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MPI_Comm_join.3.rst

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MPI_Comm_join

:ref:`MPI_Comm_join` |mdash| 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

INPUT PARAMETER

  • fd: socket file descriptor (socket).

OUTPUT PARAMETERS

  • intercomm: Intercommunicator between processes (handle).
  • ierror: Fortran only: Error status (integer).

DESCRIPTION

:ref:`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 :ref:`MPI_Comm_join` is called.

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

.. seealso::
   * socket(3SOCKET)
   * :ref:`MPI_Comm_create`
   * :ref:`MPI_Comm_group`