap
      Parameters:
      key - the key for the expired value

    • removeRandom

      public Map.Entry removeRandom()
      Description copied from interface: ConcurrentMap
      Remove an arbitrary(not strictly random) entry from the map. This allows implementation of concurrent caches with size ceilings.
      Specified by:
      removeRandom in interface ConcurrentMap
      Returns:
      the removed entry, or null if map is empty

    • randomEntryIterator

      public Iterator randomEntryIterator()
      Description copied from interface: ConcurrentMap
      Iterate over map entries, beginning at an arbitrary (not strictly random) entry.
      Specified by:
      randomEntryIterator in interface ConcurrentMap

    • putAll

      public void putAll(Map t)
      Copies all of the mappings from the specified Map to this HashMap These mappings will replace any mappings that this HashMap had for any of the keys currently in the specified Map.
      Specified by:
      putAll in interface Map
      Overrides:
      putAll in class AbstractMap
      Parameters:
      t - Mappings to be stored in this Map.

    • clear

      public void clear()
      Removes all mappings from this HashMap.
      Specified by:
      clear in interface Map
      Overrides:
      clear in class AbstractMap

    • clone

      public Object clone()
      Returns a shallow copy of this HashMap. The keys and values themselves are not cloned.
      Overrides:
      clone in class AbstractMap

    • keySet

      public Set keySet()
      Returns a Set view of the keys contained in this HashMap. The Set is backed by the HashMap, so changes to the HashMap are reflected in the Set, and vice-versa. The Set supports element removal, which removes the corresponding mapping from the HashMap, via the Iterator.remove, Set.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations.
      Specified by:
      keySet in interface Map
      Overrides:
      keySet in class AbstractMap

    • values

      public Collection values()
      Returns a Collection view of the values contained in this HashMap. The Collection is backed by the HashMap, so changes to the HashMap are reflected in the Collection, and vice-versa. The Collection supports element removal, which removes the corresponding mapping from the HashMap, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.
      Specified by:
      values in interface Map
      Overrides:
      values in class AbstractMap

    • entrySet

      public Set entrySet()
      Returns a Collection view of the mappings contained in this HashMap. Each element in the returned collection is a Map.Entry. The Collection is backed by the HashMap, so changes to the HashMap are reflected in the Collection, and vice-versa. The Collection supports element removal, which removes the corresponding mapping from the HashMap, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.
      Specified by:
      entrySet in interface Map
      Specified by:
      entrySet in class AbstractMap
      See Also: