OpenMM plugin folders are only loaded once per path per execution.

modules/mol/mm/src/simulation.cc

@@ -267,6 +267,16 @@ SimulationPtr Simulation::Load(const String& filename, SettingsPtr settings){
 }
 
 
+void Simulation::EnsurePluginsLoaded(const String& plugin_path) {
+  // note: this is guaranteed to be constructed on first use only
+  static std::set<String> already_loaded;
+  if (already_loaded.find(plugin_path) == already_loaded.end()) {
+    // not loaded yet: load directory, but only once!
+    OpenMM::Platform::loadPluginsFromDirectory(plugin_path);
+    already_loaded.insert(plugin_path);
+  }
+}
+
 
 void Simulation::Init(const TopologyPtr top,
                       const SettingsPtr settings){

modules/mol/mm/src/simulation.hh

@@ -145,6 +145,9 @@ private:
 
   int TimeToNextNotification();
 
+  // loads plugins from directory for OpenMM BUT only once per unique path!
+  static void EnsurePluginsLoaded(const String& plugin_path);
+
   SystemPtr system_;
   IntegratorPtr integrator_;
   ContextPtr context_;