MPI_Intercomm_create(3OpenMPI) MPI_Intercomm_create(3OpenMPI)
NAME
MPI_Intercomm_create - Creates an intercommuncator from two intracommunicators.
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
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
C++ Syntax
#include <mpi.h>
Intercomm Intracomm::Create_intercomm(int local_leader, const
Comm& peer_comm, int remote_leader, int tag) const
INPUT PARAMTERS
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_inter-comm_create). MPI_intercomm_create).
comm_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 repective 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 dis-joint. disjoint.
joint. 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 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 ALSO
MPI_Intercomm_merge
MPI_Comm_free
MPI_Comm_remote_group
MPI_Comm_remote_size
Open MPI 1.2 September 2006 MPI_Intercomm_create(3OpenMPI)
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