Refactor the RNTupleWriter internals and reduce some code duplication

include/podio/GenericParameters.h

@@ -6,6 +6,7 @@
 
 #include <algorithm>
 #include <iostream>
+#include <iterator>
 #include <map>
 #include <memory>
 #include <mutex>
@@ -105,6 +106,10 @@ class GenericParameters {
   template <typename T, typename = EnableIfValidGenericDataType<T>>
   std::vector<std::string> getKeys() const;
 
+  /// Get all the available values for a given type
+  template <typename T, typename = EnableIfValidGenericDataType<T>>
+  std::vector<std::vector<T>> getValues() const;
+
   /// erase all elements
   void clear() {
     _intMap.clear();
@@ -243,5 +248,17 @@ std::vector<std::string> GenericParameters::getKeys() const {
   return keys;
 }
 
+template <typename T, typename>
+std::vector<std::vector<T>> GenericParameters::getValues() const {
+  std::vector<std::vector<T>> values;
+  {
+    auto& mtx = getMutex<T>();
+    const auto& map = getMap<T>();
+    std::lock_guard lock{mtx};
+    values.reserve(map.size());
+    std::transform(map.begin(), map.end(), std::back_inserter(values), [](const auto& pair) { return pair.second; });
+  }
+  return values;
+}
 } // namespace podio
 #endif

include/podio/RNTupleReader.h

@@ -1,8 +1,6 @@
 #ifndef PODIO_RNTUPLEREADER_H
 #define PODIO_RNTUPLEREADER_H
 
-#include "podio/CollectionBranches.h"
-#include "podio/ICollectionProvider.h"
 #include "podio/ROOTFrameData.h"
 #include "podio/SchemaEvolution.h"
 #include "podio/podioVersion.h"

include/podio/RNTupleWriter.h

@@ -1,11 +1,11 @@
 #ifndef PODIO_RNTUPLEWRITER_H
 #define PODIO_RNTUPLEWRITER_H
 
-#include "podio/CollectionBase.h"
 #include "podio/Frame.h"
 #include "podio/GenericParameters.h"
 #include "podio/SchemaEvolution.h"
 #include "podio/utilities/DatamodelRegistryIOHelpers.h"
+#include "podio/utilities/RootHelpers.h"
 
 #include "TFile.h"
 #include <ROOT/RNTuple.hxx>
@@ -102,42 +102,42 @@ class RNTupleWriter {
   checkConsistency(const std::vector<std::string>& collsToWrite, const std::string& category) const;
 
 private:
-  template <typename T>
-  void fillParams(GenericParameters& params, ROOT::Experimental::REntry* entry);
+  std::unique_ptr<ROOT::Experimental::RNTupleModel>
+  createModels(const std::vector<root_utils::StoreCollection>& collections);
+
+  /// Helper struct to group all the necessary information for one category.
+  struct CategoryInfo {
+    std::unique_ptr<ROOT::Experimental::RNTupleWriter> writer{nullptr}; ///< The RNTupleWriter for this category
+
+    // The following are assumed to run in parallel!
+    std::vector<uint32_t> ids{};                  ///< The ids of all collections
+    std::vector<std::string> names{};             ///< The names of all collections
+    std::vector<std::string> types{};             ///< The types of all collections
+    std::vector<short> subsetCollections{};       ///< The flags identifying the subcollections
+    std::vector<SchemaVersionT> schemaVersions{}; ///< The schema versions of all collections
+
+    // Storage for the keys & values of all the parameters of this category
+    // (resp. at least the current entry)
+    root_utils::ParamStorage<int> intParams{};
+    root_utils::ParamStorage<float> floatParams{};
+    root_utils::ParamStorage<double> doubleParams{};
+    root_utils::ParamStorage<std::string> stringParams{};
+  };
+  CategoryInfo& getCategoryInfo(const std::string& category);
 
-  using StoreCollection = std::pair<const std::string&, podio::CollectionBase*>;
-  std::unique_ptr<ROOT::Experimental::RNTupleModel> createModels(const std::vector<StoreCollection>& collections);
+  template <typename T>
+  void fillParams(const GenericParameters& params, CategoryInfo& catInfo, ROOT::Experimental::REntry* entry);
 
