MPI_Intercomm_create(3) MPI MPI_Intercomm_create(3)NAMEMPI_Intercomm_create - Creates an intercommuncator from two intracom‐
municators
SYNOPSIS
int MPI_Intercomm_create(MPI_Comm local_comm, int local_leader,
MPI_Comm peer_comm, int remote_leader, int tag,
MPI_Comm *newintercomm)
INPUT PARAMETERS
local_comm
- Local (intra)communicator
local_leader
- Rank in local_comm of leader (often 0)
peer_comm
- Communicator used to communicate between a designated process
in the other communicator. Significant only at the process in
local_comm with rank local_leader .
remote_leader
- Rank in peer_comm of remote leader (often 0)
tag - Message tag to use in constructing intercommunicator; if mul‐
tiple MPI_Intercomm_creates are being made, they should use dif‐
ferent tags (more precisely, ensure that the local and remote
leaders are using different tags for each MPI_intercomm_create
).
OUTPUT PARAMETER
comm_out
- Created intercommunicator
NOTES
peer_comm is significant only for the process designated the
local_leader in the local_comm .
The MPI 1.1 Standard contains two mutually exclusive comments on the
input intercommunicators. 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 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.
THREAD AND INTERRUPT SAFETY
This routine is thread-safe. This means that this routine may be
safely used by multiple threads without the need for any user-provided
thread locks. However, the routine is not interrupt safe. Typically,
this is due to the use of memory allocation routines such as malloc or
other non-MPICH runtime routines that are themselves not interrupt-
safe.
NOTES FOR FORTRAN
All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have
an additional argument ierr at the end of the argument list. ierr is
an integer and has the same meaning as the return value of the routine
in C. In Fortran, MPI routines are subroutines, and are invoked with
the call statement.
All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in
Fortran.
ERRORS
All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error
value; C routines as the value of the function and Fortran routines in
the last argument. Before the value is returned, the current MPI error
handler is called. By default, this error handler aborts the MPI job.
The error handler may be changed with MPI_Comm_set_errhandler (for com‐
municators), MPI_File_set_errhandler (for files), and
MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine
MPI_Errhandler_set may be used but its use is deprecated. The prede‐
fined error handler MPI_ERRORS_RETURN may be used to cause error values
to be returned. Note that MPI does not guarentee that an MPI program
can continue past an error; however, MPI implementations will attempt
to continue whenever possible.
MPI_SUCCESS
- No error; MPI routine completed successfully.
MPI_ERR_COMM
- Invalid communicator. A common error is to use a null commu‐
nicator in a call (not even allowed in MPI_Comm_rank ).
MPI_ERR_TAG
- Invalid tag argument. Tags must be non-negative; tags in a
receive ( MPI_Recv , MPI_Irecv , MPI_Sendrecv , etc.) may also
be MPI_ANY_TAG . The largest tag value is available through the
the attribute MPI_TAG_UB .
MPI_ERR_INTERN
- This error is returned when some part of the MPICH implementa‐
tion is unable to acquire memory.
MPI_ERR_RANK
- Invalid source or destination rank. Ranks must be between
zero and the size of the communicator minus one; ranks in a
receive ( MPI_Recv , MPI_Irecv , MPI_Sendrecv , etc.) may also
be MPI_ANY_SOURCE .
SEE ALSO
MPI_Intercomm_merge, MPI_Comm_free, MPI_Comm_remote_group,
MPI_Comm_remote_size
LOCATION
src/mpi/comm/intercomm_create.c
9/20/2012 MPI_Intercomm_create(3)
