Fix GeneratorPythia8 construction

Fixes smaller issues introduced with the hybrid generator
refactoring:

- Make sure that internal configuration object is never null;
  In fact, it does not need to be a pointer.

- Make sure the internal configuration struct is initialized
  from the GeneratorPythia8Param configurable when using the
  default constructor.

This commit fixes an issue/segfault when running the following command

o2-sim-dpl-eventgen --generator external --nEvents 200 --aggregate-timeframe 10000 --configFile ${O2DPG_ROOT}/MC/config/ALICE3/ini/pythia8_pp_136tev.ini -b

(which defaults constructs a Pythia8 generator)

Generators/include/Generators/GeneratorPythia8.h

@@ -90,7 +90,7 @@ class GeneratorPythia8 : public Generator
   /** default constructor **/
   GeneratorPythia8();
   /** constructor **/
-  GeneratorPythia8(Pythia8GenConfig const& pars);
+  GeneratorPythia8(Pythia8GenConfig const&);
   /** constructor **/
   GeneratorPythia8(const Char_t* name, const Char_t* title = "ALICEo2 Pythia8 Generator");
   /** destructor **/
@@ -285,7 +285,7 @@ class GeneratorPythia8 : public Generator
   long mInitialRNGSeed = -1;   // initial seed for Pythia random number state;
                                // will be transported to Pythia in the Init function through the Pythia::readString("Random:seed") mechanism.
                                // Value of -1 means unitialized; 0 will be time-dependent and values >1 <= MAX_SEED concrete reproducible seeding
-  std::unique_ptr<Pythia8GenConfig> mGenConfig; // configuration object
+  Pythia8GenConfig mGenConfig; // configuration object
 
   constexpr static long MAX_SEED = 900000000;
 

Generators/src/GeneratorPythia8.cxx

@@ -53,33 +53,39 @@ GeneratorPythia8::GeneratorPythia8() : Generator("ALICEo2", "ALICEo2 Pythia8 Gen
   mInterfaceName = "pythia8";
 
   auto& param = GeneratorPythia8Param::Instance();
-  LOG(info) << "Instance \'Pythia8\' generator with following parameters";
+  LOG(info) << "Default Instance \'Pythia8\' generator with following parameters";
   LOG(info) << param;
 
-  setConfig(param.config);
-  setHooksFileName(param.hooksFileName);
-  setHooksFuncName(param.hooksFuncName);
+  // convert the outside singleton config to the internally used one
+  o2::eventgen::Pythia8GenConfig config{param.config,
+                                        param.hooksFileName, param.hooksFuncName, param.includePartonEvent, param.particleFilter, param.verbose};
+  mGenConfig = config;
+
+  setConfig(config.config);
+  setHooksFileName(config.hooksFileName);
+  setHooksFuncName(config.hooksFuncName);
+  // TODO: use constructor delegation to other interface
 }
 
 /*****************************************************************/
 
-GeneratorPythia8::GeneratorPythia8(Pythia8GenConfig const& pars) : Generator("ALICEo2", "ALICEo2 Pythia8 Generator")
+GeneratorPythia8::GeneratorPythia8(Pythia8GenConfig const& config) : Generator("ALICEo2", "ALICEo2 Pythia8 Generator")
 {
   /** constructor **/
 
   mInterface = reinterpret_cast<void*>(&mPythia);
   mInterfaceName = "pythia8";
 
   LOG(info) << "Instance \'Pythia8\' generator with following parameters";
-  LOG(info) << "config: " << pars.config;
-  LOG(info) << "hooksFileName: " << pars.hooksFileName;
-  LOG(info) << "hooksFuncName: " << pars.hooksFuncName;
+  LOG(info) << "config: " << config.config;
+  LOG(info) << "hooksFileName: " << config.hooksFileName;
+  LOG(info) << "hooksFuncName: " << config.hooksFuncName;
 
-  mGenConfig = std::make_unique<Pythia8GenConfig>(pars);
+  mGenConfig = config;
 
-  setConfig(pars.config);
-  setHooksFileName(pars.hooksFileName);
-  setHooksFuncName(pars.hooksFuncName);
+  setConfig(mGenConfig.config);
+  setHooksFileName(mGenConfig.hooksFileName);
+  setHooksFuncName(mGenConfig.hooksFuncName);
 }
 
 /*****************************************************************/
@@ -578,8 +584,7 @@ void GeneratorPythia8::pruneEvent(Pythia8::Event& event, Select select)
       }
     }
   }
-  int verbose = mGenConfig->verbose;
-  if (verbose) {
+  if (mGenConfig.verbose) {
     LOG(info) << "Pythia event was pruned from " << event.size()
               << " to " << pruned.size() << " particles";
   }
@@ -592,7 +597,7 @@ void GeneratorPythia8::initUserFilterCallback()
 {
   mUserFilterFcn = [](Pythia8::Particle const&) -> bool { return true; };
 
-  std::string filter = mGenConfig->particleFilter;
+  std::string filter = mGenConfig.particleFilter;
   if (filter.size() > 0) {
     LOG(info) << "Initializing the callback for user-based particle pruning " << filter;
     auto expandedFileName = o2::utils::expandShellVarsInFileName(filter);
@@ -621,7 +626,7 @@ Bool_t
   // event record in the AOD.
 
   std::function<bool(const Pythia8::Particle&)> partonSelect = [](const Pythia8::Particle&) { return true; };
-  bool includeParton = mGenConfig->includePartonEvent;
+  bool includeParton = mGenConfig.includePartonEvent;
   if (not includeParton) {
 
     // Select pythia particles