ITS: Vertexer tighten condition atomic write path

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

Author: f3sch

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

@@ -301,6 +301,10 @@ void VertexerTraits::computeTrackletMatching(const int iteration)
           bounded_vector<bool> usedTracklets(mTimeFrame->getFoundTracklets(pivotRofId, 0).size(), false, mMemoryPool.get());
           short startROF{std::max((short)0, static_cast<short>(pivotRofId - mVrtParams[iteration].deltaRof))};
           short endROF{std::min(static_cast<short>(mTimeFrame->getNrof()), static_cast<short>(pivotRofId + mVrtParams[iteration].deltaRof + 1))};
+
+          // needed only if multi-threaded using deltaRof and only at the overlap edges of the ranges
+          bool safeWrite = mTaskArena->max_concurrency() > 1 && mVrtParams[iteration].deltaRof != 0 && ((Rofs.begin() - startROF < 0) || (endROF - Rofs.end() > 0));
+
           for (short targetRofId0 = startROF; targetRofId0 < endROF; ++targetRofId0) {
             for (short targetRofId2 = startROF; targetRofId2 < endROF; ++targetRofId2) {
               if (std::abs(targetRofId0 - targetRofId2) > mVrtParams[iteration].deltaRof) { // do not allow over 3 ROFs
@@ -321,7 +325,7 @@ void VertexerTraits::computeTrackletMatching(const int iteration)
                 mTimeFrame->getLinesLabel(pivotRofId),
                 targetRofId0,
                 targetRofId2,
-                mTaskArena->max_concurrency() > 1 && mVrtParams[iteration].deltaRof != 0,
+                safeWrite,
                 mVrtParams[iteration].tanLambdaCut,
                 mVrtParams[iteration].phiCut);
             }