Package com.cedarsoftware.util

Class LRUCache<K,V>

java.lang.Object
com.cedarsoftware.util.LRUCache<K,V>
All Implemented Interfaces:
Map<K,V>
public class LRUCache<K,V> extends Object implements Map<K,V>
This class provides a thread-safe Least Recently Used (LRU) cache API that evicts the least recently used items once a threshold is met. It implements the Map interface for convenience.

This class offers two implementation strategies: a locking approach and a threaded approach.

  • The Locking strategy can be selected by using the constructor that takes only an int for capacity, or by using the constructor that takes an int and a StrategyType enum (StrategyType.LOCKING).
  • The Threaded strategy can be selected by using the constructor that takes an int and a StrategyType enum (StrategyType.THREADED). Another constructor allows specifying a cleanup delay time.

The Locking strategy allows for O(1) access for get(), put(), and remove(). For put(), remove(), and many other methods, a write-lock is obtained. For get(), it attempts to lock but does not lock unless it can obtain it right away. This 'try-lock' approach ensures that the get() API is never blocking, but it also means that the LRU order is not perfectly maintained under heavy load.

The Threaded strategy allows for O(1) access for get(), put(), and remove() without blocking. It uses a ConcurrentHashMapNullSafe internally. To ensure that the capacity is honored, whenever put() is called, a thread (from a thread pool) is tasked with cleaning up items above the capacity threshold. This means that the cache may temporarily exceed its capacity, but it will soon be trimmed back to the capacity limit by the scheduled thread.

LRUCache supports null for both key and value.

Special Thanks: This implementation was inspired by insights and suggestions from Ben Manes.

Author:
John DeRegnaucourt ([email protected])
Copyright (c) Cedar Software LLC

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

License

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
See Also:

  • Constructor Details

    • LRUCache

      public LRUCache(int capacity)
      Create a "locking-based" LRUCache with the passed in capacity.
      Parameters:
      capacity - int maximum number of entries in the cache.
      See Also:

    • LRUCache

      public LRUCache(int capacity, LRUCache.StrategyType strategyType)
      Create a "locking-based" or a "thread-based" LRUCache with the passed in capacity.
      Parameters:
      capacity - int maximum number of entries in the cache.
      strategyType - StrategyType.LOCKING or StrategyType.THREADED indicating the underlying LRUCache implementation.
      See Also:

    • LRUCache

      public LRUCache(int capacity, int cleanupDelayMillis)
      Create a "thread-based" LRUCache with the passed in capacity.
      Parameters:
      capacity - int maximum number of entries in the cache.
      cleanupDelayMillis - int number of milliseconds after a put() call when a scheduled task should run to trim the cache to no more than capacity. The default is 10ms.
      See Also:

  • Method Details

    • getCapacity

      public int getCapacity()
      Returns:
      the maximum number of entries in the cache.

    • get

      public V get(Object key)
      Retrieve a value from the cache.
      Specified by:
      get in interface Map<K,V>
      Parameters:
      key - key whose associated value is desired
      Returns:
      cached value or null if absent

    • put

      public V put(K key, V value)
      Insert a value into the cache.
      Specified by:
      put in interface Map<K,V>
      Parameters:
      key - key with which the specified value is to be associated
      value - value to be cached
      Returns:
      previous value associated with the key or null

    • putAll

      public void putAll(Map<? extends K,? extends V> m)
      Copy all of the mappings from the specified map to this cache.
      Specified by:
      putAll in interface Map<K,V>
      Parameters:
      m - mappings to be stored

    • remove

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

    • clear

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

    • size

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

    • isEmpty

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

    • containsKey

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

    • containsValue

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

    • entrySet

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

    • keySet

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

    • values

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

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • hashCode

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

    • equals

      public boolean equals(Object obj)
      Specified by:
      equals in interface Map<K,V>
      Overrides:
      equals in class Object

    • shutdown

      @Deprecated public void shutdown()
      Deprecated.
      This method is no longer needed as the ThreadedLRUCacheStrategy will automatically end because it uses a daemon thread.