HashDecay.java #1

package com.perforce.api;

import java.util.*;

/*
 * Copyright (c) 2001, Perforce Software, All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/**
 * This hashtable build to contain objects that will decay over time. The
 * objects stored must implement the Cacheable interface.
 *
 * @author <a href="mailto:david@markley.cc">David Markley</a>
 * @version $Date: 2003/12/02 $ $Revision: #1 $
 * @see java.util.Hashtable
 * @see Cacheable
 */
public final class HashDecay extends Hashtable implements Runnable { 
  /** The minimum delay allowed */
  public final static long MIN_DELAY = 0;
  private long delay = MIN_DELAY;
  private Thread decay_thread;
  private boolean runForever = true;
  private static Vector started = new Vector();

  static {
    started = new Vector();
  }

  public HashDecay() {
    super();
  }

  public HashDecay(long delay) {
    this();
    setDelay(delay);
  }

  /**
   * Sets the delay, in milliseconds, before items in the hashtable are
   * discarded.
   */
  public void setDelay(long delay) {
    this.delay = (MIN_DELAY > delay) ? MIN_DELAY : delay;
  }

  /**
   * Returns the delay.
   */
  public long getDelay() {
    return delay;
  }

  public void run() {
    while (runForever) {
      try {
	Thread.sleep(delay);
      } catch (InterruptedException iex) {
      }
      decay();
    }
  }

  private synchronized void decay() {
    long now = (new Date()).getTime();
    Enumeration en = keys();
    Object key;
    while (en.hasMoreElements()) {
      key = en.nextElement();
      if (delay >= (now - ((Cacheable)get(key)).getUpdateTime())) {
	super.remove(key);
      }
    }
  }

  public Object put(Object key, Object value) {
    if (! (value instanceof Cacheable)) return null;
    return put(key, (Cacheable)value);
  }

  public Object put(Object key, Cacheable value) {
    value.refreshUpdateTime();
    super.remove(key);
    Object obj = super.put(key,value);
    return obj;
  }

  public void start() {
    if (null != decay_thread) return;
    runForever = true;
    decay_thread = new Thread(this);
    decay_thread.start();
    started.addElement(this);
  }

  public void stop() {
    runForever = false;
    if (null == decay_thread) return;
    try {
      decay_thread.interrupt();
      decay_thread.join(100);
    } catch (InterruptedException ex) {
      decay_thread.destroy();
    } catch (SecurityException ex) {
      decay_thread.destroy();
    }
  }

  /**
   * Stops running threads for all HashDecay instances.
   */
  public static void stopAll() {
    HashDecay hd;
    Enumeration en = started.elements();
    while (en.hasMoreElements()) {
      hd = (HashDecay)en.nextElement();
      hd.stop();
    }
  }
}