Package org.apache.cayenne.util.concurrentlinkedhashmap

Class ConcurrentLinkedHashMap<K,V>

java.lang.Object
java.util.AbstractMap<K,V>
org.apache.cayenne.util.concurrentlinkedhashmap.ConcurrentLinkedHashMap<K,V>
Type Parameters:
K - the type of keys maintained by this map
V - the type of mapped values
All Implemented Interfaces:
Serializable, ConcurrentMap<K,V>, Map<K,V>
public class ConcurrentLinkedHashMap<K,V> extends AbstractMap<K,V> implements ConcurrentMap<K,V>, Serializable
A hash table supporting full concurrency of retrievals, adjustable expected concurrency for updates, and a maximum capacity to bound the map by. This implementation differs from ConcurrentHashMap in that it maintains a page replacement algorithm that is used to evict an entry when the map has exceeded its capacity. Unlike the Java Collections Framework, this map does not have a publicly visible constructor and instances are created through a ConcurrentLinkedHashMap.Builder.

An entry is evicted from the map when the weighted capacity exceeds its maximum weighted capacity threshold. A Weigher instance determines how many units of capacity that a value consumes. The default weigher assigns each value a weight of 1 to bound the map by the total number of key-value pairs. A map that holds collections may choose to weigh values by the number of elements in the collection and bound the map by the total number of elements that it contains. A change to a value that modifies its weight requires that an update operation is performed on the map.

An EvictionListener may be supplied for notification when an entry is evicted from the map. This listener is invoked on a caller's thread and will not block other threads from operating on the map. An implementation should be aware that the caller's thread will not expect long execution times or failures as a side effect of the listener being notified. Execution safety and a fast turn around time can be achieved by performing the operation asynchronously, such as by submitting a task to an ExecutorService.

The concurrency level determines the number of threads that can concurrently modify the table. Using a significantly higher or lower value than needed can waste space or lead to thread contention, but an estimate within an order of magnitude of the ideal value does not usually have a noticeable impact. Because placement in hash tables is essentially random, the actual concurrency will vary.

This class and its views and iterators implement all of the optional methods of the Map and Iterator interfaces.

Like Hashtable but unlike HashMap, this class does not allow null to be used as a key or value. Unlike LinkedHashMap, this class does not provide predictable iteration order. A snapshot of the keys and entries may be obtained in ascending and descending order of retention.

See Also:

  • Method Details

    • capacity

      public int capacity()
      Retrieves the maximum weighted capacity of the map.
      Returns:
      the maximum weighted capacity

    • setCapacity

      public void setCapacity(int capacity)
      Sets the maximum weighted capacity of the map and eagerly evicts entries until it shrinks to the appropriate size.
      Parameters:
      capacity - the maximum weighted capacity of the map
      Throws:
      IllegalArgumentException - if the capacity is negative

    • isEmpty

      public boolean isEmpty()
      Specified by:
      isEmpty in interface Map<K,V>
      Overrides:
      isEmpty in class AbstractMap<K,V>

    • size

      public int size()
      Specified by:
      size in interface Map<K,V>
      Overrides:
      size in class AbstractMap<K,V>

    • weightedSize

      public int weightedSize()
      Returns the weighted size of this map.
      Returns:
      the combined weight of the values in this map

    • clear

      public void clear()
      Specified by:
      clear in interface Map<K,V>
      Overrides:
      clear in class AbstractMap<K,V>

    • containsKey

      public boolean containsKey(Object key)
      Specified by:
      containsKey in interface Map<K,V>
      Overrides:
      containsKey in class AbstractMap<K,V>

    • containsValue

      public boolean containsValue(Object value)
      Specified by:
      containsValue in interface Map<K,V>
      Overrides:
      containsValue in class AbstractMap<K,V>

    • get

      public V get(Object key)
      Specified by:
      get in interface Map<K,V>
      Overrides:
      get in class AbstractMap<K,V>

    • put

      public V put(K key, V value)
      Specified by:
      put in interface Map<K,V>
      Overrides:
      put in class AbstractMap<K,V>

    • putIfAbsent

      public V putIfAbsent(K key, V value)
      Specified by:
      putIfAbsent in interface ConcurrentMap<K,V>
      Specified by:
      putIfAbsent in interface Map<K,V>

    • remove

      public V remove(Object key)
      Specified by:
      remove in interface Map<K,V>
      Overrides:
      remove in class AbstractMap<K,V>

    • remove

      public boolean remove(Object key, Object value)
      Specified by:
      remove in interface ConcurrentMap<K,V>
      Specified by:
      remove in interface Map<K,V>

    • replace

      public V replace(K key, V value)
      Specified by:
      replace in interface ConcurrentMap<K,V>
      Specified by:
      replace in interface Map<K,V>

    • replace

      public boolean replace(K key, V oldValue, V newValue)
      Specified by:
      replace in interface ConcurrentMap<K,V>
      Specified by:
      replace in interface Map<K,V>

    • keySet

      public Set<K> keySet()
      Specified by:
      keySet in interface Map<K,V>
      Overrides:
      keySet in class AbstractMap<K,V>

    • ascendingKeySet

      public Set<K> ascendingKeySet()
      Returns a unmodifiable snapshot Set view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

      Beware that, unlike in keySet(), obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

      Returns:
      an ascending snapshot view of the keys in this map

    • ascendingKeySetWithLimit

      public Set<K> ascendingKeySetWithLimit(int limit)
      Returns an unmodifiable snapshot Set view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

      Beware that, unlike in keySet(), obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

      Parameters:
      limit - the maximum size of the returned set
      Returns:
      a ascending snapshot view of the keys in this map
      Throws:
      IllegalArgumentException - if the limit is negative

    • descendingKeySet

      public Set<K> descendingKeySet()
      Returns an unmodifiable snapshot Set view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

      Beware that, unlike in keySet(), obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

      Returns:
      a descending snapshot view of the keys in this map

    • descendingKeySetWithLimit

      public Set<K> descendingKeySetWithLimit(int limit)
      Returns an unmodifiable snapshot Set view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

      Beware that, unlike in keySet(), obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

      Parameters:
      limit - the maximum size of the returned set
      Returns:
      a descending snapshot view of the keys in this map
      Throws:
      IllegalArgumentException - if the limit is negative

    • values

      public Collection<V> values()
      Specified by:
      values in interface Map<K,V>
      Overrides:
      values in class AbstractMap<K,V>

    • entrySet

      public Set<Map.Entry<K,V>> entrySet()
      Specified by:
      entrySet in interface Map<K,V>
      Specified by:
      entrySet in class AbstractMap<K,V>

    • ascendingMap

      public Map<K,V> ascendingMap()
      Returns an unmodifiable snapshot Map view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

      Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

      Returns:
      a ascending snapshot view of this map

    • ascendingMapWithLimit

      public Map<K,V> ascendingMapWithLimit(int limit)
      Returns an unmodifiable snapshot Map view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

      Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

      Parameters:
      limit - the maximum size of the returned map
      Returns:
      a ascending snapshot view of this map
      Throws:
      IllegalArgumentException - if the limit is negative

    • descendingMap

      public Map<K,V> descendingMap()
      Returns an unmodifiable snapshot Map view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

      Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

      Returns:
      a descending snapshot view of this map

    • descendingMapWithLimit

      public Map<K,V> descendingMapWithLimit(int limit)
      Returns an unmodifiable snapshot Map view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

      Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

      Parameters:
      limit - the maximum size of the returned map
      Returns:
      a descending snapshot view of this map
      Throws:
      IllegalArgumentException - if the limit is negative