[PING*2][PATCH 1/4 v7] gdb: Buffer output streams during events that might download debuginfo

[Aaron Merey <amerey@redhat.com>]

Ping

Thanks,
Aaron

On Sun, Nov 12, 2023 at 3:20 PM Aaron Merey <amerey@redhat.com> wrote:
>
> Ping
>
> Thanks,
> Aaron
>
> On Fri, Oct 27, 2023 at 8:20 PM Aaron Merey <amerey@redhat.com> wrote:
> >
> > v6: https://sourceware.org/pipermail/gdb-patches/2023-October/203147.html
> >
> > v7 adds support for buffering output stream flush().  Newline prefix
> > states have been removed from this patch and instead added to patch 4/4
> > in this series.
> >
> > Commit message:
> >
> > Introduce new ui_file buffering_file to temporarily collect output
> > written to gdb_std* output streams during print_thread, print_frame_info
> > and print_stop_event.
> >
> > This ensures that output during these functions is not interrupted
> > by debuginfod progress messages.
> >
> > With the addition of deferred debuginfo downloading it is possible
> > for download progress messages to print during these events.
> > Without any intervention we can end up with poorly formatted output:
> >
> >     (gdb) backtrace
> >     [...]
> >     #8  0x00007fbe8af7d7cf in pygi_invoke_c_callable (Downloading separate debug info for /lib64/libpython3.11.so.1.0
> >     function_cache=0x561221b224d0, state=<optimized out>...
> >
> > To fix this we buffer writes to gdb_std* output streams while allowing
> > debuginfod progress messages to skip the buffers and print to the
> > underlying output streams immediately.  Buffered output is then written
> > to the output streams.  This ensures that progress messages print first,
> > followed by uninterrupted frame/thread/stop info:
> >
> >     (gdb) backtrace
> >     [...]
> >     Downloading separate debug info for /lib64/libpython3.11.so.1.0
> >     #8  0x00007fbe8af7d7cf in pygi_invoke_c_callable (function_cache=0x561221b224d0, state=<optimized out>...
> >
> > Co-Authored-By: Andrew Burgess <aburgess@redhat.com>
> > ---
> >  gdb/cli-out.c            |  10 ++-
> >  gdb/cli-out.h            |   3 +
> >  gdb/debuginfod-support.c |  15 ++--
> >  gdb/infrun.c             |  16 +++-
> >  gdb/mi/mi-out.h          |   3 +
> >  gdb/python/py-mi.c       |   3 +
> >  gdb/stack.c              |  35 +++++---
> >  gdb/thread.c             | 171 ++++++++++++++++++++---------------
> >  gdb/ui-file.h            |   2 +-
> >  gdb/ui-out.c             | 144 ++++++++++++++++++++++++++++++
> >  gdb/ui-out.h             | 186 +++++++++++++++++++++++++++++++++++++++
> >  11 files changed, 493 insertions(+), 95 deletions(-)
> >
> > diff --git a/gdb/cli-out.c b/gdb/cli-out.c
> > index 20d3d93f1ad..c919622d418 100644
> > --- a/gdb/cli-out.c
> > +++ b/gdb/cli-out.c
> > @@ -299,7 +299,7 @@ cli_ui_out::do_progress_notify (const std::string &msg,
> >                                 double howmuch, double total)
> >  {
> >    int chars_per_line = get_chars_per_line ();
> > -  struct ui_file *stream = m_streams.back ();
> > +  struct ui_file *stream = get_unbuffered (m_streams.back ());
> >    cli_progress_info &info (m_progress_info.back ());
> >
> >    if (chars_per_line > MAX_CHARS_PER_LINE)
> > @@ -384,7 +384,7 @@ cli_ui_out::do_progress_notify (const std::string &msg,
> >  void
> >  cli_ui_out::clear_progress_notify ()
> >  {
> > -  struct ui_file *stream = m_streams.back ();
> > +  struct ui_file *stream = get_unbuffered (m_streams.back ());
> >    int chars_per_line = get_chars_per_line ();
> >
> >    scoped_restore save_pagination
> > @@ -413,10 +413,12 @@ void
> >  cli_ui_out::do_progress_end ()
> >  {
> >    struct ui_file *stream = m_streams.back ();
> > -  m_progress_info.pop_back ();
> > +  cli_progress_info &info (m_progress_info.back ());
