5.6.1 Inter-communicator Accessors



MPI_COMM_TEST_INTER(comm, flag)

IN
comm communicator (handle)
OUT
flag (logical)

int MPI_Comm_test_inter(MPI_Comm comm, int *flag)



MPI_COMM_TEST_INTER(COMM, FLAG, IERROR)
INTEGER COMM, IERROR
LOGICAL FLAG



This local routine allows the calling process to determine if a communicator is an inter-communicator or an intra-communicator. It returns true if it is an inter-communicator, otherwise false.

When an inter-communicator is used as an input argument to the communicator accessors described above under intra-communication, the following table describes behavior.



MPI_COMM_* Function Behavior
(in Inter-Communication Mode)
MPI_COMM_SIZE returns the size of the local group.
MPI_COMM_GROUP returns the local group.
MPI_COMM_RANK returns the rank in the local group
Furthermore, the operation MPI_COMM_COMPARE is valid for inter-communicators. Both communicators must be either intra- or inter-communicators, or else MPI_UNEQUAL results. Both corresponding local and remote groups must compare correctly to get the results MPI_CONGRUENT and MPI_SIMILAR. In particular, it is possible for MPI_SIMILAR to result because either the local or remote groups were similar but not identical.

The following accessors provide consistent access to the remote group of an inter-communicator:

The following are all local operations.



MPI_COMM_REMOTE_SIZE(comm, size)

IN
comm inter-communicator (handle)
OUT
size number of processes in the remote group of comm (integer)

int MPI_Comm_remote_size(MPI_Comm comm, int *size)



MPI_COMM_REMOTE_SIZE(COMM, SIZE, IERROR)
INTEGER COMM, SIZE, IERROR





MPI_COMM_REMOTE_GROUP(comm, group)

IN
comm inter-communicator (handle)
OUT
group remote group corresponding to comm (handle)

int MPI_Comm_remote_group(MPI_Comm comm, MPI_Group *group)



MPI_COMM_REMOTE_GROUP(COMM, GROUP, IERROR)
INTEGER COMM, GROUP, IERROR



Rationale. Symmetric access to both the local and remote groups of an inter-communicator is important, so this function, as well as MPI_COMM_REMOTE_SIZE have been provided.(End of rationale.)

MPI-Standard for MARMOT