From 80225795b9994068acdd804865b2e20d51bba452 Mon Sep 17 00:00:00 2001
From: "mergify[bot]" <37929162+mergify[bot]@users.noreply.github.com>
Date: Wed, 20 Nov 2024 08:54:22 +0800
Subject: [PATCH] Improve load times by skipping serialization of entities when
 unecessary. (backport #2596) (#2684)

* Improve load times by skipping serialization of entities when unecessary. (#2596)

* A hack to greatly improve load times

I was investigating
https://github.com/gazebosim/gazebo_test_cases/issues/1576 , in my
investigation it came to my notice that `sdf::Element` takes forever to
destroy (We should open a ticket somewhere about this). If we are
skipping serialization we might as well not create and destroy an
SDF Element. This hack greatly speeds up the load time for gazebo.

Signed-off-by: Arjo Chakravarty <arjo@openrobotics.org>
Co-authored-by: Arjo Chakravarty <arjoc@intrinsic.ai>
Co-authored-by: Arjo Chakravarty <arjo@openrobotics.org>
---
 include/gz/sim/components/Model.hh | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/include/gz/sim/components/Model.hh b/include/gz/sim/components/Model.hh
index e9aa8996df..6b23c7499e 100644
--- a/include/gz/sim/components/Model.hh
+++ b/include/gz/sim/components/Model.hh
@@ -75,10 +75,18 @@ namespace serializers
         }
       }
 
-      _out << "<?xml version=\"1.0\" ?>"
-           << "<sdf version='" << SDF_PROTOCOL_VERSION << "'>"
-           << (skip ? std::string() : modelElem->ToString(""))
-           << "</sdf>";
+      if (!skip)
+      {
+        _out << "<?xml version=\"1.0\" ?>"
+              << "<sdf version='" << SDF_PROTOCOL_VERSION << "'>"
+              << modelElem->ToString("")
+              << "</sdf>";
+
+      }
+      else
+      {
+        _out << "";
+      }
       return _out;
     }
 
@@ -89,13 +97,19 @@ namespace serializers
     public: static std::istream &Deserialize(std::istream &_in,
                 sdf::Model &_model)
     {
-      sdf::Root root;
       std::string sdf(std::istreambuf_iterator<char>(_in), {});
+      if (sdf.empty())
+      {
+        return _in;
+      }
 
+      // Its super expensive to create an SDFElement for some reason
+      sdf::Root root;
       sdf::Errors errors = root.LoadSdfString(sdf);
       if (!root.Model())
       {
-        ignwarn << "Unable to deserialize sdf::Model" << std::endl;
+        ignwarn << "Unable to deserialize sdf::Model: " << sdf
+          << std::endl;
         return _in;
       }