From 9f11f51ae82e9f1d046f2c6666fe72c768c4c872 Mon Sep 17 00:00:00 2001
From: Frank Winklmeier <frank.winklmeier@cern.ch>
Date: Thu, 25 Aug 2022 10:11:12 +0200
Subject: [PATCH] G4ExternalDecay: thread-checker fixes

Cleanup the `Pythia8ForDecays` singleton (no need for complicated mutex
logic, static initialization is thread-safe) and mark is as not
thread-safe because it exposes a non-const pointer to a static.
---
 .../G4Extensions/G4ExternalDecay/CMakeLists.txt     |  6 ++----
 .../G4ExternalDecay/ATLAS_CHECK_THREAD_SAFETY       |  1 +
 .../G4ExternalDecay/Pythia8ForDecays.h              | 13 +++++--------
 .../G4ExternalDecay/src/Pythia8ForDecays.cxx        | 13 ++++---------
 4 files changed, 12 insertions(+), 21 deletions(-)
 create mode 100644 Simulation/G4Extensions/G4ExternalDecay/G4ExternalDecay/ATLAS_CHECK_THREAD_SAFETY

diff --git a/Simulation/G4Extensions/G4ExternalDecay/CMakeLists.txt b/Simulation/G4Extensions/G4ExternalDecay/CMakeLists.txt
index 181c1a740d5..619384a27e8 100644
--- a/Simulation/G4Extensions/G4ExternalDecay/CMakeLists.txt
+++ b/Simulation/G4Extensions/G4ExternalDecay/CMakeLists.txt
@@ -1,6 +1,4 @@
-################################################################################
-# Package: G4ExternalDecay
-################################################################################
+# Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
 
 # Declare the package name:
 atlas_subdir( G4ExternalDecay )
@@ -37,5 +35,5 @@ atlas_add_library( G4ExternalDecay
                    INCLUDE_DIRS ${XERCESC_INCLUDE_DIRS} ${CLHEP_INCLUDE_DIRS} ${LHAPDF_INCLUDE_DIRS} ${GEANT4_INCLUDE_DIRS} ${PYTHIA8_INCLUDE_DIRS} ${extra_includes}
                    PRIVATE_INCLUDE_DIRS 
                    DEFINITIONS ${CLHEP_DEFINITIONS}
-                   LINK_LIBRARIES ${XERCESC_LIBRARIES} ${CLHEP_LIBRARIES} ${PYTHIA8_LIBRARIES} ${LHAPDF_LIBRARIES} ${GEANT4_LIBRARIES} Pythia8_iLib ${extra_libs}
+                   LINK_LIBRARIES ${XERCESC_LIBRARIES} ${CLHEP_LIBRARIES} ${PYTHIA8_LIBRARIES} ${LHAPDF_LIBRARIES} ${GEANT4_LIBRARIES} CxxUtils Pythia8_iLib ${extra_libs}
                    PRIVATE_LINK_LIBRARIES AtlasHepMCLib )
diff --git a/Simulation/G4Extensions/G4ExternalDecay/G4ExternalDecay/ATLAS_CHECK_THREAD_SAFETY b/Simulation/G4Extensions/G4ExternalDecay/G4ExternalDecay/ATLAS_CHECK_THREAD_SAFETY
new file mode 100644
index 00000000000..9271bccd5d6
--- /dev/null
+++ b/Simulation/G4Extensions/G4ExternalDecay/G4ExternalDecay/ATLAS_CHECK_THREAD_SAFETY
@@ -0,0 +1 @@
+Simulation/G4Extensions/G4ExternalDecay
diff --git a/Simulation/G4Extensions/G4ExternalDecay/G4ExternalDecay/Pythia8ForDecays.h b/Simulation/G4Extensions/G4ExternalDecay/G4ExternalDecay/Pythia8ForDecays.h
index a782ed4ef76..d9e5c6148e0 100644
--- a/Simulation/G4Extensions/G4ExternalDecay/G4ExternalDecay/Pythia8ForDecays.h
+++ b/Simulation/G4Extensions/G4ExternalDecay/G4ExternalDecay/Pythia8ForDecays.h
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
 */
 
 // Abused from Geant4 version of Pythai6.hh from extended examples
@@ -15,9 +15,10 @@
 #include <utility>
 // For all the various Pythia8 classes used here
 #include "Pythia8_i/Pythia8_i.h"
-// For unique_ptr and once flag
+// For unique_ptr
 #include <memory>
-#include <mutex>
+// For ATLAS THREAD macros
+#include "CxxUtils/checker_macros.h"
 
 class G4DynamicParticle;
 class G4ParticleDefinition;
@@ -28,7 +29,7 @@ class Pythia8ForDecays
 
    virtual ~Pythia8ForDecays() = default;
 
-   static Pythia8ForDecays *Instance();
+   static Pythia8ForDecays *Instance ATLAS_NOT_THREAD_SAFE ();
 
    /// Function that decays the RHadron; returns products in G4 format
    void Py1ent(const G4Track&, std::vector<G4DynamicParticle*> &);
@@ -49,10 +50,6 @@ class Pythia8ForDecays
    std::pair<int,int> fromIdWithSquark( int idRHad) const;
    bool isGluinoRHadron(int pdgId) const;
 
-   /// My own class; singleton pattern; thread safe for future-proofing
-   static std::unique_ptr<Pythia8ForDecays> s_instance;
-   static std::once_flag m_onceFlag;
-
    /// The instance of Pythia8 that will do the work
    std::unique_ptr<Pythia8::Pythia> m_pythia;
 };
diff --git a/Simulation/G4Extensions/G4ExternalDecay/src/Pythia8ForDecays.cxx b/Simulation/G4Extensions/G4ExternalDecay/src/Pythia8ForDecays.cxx
index c5173dcb754..fa7eba76cb6 100644
--- a/Simulation/G4Extensions/G4ExternalDecay/src/Pythia8ForDecays.cxx
+++ b/Simulation/G4Extensions/G4ExternalDecay/src/Pythia8ForDecays.cxx
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
 */
 
 // Abused from Pythia6.cc in Geant4 extended examples
@@ -30,15 +30,10 @@
 #include <cmath>
 #include <fstream>
 
-std::unique_ptr<Pythia8ForDecays> Pythia8ForDecays::s_instance(nullptr);
-std::once_flag Pythia8ForDecays::m_onceFlag;
 
-Pythia8ForDecays* Pythia8ForDecays::Instance() {
-  std::call_once(m_onceFlag,
-        [] {
-            s_instance.reset(new Pythia8ForDecays);
-    });
-  return s_instance.get();
+Pythia8ForDecays* Pythia8ForDecays::Instance ATLAS_NOT_THREAD_SAFE () {
+  static Pythia8ForDecays instance;
+  return &instance;
 }
 
 Pythia8ForDecays::Pythia8ForDecays()
-- 
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