CacheDependency.java

package org.cdlib.xtf.cache;


/**
 * Copyright (c) 2004, Regents of the University of California
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 * - Neither the name of the University of California nor the names of its
 *   contributors may be used to endorse or promote products derived from this
 *   software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * CacheDependency represents a dependency on an entry of the same or another
 * cache. If the cache entry changes, disappears, or its dependencies become
 * stale, then this dependency also becomes stale.
 */
public class CacheDependency extends Dependency 
{
  /**
   * Constructor.
   *
   * @param cache     The cache containing the entry to depend on
   * @param key       Key value to depend on within that cache.
   */
  public CacheDependency(Cache cache, Object key) {
    this.cache = cache;
    this.key = key;
    this.lastSet = cache.lastSet(key);
  }

  /**
   * Checks if the dependency is still valid. If the cache entry has changed,
   * disappeared, or has invalid dependencies, then this dependency is stale.
   *
   * @return  true iff the dependency is still fresh.
   */
  public boolean validate() {
    return (cache.has(key) && cache.lastSet(key) == lastSet &&
            cache.dependenciesValid(key));
  }

  /** The cache we're depending on */
  public Cache cache;

  /** The key within that cache we're depending on */
  public Object key;

  /** The set time of the cache entry when this dependency was created. */
  public long lastSet;
} // class CacheDependency