6.5.5 Task�N���X

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/**
 * All tasks (wander, leftbumber, rightbumber)
 * extend this class. This class
 * defines the lifecycle of a task. Namely:
 * Reset:   Re-initialise task
 * Execute: Attempt to run (may not succeed
 * if a higher priority task is running).
 * Run:     Execute an FSM.
 * Release: Stop running.
 */
abstract class Task
  extends Thread
  implements SensorConstants {
  public static final
  Motor LEFT_MOTOR = Motor.C;
  public static final
  Motor RIGHT_MOTOR = Motor.A;
  public static final
  Sensor LEFT_BUMBER = Sensor.S3;
  public static final
  Sensor RIGHT_BUMBER = Sensor.S1;
  public static final
  boolean FORWARD = true;
  public static final
  boolean BACKWARD = false;
  public static final
  int END = -1;
  public static final
  int START = 0;
        
  public Action actions[];
  public int fsm[];
  public int state = END;

  /**
   * Reset the FSM to its initial state.
   */        
  public void reset() {
    state = START;
  }

  /**
   * The thread entry point.
   * Either runs the action's FSM
   * to completion -
   * sleeping or yielding between
   * each state - or until 'running' is false.
   * When finished call 'release'.
   * <P>
   * FSM is really a bit of a
   * misnomer as there are no input events so
   * there is only one transition from
   * each state to the next.
   */
  public void run() {
    // Keep running until the
    // program should exit.
    do {
      // Quiesce
      while (state != START && Main.main.running) {
        yield();
      }
      // Execute the FSM
      // until it stops...
      do {
        int toSleepFor;
        synchronized (Main.main) {
          toSleepFor = actions[state].act();
          state = fsm[state];
        }
        if (toSleepFor > 0) {
          try {
            sleep(toSleepFor);
          } catch (InterruptedException ie) {
          }
        }
        else        
          yield();
      } while (state != END && Main.main.running);
      // Its over, release the actuators.
      release();
    } while (Main.main.running);
  }

  /**
   * Inform the coordinator
   * that we have released the actuators.
   */        
  public void release()  {
    Main.main.release(this);
  }

  /**
   * Request control of the actuators
   */        
  public void execute() {
    if (Main.main != null)
      Main.main.execute(this);
  }

  /**
   * Return true if the FSM
   * is executing, false otherwise.
   */
  public boolean running()  {
    return state != END;
  }
        
  /**
   * Convenience function to
   * make it appear to subclasses that
   * they have direct control of
   * the actuators when they are in
   * fact gated by the controller.
   */        
  public void setMotor(Motor motor,
                       int power,
                       boolean forward) {
    Main.main.setMotor(this,
                       motor,
                       power,
                       forward);
  }
}