SE450: TimeServer Implementation [2015/10/27]

SE450: Simulation: TimeServer Implementation [8/13]

file:Agent.java [source] [doc-public] [doc-private]
01 02 03 04 05
package agent;

public interface Agent {
  public void run();
}

file:TimeServer.java [source] [doc-public] [doc-private]

package agent;

public interface TimeServer {
  public double currentTime();
  public void enqueue(double waketime, Agent thing);
  public void run(double duration);
  public void addObserver(java.util.Observer o);
  public void deleteObserver(java.util.Observer o);
}

If you want to use this for the project:

The idea is that whenever an agent adds itself to the timeserver, it
specifies its waketime.  The waketime must be greater than
currenttime, or the enqueue method should throw an exception.  The
timeserver orders agents by their waketime, so the one to wake first is
always at the front.  So in order to run the next agent, the first
agent is dequeued, and then the currenttime is set to its waketime,
then the agent is run.

For a car:
Start the car with waketime=currenttime.
When the car is run(), it should re-enqueue itself with
waketime=currenttime+timestep.

For a light:
Start the lightController with waketime=currenttime.
When the lightController is run(), it should re-enqueue itself with
waketime=currenttime+this._state.getDuration(), where the state
duration is whatever is appropriate for this state.

For a source:
Start the source with waketime=currenttime.
When the source is run(), it should re-enqueue itself with
waketime=currenttime+this._carCreationInterval, where the interval
indicates the time between car creations for this source.

I implemented the TimeServer using a linked list with a dummy node.

file:TimeServerLinked.java [source] [doc-public] [doc-private]

package agent;

import java.util.Observable;

public final class TimeServerLinked extends Observable implements TimeServer {
  private static final class Node {
    final double waketime;
    final Agent agent;
    Node next;

    public Node(double waketime, Agent agent, Node next) {
      this.waketime = waketime;
      this.agent = agent;
      this.next = next;
    }
  }
  private double currentTime;
  private int size;
  private Node head;

  /*
   * Invariant: head != null
   * Invariant: head.agent == null
   * Invariant: (size == 0) iff (head.next == null)
   */
  public TimeServerLinked() {
    size = 0;
    head = new Node(0, null, null);
  }

  public String toString() {
    StringBuilder sb = new StringBuilder("[");
    Node node = head.next;
    String sep = "";
    while (node != null) {
      sb.append(sep).append("(").append(node.waketime).append(",")
      .append(node.agent).append(")");
      node = node.next;
      sep = ";";
    }
    sb.append("]");
    return (sb.toString());
  }

  public double currentTime() {
    return currentTime;
  }

  public void enqueue(double waketime, Agent agent)
      throws IllegalArgumentException
  {
    if (waketime < currentTime)
      throw new IllegalArgumentException();
    Node prevElement = head;
    while ((prevElement.next != null) &&
        (prevElement.next.waketime <= waketime)) {
      prevElement = prevElement.next;
    }
    Node newElement = new Node(waketime, agent, prevElement.next);
    prevElement.next = newElement;
    size++;
  }

  Agent dequeue()
  {
    if (size < 1)
      throw new java.util.NoSuchElementException();
    Agent rval = head.next.agent;
    head.next = head.next.next;
    size--;
    return rval;
  }

  int size() {
    return size;
  }

  boolean empty() {
    return size() == 0;
  }

  public void run(double duration) {
    double endtime = currentTime + duration;
    while ((!empty()) && (head.next.waketime <= endtime)) {
      if ((currentTime - head.next.waketime) < 1e-09) {
        super.setChanged();
        super.notifyObservers();
      }
      currentTime = head.next.waketime;
      dequeue().run();
    }
    currentTime = endtime;
  }
}

Note below how one tests TimeServer without any "real" agents. Instead we use Mock Objects. We also saw this in the tests for CommandHistoryObj. Tools such as easymock make this easy.

file:TimeServerTEST.java [source] [doc-public] [doc-private]

package agent;
import static org.junit.Assert.*;
import org.junit.Test;

public class TimeServerTEST {
  TimeServerQueue q = new TimeServerQueue();
  // TimeServerLinked q = new TimeServerLinked();

  @Test
  public void testThatEmptySizeIsZero() {
    assertEquals(0, q.size());
  }

  @Test
  public void testThatDequeueOnEmptyThrowsIndexOutOfBoundsException() {
    boolean exceptionOccurred = false;

    try {
      q.dequeue();
    } catch (java.util.NoSuchElementException e) {
      exceptionOccurred = true;
    }

    assertTrue(exceptionOccurred);
  }

  @Test
  public void testThatEnqueueFollowedByDequeueReturnsSameReference() {
    class TestThatEnqueueFollowedByDequeueReturnsSameReference
    implements Agent
    {
      public void run() {}
    }

    Agent x1 = new TestThatEnqueueFollowedByDequeueReturnsSameReference();
    q.enqueue(0, x1);
    assertSame(x1, q.dequeue());
    assertEquals(0, q.size());
  }

  @Test
  public void testThatElementsAreInsertedInOrder() {
    class TestThatElementsAreInsertedInOrder implements Agent {
      public void run() {}
    }

    Agent x1 = new TestThatElementsAreInsertedInOrder();
    Agent x2 = new TestThatElementsAreInsertedInOrder();
    q.enqueue(0, x2);
    q.enqueue(1, x1);
    assertSame(x2, q.dequeue());
    assertSame(x1, q.dequeue());
    q.enqueue(1, x1);
    q.enqueue(0, x2);
    assertSame(x2, q.dequeue());
    assertSame(x1, q.dequeue());
    q.enqueue(0, x1);
    q.enqueue(0, x2);
    assertSame(x1, q.dequeue());
    assertSame(x2, q.dequeue());
    q.enqueue(0, x2);
    q.enqueue(0, x1);
    assertSame(x2, q.dequeue());
    assertSame(x1, q.dequeue());
  }

  @Test
  public void testToString() {
    class TestToString implements Agent {
      public void run() {}
      public String toString() { return "x"; }
    }

    q.enqueue(0, new TestToString());
    q.enqueue(1, new TestToString());
    assertEquals("[(0.0,x);(1.0,x)]", q.toString());
  }

  @Test
  public void testCurrentTime() {
    class TestCurrentTime implements Agent {
      public void run() {}
    }

    double expected = 1230;
    q.enqueue(expected, new TestCurrentTime());

    assertEquals(0.0, q.currentTime(), .1e-6);
    q.run(expected);

    assertEquals(expected, q.currentTime(), .1e-6);
  }

  private double scratch;
  @Test
  public void testDoActionsAtOrBefore() {
    class TestDoActionsAtOrBefore implements Agent {
      private double myScratch;
      TestDoActionsAtOrBefore(double myScratch) {
        this.myScratch = myScratch;
      }
      public void run() {
        scratch = myScratch;
      }
    }

    double time1 = 12;
    double time2 = 23;
    double value1 = 42;
    double value2 = 27;

    q.enqueue(time1, new TestDoActionsAtOrBefore(value1));

    scratch = 0;
    q.run(time1 - 1);
    assertEquals(0.0, scratch, .1e-6);

    scratch = 0;
    q.run(1);
    assertEquals(value1, scratch, .1e-6);

    q.enqueue(time2, new TestDoActionsAtOrBefore(value2));

    scratch = 0;
    q.run(time2);
    assertEquals(value2, scratch, .1e-6);
  }
}