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       MPIL_Comm_id  -   LAM/MPI-specific function to return the context ID of
       the communicator


       #include <mpi.h>
       MPIL_Comm_id(MPI_Comm comm, int *pcid)


       comm   - communicator (handle)


       pcid   - communicator context id (integer)


       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)).

       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 cid;
       MPIL_Comm_id(MPI_COMM_WORLD, &cid);


       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


       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.
              - No error; MPI routine completed successfully.
              - Invalid communicator.   A  common  error  is  to  use  a  null
              communicator in a call (not even allowed in MPI_Comm_rank ).
              -  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.


       MPIL_Comm_gps, MPIL_Type_id