Intracomm.java

/*
 * File         : Intracommm.java
 * Author       : Sang Lim, Xinying Li, Bryan Carpenter
 * Created      : Thu Apr  9 12:22:15 1998
 * Revision     : $Revision: 1.14 $
 * Updated      : $Date: 2002/12/16 15:25:13 $
 * Copyright: Northeast Parallel Architectures Center
 *            at Syracuse University 1998
 */

package mpi;

public class Intracomm extends Comm {

  Intracomm() {}

  void setType(int type) {
    super.setType(type) ;

    shadow = new Comm(dup()) ;
  }

  protected Intracomm(long handle) throws MPIException {
    super(handle) ;

    shadow = new Comm(dup()) ;
  }

  public Object clone() {
    try {
      return new Intracomm(dup()) ;
    }
    catch (MPIException e) {
      throw new RuntimeException(e.getMessage()) ;
    }
  }

  /**
   * Partition the group associated with this communicator and create
   * a new communicator within each subgroup.
   * <p>
   * <table>
   * <tr><td><tt> color    </tt></td><td> control of subset assignment </tr>
   * <tr><td><tt> key      </tt></td><td> control of rank assignment </tr>
   * <tr><td><em> returns: </em></td><td> new communicator </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_COMM_SPLIT</tt>.
   */

  public Intracomm Split(int colour, int key) throws MPIException {
    long splitHandle = split(colour,key) ;
    if(splitHandle == nullHandle)
      return null ;
    else
      return new Intracomm(splitHandle) ;
  }

  private native long split(int colour, int key);

  /**
   * Create a new communicator.
   * <p>
   * <table>
   * <tr><td><tt> group    </tt></td><td> group which is a subset of the
   *                                      group of this communicator </tr>
   * <tr><td><em> returns: </em></td><td> new communicator </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_COMM_CREATE</tt>.
   */

  public Intracomm Creat(Group group) throws MPIException {
    long creatHandle = creat(group) ;
    if(creatHandle == nullHandle)
      return null ;
    else
      return new Intracomm(creatHandle) ;
  }

  private native long creat(Group group);

  // Collective Communication

  /**
   * A call to <tt>Barrier</tt> blocks the caller until all process
   * in the group have called it.
   * <p>
   * Java binding of the MPI operation <tt>MPI_BARRIER</tt>.
   */

  public native void Barrier() throws MPIException ;

  /*
   * The type signature of `incount * intype' must be equal to the type
   * signature of `outcount * outtype' (ie they must represent the same
   * number of basic elements of the same type).
   */

  private void copyBuffer(Object inbuf,
                          int inoffset, int incount, Datatype intype,
                          Object outbuf,
                          int outoffset, int outcount, Datatype outtype)
                                                      throws MPIException {
    if(intype.isObject()) {
      Object [] inbufArray = (Object[])inbuf;
      Object [] outbufArray = (Object[])outbuf;

      int outbase = outoffset, inbase = inoffset ;
      int kout = 0 ;
      for (int j = 0 ; j < incount ; j++) {
        for (int k = 0 ; k < intype.displacements.length ; k++)
          outbufArray [outbase + outtype.displacements [kout]] = 
               inbufArray [inbase + intype.displacements [k]] ;

        inbase += intype.Extent() ;

        kout++;
        if (kout == outtype.displacements.length){
          kout = 0;
          outbase += outtype.Extent() ;
        }
      }
    }
    else {
      byte [] tmpbuf = new byte [Pack_size(incount, intype)] ;
      Pack(inbuf, inoffset, incount, intype, tmpbuf, 0) ;
      Unpack(tmpbuf, 0, outbuf, outoffset, outcount, outtype) ;
    }
  }

  private Object newBuffer(Object template) {
    if(template instanceof Object[])
      return new Object [((Object[]) template).length] ;

    if(template instanceof byte[])
      return new byte [((byte[]) template).length] ;

    if(template instanceof char[])
      return new char [((char[]) template).length] ;

    if(template instanceof short[])
      return new short [((short[]) template).length] ;

    if(template instanceof boolean[])
      return new boolean [((boolean[]) template).length] ;

    if(template instanceof int[])
      return new int [((int[]) template).length] ;

    if(template instanceof long[])
      return new long [((long[]) template).length] ;

    if(template instanceof float[])
      return new float [((float[]) template).length] ;

