code: /**
   * Copyright (c) 2004-2005, 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, Los Angeles 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.
   */
  
  package avrora.sim.clock;
  
  import avrora.sim.Simulation;
  import avrora.sim.SimulatorThread;
  import cck.util.Util;
  
  /**
   * The <code>Synchronizer</code> class represents an object that controls the progress
   * of a multi-node simulation. The synchronizer preserves the timing and order of events
   * that influence other nodes' actions (e.g. communication). Since there are multiple
   * strategies for doing this, this class abstracts the actual mechanism so that clients
   * can simply create the appropriate synchronizer for their simulation.
   *
   * @author Ben L. Titzer
   */
  public abstract class Synchronizer {
  
      /**
       * The <code>addNode()</code> method adds a node to this synchronization group.
       * This method should only be called before the <code>start()</code> method is
       * called.
       * @param n the simulator representing the node to add to this group
       */
      public abstract void addNode(Simulation.Node n);
  
      /**
       * The <code>removeNode()</code> method removes a node from this synchronization
       * group, and wakes any nodes that might be waiting on it.
       * @param n the simulator thread to remove from this synchronization group
       */
      public abstract void removeNode(Simulation.Node n);
  
      /**
       * The <code>waitForNeighbors()</code> method is called from within the execution
       * of a node when that node needs to wait for its neighbors to catch up to it
       * in execution time. The node will be blocked until the other nodes in other
       * threads catch up in global time.
       * @param time the global time to wait for all neighbors to reach
       */
      public abstract void waitForNeighbors(long time);
  
      /**
       * The <code>start()</code> method starts the threads executing, and the synchronizer
       * will add whatever synchronization to their execution that is necessary to preserve
       * the global timing properties of simulation.
       */
      public abstract void start();
  
      /**
       * The <code>join()</code> method will block the caller until all of the threads in
       * this synchronization interval have terminated, either through <code>stop()</code>
       * being called, or terminating normally such as through a timeout.
       * @throws InterruptedException if the thread was interrupted
       */
      public abstract void join() throws InterruptedException;
  
      /**
       * The <code>pause()</code> method temporarily pauses the simulation. The nodes are
       * not guaranteed to stop at the same global time. This method will return when all
       * threads in the simulation have been paused and will no longer make progress until
       * the <code>start()</code> method is called again.
       */
      public abstract void pause();
  
      /**
       * The <code>stop()</code> method will terminate all the simulation threads. It is
       * not guaranteed to stop all the simulation threads at the same global time.
       */
      public abstract void stop();
  
  
      /**
       * The <code>synch()</code> method will pause all of the nodes at the same global time.
       * This method can only be called when the simulation is paused. It will run all threads
       * forward until the global time specified and pause them.
       * @param globalTime the global time in clock cycles to run all threads ahead to
       */
      public abstract void synch(long globalTime);
  
      public static class Single extends Synchronizer {
  
          public Simulation.Node node;
          public SimulatorThread thread;
  
          /**
           * The <code>addNode()</code> method adds a node to this synchronization group.
           * This method should only be called before the <code>start()</code> method is
           * called.
           * @param n the simulator representing the node to add to this group
           */
          public void addNode(Simulation.Node n) {
              if ( node != null )
                  throw Util.failure("Only one node supported at a time");
              node = n;
          }
  
          /**
           * The <code>removeNode()</code> method removes a node from this synchronization
           * group, and wakes any nodes that might be waiting on it.
           * @param n the simulator thread to remove from this synchronization group
           */
          public void removeNode(Simulation.Node n) {
              if ( node == n ) node = null;
          }
  
          /**
           * The <code>waitForNeighbors()</code> method is called from within the execution
           * of a node when that node needs to wait for its neighbors to catch up to it
           * in execution time. The node will be blocked until the other nodes in other
           * threads catch up in global time.
           */
          public void waitForNeighbors(long time) {
              // do nothing
          }
  
          /**
           * The <code>start()</code> method starts the threads executing, and the synchronizer
           * will add whatever synchronization to their execution that is necessary to preserve
           * the global timing properties of simulation.
           */
          public void start() {
              if ( node == null )
                  throw Util.failure("No nodes in simulation");
              thread = new SimulatorThread(node);
              thread.start();
          }
  
          /**
           * The <code>join()</code> method will block the caller until all of the threads in
           * this synchronization interval have terminated, either through <code>stop()</code>
           * being called, or terminating normally such as through a timeout.
           */
          public void join() throws InterruptedException {
              thread.join();
          }
  
          /**
           * The <code>pause()</code> method temporarily pauses the simulation. The nodes are
           * not guaranteed to stop at the same global time. This method will return when all
           * threads in the simulation have been paused and will no longer make progress until
           * the <code>start()</code> method is called again.
           */
          public void pause() {
              throw Util.unimplemented();
          }
  
          /**
           * The <code>stop()</code> method will terminate all the simulation threads. It is
           * not guaranteed to stop all the simulation threads at the same global time.
           */
          public void stop() {
              throw Util.unimplemented();
          }
  
  
          /**
           * The <code>synch()</code> method will pause all of the nodes at the same global time.
           * This method can only be called when the simulation is paused. It will run all threads
           * forward until the global time specified and pause them.
           * @param globalTime the global time in clock cycles to run all threads ahead to
           */
          public void synch(long globalTime) {
              throw Util.unimplemented();
          }
      }
  }
  