Support downloading simulation assets in the background

Signed-off-by: Nate Koenig <[email protected]>

include/gz/sim/ServerConfig.hh

@@ -447,6 +447,20 @@ namespace gz
       public: const std::chrono::time_point<std::chrono::system_clock> &
               Timestamp() const;
 
+      /// \brief Set whether asset download should block the start of
+      /// simulation.
+      /// The default value is true.
+      /// \param[in] _set True to wait while assets download. False will
+      /// download assets in a background thread.
+      public: void SetWaitForAssets(bool _set);
+
+      /// \brief Get whether asset download should block the start of
+      /// simulation.
+      /// The default value is true.
+      /// \return True if simulation should wait while assets download. False
+      /// indicates assets should be downloaded in a separate thread.
+      public: bool WaitForAssets() const;
+
       /// \brief Get the type of source
       /// \return The source type.
       public: SourceType Source() const;

src/SdfEntityCreator.cc

@@ -332,7 +332,6 @@ void SdfEntityCreator::CreateEntities(const sdf::World *_world,
     const sdf::Model *model = _world->ModelByIndex(modelIndex);
     if (levelEntityNames.empty() ||
         levelEntityNames.find(model->Name()) != levelEntityNames.end())
-
     {
       Entity modelEntity = this->CreateEntities(model);
 

src/Server.cc

@@ -69,6 +69,11 @@ Server::Server(const ServerConfig &_config)
     config.SetCacheLocation(_config.ResourceCache());
   this->dataPtr->fuelClient = std::make_unique<fuel_tools::FuelClient>(config);
 
+  // Turn off downloads so that we can do an initial parsing of the SDF
+  // file. This will let us get the world names, which in turn allows the
+  // GUI to not-block while simulation assets download.
+  this->dataPtr->enableDownload = false;
+
   // Configure SDF to fetch assets from Gazebo Fuel.
   sdf::setFindCallback(std::bind(&ServerPrivate::FetchResource,
         this->dataPtr.get(), std::placeholders::_1));
@@ -77,37 +82,51 @@ Server::Server(const ServerConfig &_config)
 
   addResourcePaths();
 
-  // Loads the SDF root object based on values in a ServerConfig object.
-  sdf::Errors errors = this->dataPtr->LoadSdfRootHelper(_config);
+  sdf::Root sdfRoot;
 
-  if (!errors.empty())
+  // Loads the SDF root object based on values in a ServerConfig object.
+  // Ignore the sdf::Errors returned by this function. The errors will be
+  // displayed later in the downloadThread.
+  ServerConfig cfg = _config;
+  cfg.SetBehaviorOnSdfErrors(
+    ServerConfig::SdfErrorBehavior::CONTINUE_LOADING);
+  sdf::Errors errors = this->dataPtr->LoadSdfRootHelper(
+    cfg, sdfRoot);
+
+  // Remove all the models, lights, and actors from the primary sdfRoot object
+  // so that they can be downloaded and added to simulation in the background.
+  for (uint64_t i = 0; i < sdfRoot.WorldCount(); ++i)
   {
-    for (auto &err : errors)
-      gzerr << err << "\n";
-    if (_config.BehaviorOnSdfErrors() ==
-        ServerConfig::SdfErrorBehavior::EXIT_IMMEDIATELY)
-    {
-      return;
-    }
+    sdfRoot.WorldByIndex(i)->ClearModels();
+    sdfRoot.WorldByIndex(i)->ClearActors();
+    sdfRoot.WorldByIndex(i)->ClearLights();
   }
 
-  // Add record plugin
-  if (_config.UseLogRecord())
-  {
-    this->dataPtr->AddRecordPlugin(_config);
-  }
+  // This will create the simulation runners.
+  this->dataPtr->CreateSimulationRunners(sdfRoot);
+
+  // Storing the sdf root. The ServerPrivate.hh header file mentions
+  // that other classes may keep pointers to child nodes of the root,
+  // so we need to keep this object around.
+  // However, everything seems to work fine without storing this.
+  // \todo(nkoenig): Look into removing the sdfRoot member variable.
+  this->dataPtr->sdfRoot = sdfRoot;
+
+  // Establish publishers and subscribers. Setup transport before
+  // downloading simulation assets so that the GUI is not blocked during
+  // download.
+  this->dataPtr->SetupTransport();
 
-  this->dataPtr->CreateEntities();
+  // Download the simulation assets. This function will block if
+  // _config.WaitForAssets() is true;
+  this->dataPtr->DownloadAssets(_config);
 
   // Set the desired update period, this will override the desired RTF given in
-  // the world file which was parsed by CreateEntities.
+  // the world file which was parsed by LoadSdfRootHelper.
   if (_config.UpdatePeriod())
   {
     this->SetUpdatePeriod(_config.UpdatePeriod().value());
   }
-
-  // Establish publishers and subscribers.
-  this->dataPtr->SetupTransport();
 }
 
 /////////////////////////////////////////////////

src/ServerConfig.cc

@@ -208,8 +208,10 @@ class gz::sim::ServerConfigPrivate
             seed(_cfg->seed),
             logRecordTopics(_cfg->logRecordTopics),
             isHeadlessRendering(_cfg->isHeadlessRendering),
+            sdfRoot(_cfg->sdfRoot),
             source(_cfg->source),
-            behaviorOnSdfErrors(_cfg->behaviorOnSdfErrors){ }
+            behaviorOnSdfErrors(_cfg->behaviorOnSdfErrors),
+            waitForAssets(_cfg->waitForAssets) { }
 
   // \brief The SDF file that the server should load
   public: std::string sdfFile = "";
@@ -297,6 +299,9 @@ class gz::sim::ServerConfigPrivate
   /// \brief Server loading behavior in presence of SDF errors.
   public: ServerConfig::SdfErrorBehavior behaviorOnSdfErrors{
       ServerConfig::SdfErrorBehavior::EXIT_IMMEDIATELY};
+
+  /// \brief True to block while simulation assets download.
+  public: bool waitForAssets = true;
 };
 
 //////////////////////////////////////////////////
@@ -737,6 +742,18 @@ ServerConfig::Timestamp() const
   return this->dataPtr->timestamp;
 }
 
+/////////////////////////////////////////////////
+void ServerConfig::SetWaitForAssets(bool _set)
+{
+  this->dataPtr->waitForAssets = _set;
+}
+
+/////////////////////////////////////////////////
+bool ServerConfig::WaitForAssets() const
+{
+  return this->dataPtr->waitForAssets;
+}
+
 /////////////////////////////////////////////////
 void ServerConfig::AddLogRecordTopic(const std::string &_topic)
 {