RE: [RFC 2/3] gdb: wait for inferior after attaching instead of adding a continuation

["Aktemur, Tankut Baris" <tankut.baris.aktemur@intel.com>]

On Friday, April 19, 2024 10:33 PM, Tom Tromey wrote:
> >>>>> "Tankut" == Tankut Baris Aktemur <tankut.baris.aktemur@intel.com> writes:
> 
> Tankut> In a less harmful case, the current implementation causes an unnatural
> Tankut> positioning of the GDB prompt in a single target setting when
> Tankut> executing the attach command in async mode using the '&' operator.
> 
> I'd prefer Pedro review this, since he's the infrun expert, but I was
> curious about this point -- it seems to me that "attach &" should be
> expected not to wait.
> 
> So maybe the issue is that somehow a continuation is being run for the
> wrong inferior?  Like in this part of the final patch:
> 
> -      /* Do all continuations associated with the whole inferior (not
> -	 a particular thread).  */
> -      if (inferior_ptid != null_ptid)
> -	current_inferior ()->do_all_continuations ();
> 
> ... do inferior_ptid and current_inferior disagree here?
> Or else why does this code get invoked?
> 
> Tom

In the "attach &" example, there is only one inferior, actually.  So, there
is no mismatch between inferior_ptid and current_inferior.  Here is a timeline
of important events:

 - the "attach &" command starts executing.
 - target's "attach" op is invoked.
 - GDB sends a stop request to the target.
 - the inferior is added a continuation.
 - the attach command is done, we'll go back to the event loop.
   -> because we're in async mode (&), the GDB prompt is displayed.
 - the event corresponding to the stop request is received and handled.
 - when the stop event's handling is complete, the continuation is invoked.

I'd think that a reasonable question is "why does GDB send a stop request
to the target in async (&) mode?"  I believe that's the behavior in both
sync and async cases so that GDB can finish setting up the inferior properly
(in attach_post_wait).

-Baris


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