From: Tom de Vries <tdevries@suse.de>
To: Tom Tromey <tom@tromey.com>
Cc: gdb-patches@sourceware.org
Subject: Re: [PATCH 2/2] [gdb/dap] Fix stray KeyboardInterrupt after cancel
Date: Mon, 26 Feb 2024 13:24:36 +0100 [thread overview]
Message-ID: <4d3ad0ce-81a1-478b-ba8c-62199912997c@suse.de> (raw)
In-Reply-To: <87jzmvxf9y.fsf@tromey.com>
On 2/23/24 18:27, Tom Tromey wrote:
>>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:
>
> Tom> The idea is that this interrupt triggers while in fn here in message (a nested
> Tom> function of send_gdb_with_response):
> Tom> ...
> Tom> def message():
> Tom> try:
> Tom> val = fn()
> Tom> result_q.put(val)
> Tom> except (Exception, KeyboardInterrupt) as e:
> Tom> result_q.put(e)
> Tom> ...
> Tom> but instead it triggers outside the try/except.
>
> Thanks for the clear explanation.
>
> Tom> I left the two "sleep 0.2" in the test-case, I didn't see a reason to remove
> Tom> those.
>
> Those are there to try to make the test actually interrupt the command
> in question -- removing them would make it more likely to just interrupt
> the surrounding dispatch machinery, which isn't interesting.
>
Posted v2 here (
https://sourceware.org/pipermail/gdb-patches/2024-February/206821.html ).
Ack, dropped that bit in the commit message in v2.
> Tom> @@ -435,12 +466,19 @@ def send_gdb_with_response(fn):
>
> It seems to me that send_gdb also has this issue -- that is, the
> cancellation could arrive just in time to cause a KeyboardInterrupt.
>
Fixed in v2 (though I'm not sure if there's a test-case exercising this).
> Also I wonder how multi-step / DAP-thread commands like 'continue' are
> handled.
>
I think that should be handled in v2.
> Tom> def message():
> Tom> try:
> Tom> - val = fn()
> Tom> + if not _server.canceller.enter_interruptable():
> Tom> + raise KeyboardInterrupt()
> Tom> + try:
> Tom> + val = fn()
> Tom> + finally:
> Tom> + _server.canceller.exit_interruptable()
>
> This kind of thing is better with a context manager.
>
Indeed, used that in v2.
> Tom> send_gdb(message)
> Tom> + if _server.canceller.is_cancel_pending():
> Tom> + result_q.put(KeyboardInterrupt())
> Tom> val = result_q.get()
>
> I don't understand how this addition has an effect. It seems to me that
> since a Queue is FIFO, and since the response Queue is only used for a
> single value, that this addition will just be ignored.
>
Agreed, it's unnecessary. Dropped in v2.
> FWIW, cancellation is inherently racy. I'm not opposed to trying to
> make this more reliable but I think it may be pretty hard.
>
> Maybe some kind of installable exception handler that is run when
> post_event fails would be one way. Not sure.
Not sure either. Anyway I hope v2 is an improvement.
Thanks,
- Tom
prev parent reply other threads:[~2024-02-26 12:24 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-23 16:51 [PATCH 1/2] [gdb/dap] Move send_gdb_with_response to server module Tom de Vries
2024-02-23 16:51 ` [PATCH 2/2] [gdb/dap] Fix stray KeyboardInterrupt after cancel Tom de Vries
2024-02-23 17:27 ` Tom Tromey
2024-02-26 12:24 ` Tom de Vries [this message]
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