rethread.java

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/*
 * Java Network Programming, Second Edition
 * Merlin Hughes, Michael Shoffner, Derek Hamner
 * Manning Publications Company; ISBN 188477749X
 *
 * http://nitric.com/jnp/
 *
 * Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
 * all rights reserved; see license.txt for details.
 */

import java.util.*;

public class ReThread implements Runnable {
  protected Runnable target;
  
  public ReThread (Runnable target) {
    this.target = target;
  }

  private static int id = 0;
  private static synchronized int getID () { return id ++; }

  private static Vector threads = new Vector ();
  private ReThread reThread;
  private Thread thread;

  public synchronized void start () {
    if ((thread == null) && (reThread == null)) {
      synchronized (threads) {
        if (threads.isEmpty ()) {
          thread = new Thread (this, "ReThread-" + getID ());
          thread.start ();
        } else {
          reThread = (ReThread) threads.lastElement ();
          threads.setSize (threads.size () - 1);
          reThread.start0 (this);
        }
      }
    }
  }

  protected synchronized void start0 (ReThread reThread) {
    this.reThread = reThread;
    target = reThread.target;
    notify ();
  }

  public synchronized void interrupt () {
    if ((target != null) && ((thread != null) ^ (reThread != null))) {
      if (thread != null) {
        thread.interrupt ();
      } else {
        reThread.interrupt0 (this);
      }
    }
  }
  
  protected synchronized void interrupt0 (ReThread reThread) {
    if ((target != null) && (reThread == this.reThread)) {
      thread.interrupt ();
    }
  }
  
  public void run () {
    while (true) {
      try {
        target.run ();
      } catch (RuntimeException ex) {
        ex.printStackTrace ();
      }
      waitForTarget ();
    }
  }
  
  protected synchronized void waitForTarget () {
    target = null;
    threads.addElement (this);
    while (target == null) {
      try {
        wait ();
      } catch (InterruptedException ignored) {
      }
    }
  }
}