Re: [boost] Reminder: Review for Zach's parsing library starts on Feb 19th

1 Mar 2024

On Thu, Feb 29, 2024 at 8:44 PM Peter Dimov via Boost
 wrote:
...
Zach Laine wrote:
...
I'm shocked too.  That's really crazy.  Believe me, I'm not interested in merging
something with orders of magnitude of perf overhead into Boost.  I will be
getting to the bottom of this long before a merge could take place.
My profiler (VS2022) says that the top performance problem is the construction
of a stringstream here
https://github.com/tzlaine/parser/blob/f99ae3b94ad0acef0cc92166d5108aade41da...
This constructs a std::locale, which is apparently very slow.
When I fix it

diff --git a/include/boost/parser/detail/printing.hpp b/include/boost/parser/detail/printing.hpp
index 1e204796..6cbec059 100644
--- a/include/boost/parser/detail/printing.hpp
+++ b/include/boost/parser/detail/printing.hpp
@@ -621,11 +621,19 @@ namespace boost { namespace parser { namespace detail {
         flags f,
         Attribute const & attr)
     {
-        std::stringstream oss;
         if (detail::do_trace(f))
+        {
+            std::stringstream oss;
             detail::print_parser(context, parser, oss);
-        return scoped_trace_t(
-            first, last, context, f, attr, oss.str());
+
+            return scoped_trace_t(
+                first, last, context, f, attr, oss.str());
+        }
+        else
+        {
+            return scoped_trace_t(
+                first, last, context, f, attr, {});
+        }
     }
template
the top function becomes the constructor of scoped_trace_t. (It's probably
not getting inlined.)
Thanks.  I fixed it as well, and now I get about 1.5-2X worse
performance than Boost.JSON.  I'm just building the "pretty" example
from Boost.JSON, and "json" and "callback_json" from my examples.
When I feed these the file at
https://world.openfoodfacts.org/api/v0/product/5060292302201.json ,
and prepend "time", I get these results:

pretty (Boost.JSON):
real    0m0.014s
user    0m0.004s
sys     0m0.000s

json (Parser):
real    0m0.022s
user    0m0.020s
sys     0m0.000s

callback_json (Parser, no JSON object creation):
real    0m0.023s
user    0m0.018s
sys     0m0.004s

I'm not sure what the tests reported earlier were doing, but I
definitely don't see orders of magnitude difference.
...
Looks like the tracing functionality costs a lot even when off.
If I can verify this (my fix might be a little different), I'll turn
the runtime flag into a template parameter.  That should do it.

Zach

    