    if(template instanceof double[])
      return new double [((double[]) template).length] ;

    return null ;
  }

  /**
   * Broadcast a message from the process with rank <tt>root</tt>
   * to all processes of the group.
   * <p>
   * <table>
   * <tr><td><tt> buf      </tt></td><td> buffer array </tr>
   * <tr><td><tt> offset   </tt></td><td> initial offset in buffer </tr>
   * <tr><td><tt> count    </tt></td><td> number of items in buffer </tr>
   * <tr><td><tt> datatype </tt></td><td> datatype of each item in
   *                                      buffer </tr>
   * <tr><td><tt> root     </tt></td><td> rank of broadcast root </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_BCST</tt>.
   */

  public void Bcast(Object   buf, 
                    int      offset, 
                    int      count, 
                    Datatype type,
                    int      root) throws MPIException {

    if (type.isObject()){
      if (Rank() == root){
        for (int dst = 0; dst < Size(); dst++)
          if (dst != root)
            shadow.Send(buf, offset, count, type, dst, 0);
      }
      else
        shadow.Recv(buf, offset, count, type, root, 0);
    }
    else
       bcast(buf, offset*type.Size(), count, type, root);   
  }

  private native void bcast(Object   buf, 
                            int      offset, 
                            int      count, 
                            Datatype type,
                            int      root);

  /**
   * Each process sends the contents of its send buffer to the
   * root process.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> sendcount  </tt></td><td> number of items to send </tr>
   * <tr><td><tt> sendtype   </tt></td><td> datatype of each item in send
   *                                        buffer </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> recvcount  </tt></td><td> number of items to receive </tr>
   * <tr><td><tt> recvtype   </tt></td><td> datatype of each item in receive
   *                                        buffer </tr>
   * <tr><td><tt> root       </tt></td><td> rank of receiving process </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_GATHER</tt>.
   */
  
  public void Gather(Object   sendbuf, 
                     int      sendoffset, 
                     int      sendcount,
                     Datatype sendtype, 
                     Object   recvbuf, 
                     int      recvoffset, 
                     int      recvcount,
                     Datatype recvtype, 
                     int      root) throws MPIException {
  
    if (sendtype.isObject()) {
      if (Rank() == root) {
        for (int src = 0; src < Size(); src++) {
          int dstOffset = recvoffset + recvcount * recvtype.Extent() * src ;
          if (src == root)
            copyBuffer(sendbuf, sendoffset, sendcount, sendtype,
                       recvbuf, dstOffset, recvcount, recvtype) ;
          else
            shadow.Recv(recvbuf, dstOffset, recvcount, recvtype, src, 0);
	}
      }
      else
        shadow.Send(sendbuf, sendoffset, sendcount, sendtype, root, 0);
    }
    else
      gather(sendbuf, sendoffset*sendtype.Size(), sendcount,sendtype,
	     recvbuf, recvoffset*recvtype.Size(), recvcount,recvtype,
             root);
  }

  private native void gather(Object   sendbuf, 
                             int      sendoffset, 
                             int      sendcount,
	                     Datatype sendtype, 
                             Object   recvbuf, 
                             int      recvoffset, 
                             int      recvcount,
	                     Datatype recvtype, 
                             int      root);

  /**
   * Extends functionality of <tt>Gather</tt> by allowing varying
   * counts of data from each process.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> sendcount  </tt></td><td> number of items to send </tr>
   * <tr><td><tt> sendtype   </tt></td><td> datatype of each item in send
   *                                        buffer </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> recvcounts </tt></td><td> number of elements received from
   *                                        each process </tr>
   * <tr><td><tt> displs     </tt></td><td> displacements at which to place
   *                                        incoming data </tr>
   * <tr><td><tt> recvtype   </tt></td><td> datatype of each item in receive
   *                                        buffer </tr>
   * <tr><td><tt> root       </tt></td><td> rank of receiving process </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_GATHERV</tt>.
   * <p>
   * The sizes of arrays <tt>recvcounts</tt> and <tt>displs</tt> should be the
   * size of the group.  Entry <em>i</em> of <tt>displs</tt> specifies the
   * displacement relative to element <tt>recvoffset</tt> of <tt>recvbuf</tt>
   * at which to place incoming data.
   */

