plucky (3) MPI_Comm_join.openmpi.3.gz

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

       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  return  result  of  the  function  and
       Fortran routines in the last argument.

       Before  the  error  value  is  returned,  the current MPI error handler associated with the communication
       object (e.g., communicator, window, file) is called.  If no communication object is associated  with  the
       MPI  call,  then  the call is considered attached to MPI_COMM_SELF and will call the associated MPI error
       handler.  When  MPI_COMM_SELF  is  not  initialized   (i.e.,   before   MPI_Init/MPI_Init_thread,   after
       MPI_Finalize,  or  when using the Sessions Model exclusively) the error raises the initial error handler.
       The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF  when  using
       the  World  model,  or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.  If no other appropriate error handler has been set, then the  MPI_ERRORS_RETURN
       error  handler  is  called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called  on  a  communicator,  it  acts  as if MPI_Abort was called on that communicator. If called on a
         window or file, acts as if MPI_Abort was called on a communicator containing the group of processes  in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

       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 the Error Handling section of the MPI-3.1 standard for more information.

       SEE ALSO:

          • socket(3SOCKET)

          • MPI_Comm_create

          • MPI_Comm_group

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                                  MPI_COMM_JOIN(3)