emptycache.java

pastry的java实现的2.0b版

/*************************************************************************

"FreePastry" Peer-to-Peer Application Development Substrate 

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package rice.persistence;

/*
 *  @(#) LRUCache.java
 *
 *  @author Ansley Post
 *  @author Alan Mislove
 *
 *  @version $Id: EmptyCache.java 2509 2005-05-26 17:59:07Z amislove $
 */
import java.io.*;
import java.util.*;
import java.util.zip.*;

import rice.*;
import rice.Continuation.*;
import rice.p2p.commonapi.*;
import rice.p2p.util.*;

/**
 * This class is a cahcce which doesn't store anything.
 *
 * @version $Id: pretty.settings 2305 2005-03-11 20:22:33Z jeffh $
 * @author jeffh
 */
public class EmptyCache implements Cache {

  /**
   * The facotry for building id sets
   */
  protected IdFactory factory;

  /**
   * Builds an emtpy cache
   *
   * @param factory DESCRIBE THE PARAMETER
   */
  public EmptyCache(IdFactory factory) {
    this.factory = factory;
  }

  /**
   * Returns the object identified by the given id.
   *
   * @param id The id of the object in question.
   * @param c The command to run once the operation is complete
   */
  public void getObject(Id id, Continuation c) {
    c.receiveResult(null);
  }

  /**
   * Returns the metadata associated with the provided object, or null if no
   * metadata exists. The metadata must be stored in memory, so this operation
   * is guaranteed to be fast and non-blocking.
   *
   * @param id The id for which the metadata is needed
   * @return The metadata, or null of non exists
   */
  public Serializable getMetadata(Id id) {
    return null;
  }

  /**
   * Returns the maximum size of the cache, in bytes. The result is returned via
   * the receiveResult method on the provided Continuation with an Integer
   * representing the size.
   *
   * @return The MaximumSize value
   */
  public long getMaximumSize() {
    return 0;
  }

  /**
   * Returns the total size of the stored data in bytes. The result is returned
   * via the receiveResult method on the provided Continuation with an Integer
   * representing the size.
   *
   * @return The total size, in bytes, of data stored.
   */
  public long getTotalSize() {
    return 0;
  }

  /**
   * Returns the number of Ids currently stored in the catalog
   *
   * @return The number of ids in the catalog
   */
  public int getSize() {
    return 0;
  }

  /**
   * Updates the metadata stored under the given key to be the provided value.
   * As this may require a disk access, the requestor must also provide a
   * continuation to return the result to.
   *
   * @param id The id for the metadata
   * @param metadata The metadata to store
   * @param c The command to run once the operation is complete
   */
  public void setMetadata(Id id, Serializable metadata, Continuation c) {
    c.receiveResult(new Boolean(true));
  }

  /**
   * Sets the maximum size of the cache, in bytes. Setting this value to a
   * smaller value than the current value may result in object being evicted
   * from the cache.
   *
   * @param size The new maximum size, in bytes, of the cache.
   * @param c The command to run once the operation is complete
   */
  public void setMaximumSize(final int size, final Continuation c) {
    c.receiveResult(Boolean.TRUE);
  }

  /**
   * Renames the given object to the new id. This method is potentially faster
   * than store/cache and unstore/uncache.
   *
   * @param oldId The id of the object in question.
   * @param newId The new id of the object in question.
   * @param c The command to run once the operation is complete
   */
  public void rename(final Id oldId, final Id newId, Continuation c) {
    c.receiveException(new IllegalArgumentException("EmptyCache has no objects!"));
  }

  /**
   * Caches an object in this storage. This method is non-blocking. If the
   * object has already been stored at the location id, this method has the
   * effect of calling <code>uncachr(id)</code> followed by <code>cache(id, obj)</code>
   * . This method finishes by calling receiveResult() on the provided
   * continuation with whether or not the object was cached. Note that the
   * object may not actually be cached due to the cache replacement policy.
   * Returns <code>True</code> if the cache actaully stores the object, else
   * <code>False</code> (through receiveResult on c).
   *
   * @param id The object's id.
   * @param obj The object to cache.
   * @param c The command to run once the operation is complete
   * @param metadata DESCRIBE THE PARAMETER
   */
  public void cache(Id id, Serializable metadata, Serializable obj, Continuation c) {
    c.receiveResult(new Boolean(true));
  }

  /**
   * Removes the object from the list of cached objects. This method is
   * non-blocking. If the object was not in the cached list in the first place,
   * nothing happens and <code>False</code> is returned. Returns <code>True</code>
   * if the action succeeds, else <code>False</code> (through receiveResult on
   * c).
   *
   * @param c The command to run once the operation is complete
   * @param id DESCRIBE THE PARAMETER
   */
  public void uncache(Id id, Continuation c) {
    c.receiveResult(new Boolean(true));
  }

  /**
   * Returns whether or not an object is cached in the location <code>id</code>.
   *
   * @param id The id of the object in question.
   * @return Whether or not an object is present at id.
   */
  public boolean exists(Id id) {
    return false;
  }

  /**
   * Return the objects identified by the given range of ids. The IdSet returned
   * contains the Ids of the stored objects. The range is partially inclusive,
   * the lower range is inclusive, and the upper exclusive. NOTE: This method
   * blocks so if the behavior of this method changes and uses the disk, this
   * method may be deprecated.
   *
   * @param range The range to query
   * @return The idset containg the keys
   */
  public IdSet scan(IdRange range) {
    return factory.buildIdSet();
  }

  /**
   * Return all objects currently stored by this catalog NOTE: This method
   * blocks so if the behavior of this method changes and no longer stored in
   * memory, this method may be deprecated.
   *
   * @return The idset containg the keys
   */
  public IdSet scan() {
    return factory.buildIdSet();
  }

  /**
   * Returns a map which contains keys mapping ids to the associated metadata.
   *
   * @param range The range to query
   * @return The map containg the keys
   */
  public SortedMap scanMetadata(IdRange range) {
    return new RedBlackMap();
  }

  /**
   * Returns a map which contains keys mapping ids to the associated metadata.
   *
   * @return The treemap mapping ids to metadata
   */
  public SortedMap scanMetadata() {
    return new RedBlackMap();
  }

  /**
   * Returns the submapping of ids which have metadata less than the provided
   * value.
   *
   * @param value The maximal metadata value
   * @return The submapping
   */
  public SortedMap scanMetadataValuesHead(Object value) {
    return new RedBlackMap();
  }

  /**
   * Returns the submapping of ids which have metadata null
   *
   * @return The submapping
   */
  public SortedMap scanMetadataValuesNull() {
    return new RedBlackMap();
  }

  /**
   * Method which is used to erase all data stored in the Catalog. Use this
   * method with care!
   *
   * @param c The command to run once done
   */
  public void flush(Continuation c) {
    c.receiveResult(Boolean.TRUE);
  }
}