> >
> > -  if (stream->isatty ())
> > +  if (stream->isatty () && info.state != progress_update::START)
> >      clear_progress_notify ();
> > +
> > +  m_progress_info.pop_back ();
> >  }
> >
> >  /* local functions */
> > diff --git a/gdb/cli-out.h b/gdb/cli-out.h
> > index 34016182269..89b4aa40870 100644
> > --- a/gdb/cli-out.h
> > +++ b/gdb/cli-out.h
> > @@ -35,6 +35,9 @@ class cli_ui_out : public ui_out
> >
> >    bool can_emit_style_escape () const override;
> >
> > +  ui_file *current_stream () const override
> > +  { return m_streams.back (); }
> > +
> >  protected:
> >
> >    virtual void do_table_begin (int nbrofcols, int nr_rows,
> > diff --git a/gdb/debuginfod-support.c b/gdb/debuginfod-support.c
> > index 902af405cc6..b36fb8c35de 100644
> > --- a/gdb/debuginfod-support.c
> > +++ b/gdb/debuginfod-support.c
> > @@ -155,7 +155,8 @@ progressfn (debuginfod_client *c, long cur, long total)
> >
> >    if (check_quit_flag ())
> >      {
> > -      gdb_printf ("Cancelling download of %s %s...\n",
> > +      ui_file *outstream = get_unbuffered (gdb_stdout);
> > +      gdb_printf (outstream, _("Cancelling download of %s %s...\n"),
> >                   data->desc, styled_fname.c_str ());
> >        return 1;
> >      }
> > @@ -296,10 +297,14 @@ static void
> >  print_outcome (int fd, const char *desc, const char *fname)
> >  {
> >    if (fd < 0 && fd != -ENOENT)
> > -    gdb_printf (_("Download failed: %s.  Continuing without %s %ps.\n"),
> > -               safe_strerror (-fd),
> > -               desc,
> > -               styled_string (file_name_style.style (), fname));
> > +    {
> > +      ui_file *outstream = get_unbuffered (gdb_stdout);
> > +      gdb_printf (outstream,
> > +                 _("Download failed: %s.  Continuing without %s %ps.\n"),
> > +                 safe_strerror (-fd),
> > +                 desc,
> > +                 styled_string (file_name_style.style (), fname));
> > +    }
> >  }
> >
> >  /* See debuginfod-support.h  */
> > diff --git a/gdb/infrun.c b/gdb/infrun.c
> > index 4fde96800fb..7c1a7cca74f 100644
> > --- a/gdb/infrun.c
> > +++ b/gdb/infrun.c
> > @@ -8788,10 +8788,10 @@ print_stop_location (const target_waitstatus &ws)
> >      print_stack_frame (get_selected_frame (nullptr), 0, source_flag, 1);
> >  }
> >
> > -/* See infrun.h.  */
> > +/* See `print_stop_event` in infrun.h.  */
> >
> > -void
> > -print_stop_event (struct ui_out *uiout, bool displays)
> > +static void
> > +do_print_stop_event (struct ui_out *uiout, bool displays)
> >  {
> >    struct target_waitstatus last;
> >    struct thread_info *tp;
> > @@ -8820,6 +8820,16 @@ print_stop_event (struct ui_out *uiout, bool displays)
> >      }
> >  }
> >
> > +/* See infrun.h.  This function itself sets up buffered output for the
> > +   duration of do_print_stop_event, which performs the actual event
> > +   printing.  */
> > +
> > +void
> > +print_stop_event (struct ui_out *uiout, bool displays)
> > +{
> > +  do_with_buffered_output (do_print_stop_event, uiout, displays);
> > +}
> > +
> >  /* See infrun.h.  */
> >
> >  void
> > diff --git a/gdb/mi/mi-out.h b/gdb/mi/mi-out.h
> > index 0dd7479a52f..68ff5faf632 100644
> > --- a/gdb/mi/mi-out.h
> > +++ b/gdb/mi/mi-out.h
> > @@ -45,6 +45,9 @@ class mi_ui_out : public ui_out
> >      return false;
> >    }
> >
> > +  ui_file *current_stream () const override
> > +  { return m_streams.back (); }
> > +
> >  protected:
> >
> >    virtual void do_table_begin (int nbrofcols, int nr_rows, const char *tblid)
> > diff --git a/gdb/python/py-mi.c b/gdb/python/py-mi.c
> > index a7b4f4fa3cf..ba913bf1fee 100644
> > --- a/gdb/python/py-mi.c
> > +++ b/gdb/python/py-mi.c
