memorystorage.java

pastry的java实现的2.0b版

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"FreePastry" Peer-to-Peer Application Development Substrate 

Copyright 2002, Rice University. All rights reserved.

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package rice.persistence;

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

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

/**
 * This class is an implementation of Storage which provides in-memory storage.
 * This class is specifically *NOT* designed to provide persistent storage, and
 * simply functions as an enhanced hash table.
 *
 * @version $Id: pretty.settings 2305 2005-03-11 20:22:33Z jeffh $
 * @author jeffh
 */
public class MemoryStorage implements Storage {

  // the map used to store the data
  private HashMap storage;

  // the map used to store the metadata
  private ReverseTreeMap metadata;

  // the current list of Ids
  private IdSet idSet;

  // the current total size
  private int currentSize;

  // the factory for manipulating the ids
  private IdFactory factory;

  /**
   * Builds a MemoryStorage object.
   *
   * @param factory The factory to build protocol-specific Ids from.
   */
  public MemoryStorage(IdFactory factory) {
    this.factory = factory;
    idSet = factory.buildIdSet();
    storage = new HashMap();
    metadata = new ReverseTreeMap();
    currentSize = 0;
  }

  /**
   * 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 (Serializable) metadata.get(id);
  }

  /**
   * Returns the object identified by the given id, or <code>null</code> if
   * there is no cooresponding object (through receiveResult on c).
   *
   * @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(storage.get(id));
  }

  /**
   * 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 TotalSize value
   */
  public long getTotalSize() {
    return currentSize;
  }

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

  /**
   * Returns the size of the given object, in bytes.
   *
   * @param obj The object to determine the size of
   * @return The size, in bytes
   */
  private int getSize(Object obj) {
    try {
      ByteArrayOutputStream baos = new ByteArrayOutputStream();
      ObjectOutputStream oos = new XMLObjectOutputStream(new BufferedOutputStream(new GZIPOutputStream(baos)));

      oos.writeObject(obj);
      oos.close();

      return baos.toByteArray().length;
    } catch (IOException e) {
      throw new RuntimeException("Object " + obj + " was not serialized correctly!");
    }
  }

  /**
   * 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 command The new Metadata value
   */
  public void setMetadata(Id id, Serializable metadata, Continuation command) {
    if (exists(id)) {
      this.metadata.put(id, metadata);
    }

    command.receiveResult(new Boolean(exists(id)));
  }

  /**
   * Method which is used to erase all data stored in the Storage. Use this
   * method with care!
   *
   * @param c The command to run once done
   */
  public void flush(Continuation c) {
    storage = new HashMap();
    metadata = new ReverseTreeMap();
    idSet = factory.buildIdSet();
    currentSize = 0;

    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(Id oldId, Id newId, Continuation c) {
    if (!idSet.isMemberId(oldId)) {
      c.receiveResult(new Boolean(false));
      return;
    }

    idSet.removeId(oldId);
    idSet.addId(newId);

    storage.put(newId, storage.get(oldId));
    storage.remove(oldId);

    metadata.put(newId, metadata.get(oldId));
    metadata.remove(oldId);

    c.receiveResult(new Boolean(true));
  }

  /**
   * Stores the object under the key <code>id</code>. If there is already an
   * object under <code>id</code>, that object is replaced. This method
   * completes by calling recieveResult() of the provided continuation with the
   * success or failure of the operation.
   *
   * @param obj The object to be made persistent.
   * @param id The object's id.
   * @param metadata The object's metadata
   * @param c The command to run once the operation is complete
   */
  public void store(Id id, Serializable metadata, Serializable obj, Continuation c) {
    if (id == null || obj == null) {
      c.receiveResult(new Boolean(false));
      return;
    }

    currentSize += getSize(obj);

    this.storage.put(id, obj);
    this.metadata.put(id, metadata);
    idSet.addId(id);
    c.receiveResult(new Boolean(true));
  }

  /**
   * Removes the object from the list of stored objects. If the object was not
   * in the cached list in the first place, nothing happens and <code>false</code>
   * is returned. This method completes by calling recieveResult() of the
   * provided continuation with the success or failure of the operation.
   *
   * @param id The object's persistence id
   * @param c The command to run once the operation is complete
   */
  public void unstore(Id id, Continuation c) {
    Object stored = storage.remove(id);
    metadata.remove(id);
    idSet.removeId(id);

    if (stored != null) {
      currentSize -= getSize(stored);
      c.receiveResult(new Boolean(true));
    } else {
      c.receiveResult(new Boolean(false));
    }
  }

  /**
   * Returns whether or not the provided id exists
   *
   * @param id The id to check
   * @return Whether or not the given id is stored
   */
  public boolean exists(Id id) {
    return storage.containsKey(id);
  }

  /**
   * 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 the guys don't fit in
   * memory, this method may be deprecated.
   *
   * @param range The range to query
   * @return The idset containg the keys
   */
  public IdSet scan(IdRange range) {
    return idSet.subSet(range);
  }

  /**
   * 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 idSet;
  }

  /**
   * 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) {
    if (range.isEmpty()) {
      return new RedBlackMap();
    } else if (range.getCCWId().equals(range.getCWId())) {
      return scanMetadata();
    } else {
      return new ImmutableSortedMap(metadata.keySubMap(range.getCCWId(), range.getCWId()));
    }
  }

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

  /**
   * 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 ImmutableSortedMap(metadata.valueHeadMap(value));
  }

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