public String toString() {
    String s = "[" + helper_type + ";";
    for (Enumeration e = seq.elements(); e.hasMoreElements(); ) {
      try {
        Class c = (Class) e.nextElement();
        s += c.getName() + ",";
      } catch (NoSuchElementException ee) {
        s += "???" + ",";
      }
    }

    return s + "]";
  }
  public static PiHelper load_pi_helper(
      PiHelper pi_helper_cache, ConditionalDistribution pxu, Distribution[] pi_messages)
      throws Exception {
    if (pi_messages.length == 0) return new TrivialPiHelper();

    Vector seq = new Vector();
    seq.addElement(pxu.getClass());
    for (int i = 0; i < pi_messages.length; i++) seq.addElement(pi_messages[i].getClass());

    if (pi_helper_cache != null
        && MatchClassPattern.matches(pi_helper_cache.description(), seq, new int[1], new int[1]))
      return pi_helper_cache;

    Class c = find_helper_class(seq, "pi");
    return (PiHelper) c.newInstance();
  }
  public static Object invoke_description(Class c) {
    try {
      Field f = c.getField("description_array");
      return f.get(null);
    } catch (NoSuchFieldException e) {
    } // eat the exception; apparently c is not a helper
    catch (Exception e) {
    } // HMM, SHOULD WE TRY HARDER TO FIGURE OUT WHAT'S GOING ON HERE ???

    return null;
  }
 static {
   // FIXME: RMIServerImpl_Stub is generated at build time
   // after jconsole is built.  We need to investigate if
   // the Makefile can be fixed to build jconsole in the
   // right order.  As a workaround for now, we dynamically
   // load RMIServerImpl_Stub class instead of statically
   // referencing it.
   Class<? extends Remote> serverStubClass = null;
   try {
     serverStubClass = Class.forName(rmiServerImplStubClassName).asSubclass(Remote.class);
   } catch (ClassNotFoundException e) {
     // should never reach here
     throw (InternalError) new InternalError(e.getMessage()).initCause(e);
   }
   rmiServerImplStubClass = serverStubClass;
 }
 private static void checkStub(Remote stub, Class<? extends Remote> stubClass) {
   // Check remote stub is from the expected class.
   //
   if (stub.getClass() != stubClass) {
     if (!Proxy.isProxyClass(stub.getClass())) {
       throw new SecurityException("Expecting a " + stubClass.getName() + " stub!");
     } else {
       InvocationHandler handler = Proxy.getInvocationHandler(stub);
       if (handler.getClass() != RemoteObjectInvocationHandler.class) {
         throw new SecurityException(
             "Expecting a dynamic proxy instance with a "
                 + RemoteObjectInvocationHandler.class.getName()
                 + " invocation handler!");
       } else {
         stub = (Remote) handler;
       }
     }
   }
   // Check RemoteRef in stub is from the expected class
   // "sun.rmi.server.UnicastRef2".
   //
   RemoteRef ref = ((RemoteObject) stub).getRef();
   if (ref.getClass() != UnicastRef2.class) {
     throw new SecurityException(
         "Expecting a " + UnicastRef2.class.getName() + " remote reference in stub!");
   }
   // Check RMIClientSocketFactory in stub is from the expected class
   // "javax.rmi.ssl.SslRMIClientSocketFactory".
   //
   LiveRef liveRef = ((UnicastRef2) ref).getLiveRef();
   RMIClientSocketFactory csf = liveRef.getClientSocketFactory();
   if (csf == null || csf.getClass() != SslRMIClientSocketFactory.class) {
     throw new SecurityException(
         "Expecting a "
             + SslRMIClientSocketFactory.class.getName()
             + " RMI client socket factory in stub!");
   }
 }
  /**
   * Contact a belief network context, get the helper list, and search the list to see if there's a
   * helper which matches the type sequence specified. If there's more than one helper which
   * matches, find the ``best fit.''
   *
   * <p>The class and count scores of the best-fitting helper class are written into
   * <tt>max_class_score[0]</tt> and <tt>max_count_score[0]</tt>, respectively.
   */
  public static Class find_helper_class0(
      Vector seq, String helper_type, int[] max_class_score, int[] max_count_score)
      throws ClassNotFoundException {
    long t0 = System.currentTimeMillis();
    if (bnc != null) // make sure the reference is still alive
    try {
        bnc.get_name();
      } catch (RemoteException e) {
        bnc = null;
      }

    if (bnc == null) // need to locate a context
    {
      String cb = System.getProperty("java.rmi.server.codebase", "http://localhost");
      long tt0 = System.currentTimeMillis();
      try {
        bnc = BeliefNetworkContext.locate_context(new URL(cb).getHost());
      } catch (Exception e) {
        throw new ClassNotFoundException("nested: " + e);
      }
    }

    String[] helperlist;
    try {
      helperlist = bnc.get_helper_names(helper_type);
    } catch (RemoteException e) {
      throw new ClassNotFoundException("bnc.get_helper_names failed");
    }

    int[] class_score1 = new int[1], count_score1 = new int[1];
    max_class_score[0] = -1;
    max_count_score[0] = -1;
    Class cmax_score = null;

    for (int i = 0; i < helperlist.length; i++) {
      try {
        Class c = RMIClassLoader.loadClass(helperlist[i]);
        SeqTriple[] sm = (SeqTriple[]) invoke_description(c);
        if (sm == null) continue; // apparently not a helper class
        if (MatchClassPattern.matches(sm, seq, class_score1, count_score1)) {
          if (class_score1[0] > max_class_score[0]
              || (class_score1[0] == max_class_score[0] && count_score1[0] > max_count_score[0])) {
            cmax_score = c;
            max_class_score[0] = class_score1[0];
            max_count_score[0] = count_score1[0];
          }
        }
      } catch (Exception e2) {
        System.err.println("PiHelperLoader: attempt to load " + helperlist[i] + " failed; " + e2);
      }
    }

    if (cmax_score == null) {
      System.err.println("find_helper_class0: failed; helper list:");
      for (int i = 0; i < helperlist.length; i++) System.err.println("\t" + helperlist[i]);

