Fix timeframe aggregation in dpl-eventgen

* precalculate batch size so it does not depend on the event counter
  updated in the generator loop
* use DataAllocator::make instead of snapshot to reduce memory churn

Author: aalkin

Generators/include/Generators/GeneratorService.h

@@ -20,6 +20,7 @@
 #include <SimulationDataFormat/MCTrack.h>
 #include <Generators/PrimaryGenerator.h> // could be forward declaration
 #include <DetectorsBase/Stack.h>
+#include <MemoryResources/MemoryResources.h>
 
 namespace o2
 {
@@ -66,6 +67,7 @@ class GeneratorService
   std::pair<std::vector<MCTrack>, o2::dataformats::MCEventHeader> generateEvent();
 
   void generateEvent_MCTracks(std::vector<MCTrack>& tracks, o2::dataformats::MCEventHeader& header);
+  void generateEvent_MCTracks(o2::pmr::vector<MCTrack>& tracks, o2::dataformats::MCEventHeader& header);
   void generateEvent_TParticles(std::vector<TParticle>& tparts, o2::dataformats::MCEventHeader& header);
 
  private:

Generators/src/GeneratorService.cxx

@@ -61,6 +61,18 @@ void GeneratorService::generateEvent_MCTracks(std::vector<MCTrack>& tracks, o2::
   }
 }
 
+void GeneratorService::generateEvent_MCTracks(o2::pmr::vector<MCTrack>& tracks, o2::dataformats::MCEventHeader& header)
+{
+  mPrimGen.SetEvent(&header);
+  mStack.Reset();
+  mPrimGen.GenerateEvent(&mStack); // this is the usual FairROOT interface going via stack
+
+  tracks.reserve(mStack.getPrimaries().size());
+  for (auto& tparticle : mStack.getPrimaries()) {
+    tracks.emplace_back(tparticle);
+  }
+}
+
 std::pair<std::vector<o2::MCTrack>, o2::dataformats::MCEventHeader> GeneratorService::generateEvent()
 {
   std::vector<o2::MCTrack> tracks;

run/dpl_eventgen.cxx

@@ -50,6 +50,9 @@ struct GeneratorTask {
   std::unique_ptr<o2::eventgen::GeneratorService> genservice;
   TStopwatch timer;
 
+  std::vector<o2::pmr::vector<o2::MCTrack>*> mctracks_vector;
+  std::vector<o2::dataformats::MCEventHeader*> mcheader_vector;
+
   void init(o2::framework::InitContext& /*ic*/)
   {
     genservice.reset(new o2::eventgen::GeneratorService);
@@ -85,25 +88,31 @@ struct GeneratorTask {
       outfile.reset(new TFile(kineoutfilename.c_str(), "RECREATE"));
       outtree.reset(new TTree("o2sim", "o2sim"));
     }
+
+    mctracks_vector.reserve(aggregate);
+    mcheader_vector.reserve(aggregate);
   }
 
   void run(o2::framework::ProcessingContext& pc)
   {
-    std::vector<o2::MCTrack> mctracks;
-    o2::dataformats::MCEventHeader mcheader;
-    auto mctrack_ptr = &mctracks;
-    if (outfile.get()) {
-      auto br = o2::base::getOrMakeBranch(*outtree, "MCTrack", &mctrack_ptr);
-      br->SetAddress(&mctrack_ptr);
-    }
+    mctracks_vector.clear();
+    mcheader_vector.clear();
 
-    for (auto i = 0; i < std::min((GenCount)aggregate, nEvents - eventCounter); ++i) {
-      mctracks.clear();
-      genservice->generateEvent_MCTracks(mctracks, mcheader);
-      pc.outputs().snapshot(Output{"MC", "MCHEADER", 0}, mcheader);
-      pc.outputs().snapshot(Output{"MC", "MCTRACKS", 0}, mctracks);
+    auto batch = std::min((GenCount)aggregate, nEvents - eventCounter);
+    for (auto i = 0U; i < batch; ++i) {
+      mctracks_vector.push_back(&pc.outputs().make<o2::pmr::vector<o2::MCTrack>>(Output{"MC", "MCTRACKS", 0}));
+      auto& mctracks = mctracks_vector.back();
+      mcheader_vector.push_back(&pc.outputs().make<o2::dataformats::MCEventHeader>(Output{"MC", "MCHEADER", 0}));
+      auto& mcheader = mcheader_vector.back();
+      genservice->generateEvent_MCTracks(*mctracks, *mcheader);
       ++eventCounter;
 
+      auto mctrack_ptr = mctracks;
+      if (outfile.get()) {
+        auto br = o2::base::getOrMakeBranch(*outtree, "MCTrack", &mctrack_ptr);
+        br->SetAddress(&mctrack_ptr);
+      }
+
       if (outfile.get() && outtree.get()) {
         outtree->Fill();
       }
@@ -112,6 +121,7 @@ struct GeneratorTask {
     // report number of TFs injected for the rate limiter to work
     ++tfCounter;
     pc.services().get<o2::monitoring::Monitoring>().send(o2::monitoring::Metric{(uint64_t)tfCounter, "df-sent"}.addTag(o2::monitoring::tags::Key::Subsystem, o2::monitoring::tags::Value::DPL));
+
     bool time_expired = false;
     if (ttl > 0) {
       timer.Stop();
@@ -125,7 +135,7 @@ struct GeneratorTask {
       pc.services().get<ControlService>().endOfStream();
       pc.services().get<ControlService>().readyToQuit(QuitRequest::Me);
 
-      // write out data to disc if asked
+      // write out data to disk if asked
       if (outfile.get()) {
         outtree->SetEntries(eventCounter);
         outtree->Write();