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MPIL_Comm_gps(3)                    LAM/MPI                   MPIL_Comm_gps(3)


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)


INPUT PARAMETERS

       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

LAM/MPI 7.1.5b2                    6/24/2006                  MPIL_Comm_gps(3)

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