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

4.1.6                                             Sep 30, 2023                                  MPI_Comm_join(3)