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Re: [RFA] Make continuations per-thread.
- From: Pedro Alves <pedro at codesourcery dot com>
- To: Vladimir Prus <vladimir at codesourcery dot com>
- Cc: Daniel Jacobowitz <drow at false dot org>, gdb-patches at sourceware dot org
- Date: Fri, 2 May 2008 14:45:51 +0100
- Subject: Re: [RFA] Make continuations per-thread.
- References: <200804242045.39246.vladimir@codesourcery.com> <20080502132337.GA29202@caradoc.them.org> <200805021730.33831.vladimir@codesourcery.com>
A Friday 02 May 2008 14:30:32, Vladimir Prus escreveu:
> On Friday 02 May 2008 17:23:37 Daniel Jacobowitz wrote:
> > On Fri, May 02, 2008 at 12:34:11PM +0100, Pedro Alves wrote:
> > > to not make it centralized. This is one of the things that gets much
> > > better looking when we switch completelly to always-a-thread, and
> > > get rid of context-switching. I'm introducing another variable,
> > > instead of
> >
> > So maybe we should do that in the FSF tree before the attached patch -
> > is that feasible?
> >
> > On Fri, May 02, 2008 at 03:51:10PM +0400, Vladimir Prus wrote:
> > > This is only for intermediate continations. For ordinary continuations,
> > > not running them when we hit a breakpoint in another thread is
> > > desirable. Why should a breakpoint in some other thread abort "finish"?
> > > Note that in current gdb, hitting a breakpoint in unrelated thread does
> > > not abort "next" -- say we did next, inserted step resume breakpoint,
> > > and then hit breakpoint in some other thread. Then, the step resume
> > > breakpoint will not be removed. If we decide to continue the program,
> > > we'll eventually hit it.
> > >
> > > I don't see any problem with continuations been kept for a given thread
> > > for a long time. It's not an unbounded amount of continuations -- if we
> > > get an event in this thread, continuation will run, and if we don't get
> > > an event, we won't add any futher continuations.
> >
> > In non-stop mode, the continuation will run the first time that thread
> > stops because threads only stop when there is an event. But in
> > all-stop mode the thread will be stopped with its continuations not
> > yet run.
> >
> > [Current thread is 1]
> > finish
> > [Switching to thread 2]
> > Breakpoint at....
> > thread 1
> > finish
> >
> > Now thread 1 has two finish continuations and they're at different
> > threads... is it going to do something sensible? What's sensible?
>
Yes, this seems like a problem. The second finish command installs
the continuations in the last even thread. In non-stop, this is
fixed by making the thread command context_switch instead of just
switch_to_thread. Maybe that should be done in all-stop too?
We'd context-switch to the last event thread when resuming, so
the right context is set to step over breakpoints etc.
Then the question would be:
Now thread 1 has two finish continuations in the queue. Shouldn't
the previous one be canceled?
> I think the sensible behaviour is the same as for "next" -- abort
> whatever the operation we were doing. This means that we have to wipe
> continuation inside 'proceed'. I can adjust the patch this way, but
> does it make sense to you?
>
Isn't that too late? When you get to proceed, the new finish
continuation is already installed.
--
Pedro Alves