local_comm - local communicator (handle)
local_leader - rank of leader of local communicator (integer)
peer_comm - communicator usable by leaders (handle)
remote_leader - rank of remote leader in peer communicator (integer)
tag - safe tag to use for communication over peer communicator (integer)
comm - the new intercommunicator (handle).
The MPI_Intercomm_create() function is used to create an intercommunicator comm . This is done by using two different sets of processes. Each set must have a unique local communicator local_comm of which one process is designated as local_leader . The two leaders then communicate over peer_comm to construct an intercommunicator. The leaders use the value of remote_leader and tag to communicate with each other. The resulting intercommunicator is returned in comm .
The C++ version of this function passes the new intercommunicator as the return value.
Note that the local communicator must be valid, and so must the peer communicator at the local leaders (not MPI_COMM_NULL). PMPI_Intercomm_create() is the profiling version of this function.
All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.
In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.
MPI_SUCCESS - No error;
MPI_ERR_PENDING - Pending exception;
MPI_ERR_COMM - Invalid communicator;
MPI_ERR_ARG - Invalid output pointer;
MPI_ERR_RANK - Invalid rank of a leader;
MPI_ERR_TAG - Invalid tag;
MPI_ERR_INTERN - Out of Memory. This may be fatal.
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