Re: [PATCH v2] Restore terminal state in mi_thread_exit (PR gdb/17627)

[Patrick Palka <patrick@parcs.ath.cx>]

On Tue, Dec 2, 2014 at 5:10 PM, Simon Marchi <simon.marchi@ericsson.com> wrote:
> When a thread exits, the terminal is left in mode "terminal_is_ours"
> while the target executes. This patch fixes that.
>
> From my understanding, a function calling target_terminal_ours expects
> that the terminal could be in any state at the moment it is called.
> Therefore, it should be its reponsibility to put back the terminal in
> whatever state it was before being called.

It seems to me that the other observer callbacks defined in
mi-interp.c are also affected by this issue, that is, the issue of
having to restore the original terminal state after altering it.  So I
wonder if it would make sense to shift this responsibility to the
observer module itself (i.e. generic_observer_notify()), so that all
observers implicitly restore the original terminal state when they
return.  That way this kind of pattern wouldn't have to be duplicated
for each individual observer.

>
> I find that this fits quite well the cleanup model, so I implemented a
> cleanup for that.
>
> New in v2:
>
> * Coding style fixes.
> * Use make_cleanup_dtor instead of make_cleanup.
>
> gdb/ChangeLog:
>
>         PR gdb/17627
>         * target.c (cleanup_restore_target_terminal): New function.
>         (make_cleanup_restore_target_terminal): New function.
>         * target.h (make_cleanup_restore_target_terminal): New
>         declaration.
>         * mi/mi-interp.c (mi_thread_exit): Use the new cleanup.
>
> Signed-off-by: Simon Marchi <simon.marchi@ericsson.com>
> ---
>  gdb/mi/mi-interp.c |  4 ++++
>  gdb/target.c       | 34 ++++++++++++++++++++++++++++++++++
>  gdb/target.h       |  4 ++++
>  3 files changed, 42 insertions(+)
>
> diff --git a/gdb/mi/mi-interp.c b/gdb/mi/mi-interp.c
> index df2b558..60f0666 100644
> --- a/gdb/mi/mi-interp.c
> +++ b/gdb/mi/mi-interp.c
> @@ -386,6 +386,7 @@ mi_thread_exit (struct thread_info *t, int silent)
>  {
>    struct mi_interp *mi;
>    struct inferior *inf;
> +  struct cleanup *old_chain;
>
>    if (silent)
>      return;
> @@ -393,11 +394,14 @@ mi_thread_exit (struct thread_info *t, int silent)
>    inf = find_inferior_pid (ptid_get_pid (t->ptid));
>
>    mi = top_level_interpreter_data ();
> +  old_chain = make_cleanup_restore_target_terminal ();
>    target_terminal_ours ();
>    fprintf_unfiltered (mi->event_channel,
>                       "thread-exited,id=\"%d\",group-id=\"i%d\"",
>                       t->num, inf->num);
>    gdb_flush (mi->event_channel);
> +
> +  do_cleanups (old_chain);
>  }
>
>  /* Emit notification on changing the state of record.  */
> diff --git a/gdb/target.c b/gdb/target.c
> index ab5f2b9..7161e62 100644
> --- a/gdb/target.c
> +++ b/gdb/target.c
> @@ -528,6 +528,40 @@ target_supports_terminal_ours (void)
>    return 0;
>  }
>
> +/* Restore the terminal to its previous state (helper for
> +   make_cleanup_restore_target_terminal). */
> +
> +static void
> +cleanup_restore_target_terminal (void *arg)
> +{
> +  enum terminal_state *previous_state = arg;
> +
> +  switch (*previous_state)
> +    {
> +    case terminal_is_ours:
> +      target_terminal_ours ();
> +      break;
> +    case terminal_is_ours_for_output:
> +      target_terminal_ours_for_output ();
> +      break;
> +    case terminal_is_inferior:
> +      target_terminal_inferior ();
> +      break;
> +    }
> +}
> +
> +/* See target.h. */
> +
> +struct cleanup *
> +make_cleanup_restore_target_terminal (void)
> +{
> +  enum terminal_state *ts = xmalloc (sizeof (*ts));
> +
> +  *ts = terminal_state;
> +
> +  return make_cleanup_dtor (cleanup_restore_target_terminal, ts, xfree);
> +}
> +
>  static void
>  tcomplain (void)
>  {
> diff --git a/gdb/target.h b/gdb/target.h
> index d363b61..eb3220e 100644
> --- a/gdb/target.h
> +++ b/gdb/target.h
> @@ -1413,6 +1413,10 @@ extern void target_terminal_ours (void);
>
>  extern int target_supports_terminal_ours (void);
>
> +/* Make a cleanup that restores the state of the terminal to the current
> +   value.  */
> +extern struct cleanup *make_cleanup_restore_target_terminal (void);
> +
>  /* Print useful information about our terminal status, if such a thing
>     exists.  */
>
> --
> 2.1.3
>