Re: [PATCH 1/6] new observer command_option_changed.

[Tom Tromey <tromey at redhat dot com>]

>>>>> "Yao" == Yao Qi <yao@codesourcery.com> writes:

Yao> The general goal of my work is that "when the internal state of GDB
Yao> is changed, and MI frontend and/or telnet session is not aware of
Yao> the change, notify them to keep their display up to date".

I'm fully on board with this plan.

Yao> What do you mean by "add a Python hook"?

Sorry, I wasn't clear.

Suppose we want to add a new Python event so that Python code can also
detect parameter changes.  My supposition is that in this case we'd want
to not filter, and just watch them all.

Yao> In terms of bandwidth, every "=option-changed" is sent once user
Yao> types command in console, user can't enter many commands at one
Yao> moment (one command per second and ten commands at most, I think).
Yao> This notification should not occupy much bandwidth.

In that case, why not just report them all?
I agree with your thinking here, that the rate is going to be quite
low.  I'm not sure why I didn't realize that yesterday :)

Reporting them all means simpler code on the gdb side and also lets us
avoid the new set/show constructors.  I don't see a downside.

Tom> What happens in the case where an option has a validation function that
Tom> fails?  IIRC gdb has an internal design flaw here.

Yao> If I understand you correctly, "validation function" means cli/cli-
Yao> setshow.c:parse_binary_operation and cli/cli-
Yao> setshow.c:parse_auto_binary_operation.  When validation fails, an error is 
Yao> thrown out, and observer is not called.

Sorry again for the lack of clarity.

I mean the call to c->func at the end of do_setshow_command.

There are various spots in gdb that use a hidden variable to keep the
"real" setting in case setting the value here fails.

For example, try "set input-radix 1".  This is an error, but I think
with your patch the MI client will see a notification saying that it was
changed to "1".

The design flaw here is that "set" functions do their validation after
the setting has been made, not before.

One approach to this would be to fix this design flaw.  That's likely to
be a lot of work...

Another approach might be to move the observer notification later.

Tom