Class OverflowingLRUCache<K,V>

java.lang.Object
org.aspectj.org.eclipse.jdt.internal.core.util.LRUCache<K,V>
org.aspectj.org.eclipse.jdt.internal.core.OverflowingLRUCache<K,V>
All Implemented Interfaces:
Cloneable
Direct Known Subclasses:
BufferCache, ElementCache
public abstract class OverflowingLRUCache<K,V> extends LRUCache<K,V>
The OverflowingLRUCache is an LRUCache which attempts to maintain a size equal or less than its fSpaceLimit by removing the least recently used elements.

The cache will remove elements which successfully close and all elements which are explicitly removed.

If the cache cannot remove enough old elements to add new elements it will grow beyond fSpaceLimit. Later, it will attempt to shrink back to the maximum space limit. The method close should attempt to close the element. If the element is successfully closed it will return true and the element will be removed from the cache. Otherwise the element will remain in the cache.

The cache implicitly attempts shrinks on calls to putand setSpaceLimit. Explicitly calling the shrink method will also cause the cache to attempt to shrink.

The cache calculates the used space of all elements which implement ILRUCacheable. All other elements are assumed to be of size one.

Use the #peek(Object) and #disableTimestamps() method to circumvent the timestamp feature of the cache. This feature is intended to be used only when the #close(LRUCacheEntry) method causes changes to the cache. For example, if a parent closes its children when #close(LRUCacheEntry) is called, it should be careful not to change the LRU linked list. It can be sure it is not causing problems by calling #peek(Object) instead of #get(Object) method.

See Also:

  • Field Details

    • overflow

      protected int overflow
      Indicates if the cache has been over filled and by how much.

    • timestampsOn

      protected boolean timestampsOn
      Indicates whether or not timestamps should be updated

    • loadFactor

      protected double loadFactor
      Indicates how much space should be reclaimed when the cache overflows. Inital load factor of one third.

  • Constructor Details

    • OverflowingLRUCache

      public OverflowingLRUCache(int size)
      Creates a OverflowingLRUCache.
      Parameters:
      size - Size limit of cache.

    • OverflowingLRUCache

      public OverflowingLRUCache(int size, int overflow)
      Creates a OverflowingLRUCache.
      Parameters:
      size - Size limit of cache.
      overflow - Size of the overflow.

  • Method Details

    • clone

      public OverflowingLRUCache<K,V> clone()
      Returns a new cache containing the same contents.
      Overrides:
      clone in class LRUCache<K,V>
      Returns:
      New copy of this object.

    • close

      protected abstract boolean close(LRUCache.LRUCacheEntry<K,V> entry)
      Returns true if the element is successfully closed and removed from the cache, otherwise false.

      NOTE: this triggers an external remove from the cache by closing the object.

    • elements

      public Enumeration<V> elements()
      Returns an enumerator of the values in the cache with the most recently used first.

    • fillingRatio

      public double fillingRatio()
      Overrides:
      fillingRatio in class LRUCache<K,V>

    • getEntryTable

      public Hashtable<K,LRUCache.LRUCacheEntry<K,V>> getEntryTable()
      For internal testing only. This method exposed only for testing purposes!
      Returns:
      Hashtable of entries

    • getLoadFactor

      public double getLoadFactor()
      Returns the load factor for the cache. The load factor determines how much space is reclaimed when the cache exceeds its space limit.
      Returns:
      double

    • getOverflow

      public int getOverflow()
      Returns:
      The space by which the cache has overflown.

    • makeSpace

      protected boolean makeSpace(int space)
      Ensures there is the specified amount of free space in the receiver, by removing old entries if necessary. Returns true if the requested space was made available, false otherwise. May not be able to free enough space since some elements cannot be removed until they are saved.
      Overrides:
      makeSpace in class LRUCache<K,V>
      Parameters:
      space - Amount of space to free up

    • newInstance

      protected abstract LRUCache<K,V> newInstance(int size, int newOverflow)
      Returns a new instance of the reciever.

    • printStats

      public void printStats()
      For testing purposes only

    • privateRemoveEntry

      protected void privateRemoveEntry(LRUCache.LRUCacheEntry<K,V> entry, boolean shuffle)
      Removes the entry from the entry queue. Calls privateRemoveEntry with the external functionality enabled.
      Overrides:
      privateRemoveEntry in class LRUCache<K,V>
      Parameters:
      shuffle - indicates whether we are just shuffling the queue (in which case, the entry table is not modified).

    • privateRemoveEntry

      protected void privateRemoveEntry(LRUCache.LRUCacheEntry<K,V> entry, boolean shuffle, boolean external)
      Removes the entry from the entry queue. If external is true, the entry is removed without checking if it can be removed. It is assumed that the client has already closed the element it is trying to remove (or will close it promptly). If external is false, and the entry could not be closed, it is not removed and the pointers are not changed.
      Parameters:
      shuffle - indicates whether we are just shuffling the queue (in which case, the entry table is not modified).

    • put

      public V put(K key, V value)
      Description copied from class: LRUCache
      Sets the value in the cache at the given key. Returns the value.
      Overrides:
      put in class LRUCache<K,V>
      Parameters:
      key - Key of object to add.
      value - Value of object to add.
      Returns:
      added value.

    • remove

      public V remove(K key)
      Removes and returns the value in the cache for the given key. If the key is not in the cache, returns null.
      Parameters:
      key - Key of object to remove from cache.
      Returns:
      Value removed from cache.

    • setLoadFactor

      public void setLoadFactor(double newLoadFactor) throws IllegalArgumentException
      Sets the load factor for the cache. The load factor determines how much space is reclaimed when the cache exceeds its space limit.
      Parameters:
      newLoadFactor - double
      Throws:
      IllegalArgumentException - when the new load factor is not in (0.0, 1.0]

    • setSpaceLimit

      public void setSpaceLimit(int limit)
      Description copied from class: LRUCache
      Sets the maximum amount of space that the cache can store
      Overrides:
      setSpaceLimit in class LRUCache<K,V>
      Parameters:
      limit - Number of units of cache space

    • shrink

      public boolean shrink()
      Attempts to shrink the cache if it has overflown. Returns true if the cache shrinks to less than or equal to fSpaceLimit.

    • toString

      public String toString()
      Returns a String that represents the value of this object. This method is for debugging purposes only.
      Overrides:
      toString in class LRUCache<K,V>

    • updateTimestamp

      protected void updateTimestamp(LRUCache.LRUCacheEntry<K,V> entry)
      Updates the timestamp for the given entry, ensuring that the queue is kept in correct order. The entry must exist.

      This method will do nothing if timestamps have been disabled.

      Overrides:
      updateTimestamp in class LRUCache<K,V>