> > @@ -61,6 +61,9 @@ class py_ui_out : public ui_out
> >      return current ().obj.release ();
> >    }
> >
> > +  ui_file *current_stream () const override
> > +  { return nullptr; }
> > +
> >  protected:
> >
> >    void do_progress_end () override { }
> > diff --git a/gdb/stack.c b/gdb/stack.c
> > index 0b35d62f82f..0560261144c 100644
> > --- a/gdb/stack.c
> > +++ b/gdb/stack.c
> > @@ -220,7 +220,8 @@ static void print_frame_local_vars (frame_info_ptr frame,
> >                                     const char *regexp, const char *t_regexp,
> >                                     int num_tabs, struct ui_file *stream);
> >
> > -static void print_frame (const frame_print_options &opts,
> > +static void print_frame (struct ui_out *uiout,
> > +                        const frame_print_options &opts,
> >                          frame_info_ptr frame, int print_level,
> >                          enum print_what print_what,  int print_args,
> >                          struct symtab_and_line sal);
> > @@ -1020,16 +1021,15 @@ get_user_print_what_frame_info (gdb::optional<enum print_what> *what)
> >     Used in "where" output, and to emit breakpoint or step
> >     messages.  */
> >
> > -void
> > -print_frame_info (const frame_print_options &fp_opts,
> > -                 frame_info_ptr frame, int print_level,
> > -                 enum print_what print_what, int print_args,
> > -                 int set_current_sal)
> > +static void
> > +do_print_frame_info (struct ui_out *uiout, const frame_print_options &fp_opts,
> > +                    frame_info_ptr frame, int print_level,
> > +                    enum print_what print_what, int print_args,
> > +                    int set_current_sal)
> >  {
> >    struct gdbarch *gdbarch = get_frame_arch (frame);
> >    int source_print;
> >    int location_print;
> > -  struct ui_out *uiout = current_uiout;
> >
> >    if (!current_uiout->is_mi_like_p ()
> >        && fp_opts.print_frame_info != print_frame_info_auto)
> > @@ -1105,7 +1105,8 @@ print_frame_info (const frame_print_options &fp_opts,
> >                     || print_what == LOC_AND_ADDRESS
> >                     || print_what == SHORT_LOCATION);
> >    if (location_print || !sal.symtab)
> > -    print_frame (fp_opts, frame, print_level, print_what, print_args, sal);
> > +    print_frame (uiout, fp_opts, frame, print_level,
> > +                print_what, print_args, sal);
> >
> >    source_print = (print_what == SRC_LINE || print_what == SRC_AND_LOC);
> >
> > @@ -1185,6 +1186,20 @@ print_frame_info (const frame_print_options &fp_opts,
> >    gdb_flush (gdb_stdout);
> >  }
> >
> > +/* Redirect output to a temporary buffer for the duration
> > +   of do_print_frame_info.  */
> > +
> > +void
> > +print_frame_info (const frame_print_options &fp_opts,
> > +                 frame_info_ptr frame, int print_level,
> > +                 enum print_what print_what, int print_args,
> > +                 int set_current_sal)
> > +{
> > +  do_with_buffered_output (do_print_frame_info, current_uiout,
> > +                          fp_opts, frame, print_level, print_what,
> > +                          print_args, set_current_sal);
> > +}
> > +
> >  /* See stack.h.  */
> >
> >  void
> > @@ -1309,13 +1324,13 @@ find_frame_funname (frame_info_ptr frame, enum language *funlang,
> >  }
> >
> >  static void
> > -print_frame (const frame_print_options &fp_opts,
> > +print_frame (struct ui_out *uiout,
> > +            const frame_print_options &fp_opts,
> >              frame_info_ptr frame, int print_level,
> >              enum print_what print_what, int print_args,
> >              struct symtab_and_line sal)
> >  {
> >    struct gdbarch *gdbarch = get_frame_arch (frame);
