Re: [PATCH v3 4/4] [gdb/cli] Allow source highlighting to be interrupted

[Tom de Vries <tdevries@suse.de>]

On 10/16/23 12:21, Lancelot SIX wrote:
> Hi Tom,
> 
> I have one minor nit below.
> 
> On Mon, Oct 16, 2023 at 11:17:48AM +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.
>>
>> Co-Authored-By: Lancelot Six <lancelot.six@amd.com>
>>
>> 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 | 68 ++++++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 66 insertions(+), 2 deletions(-)
>>
>> diff --git a/gdb/source-cache.c b/gdb/source-cache.c
>> index aa8e40425c2..39d8bcf7aec 100644
>> --- a/gdb/source-cache.c
>> +++ b/gdb/source-cache.c
>> @@ -37,6 +37,7 @@
>>   #include <sstream>
>>   #include <srchilite/sourcehighlight.h>
>>   #include <srchilite/langmap.h>
>> +#include <srchilite/highlighteventlistener.h>
>>   #endif
>>   
>>   /* The number of source files we'll cache.  */
>> @@ -189,6 +190,48 @@ get_language_name (enum language lang)
>>     return nullptr;
>>   }
>>   
>> +/* Class with notify function called during highlighting.  */
>> +
>> +class gdb_highlight_event_listener : public srchilite::HighlightEventListener
>> +{
>> +public:
>> +  gdb_highlight_event_listener (const std::string &fullname)
>> +    : m_fullname (fullname)
>> +  {
>> +  }
>> +
>> +  void notify(const srchilite::HighlightEvent &event) override
>                  ^
> A space is missing here before the "(".
> 
> Otherwise, and FWIW, this LGTM.
> 

Hi,

thanks for the review.

It looks like I need to start using gcc's check_GNU_style.sh / 
check_GNU_style.py again.

I fixed this, as well as a few other style issues in the series that I 
found by running the scripts, but I don't think it requires reposting.

Thanks,
- Tom

> Best, Lancelot.
> 
>> +  {
>> +    /* If the terminal is ours, we can ask the user a question and get an
>> +       answer.  */
>> +    gdb_assert (target_terminal::is_ours ());
>> +
>> +    if (!check_quit_flag ())
>> +      {
>> +	/* User didn't press ^C, nothing to do.  */
>> +	return;
>> +      }
>> +
>> +    /* Ask the user what to do.  */
>> +    int resp
>> +      = yquery (_("Cancel source styling using GNU source highlight of %s?\n"),
>> +		m_fullname.c_str ());
>> +    if (!resp)
>> +      {
>> +	/* Continue highlighting.  */
>> +	return;
>> +      }
>> +
>> +    /* Interrupt highlighting.  Note that check_quit_flag clears the
>> +       quit_flag, so we have to set it again.  */
>> +    set_quit_flag ();
>> +    QUIT;
>> +  }
>> +
>> +private:
>> +  const std::string &m_fullname;
>> +};
>> +
>>   #endif /* HAVE_SOURCE_HIGHLIGHT */
>>   
>>   /* Try to highlight CONTENTS from file FULLNAME in language LANG using
>> @@ -223,9 +266,27 @@ try_source_highlight (std::string &contents ATTRIBUTE_UNUSED,
>>   	  highlighter->setStyleFile ("esc.style");
>>   	}
>>   
>> +      gdb_highlight_event_listener event_listener (fullname);
>> +      highlighter->setHighlightEventListener (&event_listener);
>> +      /* Make sure that the highlighter's EventListener doesn't become a
>> +	 dangling pointer.  */
>> +      auto clear_event_listener = make_scope_exit ([]()
>> +      {
>> +	highlighter->setHighlightEventListener (nullptr);
>> +      });
>> +
>>         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);
>> +      }
>>         contents = std::move (output).str();
>>         styled = true;
>>       }
>> @@ -304,13 +365,16 @@ 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
>>