From a5790649e0fb231a7cbc426a7ac546686fb3fd54 Mon Sep 17 00:00:00 2001
From: Sven Dildick <sven.dildick@cern.ch>
Date: Sun, 3 Oct 2021 09:37:38 -0500
Subject: [PATCH 1/2] Fix thread-safety problems with simhit fitting

---
 Validation/MuonHits/BuildFile.xml           | 1 +
 Validation/MuonHits/src/CSCSimHitMatcher.cc | 7 ++++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/Validation/MuonHits/BuildFile.xml b/Validation/MuonHits/BuildFile.xml
index d27bfdba5b88a..bf0af0c9516a7 100644
--- a/Validation/MuonHits/BuildFile.xml
+++ b/Validation/MuonHits/BuildFile.xml
@@ -12,6 +12,7 @@
 <use name="SimDataFormats/Vertex"/>
 <use name="root"/>
 <use name="clhep"/>
+<use name="rootminuit"/>
 <export>
   <lib name="1"/>
 </export>
diff --git a/Validation/MuonHits/src/CSCSimHitMatcher.cc b/Validation/MuonHits/src/CSCSimHitMatcher.cc
index 4734f8e2637d7..429d1d6ef8b6c 100644
--- a/Validation/MuonHits/src/CSCSimHitMatcher.cc
+++ b/Validation/MuonHits/src/CSCSimHitMatcher.cc
@@ -1,6 +1,7 @@
 #include "Validation/MuonHits/interface/CSCSimHitMatcher.h"
 #include "TGraphErrors.h"
 #include "TF1.h"
+#include "TMinuitMinimizer.h"
 
 using namespace std;
 
@@ -13,6 +14,10 @@ CSCSimHitMatcher::CSCSimHitMatcher(const edm::ParameterSet& ps, edm::ConsumesCol
 
   simHitInput_ = iC.consumes<edm::PSimHitContainer>(simHitPSet_.getParameter<edm::InputTag>("inputTag"));
   geomToken_ = iC.esConsumes<CSCGeometry, MuonGeometryRecord>();
+
+  //In order to make fitting ROOT histograms thread safe
+  // one must call this undocumented function
+  TMinuitMinimizer::UseStaticMinuit(false);
 }
 
 /// initialize the event
@@ -237,7 +242,7 @@ void CSCSimHitMatcher::fitHitsInChamber(unsigned int detid, float& intercept, fl
 
   std::unique_ptr<TGraphErrors> gr(new TGraphErrors(x.size(), &x[0], &y[0], &xe[0], &ye[0]));
   std::unique_ptr<TF1> fit(new TF1("fit", "pol1", -3, 4));
-  gr->Fit("fit", "EMQ");
+  gr->Fit("fit", "EMQN");
 
   intercept = fit->GetParameter(0);
   slope = fit->GetParameter(1);

From 35bcf43f0ea73c66cedcb9ae4b4c882f923b5eca Mon Sep 17 00:00:00 2001
From: Sven Dildick <sven.dildick@cern.ch>
Date: Mon, 4 Oct 2021 12:30:58 -0500
Subject: [PATCH 2/2] Suggestion by Chris Jones

---
 Validation/MuonHits/src/CSCSimHitMatcher.cc | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/Validation/MuonHits/src/CSCSimHitMatcher.cc b/Validation/MuonHits/src/CSCSimHitMatcher.cc
index 429d1d6ef8b6c..e05554563d8f5 100644
--- a/Validation/MuonHits/src/CSCSimHitMatcher.cc
+++ b/Validation/MuonHits/src/CSCSimHitMatcher.cc
@@ -241,11 +241,11 @@ void CSCSimHitMatcher::fitHitsInChamber(unsigned int detid, float& intercept, fl
     return;
 
   std::unique_ptr<TGraphErrors> gr(new TGraphErrors(x.size(), &x[0], &y[0], &xe[0], &ye[0]));
-  std::unique_ptr<TF1> fit(new TF1("fit", "pol1", -3, 4));
-  gr->Fit("fit", "EMQN");
+  TF1 fit("fit", "pol1", -3, 4);
+  gr->Fit(&fit, "EMQN");
 
-  intercept = fit->GetParameter(0);
-  slope = fit->GetParameter(1);
+  intercept = fit.GetParameter(0);
+  slope = fit.GetParameter(1);
 }
 
 float CSCSimHitMatcher::simHitsMeanStrip(const edm::PSimHitContainer& sim_hits) const {