ITS: TrackExtension fix dangling reference on vector reallocation

Signed-off-by: Felix Schlepper <felix.schlepper@cern.ch>

Author: f3sch

Detectors/ITSMFT/ITS/tracking/src/TrackerTraits.cxx

@@ -855,36 +855,40 @@ bool TrackerTraits::trackFollowing(TrackITSExt* track, int rof, bool outward, co
   auto propInstance = o2::base::Propagator::Instance();
   const int step = -1 + outward * 2;
   const int end = outward ? mTrkParams[iteration].NLayers - 1 : 0;
-  std::vector<TrackITSExt> hypotheses(1, *track);
-  for (auto& hypo : hypotheses) {
-    int iLayer = outward ? track->getLastClusterLayer() : track->getFirstClusterLayer();
+  std::vector<TrackITSExt> hypotheses(1, *track); // possibly avoid reallocation
+  for (size_t iHypo{0}; iHypo < hypotheses.size(); ++iHypo) {
+    auto hypo{hypotheses[iHypo]};
+    int iLayer = static_cast<int>(outward ? hypo.getLastClusterLayer() : hypo.getFirstClusterLayer());
+    // per layer we add new hypotheses
     while (iLayer != end) {
-      iLayer += step;
+      iLayer += step; // step through all layers until we reach the end, this allows for skipping on empty layers
       const float r = mTrkParams[iteration].LayerRadii[iLayer];
+      // get an estimate of the trackinf-frame x for the next step
       float x{-999};
       if (!hypo.getXatLabR(r, x, mTimeFrame->getBz(), o2::track::DirAuto) || x <= 0.f) {
         continue;
       }
-
+      // estimate hypo's trk parameters at that x
       auto& hypoParam{outward ? hypo.getParamOut() : hypo.getParamIn()};
       if (!propInstance->propagateToX(hypoParam, x, mTimeFrame->getBz(), PropagatorF::MAX_SIN_PHI,
                                       PropagatorF::MAX_STEP, mTrkParams[iteration].CorrType)) {
         continue;
       }
 
-      if (mTrkParams[iteration].CorrType == PropagatorF::MatCorrType::USEMatCorrNONE) {
-        float radl = 9.36f; // Radiation length of Si [cm]
-        float rho = 2.33f;  // Density of Si [g/cm^3]
+      if (mTrkParams[iteration].CorrType == PropagatorF::MatCorrType::USEMatCorrNONE) { // account for material affects if propagator does not
+        constexpr float radl = 9.36f;                                                   // Radiation length of Si [cm]
+        constexpr float rho = 2.33f;                                                    // Density of Si [g/cm^3]
         if (!hypoParam.correctForMaterial(mTrkParams[iteration].LayerxX0[iLayer], mTrkParams[iteration].LayerxX0[iLayer] * radl * rho, true)) {
           continue;
         }
       }
+
+      // calculate the search window on this layer
       const float phi{hypoParam.getPhi()};
       const float ePhi{o2::gpu::CAMath::Sqrt(hypoParam.getSigmaSnp2() / hypoParam.getCsp2())};
       const float z{hypoParam.getZ()};
       const float eZ{o2::gpu::CAMath::Sqrt(hypoParam.getSigmaZ2())};
       const int4 selectedBinsRect{getBinsRect(iLayer, phi, mTrkParams[iteration].NSigmaCut * ePhi, z, mTrkParams[iteration].NSigmaCut * eZ)};
-
       if (selectedBinsRect.x == 0 && selectedBinsRect.y == 0 && selectedBinsRect.z == 0 && selectedBinsRect.w == 0) {
         continue;
       }
@@ -900,9 +904,9 @@ bool TrackerTraits::trackFollowing(TrackITSExt* track, int rof, bool outward, co
         continue;
       }
 
-      TrackITSExt currentHypo{hypo}, newHypo{hypo};
-      bool first{true};
-      for (int iPhiCount{0}; iPhiCount < phiBinsNum; iPhiCount++) {
+      // check all clusters in search windows for possible new hypotheses
+#pragma omp parallel for num_threads(mNThreads) shared(hypotheses)
+      for (int iPhiCount = 0; iPhiCount < phiBinsNum; iPhiCount++) {
         int iPhiBin = (selectedBinsRect.y + iPhiCount) % mTrkParams[iteration].PhiBins;
         const int firstBinIndex{mTimeFrame->mIndexTableUtils.getBinIndex(selectedBinsRect.x, iPhiBin)};
         const int maxBinIndex{firstBinIndex + selectedBinsRect.z - selectedBinsRect.x + 1};
@@ -921,7 +925,7 @@ bool TrackerTraits::trackFollowing(TrackITSExt* track, int rof, bool outward, co
 
           const TrackingFrameInfo& trackingHit = mTimeFrame->getTrackingFrameInfoOnLayer(iLayer).at(nextCluster.clusterId);
 
-          TrackITSExt& tbupdated = first ? hypo : newHypo;
+          auto tbupdated{hypo};
           auto& tbuParams = outward ? tbupdated.getParamOut() : tbupdated.getParamIn();
           if (!tbuParams.rotate(trackingHit.alphaTrackingFrame)) {
             continue;
@@ -942,12 +946,10 @@ bool TrackerTraits::trackFollowing(TrackITSExt* track, int rof, bool outward, co
           }
           tbupdated.setChi2(tbupdated.getChi2() + predChi2); /// This is wrong for outward propagation as the chi2 refers to inward parameters
           tbupdated.setExternalClusterIndex(iLayer, nextCluster.clusterId, true);
-
-          if (!first) {
+#pragma omp critical
+          {
             hypotheses.emplace_back(tbupdated);
-            newHypo = currentHypo;
           }
-          first = false;
         }
       }
     }