  public void Gatherv(Object   sendbuf,  
                      int      sendoffset, 
                      int      sendcount,
                      Datatype sendtype, 
                      Object   recvbuf, 
                      int      recvoffset, 
                      int []   recvcount,
                      int []   displs, 
                      Datatype recvtype, 
                      int      root) throws MPIException {

    if (sendtype.isObject()){
      if (Rank() == root){
        for (int src = 0; src < Size(); src++){
          int dstOffset = recvoffset + sendtype.Extent() * displs[src] ;
          if (src == root)
            copyBuffer(sendbuf, sendoffset, sendcount,sendtype,
                       recvbuf, dstOffset, recvcount[src], recvtype);
          else
            shadow.Recv(recvbuf, dstOffset, recvcount[src], recvtype, src, 0);
	}
      }
      else
        shadow.Send(sendbuf, sendoffset, sendcount, sendtype, root, 0);
    }
    else
      gatherv(sendbuf  , sendoffset*sendtype.Size(), 
              sendcount, sendtype,
              recvbuf  , recvoffset*recvtype.Size(),
              recvcount, displs,
              recvtype , root);
  }

  private native void gatherv(Object   sendbuf, 
                              int      sendoffset, 
                              int      sendcount,
  	                      Datatype sendtype, 
                              Object   recvbuf, 
                              int      recvoffset, 
                              int []   recvcount,
 	                      int []   displs, 
                              Datatype recvtype, 
                              int      root);

  /**
   * Inverse of the operation <tt>Gather</tt>.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> sendcount  </tt></td><td> number of items to send </tr>
   * <tr><td><tt> sendtype   </tt></td><td> datatype of each item in send
   *                                        buffer </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> recvcount  </tt></td><td> number of items to receive </tr>
   * <tr><td><tt> recvtype   </tt></td><td> datatype of each item in receive
   *                                        buffer </tr>
   * <tr><td><tt> root       </tt></td><td> rank of sending process </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_SCATTER</tt>.
   */

  public void Scatter(Object   sendbuf, 
                      int      sendoffset, 
                      int      sendcount,
                      Datatype sendtype, 
                      Object   recvbuf, 
                      int      recvoffset, 
                      int      recvcount,
                      Datatype recvtype, 
                      int      root) throws MPIException {

    if (sendtype.isObject()){
      if (Rank() == root){
        for (int dst = 0; dst < Size() ; dst++){
          int srcOffset = sendoffset + sendcount * sendtype.Extent() * dst ;
          if (dst == root)
            copyBuffer(sendbuf, srcOffset, sendcount, sendtype,
                       recvbuf, recvoffset, recvcount, recvtype);
          else 
            shadow.Send(sendbuf, srcOffset, sendcount, sendtype, dst, 0);
        }
      }
      else 
        shadow.Recv(recvbuf, recvoffset, recvcount, recvtype, root, 0); 
    }
    else 
      scatter(sendbuf, sendoffset*sendtype.Size(), sendcount, sendtype, 
              recvbuf, recvoffset*recvtype.Size(), recvcount, recvtype, 
              root);
  }

  private native void scatter(Object   sendbuf, 
                              int      sendoffset, 
                              int      sendcount,
                              Datatype sendtype, 
                              Object   recvbuf, 
                              int      recvoffset, 
                              int      recvcount,
                              Datatype recvtype, 
                              int      root);

  /**
   * Inverse of the operation <tt>Gatherv</tt>.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> sendcounts </tt></td><td> number of items sent to each
   *                                        process </tr>
   * <tr><td><tt> displs     </tt></td><td> displacements from which to take
   *                                        outgoing data </tr>
   * <tr><td><tt> sendtype   </tt></td><td> datatype of each item in send
   *                                        buffer </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> recvcount  </tt></td><td> number of items to receive </tr>
   * <tr><td><tt> recvtype   </tt></td><td> datatype of each item in receive
   *                                        buffer </tr>
   * <tr><td><tt> root       </tt></td><td> rank of sending process </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_SCATTERV</tt>.
   */

  public void Scatterv(Object   sendbuf, 
                       int      sendoffset,
                       int []   sendcount,
                       int []   displs,
                       Datatype sendtype, 
                       Object   recvbuf, 
                       int      recvoffset, 
                       int      recvcount,
                       Datatype recvtype, 
                       int      root) throws MPIException {
  
