Re: [PATCH] gdb/python: avoid switching threads for send_packet where possible

[Tom Tromey <tom@tromey.com>]

>>>>> "Andrew" == Andrew Burgess <aburgess@redhat.com> writes:

Andrew> Bug PR gdb/32120 identifies a case where a user tried to write a
Andrew> custom frame unwinder that made use of
Andrew> RemoteTargetConnection.send_packet

Just for the record this seems like a weird and bad choice.

Andrew>   scoped_restore_current_thread restore_thread;
Andrew>   switch_to_target_no_thread (conn->target);

Andrew> The purpose of this is to ensure that the currently selected inferior
Andrew> has the required remote connection pushed on its target stack.  This
Andrew> is necessary because `send_remote_packet` (see remote.c) still relies
Andrew> on global state read from the currently selected inferior.

Andrew> Switching inferior and thread like this, and then switching back
Andrew> thanks to the scoped restore, will flush the frame cache.

...

Andrew> I propose that we special case connpy_send_packet so if the correct
Andrew> inferior is already current then we avoid the switch completely.  This
Andrew> avoids flushing the frame cache, and all the associated problems.

No problem with the patch at all, but I wonder about the logic of
putting this check here and not elsewhere.  Like would we want some sort
of "switch to this inferior and we don't care which thread" -- which
would be a no-op if the inferior is already selected?

Tom