[mpiwg-ft] MPI_Comm_call_errhandler

[Jim Dinan]

Hi FT Folks,

I encountered this oddity while doing some hacking today.  Apparently,
MPI_ERRORS_RETURN has a different signature from all other error handlers;
it returns a value and all other error handlers (e.g. MPI_ERRORS_ARE_FATAL
and user-defined error handlers) have void return:

typedef void MPI_Comm_errhandler_function(MPI_Comm *, int *, ...);

Because of this, MPI_Comm_call_errhandler effectively does not do anything
when the error handler is set to MPI_ERRORS_RETURN.  More specifically, the
following code,

return MPI_Comm_call_errhandler(my_comm, my_err_code);

always returns success.

To summarize the issues: (1) It is difficult or impossible to use the MPI
error subsystem when the error handler is set to MPI_ERRORS_RETURN and (2)
it is impossible for a user defined error handler to return an error code.
These difficulties seem like they could be troublesome to users of FT that
want to create higher level resilience/resilient libraries that interact
with the MPI errors subsystem.

Is what I have encountered a real issue or am I misunderstanding
something?  If it is a real issue, is it something we queue up for
discussion at the upcoming F2F?

Interested to hear your thoughts,
 ~Jim.
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