RFieldSoA.hxx

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/// \file ROOT/RField/RFieldSoA.hxx
/// \author Jakob Blomer <jblomer@cern.ch>
/// \date 2026-03-03
 
/*************************************************************************
 * Copyright (C) 1995-2026, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/
 
#ifndef ROOT_RField_SoA
#define ROOT_RField_SoA
 
#ifndef ROOT_RField
#error "Please include RField.hxx!"
#endif
 
#include <ROOT/RFieldBase.hxx>
#include <ROOT/RNTupleTypes.hxx>
 
#include <cstddef>
#include <functional>
#include <memory>
#include <mutex>
#include <string_view>
#include <typeinfo>
#include <vector>
 
class TClass;
 
namespace ROOT {
 
/// The SoA field provides I/O for an in-memory SoA layout linked to an on-disk collection of the underlying record.
/// As a concrete example, for an underlying record type
/// \code{.cpp}
/// struct PointRecord {
///    float px, py;
/// };
/// \endcode
/// a corresponding SoA layout will look like
/// \code{.cpp}
/// struct PointSoA {
///    ROOT::RVec<float> px;
///    ROOT::RVec<float> py;
/// };
/// \endcode
///
/// The SoA type has to be marked in the dictionary with the rntupleSoARecord attribute.
///
/// Since the on-disk representation is a collection of record type, the class version and checksum of the SoA type
/// itself is ignored.
class RSoAField : public RRuleField {
   class RSoADeleter : public RDeleter {
   private:
      TClass *fSoAClass;
 
   public:
      explicit RSoADeleter(TClass *cl);
      void operator()(void *objPtr, bool dtorOnly) final;
   };
 
   // A rule of the SoA type itself or one of its nested SoA types or base classes, togther with the offset
   // of the nested object in the SoA type.
   struct RRule {
      const TSchemaRule *fRule = nullptr;
      std::size_t fOffset = 0;
   };
 
   /// Direct access to the member fields of the underlying record. In case of a nested SoA type, this vector
   /// contains the contents of the inner fRecordMemberFields, too. Effectively, this record will contain all the
   /// fields of the underlying record type that correspond to terminal RVec members in a nested SoA type.
   /// Pointers in this vector point into the field hierarchy owned by fSubfields[0].
   std::vector<RFieldBase *> fRecordMemberFields;
   /// The offset of the RVec members in the SoA type in the same order as fRecordMemberFields.
   std::vector<std::size_t> fSoAMemberOffsets;
   ///< A deleter returned by each record member's GetDeleter()
   std::vector<std::unique_ptr<RDeleter>> fRecordMemberDeleters;
   ROOT::Internal::RColumnIndex fNWritten;
 
   /// Contains the I/O customization rules for fClass and all nested SoA classes and base classes,
   /// and the relative offset at which the rule needs to be applied.
   std::vector<RRule> fRules;
 
   /// For reading and writing, the RVecs of the SoA class do not have a dedicated field. The in-memory RVecs of the
   /// SoA object are used directly with the subfields of the underlying record type. For splitting a SoA class object
   /// (SplitValue()), however, we need actual RRVecFields so that we can recursively split the in-memory SoA value.
   /// The split fields are created only when SplitField() is called.
   /// In general, the number of split fields is different from the number of record member fields because there is
   /// one split field for every _direct_ member of the SoA class. Because nested SoA structs can have transient
   /// members, we can also not reuse fSoAMemberOffsets but we need to store the data member offsets.
   mutable std::unique_ptr<std::vector<std::unique_ptr<ROOT::RFieldBase>>> fSplitFields;
   mutable std::unique_ptr<std::vector<std::size_t>> fSplitOffsets;
   mutable std::unique_ptr<std::mutex> fLockSplitFields; ///< protects the fSplitFields member.
 
   RSoAField(std::string_view fieldName, const RSoAField &source); ///< Used by CloneImpl
   RSoAField(std::string_view fieldName, TClass *clSoA);
 
   /// Called during construction, picks up the (nested) member fields of the underlying record type(s) and its
   /// base classes. Also fills fRules.
   void CollectRecordMemberFields();
   /// For a nested SoA struct (either as a member of as a base class), use their fRecordMemberFields in this class,
   /// i.e. "unroll" the vectors in the nested SoA struct into the SoA base class.
   void GraftNestedMemberFields(const RSoAField &nestedSoA, std::size_t offsetInParent,
                                const std::function<RFieldBase *(const std::string &)> &fnRecordFieldFinder);
 
   void ReconstructSplitFields() const;
 
protected:
   std::unique_ptr<RFieldBase> CloneImpl(std::string_view newName) const final;
 
   const RColumnRepresentations &GetColumnRepresentations() const final;
   void GenerateColumns() final;
   void GenerateColumns(const ROOT::RNTupleDescriptor &desc) final;
 
   void ConstructValue(void *where) const final;
   std::unique_ptr<RDeleter> GetDeleter() const final { return std::make_unique<RSoADeleter>(fClass); }
 
   std::size_t AppendImpl(const void *from) final;
   void ReadGlobalImpl(ROOT::NTupleSize_t globalIndex, void *to) final;
 
   void CommitClusterImpl() final { fNWritten = 0; }
 
   std::unique_ptr<RFieldBase> BeforeConnectPageSource(ROOT::Internal::RPageSource &pageSource) final;
   void ReconcileOnDiskField(const RNTupleDescriptor &desc) final;
 
public:
   RSoAField(std::string_view fieldName, std::string_view className);
   RSoAField(RSoAField &&other) = default;
   RSoAField &operator=(RSoAField &&other) = default;
   ~RSoAField() override = default;
 
   std::vector<RValue> SplitValue(const RValue &value) const final;
   size_t GetValueSize() const final;
   size_t GetAlignment() const final;
   std::uint32_t GetTypeVersion() const final;
   std::uint32_t GetTypeChecksum() const final;
   /// For polymorphic classes (that declare or inherit at least one virtual method), return the expected dynamic type
   /// of any user object. If the class is not polymorphic, return nullptr.
   /// TODO(jblomer): use information in unique pointer field
   const std::type_info *GetPolymorphicTypeInfo() const;
   void AcceptVisitor(ROOT::Detail::RFieldVisitor &visitor) const final;
 
   TClass *GetSoAClass() const { return fClass; }
};
 
} // namespace ROOT
 
#endif // ROOT_RField_SoA