    if (sendtype.isObject()){
      if (Rank() == root){
        for (int dst = 0 ; dst < Size() ; dst++){
          int srcOffset = sendoffset + sendtype.Extent() * displs[dst] ;
          if (dst == root)
            copyBuffer(sendbuf, srcOffset, sendcount[dst], sendtype,
                       recvbuf, recvoffset, recvcount, recvtype);
          else 
            shadow.Send(sendbuf, srcOffset, sendcount[dst], sendtype, dst, 0);
        }
      }
      else 
        shadow.Recv(recvbuf, recvoffset, recvcount, recvtype, root, 0); 
    }
    else 
      scatterv(sendbuf, sendoffset * sendtype.Size(), sendcount,
               displs, sendtype,
               recvbuf, recvoffset * recvtype.Size(), recvcount, recvtype,
               root);
  }

  private native void scatterv(Object   sendbuf, 
                               int      sendoffset, 
          	               int []   sendcount,
                               int []   displs,
                               Datatype sendtype, 
                               Object   recvbuf, 
                               int      recvoffset, 
                               int      recvcount,
                               Datatype recvtype, 
                               int      root);

  /**
   * Similar to <tt>Gather</tt>, but all processes receive the result.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> sendcount  </tt></td><td> number of items to send </tr>
   * <tr><td><tt> sendtype   </tt></td><td> datatype of each item in send
   *                                        buffer </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> recvcount  </tt></td><td> number of items to receive </tr>
   * <tr><td><tt> recvtype   </tt></td><td> datatype of each item in receive
   *                                        buffer </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_ALLGATHER</tt>.
   */

  public void Allgather(Object   sendbuf, 
                        int      sendoffset, 
                        int      sendcount,
                        Datatype sendtype, 
                        Object   recvbuf, 
                        int      recvoffset, 
                        int      recvcount,
                        Datatype recvtype) throws MPIException {
 
    if (sendtype.isObject()){
      Gather(sendbuf, sendoffset, sendcount, sendtype, 
             recvbuf, recvoffset, recvcount, recvtype, 0);
      Bcast(recvbuf, recvoffset, Size() * recvcount, recvtype, 0);
    }
    else 
      allgather(sendbuf,   sendoffset*sendtype.Size(), 
                sendcount, sendtype, 
                recvbuf,   recvoffset*recvtype.Size(), 
                recvcount, recvtype);
  }

  private native void allgather(Object   sendbuf, 
                                int      sendoffset, 
                                int      sendcount,
                                Datatype sendtype, 
                                Object   recvbuf, 
                                int      recvoffset, 
                                int      recvcount,
                                Datatype recvtype);


  /**
   * Similar to <tt>Gatherv</tt>, but all processes receive the result.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> sendcount  </tt></td><td> number of items to send </tr>
   * <tr><td><tt> sendtype   </tt></td><td> datatype of each item in send
   *                                        buffer </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> recvcounts </tt></td><td> number of elements received from
   *                                        each process </tr>
   * <tr><td><tt> displs     </tt></td><td> displacements at which to place
   *                                        incoming data </tr>
   * <tr><td><tt> recvtype   </tt></td><td> datatype of each item in receive
   *                                        buffer </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_ALLGATHERV</tt>.
   */

  public void Allgatherv(Object   sendbuf, 
                         int      sendoffset, 
                         int      sendcount,
                         Datatype sendtype, 
                         Object   recvbuf, 
                         int      recvoffset, 
                         int []   recvcount,
                         int []   displs, 
                         Datatype recvtype) throws MPIException {

    if (sendtype.isObject()){
      Gatherv(sendbuf, sendoffset, sendcount, sendtype, 
              recvbuf, recvoffset, recvcount, displs, recvtype, 0);

      for (int src = 0; src < Size(); src++){
        int dstOffset = recvoffset + sendtype.Extent() * displs[src] ;
        Bcast(recvbuf, dstOffset, recvcount[src], recvtype, 0);
      }
    }
    else 
      allgatherv(sendbuf  , sendoffset*sendtype.Size(), 
                 sendcount, sendtype, 
                 recvbuf  , recvoffset*recvtype.Size(), 
                 recvcount, displs, 
                 recvtype);
  }

  private native void allgatherv(Object   sendbuf, 
                                 int      sendoffset, 
                                 int      sendcount,
                                 Datatype sendtype, 
                                 Object   recvbuf, 
                                 int      recvoffset, 
                                 int []   recvcount,
                                 int []   displs, 
                                 Datatype recvtype);