> > -  struct ui_out *uiout = current_uiout;
> >    enum language funlang = language_unknown;
> >    struct value_print_options opts;
> >    struct symbol *func;
> > diff --git a/gdb/thread.c b/gdb/thread.c
> > index c8145da59bc..f6cf2eb9cf4 100644
> > --- a/gdb/thread.c
> > +++ b/gdb/thread.c
> > @@ -1064,6 +1064,103 @@ thread_target_id_str (thread_info *tp)
> >      return target_id;
> >  }
> >
> > +/* Print thread TP.  GLOBAL_IDS indicates whether REQUESTED_THREADS
> > +   is a list of global or per-inferior thread ids.  */
> > +
> > +static void
> > +do_print_thread (ui_out *uiout, const char *requested_threads,
> > +                int global_ids, int pid, int show_global_ids,
> > +                int default_inf_num, thread_info *tp,
> > +                thread_info *current_thread)
> > +{
> > +  int core;
> > +
> > +  if (!should_print_thread (requested_threads, default_inf_num,
> > +                           global_ids, pid, tp))
> > +    return;
> > +
> > +  ui_out_emit_tuple tuple_emitter (uiout, NULL);
> > +
> > +  if (!uiout->is_mi_like_p ())
> > +    {
> > +      if (tp == current_thread)
> > +       uiout->field_string ("current", "*");
> > +      else
> > +       uiout->field_skip ("current");
> > +
> > +      uiout->field_string ("id-in-tg", print_thread_id (tp));
> > +    }
> > +
> > +  if (show_global_ids || uiout->is_mi_like_p ())
> > +    uiout->field_signed ("id", tp->global_num);
> > +
> > +  /* Switch to the thread (and inferior / target).  */
> > +  switch_to_thread (tp);
> > +
> > +  /* For the CLI, we stuff everything into the target-id field.
> > +     This is a gross hack to make the output come out looking
> > +     correct.  The underlying problem here is that ui-out has no
> > +     way to specify that a field's space allocation should be
> > +     shared by several fields.  For MI, we do the right thing
> > +     instead.  */
> > +
> > +  if (uiout->is_mi_like_p ())
> > +    {
> > +      uiout->field_string ("target-id", target_pid_to_str (tp->ptid));
> > +
> > +      const char *extra_info = target_extra_thread_info (tp);
> > +      if (extra_info != nullptr)
> > +       uiout->field_string ("details", extra_info);
> > +
> > +      const char *name = thread_name (tp);
> > +      if (name != NULL)
> > +       uiout->field_string ("name", name);
> > +    }
> > +  else
> > +    {
> > +      uiout->field_string ("target-id", thread_target_id_str (tp));
> > +    }
> > +
> > +  if (tp->state == THREAD_RUNNING)
> > +    uiout->text ("(running)\n");
> > +  else
> > +    {
> > +      /* The switch above put us at the top of the stack (leaf
> > +        frame).  */
> > +      print_stack_frame (get_selected_frame (NULL),
> > +                        /* For MI output, print frame level.  */
> > +                        uiout->is_mi_like_p (),
> > +                        LOCATION, 0);
> > +    }
> > +
> > +  if (uiout->is_mi_like_p ())
> > +    {
> > +      const char *state = "stopped";
> > +
> > +      if (tp->state == THREAD_RUNNING)
> > +       state = "running";
> > +      uiout->field_string ("state", state);
> > +    }
> > +
> > +  core = target_core_of_thread (tp->ptid);
> > +  if (uiout->is_mi_like_p () && core != -1)
> > +    uiout->field_signed ("core", core);
> > +}
> > +
> > +/* Redirect output to a temporary buffer for the duration
> > +   of do_print_thread.  */
> > +
> > +static void
> > +print_thread (ui_out *uiout, const char *requested_threads,
> > +             int global_ids, int pid, int show_global_ids,
> > +             int default_inf_num, thread_info *tp, thread_info *current_thread)
> > +
> > +{
> > +  do_with_buffered_output (do_print_thread, uiout, requested_threads,
