Re: [PATCH:MI] Use observers for breakpoints

[Nick Roberts <nickrob@snap.net.nz>]

 > > Following Aleksandar Ristovski's patch for catchpoints in GDB/MI,
 > > here's a patch to demonstrate the use of observers for breakpoints.
 > > This relates to earlier patches I've submitted which uses event
 > > notification to communicate a change in state rather than using
 > > command output directly.  Among other things this allows the use of
 > > CLI commands with MI.
 > 
 > I missed the earlier patch, but I think that the idea is sound.

Here's one reference:

http://sourceware.org/ml/gdb-patches/2008-04/msg00377.html

Like Daniel says, the frame-changed notification would probably fire too often,
but the thread-changed one still seems a good idea and I have submitted a patch
to do this with annotations too:

http://sourceware.org/ml/gdb-patches/2008-05/msg00611.html


 > I suggest you change the observer profile to take a breakpoint
 > rather than a breakpoint number, to avoid having going from
 > the breakpoint number back to the breakpoint itself should an
 > observer need it.

My observer just uses a function called breakpoint_query (based on
gdb_breakpoint_query) which only needs the breakpoint number.  I
think this is an internal detail which could easily be changed should
the need arise.


 > I'm wondering if it might be useful to create two specific events
 > for breakpoint created and deleted. Particularly for the "deleted"
 > event, where you end up outputing the entire description of a breakpoint
 > that is obsolete.

Sure, it's just a sketch.  There are three types of event:

breakpoint_create_event
breakpoint_modify_event
breakpoint_delete_event

I don't know if there's much to be gained in differentiating between
creating and modifying a breakpoint but it would certainly make sense
to have two observers, breakpoints_changed and breakpoints_deleted, say.

If this patch goes in we could start dismantling the events mechanism.  They're
only used in a few other places, e.g, tracepoints, and presumably observers
could be used there too.


 > Just as an aside, I don't know how others would feel about that,
 > but I wouldn't mind seeing annotate.c:breakpoints_changed being
 > renamed to annotate_breakpoints_changed.

This function was moved from breakpoint.c.  A couple of years ago I submitted
a patch to remove this and some other annotations, just keeping the level
three annotations.  If we are going to keep it, I suggest calling it
annotate_breakpoints_invalid after the name of the associated annotation
and to be consistent with annotate_frames_invalid.

-- 
Nick                                           http://www.inet.net.nz/~nickrob