-  std::unique_ptr<ROOT::Experimental::RNTupleModel> m_metadata{};
-  std::unique_ptr<ROOT::Experimental::RNTupleWriter> m_metadataWriter{};
+  template <typename T>
+  root_utils::ParamStorage<T>& getParamStorage(CategoryInfo& catInfo);
 
   std::unique_ptr<TFile> m_file{};
 
   DatamodelDefinitionCollector m_datamodelCollector{};
 
-  struct CollectionInfo {
-    std::vector<uint32_t> id{};
-    std::vector<std::string> name{};
-    std::vector<std::string> type{};
-    std::vector<short> isSubsetCollection{};
-    std::vector<SchemaVersionT> schemaVersion{};
-    std::unique_ptr<ROOT::Experimental::RNTupleWriter> writer{nullptr};
-  };
-  CollectionInfo& getCategoryInfo(const std::string& category);
-
-  std::unordered_map<std::string, CollectionInfo> m_categories{};
+  std::unordered_map<std::string, CategoryInfo> m_categories{};
 
   bool m_finished{false};
-
-  std::vector<std::string> m_intkeys{}, m_floatkeys{}, m_doublekeys{}, m_stringkeys{};
-
-  std::vector<std::vector<int>> m_intvalues{};
-  std::vector<std::vector<float>> m_floatvalues{};
-  std::vector<std::vector<double>> m_doublevalues{};
-  std::vector<std::vector<std::string>> m_stringvalues{};
-
-  template <typename T>
-  std::pair<std::vector<std::string>&, std::vector<std::vector<T>>&> getKeyValueVectors();
 };
 
 } // namespace podio

include/podio/ROOTLegacyReader.h

@@ -1,13 +1,12 @@
 #ifndef PODIO_ROOTLEGACYREADER_H
 #define PODIO_ROOTLEGACYREADER_H
 
-#include "podio/CollectionBranches.h"
 #include "podio/ROOTFrameData.h"
 #include "podio/podioVersion.h"
+#include "podio/utilities/RootHelpers.h"
 
 #include "TChain.h"
 
-#include <iostream>
 #include <memory>
 #include <string>
 #include <tuple>
@@ -114,7 +113,7 @@ class ROOTLegacyReader {
 private:
   std::pair<TTree*, unsigned> getLocalTreeAndEntry(const std::string& treename);
 
-  void createCollectionBranches(const std::vector<std::tuple<uint32_t, std::string, bool, unsigned int>>& collInfo);
+  void createCollectionBranches(const std::vector<root_utils::CollectionWriteInfoT>& collInfo);
 
   podio::GenericParameters readEventMetaData();
 

include/podio/ROOTReader.h

@@ -1,14 +1,13 @@
 #ifndef PODIO_ROOTREADER_H
 #define PODIO_ROOTREADER_H
 
-#include "podio/CollectionBranches.h"
 #include "podio/ROOTFrameData.h"
 #include "podio/podioVersion.h"
 #include "podio/utilities/DatamodelRegistryIOHelpers.h"
+#include "podio/utilities/RootHelpers.h"
 
 #include "TChain.h"
 
-#include <iostream>
 #include <memory>
 #include <string>
 #include <string_view>

include/podio/ROOTWriter.h

@@ -1,9 +1,9 @@
 #ifndef PODIO_ROOTWRITER_H
 #define PODIO_ROOTWRITER_H
 
-#include "podio/CollectionBranches.h"
 #include "podio/CollectionIDTable.h"
 #include "podio/utilities/DatamodelRegistryIOHelpers.h"
+#include "podio/utilities/RootHelpers.h"
 
 #include "TFile.h"
 
