NAME¶
MPI_Intercomm_create - Creates an intercommunicator 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
- 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 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