  /**
   * Extension of <tt>Allgather</tt> to the case where each process sends
   * distinct data to each of the receivers.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> sendcount  </tt></td><td> number of items sent to each
   *                                        process </tr>
   * <tr><td><tt> sendtype   </tt></td><td> datatype send buffer items </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> recvcount  </tt></td><td> number of items received from any
   *                                        process
   * <tr><td><tt> recvtype   </tt></td><td> datatype of receive buffer
   *                                        items </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_ALLTOALL</tt>.
   */

  public void Alltoall(Object   sendbuf, 
                       int      sendoffset, 
                       int      sendcount,
                       Datatype sendtype, 
                       Object   recvbuf, 
                       int      recvoffset, 
                       int      recvcount,
                       Datatype recvtype) throws MPIException {

    if (sendtype.isObject())
      for (int dst = 0; dst < Size(); dst++) {
        int srcOffset = sendoffset + sendcount * sendtype.Extent() * dst ;
        Gather(sendbuf, srcOffset, sendcount, sendtype, 
               recvbuf, recvoffset, recvcount, recvtype, dst);
      }
    else 
      alltoall(sendbuf,   sendoffset*sendtype.Size(), 
               sendcount, sendtype, 
               recvbuf,   recvoffset*recvtype.Size(), 
               recvcount, recvtype);
  }

  private native void alltoall(Object   sendbuf, 
                               int      sendoffset, 
                               int      sendcount,
                               Datatype sendtype, 
                               Object   recvbuf, 
                               int      recvoffset, 
                               int      recvcount,
                               Datatype recvtype);

  /**
   * Adds flexibility to <tt>Alltoall</tt>: location of data for send is
   * specified by <tt>sdispls</tt> and location to place data on receive
   * side is specified by <tt>rdispls</tt>.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> sendcounts </tt></td><td> number of items sent to each
   *                                        process </tr>
   * <tr><td><tt> sdispls    </tt></td><td> displacements from which to take
   *                                        outgoing data </tr>
   * <tr><td><tt> sendtype   </tt></td><td> datatype send buffer items </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> recvcounts </tt></td><td> number of elements received from
   *                                        each process
   * <tr><td><tt> rdispls    </tt></td><td> displacements at which to place
   *                                        incoming data </tr>
   * <tr><td><tt> recvtype   </tt></td><td> datatype of each item in receive
   *                                        buffer </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_ALLTOALLV</tt>.
   */

  public void Alltoallv(Object   sendbuf, 
                        int      sendoffset, 
                        int []   sendcount,
                        int []   sdispls,
                        Datatype sendtype, 
                        Object   recvbuf, 
                        int      recvoffset, 
                        int []   recvcount,
                        int []   rdispls, 
                        Datatype recvtype) throws MPIException {

    if (sendtype.isObject())
      for (int dst = 0; dst < Size(); dst++) {
        int srcOffset = sendoffset + sendtype.Extent() * sdispls[dst] ;
        Gatherv(sendbuf, srcOffset, sendcount[dst], sendtype, 
                recvbuf, recvoffset, recvcount, rdispls, recvtype, dst);
      }
    else 
      alltoallv(sendbuf,   sendoffset*sendtype.Size(), 
                sendcount, sdispls, sendtype, 
                recvbuf,   recvoffset*recvtype.Size(), 
                recvcount, rdispls, recvtype);
  }

  private native void alltoallv(Object   sendbuf, 
                                int      sendoffset, 
                                int []   sendcount,
           	                int []   sdispls,
                                Datatype sendtype, 
                                Object   recvbuf, 
                                int      recvoffset, 
                                int []   recvcount,
                                int []   displs, 
                                Datatype recvtype);

