Implemented suggestions from code review

Author: jackal1-66

Generators/include/Generators/Generator.h

@@ -104,6 +104,7 @@ class Generator : public FairGenerator
 
   // Number of parallel sub-generator clones a Hyperloop-aware generator expands into
   // (currently used by the external-generator-to-hybrid expansion in GeneratorFactory).
+  // 8 matches the standard core counts of Grid/Hyperloop nodes
   static constexpr int NHyperloopParallelGenerators = 8;
 
   /** other **/

Generators/src/GeneratorFactory.cxx

@@ -60,6 +60,11 @@ namespace eventgen
 // using the configured GeneratorExternalParam. This makes the simulation parallelisation automatic
 // on Hyperloop.
 // To-do: Define the behaviour with ini configuration which are already definining a hybrid gen
+//
+// Note on GeneratorHybrid.num_workers: expanding to 8 sub-generators does not by itself raise
+// the number of TBB workers that actually run them in parallel. This is controlled by
+// the parameter GeneratorHybrid.num_workers. On Hyperloop this will be part
+// of the standard train configuration
 std::string buildHyperloopExternalHybridConfig(GeneratorExternalParam const& extparams)
 {
   rapidjson::Document doc;
@@ -84,10 +89,12 @@ std::string buildHyperloopExternalHybridConfig(GeneratorExternalParam const& ext
   doc.AddMember("generators", generators, alloc);
   doc.AddMember("fractions", fractions, alloc);
 
+  // The generated config file is deliberatelly left on disk for possible inspection after the process ran.
   std::string path = "hyperloop_exttohybrid_" + std::to_string(getpid()) + ".json";
   std::ofstream ofs(path);
   if (!ofs.is_open()) {
     LOG(fatal) << "Failed to open " << path << " for writing the Hyperloop hybrid generator configuration";
+    exit(1);
   }
   rapidjson::OStreamWrapper osw(ofs);
   rapidjson::Writer<rapidjson::OStreamWrapper> writer(osw);

Generators/src/GeneratorHybrid.cxx

@@ -122,6 +122,13 @@ GeneratorHybrid::GeneratorHybrid(const std::string& inputgens)
         mGens.push_back(gen);
       } else if (gen.compare("external") == 0) {
         int confextIndex = std::stoi(mConfigs[index].substr(9));
+        // Hybrid configs can clone the same external generator config multiple times so
+        // an external macro that self-seeds from gRandom could sample the same seed.
+        // For this reason the shared RNG state is advanced as a precaution
+        // mirroring what GeneratorPythia8::seedGenerator() does for multiple Pythia8 instances.
+        if (std::count(mGens.begin(), mGens.end(), "external") > 0) {
+          gRandom->Rndm();
+        }
         // we need analyse the ini file to update the config key param
         if (mExternalGenConfigs[confextIndex]->iniFile.size() > 0) {
           LOG(info) << "Setting up external gen using the given INI file";