[petsc-dev] PetscOptionsBegin etc all use global variables

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:
>     I don’t see how you are going to manage making them optional but
>     allowing them to be passed around (since C has no optional
>     arguments). If we want that route then I think we need to bit the
>     bullet and just attach a PetscOptions thing to a PetscObject and
>     if it has one it uses it to look for options, otherwise it looks
>     in the “global” one. I don’t see how some PETSc routines can take
>     a PetscOptions argument and others don’t.

I was thinking of making an entire set of functions that take an
explicit argument, then implementing the current interface in terms of
those (getting the thread-local object and passing it in).  The idea is
to allow people to use the current interface because it's convenient,
while moving PETSc's own implementation to explicitly pass the options
object.

It's certainly not a trivial amount of work, but if we have to overhaul
it anyway, I'd be in favor of providing an interface where the database
is an explicit parameter.

The more disrupting thing would be to change all the functions to take
an explicit argument, but allow NULL, which means "get it from
thread-local".  That would require changing all existing code and
creates one more argument to keep track of.
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