queuethresholdpredicate.java

The Staged Event-Driven Architecture (SEDA) is a new design for building scalable Internet services.

/* 
 * Copyright (c) 2001 by Matt Welsh and The Regents of the University of 
 * California. All rights reserved.
 *
 * Permission to use, copy, modify, and distribute this software and its
 * documentation for any purpose, without fee, and without written agreement is
 * hereby granted, provided that the above copyright notice and the following
 * two paragraphs appear in all copies of this software.
 * 
 * IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR
 * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT
 * OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF
 * CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * 
 * THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
 * ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATION TO
 * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 *
 * Author: Matt Welsh <[e-mail]>
 * 
 */

package seda.sandStorm.core;

import seda.sandStorm.api.*;

/**
 * This enqueue predicate implements a simple threshold for the
 * size of the queue.
 */
public class QueueThresholdPredicate implements EnqueuePredicateIF {

  private static final boolean DEBUG = false;

  private SinkIF thesink;
  private int threshold;

  /**
   * Create a new QueueThresholdPredicate for the given sink and
   * threshold. A threshold of -1 indicates no threshold.
   */
  public QueueThresholdPredicate(SinkIF sink, int threshold) {
    this.thesink = sink;
    this.threshold = threshold;
  }

  /**
   * Returns true if the given element can be accepted into the queue.
   */
  public boolean accept(QueueElementIF qel) {
    if (DEBUG) System.err.println("QueueThresholdPredicate.accept ["+thesink+"]: size "+thesink.size()+", thresh "+threshold);
    if (threshold == -1) return true;
    if ((thesink.size() + 1) > threshold) return false;
    return true;
  }

  /**
   * Return the current queue threshold.
   */
  public int getThreshold() {
    return threshold;
  }

  /**
   * Set the current queue threshold. A queue threshold of -1 indicates
   * an infinite threshold.
   */
  public void setThreshold(int threshold) {
    this.threshold = threshold;
  }

}