> > +                          global_ids, pid, show_global_ids,
> > +                          default_inf_num, tp, current_thread);
> > +}
> > +
> >  /* Like print_thread_info, but in addition, GLOBAL_IDS indicates
> >     whether REQUESTED_THREADS is a list of global or per-inferior
> >     thread ids.  */
> > @@ -1147,82 +1244,12 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
> >      for (inferior *inf : all_inferiors ())
> >        for (thread_info *tp : inf->threads ())
> >         {
> > -         int core;
> > -
> >           any_thread = true;
> >           if (tp == current_thread && tp->state == THREAD_EXITED)
> >             current_exited = true;
> >
> > -         if (!should_print_thread (requested_threads, default_inf_num,
> > -                                   global_ids, pid, tp))
> > -           continue;
> > -
> > -         ui_out_emit_tuple tuple_emitter (uiout, NULL);
> > -
> > -         if (!uiout->is_mi_like_p ())
> > -           {
> > -             if (tp == current_thread)
> > -               uiout->field_string ("current", "*");
> > -             else
> > -               uiout->field_skip ("current");
> > -
> > -             uiout->field_string ("id-in-tg", print_thread_id (tp));
> > -           }
> > -
> > -         if (show_global_ids || uiout->is_mi_like_p ())
> > -           uiout->field_signed ("id", tp->global_num);
> > -
> > -         /* Switch to the thread (and inferior / target).  */
> > -         switch_to_thread (tp);
> > -
> > -         /* For the CLI, we stuff everything into the target-id field.
> > -            This is a gross hack to make the output come out looking
> > -            correct.  The underlying problem here is that ui-out has no
> > -            way to specify that a field's space allocation should be
> > -            shared by several fields.  For MI, we do the right thing
> > -            instead.  */
> > -
> > -         if (uiout->is_mi_like_p ())
> > -           {
> > -             uiout->field_string ("target-id", target_pid_to_str (tp->ptid));
> > -
> > -             const char *extra_info = target_extra_thread_info (tp);
> > -             if (extra_info != nullptr)
> > -               uiout->field_string ("details", extra_info);
> > -
> > -             const char *name = thread_name (tp);
> > -             if (name != NULL)
> > -               uiout->field_string ("name", name);
> > -           }
> > -         else
> > -           {
> > -             uiout->field_string ("target-id", thread_target_id_str (tp));
> > -           }
> > -
> > -         if (tp->state == THREAD_RUNNING)
> > -           uiout->text ("(running)\n");
> > -         else
> > -           {
> > -             /* The switch above put us at the top of the stack (leaf
> > -                frame).  */
> > -             print_stack_frame (get_selected_frame (NULL),
> > -                                /* For MI output, print frame level.  */
> > -                                uiout->is_mi_like_p (),
> > -                                LOCATION, 0);
> > -           }
> > -
> > -         if (uiout->is_mi_like_p ())
> > -           {
> > -             const char *state = "stopped";
> > -
> > -             if (tp->state == THREAD_RUNNING)
> > -               state = "running";
> > -             uiout->field_string ("state", state);
> > -           }
> > -
> > -         core = target_core_of_thread (tp->ptid);
> > -         if (uiout->is_mi_like_p () && core != -1)
> > -           uiout->field_signed ("core", core);
> > +         print_thread (uiout, requested_threads, global_ids, pid,
> > +                       show_global_ids, default_inf_num, tp, current_thread);
> >         }
> >
