Do not take ownership of CCDB distortion maps in the TPC digitizer

This fixes a double ownership of the TPC space-charge maps and prepares sharing them between digitizers.

- setUseSCDistortions(SC*) and setSCDistortionsDerivative(SC*) took ownership of objects that the DPL CCDB cache owns and deletes itself when a newer object replaces them.
- The Digitizer now owns only the maps it creates itself.
- The map members are transient for ROOT I/O.

https://its.cern.ch/jira/browse/O2-7309

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: sawenzel

Detectors/TPC/simulation/include/TPCSimulation/Digitizer.h

@@ -118,10 +118,10 @@ class Digitizer
   /// \param nRBins number of grid points in r, must be (2**N)+1
   void setUseSCDistortions(const SCDistortionType& distortionType, const TH3* hisInitialSCDensity);
   /// Enable the use of space-charge distortions and provide SpaceCharge object as input
-  /// \param spaceCharge unique pointer to spaceCharge object
+  /// \param spaceCharge spaceCharge object, not owned: the caller (e.g. the DPL CCDB cache) keeps it alive
   void setUseSCDistortions(SC* spaceCharge);
 
-  /// \param spaceCharge unique pointer to spaceCharge object
+  /// \param spaceCharge spaceCharge object of the derivative map, not owned: the caller keeps it alive
   void setSCDistortionsDerivative(SC* spaceCharge);
 
   /// Enable the use of space-charge distortions by providing global distortions and global corrections stored in a ROOT file
@@ -142,20 +142,21 @@ class Digitizer
   void recalculateDistortions();
 
  private:
-  DigitContainer mDigitContainer;      ///< Container for the Digits
-  std::unique_ptr<SC> mSpaceCharge;    ///< Handler of full distortions (static + IR dependant)
-  std::unique_ptr<SC> mSpaceChargeDer; ///< Handler of reference static distortions
-  Sector mSector = -1;                 ///< ID of the currently processed sector
-  double mEventTime = 0.f;             ///< Time of the currently processed event
-  double mOutputDigitTimeOffset = 0;   ///< Time of the first IR sampled in the digitizer
-  float mVDrift = 0;                   ///< VDrift for current timestamp
-  float mTDriftOffset = 0;             ///< drift time additive offset in \mus
-  bool mIsContinuous;                  ///< Switch for continuous readout
-  bool mUseSCDistortions = false;      ///< Flag to switch on the use of space-charge distortions
-  int mDistortionScaleType = 0;        ///< type=0: no scaling of distortions, type=1 distortions without any scaling, type=2 distortions scaling with lumi
-  float mLumiScaleFactor = 0;          ///< value used to scale the derivative map
-  bool mUseScaledDistortions = false;  ///< whether the distortions are already scaled
-  ClassDefNV(Digitizer, 3);
+  DigitContainer mDigitContainer;        ///< Container for the Digits
+  std::unique_ptr<SC> mSpaceChargeOwned; //!< Distortions created by the digitizer itself
+  SC* mSpaceCharge = nullptr;            //!< Handler of full distortions (static + IR dependant), owned by mSpaceChargeOwned or by the caller
+  SC* mSpaceChargeDer = nullptr;         //!< Handler of reference static distortions, owned by the caller
+  Sector mSector = -1;                   ///< ID of the currently processed sector
+  double mEventTime = 0.f;               ///< Time of the currently processed event
+  double mOutputDigitTimeOffset = 0;     ///< Time of the first IR sampled in the digitizer
+  float mVDrift = 0;                     ///< VDrift for current timestamp
+  float mTDriftOffset = 0;               ///< drift time additive offset in \mus
+  bool mIsContinuous;                    ///< Switch for continuous readout
+  bool mUseSCDistortions = false;        ///< Flag to switch on the use of space-charge distortions
+  int mDistortionScaleType = 0;          ///< type=0: no scaling of distortions, type=1 distortions without any scaling, type=2 distortions scaling with lumi
+  float mLumiScaleFactor = 0;            ///< value used to scale the derivative map
+  bool mUseScaledDistortions = false;    ///< whether the distortions are already scaled
+  ClassDefNV(Digitizer, 4);
 };
 } // namespace tpc
 } // namespace o2

Detectors/TPC/simulation/src/Digitizer.cxx

@@ -83,7 +83,7 @@ void Digitizer::process(const std::vector<o2::tpc::HitGroup>& hits,
       if (mDistortionScaleType == 1) {
         mSpaceCharge->distortElectron(posEle);
       } else if (mDistortionScaleType == 2) {
-        mSpaceCharge->distortElectron(posEle, (mUseScaledDistortions ? nullptr : mSpaceChargeDer.get()), mLumiScaleFactor);
+        mSpaceCharge->distortElectron(posEle, (mUseScaledDistortions ? nullptr : mSpaceChargeDer), mLumiScaleFactor);
       }
 
       /// Remove electrons that end up more than three sigma of the hit's average diffusion away from the current sector
@@ -182,7 +182,8 @@ void Digitizer::setUseSCDistortions(const SCDistortionType& distortionType, cons
 {
   mUseSCDistortions = true;
   if (!mSpaceCharge) {
-    mSpaceCharge = std::make_unique<SC>();
+    mSpaceChargeOwned = std::make_unique<SC>();
+    mSpaceCharge = mSpaceChargeOwned.get();
   }
   mSpaceCharge->setSCDistortionType(distortionType);
   if (hisInitialSCDensity) {
@@ -194,14 +195,17 @@ void Digitizer::setUseSCDistortions(const SCDistortionType& distortionType, cons
 void Digitizer::setUseSCDistortions(SC* spaceCharge)
 {
   mUseSCDistortions = true;
-  mSpaceCharge.reset(spaceCharge);
+  if (spaceCharge != mSpaceChargeOwned.get()) {
+    mSpaceChargeOwned.reset();
+  }
+  mSpaceCharge = spaceCharge;
   mSpaceCharge->initAfterReadingFromFile();
   mSpaceCharge->printMetaData();
 }
 
 void Digitizer::setSCDistortionsDerivative(SC* spaceCharge)
 {
-  mSpaceChargeDer.reset(spaceCharge);
+  mSpaceChargeDer = spaceCharge;
   mSpaceChargeDer->initAfterReadingFromFile();
   mSpaceChargeDer->printMetaData();
 }
@@ -210,7 +214,8 @@ void Digitizer::setUseSCDistortions(std::string_view finp)
 {
   mUseSCDistortions = true;
   if (!mSpaceCharge) {
-    mSpaceCharge = std::make_unique<SC>();
+    mSpaceChargeOwned = std::make_unique<SC>();
+    mSpaceCharge = mSpaceChargeOwned.get();
   }
 
   // in case analytical distortions are loaded from file they are applied
@@ -268,7 +273,7 @@ void Digitizer::recalculateDistortions()
       mSpaceChargeDer->calcGlobalCorrWithGlobalDistIterative(side, nullptr, 0);
 
       LOGP(info, "Calculating scaled distortions with scaling factor {}", mLumiScaleFactor);
-      mSpaceCharge->calcGlobalDistWithGlobalCorrIterativeLinearCartesian(side, mSpaceChargeDer.get(), mLumiScaleFactor);
+      mSpaceCharge->calcGlobalDistWithGlobalCorrIterativeLinearCartesian(side, mSpaceChargeDer, mLumiScaleFactor);
     }
     // set new lumi of avg map
     mSpaceCharge->setMeanLumi(CorrMapParam::Instance().lumiInst);