timertask.java

pastry的java实现的2.0b版

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

"FreePastry" Peer-to-Peer Application Development Substrate 

Copyright 2002, Rice University. All rights reserved.

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********************************************************************************/
/*
 *  Created on Nov 17, 2004
 */
package rice.selector;

import rice.environment.time.TimeSource;
import rice.p2p.commonapi.CancellableTask;

/**
 * @version $Id: pretty.settings 2305 2005-03-11 20:22:33Z jeffh $
 * @author Jeff Hoye
 */
public abstract class TimerTask implements Comparable, CancellableTask {
  /**
   * DESCRIBE THE FIELD
   */
  protected long nextExecutionTime;
  /**
   * DESCRIBE THE FIELD
   */
  protected boolean cancelled = false;

  /**
   * If period is positive, task will be rescheduled.
   */
  protected int period = -1;

  /**
   * DESCRIBE THE FIELD
   */
  protected boolean fixedRate = false;

  /**
   * Gets the Cancelled attribute of the TimerTask object
   *
   * @return The Cancelled value
   */
  public boolean isCancelled() {
    return cancelled;
  }

  /**
   * Main processing method for the TimerTask object
   */
  public abstract void run();

  /**
   * Returns true if should re-insert.
   *
   * @param ts DESCRIBE THE PARAMETER
   * @return
   */
  public boolean execute(TimeSource ts) {
    if (cancelled) {
      return false;
    }
    run();
    // often cancelled in the execution
    if (cancelled) {
      return false;
    }
    if (period > 0) {
      if (fixedRate) {
        nextExecutionTime += period;
        return true;
      } else {
        nextExecutionTime = ts.currentTimeMillis() + period;
        return true;
      }
    } else {
      return false;
    }
  }

  /**
   * DESCRIBE THE METHOD
   *
   * @return DESCRIBE THE RETURN VALUE
   */
  public boolean cancel() {
    if (cancelled) {
      return false;
    }
    cancelled = true;
    return true;
  }

  /**
   * DESCRIBE THE METHOD
   *
   * @return DESCRIBE THE RETURN VALUE
   */
  public long scheduledExecutionTime() {
    return nextExecutionTime;
  }

  /**
   * DESCRIBE THE METHOD
   *
   * @param arg0 DESCRIBE THE PARAMETER
   * @return DESCRIBE THE RETURN VALUE
   */
  public int compareTo(Object arg0) {
    TimerTask tt = (TimerTask) arg0;
    if (tt == this) {
      return 0;
    }
//    return (int)(tt.nextExecutionTime-nextExecutionTime);
    int diff = (int) (nextExecutionTime - tt.nextExecutionTime);
    if (diff == 0) {
      return System.identityHashCode(this) < System.identityHashCode(tt) ? 1 : -1;
    }
    return diff;
  }

}