  /**
   * Combine elements in input buffer of each process using the reduce
   * operation, and return the combined value in the output buffer of the
   * root process.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> count      </tt></td><td> number of items in send buffer </tr>
   * <tr><td><tt> datatype   </tt></td><td> data type of each item in send
   *                                        buffer </tr>
   * <tr><td><tt> op         </tt></td><td> reduce operation </tr>
   * <tr><td><tt> root       </tt></td><td> rank of root process </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_REDUCE</tt>.
   * <p>
   * The predefined operations are available in Java as <tt>MPI.MAX</tt>,
   * <tt>MPI.MIN</tt>, <tt>MPI.SUM</tt>, <tt>MPI.PROD</tt>, <tt>MPI.LAND</tt>,
   * <tt>MPI.BAND</tt>, <tt>MPI.LOR</tt>, <tt>MPI.BOR</tt>, <tt>MPI.LXOR</tt>,
   * <tt>MPI.BXOR</tt>, <tt>MPI.MINLOC</tt> and <tt>MPI.MAXLOC</tt>.
   */
  
  public void Reduce(Object sendbuf, int sendoffset,
                     Object recvbuf, int recvoffset, int count,
                     Datatype datatype, Op op, int root) throws MPIException {

    if (op.isUser()) {
      if (Rank() == root) {
        copyBuffer(sendbuf,sendoffset,count,datatype,
                   recvbuf,recvoffset,count,datatype);

        Object tempbuf = newBuffer(recvbuf) ;
        for (int src = 0; src < Size(); src++)
          if(src != root) {
            shadow.Recv(tempbuf, 0, count, datatype, src, 0);
            op.Call(tempbuf, 0, recvbuf, recvoffset, count, datatype);
          }
      }
      else
        shadow.Send(sendbuf, sendoffset, count, datatype, root, 0);
    }
    else
      reduce(sendbuf, sendoffset, recvbuf, recvoffset, count,
             datatype, op, root) ;
  }

  private native void reduce(Object sendbuf, int sendoffset, 
                             Object recvbuf, int recvoffset, int count,
                             Datatype datatype, Op op, int root);

  /**
   * Same as <tt>reduce</tt> except that the result appears in receive
   * buffer of all process in the group.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> count      </tt></td><td> number of items in send buffer </tr>
   * <tr><td><tt> datatype   </tt></td><td> data type of each item in send
   *                                        buffer </tr>
   * <tr><td><tt> op         </tt></td><td> reduce operation </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_ALLREDUCE</tt>.
   */

  public void Allreduce(Object sendbuf, int sendoffset,
                        Object recvbuf, int recvoffset, int count,
                        Datatype datatype, Op op) throws MPIException {

    if (op.isUser()){
      Reduce(sendbuf, sendoffset,
             recvbuf, recvoffset, count, datatype, op, 0);

      Bcast(recvbuf, recvoffset, count, datatype, 0);
    }
    else {
      allreduce(sendbuf, sendoffset, recvbuf, recvoffset, count,
                datatype, op) ;
    }
  }

  private native void allreduce(Object sendbuf, int sendoffset, 
                                Object recvbuf, int recvoffset, int count,
                                Datatype datatype, Op op) ;

  /**
   * Combine elements in input buffer of each process using the reduce
   * operation, and scatter the combined values over the output buffers
   * of the processes.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> recvcounts </tt></td><td> numbers of result elements
   *                                        distributed to each process </tr>
   * <tr><td><tt> datatype   </tt></td><td> data type of each item in send
   *                                        buffer </tr>
   * <tr><td><tt> op         </tt></td><td> reduce operation </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_REDUCE_SCATTER</tt>.
   */

  public void Reduce_scatter(Object sendbuf, int sendoffset,
                             Object recvbuf, int recvoffset, int [] recvcounts,
                             Datatype datatype, Op op) throws MPIException {

    if (op.isUser()) {
      int [] displs = new int [recvcounts.length] ;
      int count = 0 ;
      for (int i = 0; i < recvcounts.length; i++) {
        displs [i] = count ;
        count += recvcounts [i] ;
      }

      Object tempbuf = newBuffer(sendbuf) ;
      copyBuffer(sendbuf,sendoffset,count,datatype,
                 tempbuf,sendoffset,count,datatype);

      Reduce(tempbuf, sendoffset, sendbuf, sendoffset, count,
             datatype, op, 0);
      
      Scatterv(tempbuf, sendoffset, recvcounts, displs, datatype, 
               recvbuf, recvoffset, recvcounts[Rank()], datatype, 0);
    }
    else 
      reduce_scatter(sendbuf, sendoffset, recvbuf, recvoffset, recvcounts, 
	             datatype, op) ;
  }

  private native void reduce_scatter(Object sendbuf, int sendoffset, 
                                     Object recvbuf, int recvoffset,
                                     int [] recvcounts, 
	                             Datatype datatype, Op op) ;

