Class WeakIdentityMap<TKey, TValue>

Implements a combination of java.util.WeakHashMap and java.util.IdentityHashMap. Useful for caches that need to key off of a == comparison instead of a .Equals(object).

This class is not a general-purpose System.Collections.Generic.IDictionary<TKey, TValue> implementation! It intentionally violates System.Collections.Generic.IDictionary<TKey, TValue>'s general contract, which mandates the use of the System.Object.Equals(System.Object) method when comparing objects. This class is designed for use only in the rare cases wherein reference-equality semantics are required.

This implementation was forked from Apache CXF but modified to not implement the System.Collections.Generic.IDictionary<TKey, TValue> interface and without any set views on it, as those are error-prone and inefficient, if not implemented carefully. The map only contains System.Collections.Generic.IEnumerable<T>.GetEnumerator() implementations on the values and not-GCed keys. Lucene's implementation also supports null keys, but those are never weak!

The map supports two modes of operation:

  • reapOnRead = true: This behaves identical to a java.util.WeakHashMap where it also cleans up the reference queue on every read operation (Get(Object), ContainsKey(Object), Count, GetValueEnumerator()), freeing map entries of already GCed keys.
  • reapOnRead = false: This mode does not call Reap() on every read operation. In this case, the reference queue is only cleaned up on write operations (like Put(TKey, TValue)). This is ideal for maps with few entries where the keys are unlikely be garbage collected, but there are lots of Get(Object) operations. The code can still call Reap() to manually clean up the queue without doing a write operation.

This is a Lucene.NET INTERNAL API, use at your own risk
Inheritance
System.Object
WeakIdentityMap<TKey, TValue>
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
System.Object.ToString()
Namespace: Lucene.Net.Util
Assembly: Lucene.Net.dll
Syntax
public sealed class WeakIdentityMap<TKey, TValue>

    where TKey : class
Type Parameters
Name Description
TKey
TValue

Properties

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Count

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.

NOTE: This was size() in Lucene.

Declaration
public int Count { get; }
Property Value
Type Description
System.Int32
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IsEmpty

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

Declaration
public bool IsEmpty { get; }
Property Value
Type Description
System.Boolean
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Keys

Gets an System.Collections.Generic.IEnumerable<T> object containing the keys of the WeakIdentityMap<TKey, TValue>.

Declaration
public IEnumerable<TKey> Keys { get; }
Property Value
Type Description
System.Collections.Generic.IEnumerable<TKey>
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Values

Gets an System.Collections.Generic.IEnumerable<T> object containing the values of the WeakIdentityMap<TKey, TValue>.

Declaration
public IEnumerable<TValue> Values { get; }
Property Value
Type Description
System.Collections.Generic.IEnumerable<TValue>

Methods

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Clear()

Removes all of the mappings from this map.

Declaration
public void Clear()
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ContainsKey(Object)

Returns true if this map contains a mapping for the specified key.

Declaration
public bool ContainsKey(object key)
Parameters
Type Name Description
System.Object key
Returns
Type Description
System.Boolean
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Get(Object)

Returns the value to which the specified key is mapped.

Declaration
public TValue Get(object key)
Parameters
Type Name Description
System.Object key
Returns
Type Description
TValue
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GetValueEnumerator()

Returns an iterator over all values of this map. This iterator may return values whose key is already garbage collected while iterator is consumed, especially if Lucene.Net.Util.WeakIdentityMap`2.reapOnRead is false.

NOTE: This was valueIterator() in Lucene.

Declaration
public IEnumerator<TValue> GetValueEnumerator()
Returns
Type Description
System.Collections.Generic.IEnumerator<TValue>
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NewConcurrentHashMap()

Creates a new WeakIdentityMap<TKey, TValue> based on a System.Collections.Concurrent.ConcurrentDictionary<TKey, TValue>. The map cleans up the reference queue on every read operation.

Declaration
public static WeakIdentityMap<TKey, TValue> NewConcurrentHashMap()
Returns
Type Description
WeakIdentityMap<TKey, TValue>
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NewConcurrentHashMap(Boolean)

Creates a new WeakIdentityMap<TKey, TValue> based on a System.Collections.Concurrent.ConcurrentDictionary<TKey, TValue>.

Declaration
public static WeakIdentityMap<TKey, TValue> NewConcurrentHashMap(bool reapOnRead)
Parameters
Type Name Description
System.Boolean reapOnRead

controls if the map cleans up the reference queue on every read operation.

Returns
Type Description
WeakIdentityMap<TKey, TValue>
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NewHashMap()

Creates a new WeakIdentityMap<TKey, TValue> based on a non-synchronized System.Collections.Generic.Dictionary`2. The map cleans up the reference queue on every read operation.

Declaration
public static WeakIdentityMap<TKey, TValue> NewHashMap()
Returns
Type Description
WeakIdentityMap<TKey, TValue>
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NewHashMap(Boolean)

Creates a new WeakIdentityMap<TKey, TValue> based on a non-synchronized System.Collections.Generic.Dictionary`2.

Declaration
public static WeakIdentityMap<TKey, TValue> NewHashMap(bool reapOnRead)
Parameters
Type Name Description
System.Boolean reapOnRead

controls if the map cleans up the reference queue on every read operation.

Returns
Type Description
WeakIdentityMap<TKey, TValue>
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Put(TKey, TValue)

Associates the specified value with the specified key in this map. If the map previously contained a mapping for this key, the old value is replaced.

Declaration
public TValue Put(TKey key, TValue value)
Parameters
Type Name Description
TKey key
TValue value
Returns
Type Description
TValue
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Reap()

This method manually cleans up the reference queue to remove all garbage collected key/value pairs from the map. Calling this method is not needed if reapOnRead = true. Otherwise it might be a good idea to call this method when there is spare time (e.g. from a background thread). Information about the reapOnRead setting

Declaration
public void Reap()
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Remove(Object)

Removes the mapping for a key from this weak hash map if it is present. Returns the value to which this map previously associated the key, or null if the map contained no mapping for the key. A return value of null does not necessarily indicate that the map contained.

Declaration
public bool Remove(object key)
Parameters
Type Name Description
System.Object key
Returns
Type Description
System.Boolean

Extension Methods