On Wednesday, October 2, 2002, at 08:01 AM, Keith Seitz wrote:
On Tue, 1 Oct 2002, Jim Ingham wrote:
I don't want a tight coupling in TIME, or in the output sequence. I
want meta-info which tells me with 100% certainty that this result is
the result of command foo, that I sent some time in the past, precisely
so I DON'T have to rely on anything about the sequencing of input or
output to make this connection.
Ok, but this is exactly what I don't understand: what does it matter where
the breakpoint comes from? All that matters is that you have issued a
command, and you don't do anything out of the normaluntil an event from
GDB telling you that it has set a breakpoint. You just sit in your event
loop waiting for any event (GUI, paint, GDB, blah blah blah).
In large part, it is just that if I can track cause & effect unambiguously, everything is much cleaner. From PB, I issue a command, I want to tick off when that command succeeded, and gather all the data from the result I need. If I get a note back from gdb saying, "The third command down in the command stream that you issued, here is the result to it." then I can do this without any effort. However, in your proposed implementation, I have to peer at the command stream and wait both for an anonymous breakpoint created message, and a for the done message (to know things are formally done, and because it would be very dangerous to just toss aside bits of the output stream, since it reduces your chances of catching & handling errors intelligently.) Then I have to use some smarts to tie the breakpoint created message to the particular message I sent to gdb. This is harder to do, and fragile.
In my mind, one of the major advantages of the MI was that it made this tie between the command you sent and the result that came from it explicit and unambiguous. This was in response to a lot of the pain that we suffered in insight where any random spew from the command line would get itself inserted into the "results" of the command you thought you were executing. You are breaking this tie by moving the results of a command from the command result to an untagged asynchronous event. For breakpoints, this is probably just an inconvenience. But if we follow this as a principle, then in more complex cases, where it is not so easy to tell whether an asynchronous notification arose from a command initiated by the MI, or from some other action we will likely start getting confused again. For instance, we might have something happening in the target, or some console command, or something more gnarly like the results of a breakpoint command which also continued the target wh
ile you thought it was just running...