> >      /* This end scope restores the current thread and the frame
> > diff --git a/gdb/ui-file.h b/gdb/ui-file.h
> > index 31f87ffd51d..8385033b441 100644
> > --- a/gdb/ui-file.h
> > +++ b/gdb/ui-file.h
> > @@ -224,7 +224,7 @@ class string_file : public ui_file
> >    bool empty () const { return m_string.empty (); }
> >    void clear () { return m_string.clear (); }
> >
> > -private:
> > +protected:
> >    /* The internal buffer.  */
> >    std::string m_string;
> >
> > diff --git a/gdb/ui-out.c b/gdb/ui-out.c
> > index defa8f9dfa4..9f643b1ce95 100644
> > --- a/gdb/ui-out.c
> > +++ b/gdb/ui-out.c
> > @@ -871,3 +871,147 @@ ui_out::ui_out (ui_out_flags flags)
> >  ui_out::~ui_out ()
> >  {
> >  }
> > +
> > +/* See ui-out.h.  */
> > +
> > +void
> > +buffer_group::output_unit::flush () const
> > +{
> > +  if (!m_msg.empty ())
> > +    m_stream->puts (m_msg.c_str ());
> > +
> > +  if (m_wrap_hint >= 0)
> > +    m_stream->wrap_here (m_wrap_hint);
> > +
> > +  if (m_flush)
> > +    m_stream->flush ();
> > +}
> > +
> > +/* See ui-out.h.  */
> > +
> > +void
> > +buffer_group::write (const char *buf, long length_buf, ui_file *stream)
> > +{
> > +  /* Record each line separately.  */
> > +  for (size_t prev = 0, cur = 0; cur < length_buf; ++cur)
> > +    if (buf[cur] == '\n' || cur == length_buf - 1)
> > +      {
> > +       std::string msg (buf + prev, cur - prev + 1);
> > +
> > +       if (m_buffered_output.size () > 0
> > +           && m_buffered_output.back ().m_wrap_hint == -1
> > +           && m_buffered_output.back ().m_stream == stream
> > +           && m_buffered_output.back ().m_msg.size () > 0
> > +           && m_buffered_output.back ().m_msg.back () != '\n')
> > +         m_buffered_output.back ().m_msg.append (msg);
> > +       else
> > +         {
> > +           m_buffered_output.emplace_back (msg);
> > +           m_buffered_output.back ().m_stream = stream;
> > +         }
> > +       prev = cur + 1;
> > +      }
> > +}
> > +
> > +/* See ui-out.h.  */
> > +
> > +void
> > +buffer_group::wrap_here (int indent, ui_file *stream)
> > +{
> > +  m_buffered_output.emplace_back ("", indent);
> > +  m_buffered_output.back ().m_stream = stream;
> > +}
> > +
> > +/* See ui-out.h.  */
> > +
> > +void
> > +buffer_group::flush_here (ui_file *stream)
> > +{
> > +  m_buffered_output.emplace_back ("", -1, true);
> > +  m_buffered_output.back ().m_stream = stream;
> > +}
> > +
> > +/* See ui-out.h.  */
> > +
> > +ui_file *
> > +get_unbuffered (ui_file * stream)
> > +{
> > +  buffering_file *buf = dynamic_cast<buffering_file *> (stream);
> > +
> > +  if (buf == nullptr)
> > +    return stream;
> > +
> > +  return get_unbuffered (buf->stream ());
> > +}
> > +
> > +buffered_streams::buffered_streams (buffer_group *group, ui_out *uiout)
> > +    : m_buffered_stdout (group, gdb_stdout),
> > +      m_buffered_stderr (group, gdb_stderr),
> > +      m_buffered_stdlog (group, gdb_stdlog),
> > +      m_buffered_stdtarg (group, gdb_stdtarg),
> > +      m_buffered_stdtargerr (group, gdb_stdtargerr),
> > +      m_uiout (uiout)
> > +  {
> > +    gdb_stdout = &m_buffered_stdout;
> > +    gdb_stderr = &m_buffered_stderr;
> > +    gdb_stdlog = &m_buffered_stdlog;
> > +    gdb_stdtarg = &m_buffered_stdtarg;
> > +    gdb_stdtargerr = &m_buffered_stdtargerr;
> > +
> > +    ui_file *stream = current_uiout->current_stream ();
> > +    if (stream != nullptr)
> > +      {
> > +       m_buffered_current_uiout.emplace (group, stream);
> > +       current_uiout->redirect (&(*m_buffered_current_uiout));
> > +      }
> > +
> > +    stream = m_uiout->current_stream ();
> > +    if (stream != nullptr && current_uiout != m_uiout)
> > +      {
> > +       m_buffered_uiout.emplace (group, stream);
