From d1fff288f4f5f578987acfabb6303fbe641c0b61 Mon Sep 17 00:00:00 2001
From: Arjo Chakravarty <arjoc@intrinsic.ai>
Date: Tue, 19 Nov 2024 04:46:50 +0800
Subject: [PATCH] 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 <arjoc@intrinsic.ai>

* Remove magic word

Signed-off-by: Arjo Chakravarty <arjoc@intrinsic.ai>

* Send empty string instead of using sentinel value.

Signed-off-by: Arjo Chakravarty <arjoc@intrinsic.ai>

* Style

Signed-off-by: Arjo Chakravarty <arjoc@intrinsic.ai>

* fix custom sensor system example build (#2649)

Signed-off-by: Ian Chen <ichen@openrobotics.org>

* remove stray change

Signed-off-by: Arjo Chakravarty <arjoc@intrinsic.ai>

---------

Signed-off-by: Arjo Chakravarty <arjoc@intrinsic.ai>
Signed-off-by: Ian Chen <ichen@openrobotics.org>
Co-authored-by: Ian Chen <ichen@openrobotics.org>
(cherry picked from commit 1a881310cfe2e1c97bdb7d606cf973eebc17a6c1)
---
 include/gz/sim/components/Model.hh | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/include/gz/sim/components/Model.hh b/include/gz/sim/components/Model.hh
index decd6776ed..524581f6c0 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 +97,18 @@ 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())
       {
-        gzwarn << "Unable to deserialize sdf::Model" << std::endl;
+        gzwarn << "Unable to deserialize sdf::Model " << sdf<< std::endl;
         return _in;
       }