NAME

       MPI_Comm_join -  Connect two MPI processed joined by a socket

SYNOPSIS

       #include <mpi.h>
       int
       MPI_Comm_join(int fd, MPI_Comm *newcomm)

INPUT PARAMETER

       fd     - socket file descriptor

OUTPUT PARAMETER

       newcomm
              - intercommunicator with client as remote group

DESCRIPTION

       This  function  only  works  between two LAM/MPI processes that are connected by a socket.
       They either must have the same endian orientation, or not have used the  homogeneous  flag
       to  mpirun  (1)  (-O).  Both processes must be in a single LAM universe -- they must share
       LAM daemons that are already connected to each other.  That is, they were either initially
       lamboot(1)ed  together,  or a lamgrow(1) command was given to grow an initial LAM universe
       such that the resulting set includes the two hosts in question.

       The socket may not be used by the calling application until MPI_Comm_join  has  completed.
       When  MPI_Comm_join  completes, fd may be used by the calling application.  Per MPI-2, the
       socket is only used for initial handshaking -- it will not be used as  the  communications
       channel between the newly connected processes.

SAMPLE

       The  following  code  shows an abbreviated example using MPI_Comm_join since no example is
       provided in the MPI-2 standard.  Note that only one rank in each  MPI  application  should
       call  this  function  since  each socket can only have two endpoints (i.e., an endpoint in
       each process).  Upon successful completion, the intercommunicator that  is  returned  will
       have two members -- the local process and the remote process.

       MPI_Comm
       do_join(char* server_name, int port) {
       int sfd, fd = -1;
       unsigned char addr[4];
       MPI_Comm intercomm;
       if (server_name != NULL) {
       if (getinetaddr(server_name, &addr) == 0)
       fd = open_socket_to_server(addr, port);
       } else {
       if ((sfd = open_listening_socket(&port)) >= 0) {
       fd = accept_client_socket(sfd, -1);
       close(sfd);
       }
       }
       if (fd < 0)
       MPI_Abort(MPI_COMM_WORLD, 0);
       MPI_Comm_join(fd, &intercomm);
       return intercomm;
       }

NOTES FOR FORTRAN

       All  MPI  routines  in  Fortran  (except  for MPI_WTIME and MPI_WTICK ) have an additional
       argument ierr at the end of the argument list.  ierr  is  an  integer  and  has  the  same
       meaning  as  the  return  value  of  the  routine  in  C.   In  Fortran,  MPI routines are
       subroutines, and are invoked with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.

USAGE WITH IMPI EXTENSIONS

       The IMPI standard only supports MPI-1 functions.  Hence, this function  is  currently  not
       designed to operate within an IMPI job.

ERRORS

       If  an  error occurs in an MPI function, the current MPI error handler is called to handle
       it.  By default, this error handler aborts the MPI job.  The error handler may be  changed
       with  MPI_Errhandler_set  ;  the predefined error handler MPI_ERRORS_RETURN may be used to
       cause error values to be returned (in C and Fortran; this error handler is less useful  in
       with  the  C++  MPI  bindings.   The predefined error handler MPI::ERRORS_THROW_EXCEPTIONS
       should be used in C++ if the error value needs to be recovered).  Note that MPI  does  not
       guarantee that an MPI program can continue past an error.

       All  MPI  routines  (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as
       the value of the function and Fortran routines in the last argument.  The C++ bindings for
       MPI  do  not  return  error  values;  instead,  error  values are communicated by throwing
       exceptions of type MPI::Exception (but not by default).  Exceptions are only thrown if the
       error value is not MPI::SUCCESS .

       Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return
       upon an error, there will be no way to recover what the actual error value was.
       MPI_SUCCESS
              - No error; MPI routine completed successfully.
       MPI_ERR_ARG
              - Invalid argument.  Some argument is invalid and is not identified by  a  specific
              error class.  This is typically a NULL pointer or other such error.
       MPI_ERR_INTERN
              - An internal error has been detected.  This is fatal.  Please send a bug report to
              the LAM mailing list (see http://www.lam-mpi.org/contact.php ).
       MPI_ERR_OTHER
              - Other error; use MPI_Error_string to get more information about this error code.

SEE ALSO

       lamboot(1), lamgrow(1), mpirun(1), MPI_Finalize(3)

MORE INFORMATION

       For more information, please see the official MPI Forum web site, which contains the  text
       of both the MPI-1 and MPI-2 standards.  These documents contain detailed information about
       each MPI function (most of which is not duplicated in these man pages).

       http://www.mpi-forum.org/

LOCATION

       join.c