  /**
   * Perform a prefix reduction on data distributed across the group.
   * <p>
   * <table>
   * <tr><td><tt> sendbuf    </tt></td><td> send buffer array </tr>
   * <tr><td><tt> sendoffset </tt></td><td> initial offset in send buffer </tr>
   * <tr><td><tt> recvbuf    </tt></td><td> receive buffer array </tr>
   * <tr><td><tt> recvoffset </tt></td><td> initial offset in receive
   *                                        buffer </tr>
   * <tr><td><tt> count      </tt></td><td> number of items in input
   *                                        buffer </tr>
   * <tr><td><tt> datatype   </tt></td><td> data type of each item in input
   *                                        buffer </tr>
   * <tr><td><tt> op         </tt></td><td> reduce operation </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_SCAN</tt>.
   */

  public void Scan(Object sendbuf, int sendoffset,
                   Object recvbuf, int recvoffset, int count,
                   Datatype datatype, Op op) throws MPIException {

    if (op.isUser()){
      if (Rank() == 0)
        copyBuffer(sendbuf,sendoffset,count,datatype,
                        recvbuf,recvoffset,count,datatype);
      else{
        shadow.Recv(recvbuf, recvoffset, count, datatype, Rank() - 1, 0);

        op.Call(sendbuf, sendoffset, recvbuf, recvoffset, count, datatype);
      }
      if (Rank() < Size() - 1) 
        shadow.Send(recvbuf, recvoffset, count, datatype, Rank() + 1, 0);
    }
    else
      scan(sendbuf, sendoffset, recvbuf, recvoffset, count, datatype, op);
  }

  private native void scan(Object sendbuf, int sendoffset, 
                           Object recvbuf, int recvoffset, int count,
                           Datatype datatype, Op op) ;

  // Topology Constructors

  /**
   * Create a Cartesian topology communicator whose group is a subset
   * of the group of this communicator.
   * <p>
   * <table>
   * <tr><td><tt> dims     </tt></td><td> the number of processes in each
   *                                      dimension </tr>
   * <tr><td><tt> periods  </tt></td><td> <tt>true</tt> if grid is periodic,
   *                                      <tt>false</tt> if not, in each
   *                                      dimension </tr>
   * <tr><td><tt> reorder  </tt></td><td> <tt>true</tt> if ranking may be
   *                                      reordered, <tt>false</tt> if not </tr>
   * <tr><td><em> returns: </em></td><td> new Cartesian topology
   *                                      communicator </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_CART_CREATE</tt>.
   * <p>
   * The number of dimensions of the Cartesian grid is taken to be the size
   * of the <tt>dims</tt> argument.  The array <tt>periods</tt> must be the
   * same size.
   */

  public Cartcomm Create_cart(int [] dims, boolean [] periods, 
	                      boolean reorder) throws MPIException {
    long cartHandle = GetCart(dims, periods, reorder) ;
    if(cartHandle == nullHandle)
      return null ;
    else
      return new Cartcomm(cartHandle) ;
  }

  private native long GetCart(int [] dims, boolean [] periods,
                              boolean reorder) ;

  /**
   * Create a graph topology communicator whose group is a subset
   * of the group of this communicator.
   * <p>
   * <table>
   * <tr><td><tt> index    </tt></td><td> node degrees </tr>
   * <tr><td><tt> edges    </tt></td><td> graph edges </tr>
   * <tr><td><tt> reorder  </tt></td><td> <tt>true</tt> if ranking may be
   *                                      reordered, <tt>false</tt> if not </tr>
   * <tr><td><em> returns: </em></td><td> new graph topology communicator </tr>
   * </table>
   * <p>
   * Java binding of the MPI operation <tt>MPI_GRAPH_CREATE</tt>.
   * <p>
   * The number of nodes in the graph, <em>nnodes</em>, is taken
   * to be size of the <tt>index</tt> argument.  The size of array
   * <tt>edges</tt> must be <tt>index [nnodes} - 1]</tt>.
   */

  public Graphcomm Create_graph(int [] index, int [] edges, boolean reorder)
                                                         throws MPIException {
    long graphHandle = GetGraph(index,edges,reorder) ;
    if(graphHandle == nullHandle)
      return null ;
    else
      return new Graphcomm(graphHandle) ;
  }

  private native long GetGraph(int [] index,int [] edges, boolean reorder);

  private Comm shadow ;  // Used by non-native collectives.
}


// Things to do
//