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

Tom de Vries
2023-10-13T12:19:57Z

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
@@ -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
+ {
+ /* 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 +266,21 @@ try_source_highlight (std::string &contents ATTRIBUTE_UNUSED,
highlighter->setStyleFile ("esc.style");
}

+ gdb_highlight_event_listener event_listener (fullname);
+ highlighter->setHighlightEventListener (&event_listener);
+
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