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       MPI_Comm_join -  Connect two MPI processed joined by a socket


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


       fd     - socket file descriptor


              - intercommunicator with client as remote group


       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.


       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.

       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);
       if (fd < 0)
       MPI_Abort(MPI_COMM_WORLD, 0);
       MPI_Comm_join(fd, &intercomm);
       return intercomm;


       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


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


       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.
              - No error; MPI routine completed successfully.
              - 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.
              - An internal error has been detected.  This is  fatal.   Please
              send  a  bug report to the LAM mailing list (see http://www.lam-
              - Other error; use  MPI_Error_string  to  get  more  information
              about this error code.


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


       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).