@@ -100,31 +100,25 @@ class ROOTWriter {
   checkConsistency(const std::vector<std::string>& collsToWrite, const std::string& category) const;
 
 private:
-  using StoreCollection = std::pair<const std::string&, podio::CollectionBase*>;
-
-  // collectionID, collectionType, subsetCollection
-  // @note same as in rootUtils.h private header!
-  using CollectionInfoT = std::tuple<uint32_t, std::string, bool, unsigned int>;
-
   /// Helper struct to group together all necessary state to write / process a
   /// given category. Created during the first writing of a category
   struct CategoryInfo {
-    TTree* tree{nullptr};                                   ///< The TTree to which this category is written
-    std::vector<root_utils::CollectionBranches> branches{}; ///< The branches for this category
-    std::vector<CollectionInfoT> collInfo{};                ///< Collection info for this category
-    podio::CollectionIDTable idTable{};                     ///< The collection id table for this category
-    std::vector<std::string> collsToWrite{};                ///< The collections to write for this category
+    TTree* tree{nullptr};                                     ///< The TTree to which this category is written
+    std::vector<root_utils::CollectionBranches> branches{};   ///< The branches for this category
+    std::vector<root_utils::CollectionWriteInfoT> collInfo{}; ///< Collection info for this category
+    podio::CollectionIDTable idTable{};                       ///< The collection id table for this category
+    std::vector<std::string> collsToWrite{};                  ///< The collections to write for this category
   };
 
   /// Initialize the branches for this category
-  void initBranches(CategoryInfo& catInfo, const std::vector<StoreCollection>& collections,
+  void initBranches(CategoryInfo& catInfo, const std::vector<root_utils::StoreCollection>& collections,
                     /*const*/ podio::GenericParameters& parameters);
 
   /// Get the (potentially uninitialized category information for this category)
   CategoryInfo& getCategoryInfo(const std::string& category);
 
   static void resetBranches(std::vector<root_utils::CollectionBranches>& branches,
-                            const std::vector<ROOTWriter::StoreCollection>& collections,
+                            const std::vector<root_utils::StoreCollection>& collections,
                             /*const*/ podio::GenericParameters* parameters);
 
   std::unique_ptr<TFile> m_file{nullptr};                       ///< The storage file

include/podio/utilities/RootHelpers.h

@@ -0,0 +1,44 @@
+#ifndef PODIO_UTILITIES_ROOTHELPERS_H
+#define PODIO_UTILITIES_ROOTHELPERS_H
+
+#include "TBranch.h"
+
+#include <string>
+#include <tuple>
+#include <vector>
+
+namespace podio {
+class CollectionBase;
+
+namespace root_utils {
+
+  // A collection of additional information that describes the collection: the
+  // collectionID, the collection (data) type, whether it is a subset
+  // collection, and its schema version
+  using CollectionWriteInfoT = std::tuple<uint32_t, std::string, bool, unsigned int>;
+  // for backwards compatibility
+  using CollectionInfoWithoutSchemaT = std::tuple<int, std::string, bool>;
+
+  /// A collection name and a base pointer grouped together for writing
+  using StoreCollection = std::tuple<const std::string&, podio::CollectionBase*>;
+
+  /// Small helper struct to collect all branches that are necessary to read or
+  /// write a collection. Needed to cache the branch pointers and avoid having to
+  /// get them from a TTree/TChain for every event.
+  struct CollectionBranches {
+    TBranch* data{nullptr};
+    std::vector<TBranch*> refs{};
+    std::vector<TBranch*> vecs{};
+    std::vector<std::string> refNames{}; ///< The names of the relation branches
+    std::vector<std::string> vecNames{}; ///< The names of the vector member branches
+  };
+
+  /// Pair of keys and values for one type of the ones that can be stored in
+  /// GenericParameters
+  template <typename T>
+  using ParamStorage = std::tuple<std::vector<std::string>, std::vector<std::vector<T>>>;
+
+} // namespace root_utils
+} // namespace podio
+
+#endif // PODIO_UTILITIES_ROOTHELPERS_H

src/CMakeLists.txt

@@ -94,6 +94,7 @@ SET(root_headers
   ${PROJECT_SOURCE_DIR}/include/podio/ROOTLegacyReader.h
   ${PROJECT_SOURCE_DIR}/include/podio/ROOTWriter.h
   ${PROJECT_SOURCE_DIR}/include/podio/ROOTFrameData.h
+  ${PROJECT_SOURCE_DIR}/include/podio/utilities/RootHelpers.h
   )
 if(ENABLE_RNTUPLE)
   list(APPEND root_headers