Re: [PATCH v2 4/4] [gdb/cli] Allow source highlighting to be interrupted

[Lancelot SIX <lsix@lancelotsix.com>]

Hi Tom,

I have a comment below.

On Fri, Oct 13, 2023 at 02:19:53PM +0200, Tom de Vries wrote:
> In PR cli/30934, a problem is reported where gdb becomes unresponsive for
> 2m13s because the GNU source-highlight library is taking a lot of time to
> annotate the source.
> 
> This is due to a problem in the library [1], for which I've posted a
> patch [2], which brings down the annotation time to 3s.
> 
> However, GDB should not become unresponsive due to such a problem.
> 
> Fix this by installing a srchilite::HighlightEventListener that:
> - checks whether ^C was pressed, and if so
> - asks the user whether it should interrupt highlighting, and if so
> - abandons the highlighting by throwing an exception.
> 
> Interrupting the highlighting looks like this to the user:
> ...
> $ gdb -q a.out -ex "b 56"
> Reading symbols from a.out...
> Breakpoint 1 at 0x400e2a: file test.cpp, line 56.
> (gdb) r
> Starting program: /data/vries/gdb/a.out
> 
> Breakpoint 1, Solution::numOfSubarrays () at test.cpp:56
> ^CCancel source styling using GNU source highlight of /data/vries/gdb/test.cpp?
> ([y] or n) y
> 56	        return (int) t;
> (gdb)
> ...
> Note that line 56 still can be highlighted, just by pygments instead of
> source-highlight.
> 
> Tested on x86_64-linux.
> 
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30934
> 
> [1] https://savannah.gnu.org/bugs/?64747
> [2] https://savannah.gnu.org/patch/index.php?10400
> ---
>  gdb/source-cache.c | 62 ++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 60 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/source-cache.c b/gdb/source-cache.c
> index f8c98d7e23f..57d9f3b8ab4 100644
> --- a/gdb/source-cache.c
> +++ b/gdb/source-cache.c
> @@ -223,9 +266,21 @@ try_source_highlight (std::string &contents ATTRIBUTE_UNUSED,
>  	  highlighter->setStyleFile ("esc.style");
>  	}
>  
> +      gdb_highlight_event_listener event_listener (fullname);
> +      highlighter->setHighlightEventListener (&event_listener);

In this instance, highlighter outlives event_listener but keeps a
reference to it.  Arguably, the event listener will be reset to point to
another instance before the next invocation of highlight, but I think it
would be cleaner to make sure that the event listener is cleared anyway:

    auto clear_event_listener = make_scope_exit ([highlighter]()
      {
        highlighter->setHighlightEventListener (nullptr);
      });

Who knows, maybe one day highlighter's dtor might want to notify
something.

WDYT?

Best,
Lancelot.

> +
>        std::istringstream input (contents);
>        std::ostringstream output;
> -      highlighter->highlight (input, output, lang_name, fullname);
> +      {
> +	/* We want to be able to interrupt the call to source-highlight.  If
> +	   the current quit_handler is infrun_quit_handler, pressing ^C is
> +	   ignored by QUIT (assuming target_terminal::is_ours), so install the
> +	   default quit handler.  */
> +	scoped_restore restore_quit_handler
> +	  = make_scoped_restore (&quit_handler, default_quit_handler);
> +
> +	highlighter->highlight (input, output, lang_name, fullname);
> +      }
>  #if __cplusplus >= 202002L
>        contents = std::move (output).str();
>  #else
> @@ -308,13 +363,16 @@ source_cache::ensure (struct symtab *s)
>  	     reasons:
>  	     - the language is not supported.
>  	     - the language cannot not be auto-detected from the file name.
> +	     - styling took too long and was interrupted by the user.
>  	     - no stylers available.
>  
>  	     Since styling failed, don't try styling the file again after it
>  	     drops from the cache.
>  
>  	     Note that clearing the source cache also clears
> -	     m_no_styling_files.  */
> +	     m_no_styling_files, so if styling took too long, and the user
> +	     interrupted it, and the source cache gets cleared, the user will
> +	     need to interrupt styling again.  */
>  	  m_no_styling_files.insert (fullname);
>  	}
>      }
> -- 
> 2.35.3
>