Re: [MI] Synchronous event notification

[Andrew Cagney <ac131313 at cygnus dot com>]

(I had to go and read over some old notes).


> I've been working on integrating Apple's "-interpreter-exec" changes, and
> I wanted to see if I could get some sort of consensus on how event
> notifications should be defined.
> 
> In the trunk right now, MI ignores event notifications. Adding a mechanism
> is vital to the success of MI.
> 
> Apple has added this, and all event notifications are tacked onto the
> mi-command result:
> 
>   (gdb)
>   -interpreter-exec console "break main"
>   Breakpoint 1 at ...
>   ^done,MI_HOOK_RESULT=[HOOK_TYPE="breakpoint_create",bkpt={number="1",...}]

Looking at the old notes, I think the intent was:

(gdb)
-interpreter-exec console "break main"
&"Breakpoint 1 at ..."
*breakpoint-create,pkpt={number="1',...}
^done

The actual example I found was:

> Command with side effects:
> -> -symbol-file xyz.exe
> <- *breakpoint nr=3 address=0x123 source=a.c:123
> <- (gdb)

It is a really old example and you can see how the syntax evolved :-)

> Right now, this is done by defining a bunch of (existing) hooks when mi
> runs. I presume that we want to switch over to using gdb-events, hoping
> one day to deprecate the hooks, but that's not really the issue (since
> they behave essentially the same in non-asynch).

Yes, they are essentially the same.  The gdb-events just tries to 
collect everything together.  The idea being that, for instance, several 
things could ``observe'' GDB.  However, it might just be over-engineering.

> The real question is, how
> do maintainers want this information communicated to mi clients?

> The example above shows that Apple has added a syntax like:
> 
>   result ==>
>      stuff [ "," event-list ]
>   event-list ==>
>      "MI_HOOK_RESULT=[" event ( "," event )* "]"
>   event ==>
>      "HOOK_TYPE=" event-name [ event-data ]
>   event-name ==>
>      "breakpoint_create" | "breakpoint_delete" | ...
> 
> and such.
> 
> Since hooks are really just event notifications, I would like to propose
> that we use a definition like the above, but changing the string literals
> a litte:
> 
>   event-list ==>
>     "events=[" event ( "," event )* "]"
>   event ==>
>     "name=" event-name [ event-data ]
>   event-name ==>
>     "breakpoint_create" | "breakpoint_delete" | ...

So:

^done,result=...,events=...

So that, for a ``synchronous'' command the events just get bundled with 
the result.  Sounds ok, definitly has a certain elegance - here is the 
result, here are all the sideeffects.

One question, what about a more asynchronous operation?  A running 
target starts loading shared libraries, inserting breakpoints, running 
scripts, et.al.  There the synchronous nature is gone.  I guess:

- notify of all the events when the target next ``stops''

- notify the events on-the-fly (possibly incuring an overhead?)

Andrew


> Please discuss.
> Keith