Re: Python and structured output from breakpoint_ops

[Pedro Alves <pedro at codesourcery dot com>]

On Monday 10 October 2011 10:22:20, Phil Muldoon wrote:
> Pedro Alves <pedro@codesourcery.com> writes:
> 
> > I still think we should cleanup the breakpoint printing machinery before
> > exporting it to python.  These methods were not converted to
> > breakpoint_ops yet.  By only considering a single string, you're leaving
> > out breakpoints with multiple locations.  And those will become even more
> > important with Tom's linespec/multi-location rework.
> 
> I've no problem with this as long as we have a plan in place, when we
> think it will be released, etc.  Right now (you) did an excellent
> refactor internally, but what are the future plans?  

The next step is to make breakpoint_ops->print_one work
with regular breakpoints.  print_one_breakpoint / 
print_one_breakpoint_location were never converted to breakpoint_ops.
This is not a case of the internal abstractions being too
detailed/internal to want to expose to python.  Rather it's a case
of the internal abstraction not being good even for GDBs own internals!
If we fix this (pick print_one_breakpoint / print_one_breakpoint_location
apart in a way that the core breakpoint print code doesn't know about
specific breakpoint types), then you win a good python abstraction
as a co/by-product. IOW, or from a different angle, if you come up with
a nice python abstraction for this, there's no reason that the core
wouldn't want the same nice abstraction too.  But only by cleaning up
the core can you know you _have_ a good abstraction.

> When do we plan to have them in place?  The usual tricky question ;)

Ah, if days had infinite hours... :-)  I don't have time presently
to work on that myself until next January.

> I guess I am asking what you mean by clean-ups in this context?  

See above.

> >> It seems like it could have multiple lines, just nothing does this yet.
> >
> > Yeah.  Random catchpoints are likely to want it.
> 
> In a deeper context, fully implementing catchpoint creation in Python
> seems quite tricky.  Many of the catchpoint APIs seem to need to know
> about deep internal GDB state.  Do we want to expose those decisions
> coupled with that information externally?  We made a promise with the
> Python API that it will be stable.  I've not really though about this
> too much yet; there might be a clean answer just around the corner.

Catchpoints that I'd find useful to write in python would for example
be things like putting a breakpoint in a special routine in your
special domain specific or embedded OS runtime -- "catch my-special-event".
You'd want to hide the fact that that's implemented by placing a
breakpoint, and the support is all there (I believe).

> >> Phil> In fact, if you look at the mi command -break-list, it just maps
> >> Phil> to info break and captures that output.  Maybe that conversation
> >> Phil> is what Jan was talking about when there is an explicit mention
> >> Phil> that any field change has to be made by Vlad?
> >
> > The thing is that the fields that are output aren't constrained at all
> > by the "address" / "what" columns you see in the CLI.  Look at all
> > the "ui_out_*" calls.  It seems quite reasonable to me to be able to
> > output random fields from python too, so you could implement new
> > breakpoint/catchpoints in python and forward whatever necessary info
> > to the frontend through MI.
> 
> Doing that from Python would be a good idea, I agree.  We could have a
> field:data structure for the user to output whatever they wish, and MI
> could be taught to learn, beyond the usual fields it expects, there are
> "extra" fields: ignore them or print them.  I'm not sure why the
> explicit field creations needs express approval from Vlad.  Are MI
> clients parsing expected only fields? Order of fields?

I'm not really sure I understand what you're asking.

-- 
Pedro Alves