MPIL_Type_id  -   LAM/MPI-specific  function to return the
       type ID of an MPI datatype


SYNOPSIS

       #include <mpi.h>
       int MPIL_Type_id(MPI_Datatype dtype, int *ptid)


INPUT PARAMETER

       dtype  - MPI datatype (handle)


OUTPUT PARAMETER

       ptid   - datatype ID (integer)


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  pro­
       cesses  in  the communicator's group, and uniquely identi­
       fies 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 commu­
       nicators 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  communi­
       cators  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)).

       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 tid
       MPIL_Type_id(MPI_INT, &tid);
       #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  For­
       tran,  MPI  routines are subroutines, and are invoked with
       the call statement.

       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 val­
       ues to be returned (in C and Fortran; this  error  handler
       is  less  useful in with the C++ MPI bindings.  The prede­
       fined 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++ bind­
       ings 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_TYPE
              - Invalid datatype argument.  May be an uncommitted
              MPI_Datatype (see MPI_Type_commit ).
       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_gps, MPIL_Comm_id


LOCATION

       mpil_id.c


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