NAME¶
MPIL_Comm_gps - LAM/MPI-specific function to return the GPS information of a
given rank from a communicator
SYNOPSIS¶
#include <mpi.h>
int MPIL_Comm_gps(MPI_Comm comm, int rank, int *pnid,
int *ppid)
- comm
- - communicator (handle)
- rank
- - rank of process to query (integer)
OUTPUT PARAMETERS¶
- pnid
- - LAM node ID
- ppid
- - LAM process ID
NOTES¶
In the LAM implementation of MPI, each communicator has an integer context ID
associated with it for synchronizing on different contexts. This ID is global
to all the processes in the communicator's group, and uniquely identifies that
communicator for each process. These properties allow the processes to safely
exchange messages without interference from operations on other communicators.
The MPI standard does not provide a way to access/view this
implementation-dependent synchronization since communicators are opaque
objects. Users do not need such access for normal MPI operations. On the other
hand, when debugging MPI applications, the opaque nature of communicators
hinders the user's efforts. This is especially true on fully observable
systems such as LAM, where users can monitor the full state of the processes
and message queues, which includes the context ID (see
mpitask (1) and
mpimsg (1)).
LAM supplementary functions do not operate with communicators and ranks but with
nodes and process identifiers.
MPIL_Comm_gps accepts the MPI values and
returns the LAM values. In the case of an intercommunicator the values
returned are those of the process with the given rank in the remote group.
This is a LAM/MPI-specific function and is intended mainly for debugging. If
this function is used, it should be used in conjunction with the
LAM_MPI C preprocessor macro
#if LAM_MPI
int nid, pid;
MPIL_Comm_gps(MPI_COMM_WORLD, 0, &nid, &pid);
#endif
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¶
If an error occurs in an MPI function, the current MPI error handler is called
to handle it. By default, this error handler aborts the MPI job. The error
handler may be changed with
MPI_Errhandler_set ; the predefined error
handler
MPI_ERRORS_RETURN may be used to cause error values to be
returned (in C and Fortran; this error handler is less useful in with the C++
MPI bindings. The predefined error handler
MPI::ERRORS_THROW_EXCEPTIONS
should be used in C++ if the error value needs to be recovered). Note that MPI
does
not guarantee that an MPI program can continue past an error.
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. The C++ bindings for MPI do not return error values; instead,
error values are communicated by throwing exceptions of type
MPI::Exception (but not by default). Exceptions are only thrown if the
error value is not
MPI::SUCCESS .
Note that if the
MPI::ERRORS_RETURN handler is set in C++, while MPI
functions will return upon an error, there will be no way to recover what the
actual error value was.
- MPI_SUCCESS
- - No error; MPI routine completed successfully.
- MPI_ERR_COMM
- - Invalid communicator. A common error is to use a null communicator in a
call (not even allowed in MPI_Comm_rank ).
- 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 .
- MPI_ERR_ARG
- - Invalid argument. Some argument is invalid and is not identified by a
specific error class. This is typically a NULL pointer or other such
error.
SEE ALSO¶
MPIL_Comm_id, MPIL_Type_id
LOCATION¶
mpil_id.c