> > +       m_uiout->redirect (&(*m_buffered_uiout));
> > +      }
> > +
> > +    m_buffers_in_place = true;
> > +  };
> > +
> > +/* See ui-out.h.  */
> > +
> > +void
> > +buffered_streams::remove_buffers ()
> > +  {
> > +    if (!m_buffers_in_place)
> > +      return;
> > +
> > +    m_buffers_in_place = false;
> > +
> > +    gdb_stdout = m_buffered_stdout.stream ();
> > +    gdb_stderr = m_buffered_stderr.stream ();
> > +    gdb_stdlog = m_buffered_stdlog.stream ();
> > +    gdb_stdtarg = m_buffered_stdtarg.stream ();
> > +    gdb_stdtargerr = m_buffered_stdtargerr.stream ();
> > +
> > +    if (m_buffered_current_uiout.has_value ())
> > +      current_uiout->redirect (nullptr);
> > +
> > +    if (m_buffered_uiout.has_value ())
> > +      m_uiout->redirect (nullptr);
> > +  }
> > +
> > +buffer_group::buffer_group (ui_out *uiout)
> > +  : m_buffered_streams (new buffered_streams (this, uiout))
> > +{ /* Nothing.  */ }
> > +
> > +buffer_group::~buffer_group ()
> > +{ /* Nothing.  */ }
> > +
> > +/* See ui-out.h.  */
> > +
> > +void
> > +buffer_group::flush () const
> > +{
> > +  m_buffered_streams->remove_buffers ();
> > +
> > +  for (const output_unit &ou : m_buffered_output)
> > +    ou.flush ();
> > +}
> > diff --git a/gdb/ui-out.h b/gdb/ui-out.h
> > index 07567a1df35..70a7145741f 100644
> > --- a/gdb/ui-out.h
> > +++ b/gdb/ui-out.h
> > @@ -278,6 +278,9 @@ class ui_out
> >       escapes.  */
> >    virtual bool can_emit_style_escape () const = 0;
> >
> > +  /* Return the ui_file currently used for output.  */
> > +  virtual ui_file *current_stream () const = 0;
> > +
> >    /* An object that starts and finishes displaying progress updates.  */
> >    class progress_update
> >    {
> > @@ -470,4 +473,187 @@ class ui_out_redirect_pop
> >    struct ui_out *m_uiout;
> >  };
> >
> > +struct buffered_streams;
> > +
> > +/* Organizes writes to a collection of buffered output streams
> > +   so that when flushed, output is written to all streams in
> > +   chronological order.  */
> > +
> > +struct buffer_group
> > +{
> > +  buffer_group (ui_out *uiout);
> > +
> > +  ~buffer_group ();
> > +
> > +  /* Flush all buffered writes to the underlying output streams.  */
> > +  void flush () const;
> > +
> > +  /* Record contents of BUF and associate it with STREAM.  */
> > +  void write (const char *buf, long length_buf, ui_file *stream);
> > +
> > +  /* Record a wrap_here and associate it with STREAM.  */
> > +  void wrap_here (int indent, ui_file *stream);
> > +
> > +  /* Record a call to flush and associate it with STREAM.  */
> > +  void flush_here (ui_file *stream);
> > +
> > +private:
> > +
> > +  struct output_unit
> > +  {
> > +    output_unit (std::string msg, int wrap_hint = -1, bool flush = false)
> > +      : m_msg (msg), m_wrap_hint (wrap_hint), m_flush (flush)
> > +    {}
> > +
> > +    /* Write contents of this output_unit to the underlying stream.  */
> > +    void flush () const;
> > +
> > +    /* Underlying stream for which this output unit will be written to.  */
> > +    ui_file *m_stream;
> > +
> > +    /* String to be written to underlying buffer.  */
> > +    std::string m_msg;
> > +
> > +    /* Argument to wrap_here.  -1 indicates no wrap.  Used to call wrap_here
> > +       during buffer flush.  */
> > +    int m_wrap_hint;
> > +
> > +    /* Indicate that the underlying output stream's flush should be called.  */
> > +    bool m_flush;
> > +  };
> > +
> > +  /* Output_units to be written to buffered output streams.  */
> > +  std::vector<output_unit> m_buffered_output;
> > +
> > +  /* Buffered output streams.  */
> > +  std::unique_ptr<buffered_streams> m_buffered_streams;
> > +};
> > +
> > +/* If FILE is a buffering_file, return it's underlying stream.  */
