A class to process the entries of a TTree in parallel.

By means of its Process method, ROOT::TTreeProcessorMT provides a way to process the entries of a TTree in parallel. When invoking TTreeProcessor::Process, the user passes a function whose only parameter is a TTreeReader. The function iterates on a subrange of entries by using that TTreeReader.

The implementation of ROOT::TTreeProcessorMT parallelizes the processing of the subranges, each corresponding to a cluster in the TTree. This is possible thanks to the use of a ROOT::TThreadedObject, so that each thread works with its own TFile and TTree objects.

Definition at line 316 of file TTreeProcessorMT.hxx.

Public Member Functions
	TTreeProcessorMT (std::string_view filename, std::string_view treename="")
	Constructor based on a file name. More...

	TTreeProcessorMT (const std::vector< std::string_view > &filenames, std::string_view treename="")
	Constructor based on a collection of file names. More...

	TTreeProcessorMT (TTree &tree)
	Constructor based on a TTree. More...

	TTreeProcessorMT (TTree &tree, TEntryList &entries)
	Constructor based on a TTree and a TEntryList. More...

void	Process (std::function< void(TTreeReader &)> func)
	Process the entries of a TTree in parallel. More...

Private Attributes
ROOT::TThreadedObject< ROOT::Internal::TTreeView >	treeView
	! Thread-local TreeViews More...

#include <ROOT/TTreeProcessorMT.hxx>

Constructor & Destructor Documentation

◆ TTreeProcessorMT() [1/4]

TTreeProcessorMT::TTreeProcessorMT	(	std::string_view	filename,
		std::string_view	treename = `""`
	)

Constructor based on a file name.

Parameters

[in]	filename	Name of the file containing the tree to process.
[in]	treename	Name of the tree to process. If not provided, the implementation will automatically search for a tree in the file.

Definition at line 152 of file TTreeProcessorMT.cxx.

◆ TTreeProcessorMT() [2/4]

TTreeProcessorMT::TTreeProcessorMT	(	const std::vector< std::string_view > &	filenames,
		std::string_view	treename = `""`
	)

Constructor based on a collection of file names.

Parameters

[in]	filenames	Collection of the names of the files containing the tree to process.
[in]	treename	Name of the tree to process. If not provided, the implementation will automatically search for a tree in the collection of files.

Definition at line 160 of file TTreeProcessorMT.cxx.

◆ TTreeProcessorMT() [3/4]

TTreeProcessorMT::TTreeProcessorMT ( TTree & tree )

Constructor based on a TTree.

Parameters

[in] tree Tree or chain of files containing the tree to process.

Definition at line 165 of file TTreeProcessorMT.cxx.

◆ TTreeProcessorMT() [4/4]

TTreeProcessorMT::TTreeProcessorMT	(	TTree &	tree,
		TEntryList &	entries
	)

Constructor based on a TTree and a TEntryList.

Parameters

[in]	tree	Tree or chain of files containing the tree to process.
[in]	entries	List of entry numbers to process.

Definition at line 171 of file TTreeProcessorMT.cxx.

Member Function Documentation

◆ Process()

void TTreeProcessorMT::Process ( std::function< void(TTreeReader &)> func )

Process the entries of a TTree in parallel.

The user-provided function receives a TTreeReader which can be used to iterate on a subrange of entries

TTreeProcessorMT::Process([](TTreeReader& readerSubRange) {
                           // Select branches to read
                           while (readerSubRange.next()) {
                               // Use content of current entry
                           }
                        });

The user needs to be aware that each of the subranges can potentially be processed in parallel. This means that the code of the user function should be thread safe.

Parameters

[in] func User-defined function that processes a subrange of entries

Definition at line 190 of file TTreeProcessorMT.cxx.