From 2e1cba92ce47533314e98405675ade9063bfc916 Mon Sep 17 00:00:00 2001
From: Roberto Preghenella <preghenella@bo.infn.it>
Date: Mon, 25 Jan 2021 14:45:35 +0100
Subject: [PATCH] Fix daughter labels when running parallel merger

---
 .../simulation/include/SimulationDataFormat/MCTrack.h        | 2 ++
 run/O2HitMerger.h                                            | 5 ++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/DataFormats/simulation/include/SimulationDataFormat/MCTrack.h b/DataFormats/simulation/include/SimulationDataFormat/MCTrack.h
index 87f57c3a0f406..851aca47823ed 100644
--- a/DataFormats/simulation/include/SimulationDataFormat/MCTrack.h
+++ b/DataFormats/simulation/include/SimulationDataFormat/MCTrack.h
@@ -202,6 +202,8 @@ class MCTrackT
   }
   bool getInhibited() const { return ((PropEncoding)mProp).inhibited; }
 
+  bool isTransported() const { return getToBeDone() && !getInhibited(); };
+
   /// get the string representation of the production process
   const char* getProdProcessAsString() const;
 
diff --git a/run/O2HitMerger.h b/run/O2HitMerger.h
index 2b90119ea2715..edf69637d1981 100644
--- a/run/O2HitMerger.h
+++ b/run/O2HitMerger.h
@@ -343,7 +343,10 @@ class O2HitMerger : public FairMQDevice
       originbr->GetEntry(index);
       for (Int_t i = 0; i < nprimaries[index]; i++) {
         auto& track = incomingdata->at(i);
-        track.SetFirstDaughterTrackId(-1);
+        if (track.isTransported()) { // reset daughters only if track was transported, it will be fixed below
+          track.SetFirstDaughterTrackId(-1);
+          track.SetLastDaughterTrackId(-1);
+        }
         targetdata->push_back(track);
       }
       incomingdata->clear();