[SofaPython3] Separates the pre-loaded python modules out of the python environment (BUGFIX)

The execution of Sofa from a python3 environement is not working anymore because
some features need Sofa & SofaRuntime modules to be loaded but the loading is done when
initializing only in the embeded python interpreter.

To fix this, the PR move the module loading and access into its own singleton that initialize at
first use.

Fixing that is important for 22.06 release.
For the future, refactoring the PythonEnvironment file to split PythonEnvironment in two, to separate what is actually relevant for the PythonEnvironment and what
should be part something like PythonEmbededInterpreter.

Author: damienmarchal

Plugin/src/SofaPython3/PythonEnvironment.cpp

@@ -60,6 +60,13 @@ MSG_REGISTER_CLASS(sofapython3::PythonEnvironment, "SofaPython3::PythonEnvironme
 namespace sofapython3
 {
 
+class PythonEnvironmentModule
+{
+public:
+    py::module m_sofaModule ;
+    py::module m_sofaRuntimeModule ;
+};
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 /// \brief The PythonEnvironmentData class which hold "static" data as long as python is running
 ///
@@ -102,9 +109,6 @@ class PythonEnvironmentData
     }
 
     std::set<std::string> addedPath;
-
-    py::module m_sofaModule ;
-    py::module m_sofaRuntimeModule ;
 private:
     std::vector<wchar_t*> m_argv;
 };
@@ -114,11 +118,28 @@ PythonEnvironmentData* PythonEnvironment::getStaticData()
     static PythonEnvironmentData* m_staticdata { nullptr } ;
 
     if( !m_staticdata )
+    {
         m_staticdata = new PythonEnvironmentData();
-
+    }
     return m_staticdata;
 }
 
+PythonEnvironmentModule* PythonEnvironment::getStaticModule()
+{
+    PythonEnvironment::gil lock;
+
+    static PythonEnvironmentModule* m_staticmodule { nullptr } ;
+    if( !m_staticmodule )
+    {
+        m_staticmodule = new PythonEnvironmentModule();
+        executePython([]{
+            getStaticModule()->m_sofaModule = py::module::import("Sofa");
+            getStaticModule()->m_sofaRuntimeModule = py::module::import("SofaRuntime");
+        });
+    }
+    return m_staticmodule;
+}
+
 std::string PythonEnvironment::pluginLibraryPath = "";
 
 SOFAPYTHON3_API py::module PythonEnvironment::importFromFile(const std::string& module, const std::string& path, py::object* globals)
@@ -156,7 +177,6 @@ void PythonEnvironment::Init()
         SceneLoaderFactory::getInstance()->addEntry(new SceneLoaderPY3());
     }
 
-
 #if defined(__linux__)
     // WARNING: workaround to be able to import python libraries on linux (like
     // numpy), at least on Ubuntu (see http://bugs.python.org/issue4434). It is
@@ -237,8 +257,6 @@ void PythonEnvironment::Init()
     // Lastly, we (try to) add modules from the root of SOFA
     addPythonModulePathsFromDirectory( Utils::getSofaPathPrefix() );
 
-    executePython([]{ getStaticData()->m_sofaModule = py::module::import("Sofa"); });
-    executePython([]{ getStaticData()->m_sofaRuntimeModule = py::module::import("SofaRuntime"); });
     executePython([]{ PyRun_SimpleString("import SofaRuntime");});
 
     // python livecoding related
@@ -365,7 +383,7 @@ void PythonEnvironment::addPythonModulePathsFromDirectory(const std::string& dir
     }
 
     // For each of the directories in pythonDirs, search for a site-packages entry
-    for(std::string searchDir : searchDirs)
+    for(std::string& searchDir : searchDirs)
     {
         // Search for a subdir "site-packages"
         if (FileSystem::exists(searchDir + "/site-packages") && FileSystem::isDirectory(searchDir + "/site-packages"))
@@ -508,13 +526,13 @@ std::string PythonEnvironment::getStackAsString()
 std::string PythonEnvironment::getPythonCallingPointString()
 {
     gil lock;
-    return py::cast<std::string>(getStaticData()->m_sofaModule.attr("getPythonCallingPointAsString")());
+    return py::cast<std::string>(getStaticModule()->m_sofaModule.attr("getPythonCallingPointAsString")());
 }
 
 sofa::helper::logging::FileInfo::SPtr PythonEnvironment::getPythonCallingPointAsFileInfo()
 {
     gil lock;
-    py::tuple cp = getStaticData()->m_sofaRuntimeModule.attr("getPythonCallingPoint")();
+    py::tuple cp = getStaticModule()->m_sofaRuntimeModule.attr("getPythonCallingPoint")();
     return SOFA_FILE_INFO_COPIED_FROM(py::cast<std::string>(cp[0]), py::cast<int>(cp[1]));
 }
 

Plugin/src/SofaPython3/PythonEnvironment.h

@@ -52,6 +52,7 @@ using sofa::simulation::SceneLoader ;
 
 /// Forward definition
 class PythonEnvironmentData ;
+class PythonEnvironmentModule ;
 
 class SOFAPYTHON3_API PythonEnvironment
 {
@@ -154,6 +155,7 @@ class SOFAPYTHON3_API PythonEnvironment
 
 private:
     static PythonEnvironmentData* getStaticData() ;
+    static PythonEnvironmentModule* getStaticModule() ;
     static std::string pluginLibraryPath;
     static inline bool s_isInitialized{false};
 };