> > +
> > +extern ui_file *get_unbuffered (ui_file *file);
> > +
> > +/* Buffer output to gdb_stdout and gdb_stderr for the duration of FUNC.  */
> > +
> > +template<typename F, typename... Arg>
> > +void
> > +do_with_buffered_output (F func, ui_out *uiout, Arg... args)
> > +{
> > +  buffer_group g (uiout);
> > +
> > +  try
> > +    {
> > +      func (uiout, std::forward<Arg> (args)...);
> > +    }
> > +  catch (gdb_exception &ex)
> > +    {
> > +      /* Ideally flush would be called in the destructor of buffer_group,
> > +        however flushing might cause an exception to be thrown.  Catch it
> > +        and ensure the first exception propagates.  */
> > +      try
> > +       {
> > +         g.flush ();
> > +       }
> > +      catch (const gdb_exception &)
> > +       {
> > +       }
> > +
> > +      throw_exception (std::move (ex));
> > +    }
> > +
> > +  /* Try was successful.  Let any further exceptions propagate.  */
> > +  g.flush ();
> > +}
> > +
> > +/* Accumulate writes to an underlying ui_file.  Output to the
> > +   underlying file is deferred until required.  */
> > +
> > +struct buffering_file : public ui_file
> > +{
> > +  buffering_file (buffer_group *group, ui_file *stream)
> > +    : m_group (group),
> > +      m_stream (stream)
> > +  { /* Nothing.  */ }
> > +
> > +  /* Return the underlying output stream.  */
> > +  ui_file *stream () const
> > +  {
> > +    return m_stream;
> > +  }
> > +
> > +  /* Record the contents of BUF.  */
> > +  void write (const char *buf, long length_buf) override
> > +  {
> > +    m_group->write (buf, length_buf, m_stream);
> > +  }
> > +
> > +  /* Record a wrap_here call with argument INDENT.  */
> > +  void wrap_here (int indent) override
> > +  {
> > +    m_group->wrap_here (indent, m_stream);
> > +  }
> > +
> > +  /* Return true if the underlying stream is a tty.  */
> > +  bool isatty () override
> > +  {
> > +    return m_stream->isatty ();
> > +  }
> > +
> > +  /* Return true if ANSI escapes can be used on the underlying stream.  */
> > +  bool can_emit_style_escape () override
> > +  {
> > +    return m_stream->can_emit_style_escape ();
> > +  }
> > +
> > +  /* Flush the underlying output stream.  */
> > +  void flush () override
> > +  {
> > +    return m_group->flush_here (m_stream);
> > +  }
> > +
> > +private:
> > +
> > +  /* Coordinates buffering across multiple buffering_files.  */
> > +  buffer_group *m_group;
> > +
> > +  /* The underlying output stream.  */
> > +  ui_file *m_stream;
> > +};
> > +
> > +/* Attaches and detaches buffers for each of the gdb_std* streams.  */
> > +
> > +struct buffered_streams
> > +{
> > +  buffered_streams (buffer_group *group, ui_out *uiout);
> > +
> > +  ~buffered_streams ()
> > +  {
> > +    this->remove_buffers ();
> > +  }
> > +
> > +  /* Remove buffering_files from all underlying streams.  */
> > +  void remove_buffers ();
> > +
> > +private:
> > +
> > +  /* True if buffers are still attached to each underlying output stream.  */
> > +  bool m_buffers_in_place;
> > +
> > +  /* Buffers for each gdb_std* output stream.  */
> > +  buffering_file m_buffered_stdout;
> > +  buffering_file m_buffered_stderr;
> > +  buffering_file m_buffered_stdlog;
> > +  buffering_file m_buffered_stdtarg;
> > +  buffering_file m_buffered_stdtargerr;
> > +
> > +  /* Buffer for current_uiout's output stream.  */
> > +  gdb::optional<buffering_file> m_buffered_current_uiout;
> > +
> > +  /* Additional ui_out being buffered.  */
> > +  ui_out *m_uiout;
> > +
> > +  /* Buffer for m_uiout's output stream.  */
> > +  gdb::optional<buffering_file> m_buffered_uiout;
> > +};
> > +
> >  #endif /* UI_OUT_H */
> > --
> > 2.41.0
> >