      String s = "";
      for (Enumeration e = seq.elements(); e.hasMoreElements(); ) {
        try {
          Class c = (Class) e.nextElement();
          s += c.getName() + ",";
        } catch (NoSuchElementException ee) {
          s += "???" + ",";
        }
      }

      throw new ClassNotFoundException("no " + helper_type + " helper for sequence [" + s + "]");
    }

    // FOR NOW IGNORE THE POSSIBILITY OF TWO OR MORE MATCHES !!!
    return cmax_score;
  }
  /**
   * This method returns a <tt>Class</tt> for a helper which can handle the list of distributions
   * specified by <tt>seq1</tt>. We maintain a cache of recently-loaded helpers, so check the cache
   * before going to the trouble of searching for a helper. The cache is blown away every
   * <tt>HELPER_CACHE_REFRESH</tt> seconds.
   *
   * <p>If we can't find a helper in the cache, we must search through the list of available helpers
   * to find an appropriate one. First try to find helper using class sequence as specified by
   * <tt>seq</tt>. Whether or not that succeeds, promote any <tt>Gaussian</tt> in the sequence to
   * <tt>MixGaussians</tt>, and try again. If we get a better match on the second try, return the
   * helper thus found.
   */
  public static Class find_helper_class(Vector seq1, String helper_type)
      throws ClassNotFoundException {
    // Let's see if an appropriate helper is in the cache.
    // If the cache is too old, empty it and search for the helper anew.

    if (System.currentTimeMillis() - cache_timestamp > HELPER_CACHE_REFRESH) {
      helper_cache = new Hashtable();
      cache_timestamp = System.currentTimeMillis();
      // Go on and search for appropriate helper.
    } else {
      HelperCacheKey key = new HelperCacheKey(helper_type, seq1);
      Class helper_class = (Class) helper_cache.get(key);
      if (helper_class != null) {
        if (Global.debug > -1)
          System.err.println(
              "PiHelperLoader.find_helper_class: found helper class: "
                  + helper_class
                  + "; no need to search.");
        return helper_class;
      }
      // else no luck; we have to search for helper.
    }

    // Well, we didn't find a helper in the cache, so let's go to work.
    if (Global.debug > -1)
      System.err.println(
          "PiHelperLoader.find_helper_class: DID NOT FIND HELPER CLASS; NOW SEARCH.");

    Class c1 = null, c2 = null;
    ClassNotFoundException cnfe1 = null, cnfe2 = null;
    int[] class_score1 = new int[1], count_score1 = new int[1];
    int[] class_score2 = new int[1], count_score2 = new int[1];

    try {
      c1 = find_helper_class1(seq1, helper_type, class_score1, count_score1);
    } catch (ClassNotFoundException e) {
      cnfe1 = e;
    } // hang on, we may need to re-throw later.

    Class gaussian_class = Class.forName("riso.distributions.Gaussian");
    MixGaussians mog = new MixGaussians(1, 1);

    Vector seq2 = new Vector(seq1.size());
    for (int i = 0; i < seq1.size(); i++)
      if (gaussian_class.isAssignableFrom((Class) seq1.elementAt(i)))
        seq2.addElement(mog.getClass());
      else seq2.addElement(seq1.elementAt(i));

    try {
      c2 = find_helper_class1(seq2, helper_type, class_score2, count_score2);
    } catch (ClassNotFoundException e) {
      cnfe2 = e;
    }

    if (cnfe1 == null && cnfe2 == null) {
      // Both matched; see which one fits better.
      // Break ties in favor of the helper for non-promoted messages.

      if (class_score1[0] >= class_score2[0]
          || (class_score1[0] == class_score2[0] && count_score1[0] >= count_score2[0])) {
        if (Global.debug > 1)
          System.err.println(
              "\taccept helper " + c1 + " for non-promoted classes instead of " + c2);
        if (Global.debug > 1)
          System.err.println(
              "\t\t"
                  + class_score1[0]
                  + ", "
                  + class_score2[0]
                  + "; "
                  + count_score1[0]
                  + ", "
                  + count_score2[0]);
        helper_cache.put(new HelperCacheKey(helper_type, seq1), c1);
        return c1;
      } else {
        if (Global.debug > 1)
          System.err.println("\taccept helper " + c2 + " for promoted classes instead of " + c1);
        if (Global.debug > 1)
          System.err.println(
              "\t\t"
                  + class_score1[0]
                  + ", "
                  + class_score2[0]
                  + "; "
                  + count_score1[0]
                  + ", "
                  + count_score2[0]);
        helper_cache.put(new HelperCacheKey(helper_type, seq1), c2);
        return c2;
      }
    } else if (cnfe1 == null && cnfe2 != null) {
      // Only the first try matched, return it.
      helper_cache.put(new HelperCacheKey(helper_type, seq1), c1);
      return c1;
    } else if (cnfe1 != null && cnfe2 == null) {
      // Only the second try matched, return it.
      helper_cache.put(new HelperCacheKey(helper_type, seq1), c2);
      return c2;
    } else {
      // Neither try matched. Re-throw the exception generated by the first try.
      throw cnfe1;
    }
  }