Add Init protection + stop() subgens + protection against nextEvent

Author: jackal1-66

Generators/include/Generators/GeneratorHybrid.h

@@ -64,7 +64,7 @@ class GeneratorHybrid : public Generator
   Bool_t generateEvent() override;
   Bool_t importParticles() override;
   void updateHeader(o2::dataformats::MCEventHeader* eventHeader) override;
-  void stop() override; // end-of-stream hook that closes the TBB task arena
+  void stop() override; // end-of-stream hook that joins the TBB task pool
 
   Bool_t parseJSON(const std::string& path);
   Bool_t confSetter(const auto& gen);

Generators/src/GeneratorHybrid.cxx

@@ -210,10 +210,20 @@ void GeneratorHybrid::stop()
     auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now() - t0).count();
     LOG(info) << "HybridGen: stop() joined TBB task pool after " << ms << " ms";
   }
+  // Forward the hook to the sub-generators
+  for (auto& gen : gens) {
+    if (gen) {
+      gen->stop();
+    }
+  }
 }
 
 Bool_t GeneratorHybrid::Init()
 {
+  // protection against additional Init() which would assign over a joinable mTBBTaskPoolRunner, which calls std::terminate
+  if (mIsInitialized) {
+    return true;
+  }
   // init all sub-gens
   int count = 0;
   for (auto& gen : mGens) {
@@ -474,6 +484,9 @@ bool GeneratorHybrid::importParticles()
   // this is important when using event pools where the full header information is forwarded from the generator
   // otherwise some events might have mixed header information from different generators
   mMCEventHeader.Reset();
+  // Once the event budget is exhausted there is no further event to prepare, and re-queueing a
+  // sub-generator would start an event nobody consumes and that stop() then has to wait for
+  const bool queueNextEvent = getTotalNEvents() == 0 || mEventCounter + 1 < getTotalNEvents();
   if (mCocktailMode) {
     // in cocktail mode we need to merge the particles from the different generators
     for (auto subIndex : subGenIndex) {
@@ -504,8 +517,10 @@ bool GeneratorHybrid::importParticles()
         gens[subIndex]->updateHeader(&mMCEventHeader);
         mHeaderGeneratorIndex = subIndex; // store index of generator updating the header
       }
-      mInputTaskQueue.push(subIndex);
-      mTasksStarted++;
+      if (queueNextEvent) {
+        mInputTaskQueue.push(subIndex);
+        mTasksStarted++;
+      }
     }
   } else {
     if (!mIsHyperloop) {
@@ -528,8 +543,10 @@ bool GeneratorHybrid::importParticles()
     // fetch the event Header information from the underlying generator
     gens[genIndex]->updateHeader(&mMCEventHeader);
     mHeaderGeneratorIndex = genIndex; // store index of generator updating the header
-    mInputTaskQueue.push(genIndex);
-    mTasksStarted++;
+    if (queueNextEvent) {
+      mInputTaskQueue.push(genIndex);
+      mTasksStarted++;
+    }
   }
 
   mseqCounter++;