[mpiwg-sessions] MPI sessions and MPI T

[Pritchard Jr., Howard]

Hi Folks,

I finally got around to a to-do item for the MPI sessions WG.  I’d said
I’d look through the MPI_T portion of the tools chapter of the standard
and see what consequences the MPI Sessions concept would have on that
section.

I came up with the following short list:

  *   terminology collision.  For performance variables, there is an MPI_T_pvar_session construct.  However, it seems to me this is sufficiently distinct from what we’re proposing for sessions that there should not be an issue.
  *   MPI_T_CVAR_GET_INFO   and MPI_T_CVAR_HANDLE_ALLOC.  These have a handle to a MPI object argument.  It is legal to pass MPI COMM WORLD/COMM SELF in as the argument.  So we’d need to figure out how to handle these cases in the context of an application that doesn’t explicitly call MPI_INIT or one of the other MPI functions that, according to our proposal, has the side effect of creating MPI_COMM_WORLD/SELF.  One option might be to return MPI_ T_ ERR_ CVAR_ SET_ NOT_ NOW error code.
  *   A similar problem exists for MPI_T_PVAR_GET_INFO and MPI_T_PVAR_HANDLE_ALLOC.  Curiously, there is no analogous MPI_T_ERR_PVAR_SET_NOT_NOW error code.

That’s what I came up with for first order items that would be impacted by Sessions, beyond minor languages changes in the text to indicate, for instance, that a Session handle could be passed to MPI_T_CVAR_HANDLE_ALLOC, etc.

Howard


--
Howard Pritchard
HPC-DES
Los Alamos National Laboratory

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