plucky (3) MPI_Intercomm_create.openmpi.3.gz

SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_Intercomm_create(MPI_Comm local_comm, int local_leader,
               MPI_Comm peer_comm, int remote_leader, int tag, MPI_Comm *newintercomm)

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_INTERCOMM_CREATE(LOCAL_COMM, LOCAL_LEADER, PEER_COMM,
                       REMOTE_LEADER, TAG, NEWINTERCOMM, IERROR)
               INTEGER LOCAL_COMM, LOCAL_LEADER, PEER_COMM, REMOTE_LEADER
               INTEGER TAG, NEWINTERCOMM, IERROR

   Fortran 2008 Syntax
          USE mpi_f08
          MPI_Intercomm_create(local_comm, local_leader, peer_comm, remote_leader,
                       tag, newintercomm, ierror)
               TYPE(MPI_Comm), INTENT(IN) :: local_comm, peer_comm
               INTEGER, INTENT(IN) :: local_leader, remote_leader, tag
               TYPE(MPI_Comm), INTENT(OUT) :: newintercomm
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

       • local_comm: The communicator containing the process that initiates the inter-communication (handle).

       • local_leader: Rank of local group leader in local_comm (integer).

       • peer_comm: “Peer” communicator; significant only at the local_leader (handle).

       • remote_leader:  Rank  of  remote  group  leader  in  peer_comm;  significant  only  at the local_leader
         (integer).

       • tag: Message tag used to identify new intercommunicator (integer).

OUTPUT PARAMETERS

       • newintercomm: Created intercommunicator (handle).

       • ierror: Fortran only: Error status (integer).

DESCRIPTION

       This call creates an intercommunicator. It is collective over the union of the local and  remote  groups.
       Processes should provide identical local_comm and local_leader arguments within each group. Wildcards are
       not permitted for remote_leader, local_leader, and tag.

       This call uses point-to-point communication with communicator peer_comm, and with  tag  tag  between  the
       leaders.  Thus,  care  must  be  taken  that  there  be  no pending communication on peer_comm that could
       interfere with this communication.

       If multiple MPI_Intercomm_creates are being made, they should use different tags  (more  precisely,  they
       should ensure that the local and remote leaders are using different tags for each MPI_intercomm_create).

NOTES

       We recommend using a dedicated peer communicator, such as a duplicate of MPI_COMM_WORLD, to avoid trouble
       with peer communicators.

       The MPI 1.1 Standard contains two mutually exclusive comments on the input intracommunicators.  One  says
       that  their respective groups must be disjoint; the other that the leaders can be the same process. After
       some discussion by the MPI Forum, it has been decided that the groups must be  disjoint.  Note  that  the
       reason  given for this in the standard is not the reason for this choice; rather, the other operations on
       intercommunicators (like MPI_Intercomm_merge ) do not make sense if the groups are not disjoint.

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:

          • MPI_Intercomm_merge

          • MPI_Comm_free

          • MPI_Comm_remote_group

          • MPI_Comm_remote_size

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                           MPI_INTERCOMM_CREATE(3)