RE: [PATCH 2/4] gdb: remove use of iterate_over_inferiors in mi/mi-interp.c

["Aktemur, Tankut Baris" <tankut dot baris dot aktemur at intel dot com>]

On Thursday, January 16, 2020 4:24 PM, Simon Marchi wrote:
> On 2020-01-16 4:01 a.m., Aktemur, Tankut Baris wrote:
> >> @@ -140,8 +138,22 @@ mi_interp::init (bool top_level)
> >>        /* The initial inferior is created before this function is
> >>  	 called, so we need to report it explicitly.  Use iteration in
> >>  	 case future version of GDB creates more than one inferior
> >> -	 up-front.  */
> >> -      iterate_over_inferiors (report_initial_inferior, mi);
> >> +	 up-front.
> >> +
> >> +         This function is called from mi_interpreter_init, and since
> >
> > There is an 8-spaces/tab issue above.  And also, the comment piece "This
> > function is called from mi_interpreter_init, and" seems obsolete now.
> 
> Thanks for spotting these.
> 
> That made me realize there are many issues with that comment.
> 
> - The part about not being able to use mi_inferior_added because top_level_interpreter_data
>   is not set is stale.  That was true before the interps were made into C++ classes.  Back
>   then, the mi_interpreter_init function would return the pointer to be used as interpreter
>   data, which the caller (the interp_set function) would assign to interp->data.  So it was
>   indeed not possible to call mi_inferior_added, because it required interp->data to be set.
> 
> - It is still not possible today to use mi_inferior_added, because it iterates over all MI UIs
>   and to print the event on all of them.  So if you do:
> 
>   1. Start GDB with `-i mi`
>   2. Add some inferiors
>   3. Create a new MI UI, with `new-ui mi /dev/pts/X`
> 
>   When initializing the new MI UI, it will print the inferior-added events on both MI UIs.
> 
> - It is necessary to use iteration, not only in case GDB creates more than one inferior
>   up front, but also because there might be multiple inferiors when initializing a secondary
>   MI UI, as shown above.
> 
> I don't know if it is by design, that the =inferior-added events are sent to a new MI UI added
> with new-ui, but in any case I don't want to change the behavior with this patch.
> 
> Also, when testing this, I realized it was wrong to put the gdb_flush out of the loop.  It's not
> a simple flush as in "make sure the data is all sent to the underlying device", it's also what
> adds the final \n!  So with the gdb_flush outside the loop, all the events were printed on the same
> line.  I've put the terminal setting calls and the gdb_flush back into the loop, to minimize the
> changes.
> 
> The patch would now look like this:

Thank you for the detailed explanation.  I think the revised patch is very clear.

-Baris

> 
> From cb845a4f28d1761feb463914c13b0a45c97d9974 Mon Sep 17 00:00:00 2001
> From: Simon Marchi <simon.marchi@efficios.com>
> Date: Wed, 15 Jan 2020 14:12:20 -0500
> Subject: [PATCH] gdb: remove use of iterate_over_inferiors in mi/mi-interp.c
> 
> Replace it with a range-based for.  I've updated the comment in
> mi_interp::init, which was a bit stale.
> 
> gdb/ChangeLog:
> 
> 	* mi/mi-interp.c (report_initial_inferior): Remove.
> 	(mi_interp::init): Use range-based for to iterate over inferiors.
> ---
>  gdb/mi/mi-interp.c | 49 ++++++++++++++++++++--------------------------
>  1 file changed, 21 insertions(+), 28 deletions(-)
> 
> diff --git a/gdb/mi/mi-interp.c b/gdb/mi/mi-interp.c
> index 2ac4c119961c..e77093cfa282 100644
> --- a/gdb/mi/mi-interp.c
> +++ b/gdb/mi/mi-interp.c
> @@ -91,8 +91,6 @@ static void mi_memory_changed (struct inferior *inf, CORE_ADDR memaddr,
>  			       ssize_t len, const bfd_byte *myaddr);
>  static void mi_on_sync_execution_done (void);
> 
> -static int report_initial_inferior (struct inferior *inf, void *closure);
> -
>  /* Display the MI prompt.  */
> 
>  static void
> @@ -137,12 +135,27 @@ mi_interp::init (bool top_level)
> 
>    if (top_level)
>      {
> -      /* The initial inferior is created before this function is
> -	 called, so we need to report it explicitly.  Use iteration in
> -	 case future version of GDB creates more than one inferior
> -	 up-front.  */
> -      iterate_over_inferiors (report_initial_inferior, mi);
> -    }
> +      /* The initial inferior is created before this function is called, so we
> +	 need to report it explicitly when initializing the top-level MI
> +	 interpreter.
> +
> +	 This is also called when additional MI interpreters are added (using
> +	 the new-ui command), when multiple inferiors possibly exist, so we need
> +	 to use iteration to report all the inferiors.  mi_inferior_added can't
> +	 be used, because it would print the event on all the other MI UIs.  */
> +
> +      for (inferior *inf : all_inferiors ())
> +	{
> +	  target_terminal::scoped_restore_terminal_state term_state;
> +	  target_terminal::ours_for_output ();
> +
> +	  fprintf_unfiltered (mi->event_channel,
> +			      "thread-group-added,id=\"i%d\"",
> +			      inf->num);
> +
> +	  gdb_flush (mi->event_channel);
> +	}
> +  }
>  }
> 
>  void
> @@ -1253,26 +1266,6 @@ mi_user_selected_context_changed (user_selected_what selection)
>      }
>  }
> 
> -static int
> -report_initial_inferior (struct inferior *inf, void *closure)
> -{
> -  /* This function is called from mi_interpreter_init, and since
> -     mi_inferior_added assumes that inferior is fully initialized
> -     and top_level_interpreter_data is set, we cannot call
> -     it here.  */
> -  struct mi_interp *mi = (struct mi_interp *) closure;
> -
> -  target_terminal::scoped_restore_terminal_state term_state;
> -  target_terminal::ours_for_output ();
> -
> -  fprintf_unfiltered (mi->event_channel,
> -		      "thread-group-added,id=\"i%d\"",
> -		      inf->num);
> -  gdb_flush (mi->event_channel);
> -
> -  return 0;
> -}
> -
>  ui_out *
>  mi_interp::interp_ui_out ()
>  {
> --
> 2.24.1
> 

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