Re: [PATCH v2 4/6] gdb/infrun: in condition evaluation wait only for the current inferior.

[Kevin Buettner <kevinb@redhat.com>]

Hi Natalia,

I have a question about this commit.  See below.

On Fri,  9 Oct 2020 13:27:16 +0200
Natalia Saiapova via Gdb-patches <gdb-patches@sourceware.org> wrote:

> In the middle of a condition evaluation, to successfully finish the
> inferior call we need to wait for events from the current thread.
> Otherwise, a pending event from another thread might be taken and
> the inferior call is abandoned.
> 
> gdb/ChangeLog:
> 2020-08-26  Natalia Saiapova  <natalia.saiapova@intel.com>
> 	    Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
> 
> 	* infrun.c (do_target_wait): Match an inferior PID with the
> 	expected PID.
> 	(fetch_inferior_event): In condition evaluation, wait for the
> 	event from the current inferior.
> 
> Co-authored-by: Natalia Saiapova <natalia.saiapova@intel.com>
> Co-authored-by: Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
> 
> Signed-off-by: Natalia Saiapova <natalia.saiapova@intel.com>
> ---
>  gdb/infrun.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 91271c2ddbe..d260eb6e3a7 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -3565,10 +3565,11 @@ do_target_wait (ptid_t wait_ptid, execution_control_state *ecs,
>       polling the rest of the inferior list starting from that one in a
>       circular fashion until the whole list is polled once.  */
>  
> -  auto inferior_matches = [&wait_ptid] (inferior *inf)
> +  ptid_t wait_pid_ptid {wait_ptid.pid ()};
> +  auto inferior_matches = [&wait_pid_ptid] (inferior *inf)
>      {
> -      return (inf->process_target () != NULL
> -	      && ptid_t (inf->pid).matches (wait_ptid));
> +      return (inf->process_target () != nullptr
> +	      && ptid_t (inf->pid).matches (wait_pid_ptid));
>      };

I'm puzzled by the changes above.  Can you explain what this is
about?  (And perhaps add a comment...)

>  
>    /* First see how many matching inferiors we have.  */
> @@ -3906,7 +3907,15 @@ fetch_inferior_event ()
>        = make_scoped_restore (&execution_direction,
>  			     target_execution_direction ());
>  
> -    if (!do_target_wait (minus_one_ptid, ecs, TARGET_WNOHANG))
> +    ptid_t waiton_ptid = minus_one_ptid;
> +
> +    /* If the thread is in the middle of the condition evaluation,
> +       wait for the event from the current inferior.  */
> +    if (inferior_ptid != null_ptid
> +	&& inferior_thread ()->control.in_cond_eval)
> +      waiton_ptid = inferior_ptid;
> +
> +    if (!do_target_wait (waiton_ptid, ecs, TARGET_WNOHANG))
>        return;
>  
>      gdb_assert (ecs->ws.kind != TARGET_WAITKIND_IGNORE);
> -- 
> 2.17.1
> 
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