NAME

       MPI_Comm_join - Establishes communication between MPI jobs

SYNTAX

C Syntax

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

Fortran Syntax

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_COMM_JOIN(FD, INTERCOMM, IERROR)
            INTEGER   FD, INTERCOMM, IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Comm_join(fd, intercomm, ierror)
            INTEGER, INTENT(IN) :: fd
            TYPE(MPI_Comm), INTENT(OUT) :: intercomm
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror

C++ Syntax

       #include <mpi.h>
       MPI::Intercomm MPI::Comm::Join(const int fd)

INPUT PARAMETER

       fd        socket file descriptor (socket).

OUTPUT PARAMETERS

       intercomm Intercommunicator between processes (handle).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       MPI_Comm_join  creates  an  intercommunicator from the union of two MPI processes that are
       connected by a socket. fd is a file descriptor representing a socket of  type  SOCK_STREAM
       (a two-way reliable byte-stream connection). Nonblocking I/O and asynchronous notification
       via SIGIO must not be enabled for the socket. The socket must be in a connected state, and
       must be quiescent when MPI_Comm_join is called.

       MPI_Comm_join  must be called by the process at each end of the socket. It does not return
       until both processes have called MPI_Comm_join.

NOTES

       There are no MPI library calls for opening and manipulating a socket.  The socket  fd  can
       be  opened  using standard socket API calls.  MPI uses the socket to bootstrap creation of
       the intercommunicator, and for nothing else. Upon return, the file descriptor will be open
       and quiescent.

       In  a  multithreaded process, the application must ensure that other threads do not access
       the socket while one is in the midst of calling MPI_Comm_join.

       The returned communicator will contain the two processes connected by the socket, and  may
       be  used  to  establish MPI communication with additional processes, through the usual MPI
       communicator-creation mechanisms.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran  routines in the last argument. C++ functions do not return errors. If the default
       error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then  on  error  the  C++  exception
       mechanism will be used to throw an MPI::Exception object.

       Before  the  error value is returned, the current MPI error handler is called. By default,
       this error handler aborts the MPI job, except for I/O function errors. The  error  handler
       may    be   changed   with   MPI_Comm_set_errhandler;   the   predefined   error   handler
       MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not
       guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

SEE ALSO

       socket(3SOCKET)
       MPI_Comm_create
       MPI_Comm_group