Merge pull request #35204 from Dr15Jones/moveMPIInitSherpaHadronizer

Fixed exceptional case handling in SherpaHadronizer

GeneratorInterface/SherpaInterface/src/SherpaHadronizer.cc

@@ -23,6 +23,8 @@
 
 #include "CLHEP/Random/RandomEngine.h"
 
+#include "FWCore/Utilities/interface/Exception.h"
+
 //This unnamed namespace is used (instead of static variables) to pass the
 //randomEngine passed to doSetRandomEngine to the External Random
 //Number Generator CMS_SHERPA_RNG of sherpa
@@ -95,8 +97,11 @@ void SherpaHadronizer::doSetRandomEngine(CLHEP::HepRandomEngine *v) {
       SetExternalEngine(v);
       // Throw exception if there is no reference to an external RNG and it is not the first call!
     } else {
-      throw edm::Exception(edm::errors::LogicError) << "The Sherpa interface got a randomEngine reference but there is "
-                                                       "no reference to the external RNG to hand it over to\n";
+      if (isInitialized and v != nullptr) {
+        throw edm::Exception(edm::errors::LogicError)
+            << "The Sherpa interface got a randomEngine reference but there is "
+               "no reference to the external RNG to hand it over to\n";
+      }
     }
   } else {
     cmsSherpaRng->setRandomEngine(v);
@@ -199,6 +204,9 @@ SherpaHadronizer::SherpaHadronizer(const edm::ParameterSet &params)
   arguments.push_back(shRng);
   isInitialized = false;
   //initialization of Sherpa moved to initializeForInternalPartons
+#ifdef USING__MPI
+  MPI::Init();
+#endif
 }
 
 SherpaHadronizer::~SherpaHadronizer() {
@@ -210,14 +218,12 @@ SherpaHadronizer::~SherpaHadronizer() {
 
 bool SherpaHadronizer::initializeForInternalPartons() {
   //initialize Sherpa but only once
+  throw cms::Exception("TEST");
   if (!isInitialized) {
     int argc = arguments.size();
     char *argv[argc];
     for (int l = 0; l < argc; l++)
       argv[l] = (char *)arguments[l].c_str();
-#ifdef USING__MPI
-    MPI::Init();
-#endif
     Generator->InitializeTheRun(argc, argv);
     Generator->InitializeTheEventHandler();
     isInitialized = true;