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 75 of file TTreeProcessorMT.hxx.

Public Member Functions
	TTreeProcessorMT (const std::vector< std::string_view > &filenames, std::string_view treename="", UInt_t nThreads=0u)
	Constructor based on a collection of file names.

	TTreeProcessorMT (std::string_view filename, std::string_view treename="", UInt_t nThreads=0u)
	Constructor based on a file name.

	TTreeProcessorMT (TTree &tree, const TEntryList &entries, UInt_t nThreads=0u)
	Constructor based on a TTree and a TEntryList.

	TTreeProcessorMT (TTree &tree, UInt_t nThreads=0u)
	Constructor based on a TTree.

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

Static Public Member Functions
static unsigned int	GetTasksPerWorkerHint ()
	Retrieve the current value for the desired number of tasks per worker.

static void	SetTasksPerWorkerHint (unsigned int m)
	Set the hint for the desired number of tasks created per worker.

Private Member Functions
std::vector< std::string >	FindTreeNames ()
	Retrieve the names of the TTrees in each of the input files, throw if a TTree cannot be found.

Private Attributes
TEntryList	fEntryList
	User-defined selection of entry numbers to be processed, empty if none was provided.

const std::vector< std::string >	fFileNames
	Names of the files.

const Internal::TreeUtils::RFriendInfo	fFriendInfo

ROOT::TThreadExecutor	fPool
	! Thread pool for processing.

const std::vector< std::string >	fTreeNames
	TTree names (always same size and ordering as fFileNames)

ROOT::TThreadedObject< ROOT::Internal::TTreeView >	fTreeView {TNumSlots{ROOT::GetThreadPoolSize()}}
	Thread-local TreeViews.

Static Private Attributes
static unsigned int	fgTasksPerWorkerHint = 10U

#include <ROOT/TTreeProcessorMT.hxx>

Constructor & Destructor Documentation

◆ TTreeProcessorMT() [1/4]

TTreeProcessorMT::TTreeProcessorMT	(	std::string_view	filename,
		std::string_view	treename = `""`,
		UInt_t	nThreads = `0u`
	)

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 search for a TTree key in the file and will use the first one it finds.
[in]	nThreads	Number of threads to create in the underlying thread-pool. The semantics of this argument are the same as for TThreadExecutor.

Definition at line 427 of file TTreeProcessorMT.cxx.

◆ TTreeProcessorMT() [2/4]

TTreeProcessorMT::TTreeProcessorMT	(	const std::vector< std::string_view > &	filenames,
		std::string_view	treename = `""`,
		UInt_t	nThreads = `0u`
	)

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 search filenames for a TTree key and will use the first one it finds in each file.
[in]	nThreads	Number of threads to create in the underlying thread-pool. The semantics of this argument are the same as for TThreadExecutor.

If different files contain TTrees with different names and automatic TTree name detection is not an option (for example, because some of the files contain multiple TTrees) please manually create a TChain and pass it to the appropriate TTreeProcessorMT constructor.

Definition at line 458 of file TTreeProcessorMT.cxx.

◆ TTreeProcessorMT() [3/4]

TTreeProcessorMT::TTreeProcessorMT	(	TTree &	tree,
		const TEntryList &	entries,
		UInt_t	nThreads = `0u`
	)

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.
[in]	nThreads	Number of threads to create in the underlying thread-pool. The semantics of this argument are the same as for TThreadExecutor.

Definition at line 474 of file TTreeProcessorMT.cxx.

◆ TTreeProcessorMT() [4/4]

TTreeProcessorMT::TTreeProcessorMT	(	TTree &	tree,
		UInt_t	nThreads = `0u`
	)

Constructor based on a TTree.

Parameters

[in]	tree	Tree or chain of files containing the tree to process.
[in]	nThreads	Number of threads to create in the underlying thread-pool. The semantics of this argument are the same as for TThreadExecutor.

Definition at line 487 of file TTreeProcessorMT.cxx.

Member Function Documentation

◆ FindTreeNames()

std::vector< std::string > TTreeProcessorMT::FindTreeNames ( )

private

Retrieve the names of the TTrees in each of the input files, throw if a TTree cannot be found.

Definition at line 393 of file TTreeProcessorMT.cxx.

◆ GetTasksPerWorkerHint()

unsigned int TTreeProcessorMT::GetTasksPerWorkerHint ( )

static

Retrieve the current value for the desired number of tasks per worker.

Returns: The desired number of tasks to be created per worker. TTreeProcessorMT uses this value as an hint.

Definition at line 578 of file TTreeProcessorMT.cxx.

◆ 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 506 of file TTreeProcessorMT.cxx.

◆ SetTasksPerWorkerHint()

void TTreeProcessorMT::SetTasksPerWorkerHint ( unsigned int tasksPerWorkerHint )

static

Set the hint for the desired number of tasks created per worker.

Parameters

[in] tasksPerWorkerHint Desired number of tasks per worker.

This allows to create a reasonable number of tasks even if any of the processed files features a bad clustering, for example with a lot of entries and just a few entries per cluster, or to limit the number of tasks spawned when a very large number of files and workers is used.

Definition at line 591 of file TTreeProcessorMT.cxx.

Member Data Documentation

◆ fEntryList

TEntryList ROOT::TTreeProcessorMT::fEntryList

private

User-defined selection of entry numbers to be processed, empty if none was provided.

Definition at line 80 of file TTreeProcessorMT.hxx.

◆ fFileNames

const std::vector<std::string> ROOT::TTreeProcessorMT::fFileNames

private

Names of the files.

Definition at line 77 of file TTreeProcessorMT.hxx.

◆ fFriendInfo

const Internal::TreeUtils::RFriendInfo ROOT::TTreeProcessorMT::fFriendInfo

private

Definition at line 81 of file TTreeProcessorMT.hxx.

◆ fgTasksPerWorkerHint

unsigned int ROOT::TTreeProcessorMT::fgTasksPerWorkerHint = 10U

staticprivate

Definition at line 89 of file TTreeProcessorMT.hxx.

◆ fPool

ROOT::TThreadExecutor ROOT::TTreeProcessorMT::fPool

private

! Thread pool for processing.

Definition at line 82 of file TTreeProcessorMT.hxx.

◆ fTreeNames

const std::vector<std::string> ROOT::TTreeProcessorMT::fTreeNames

private

TTree names (always same size and ordering as fFileNames)

Definition at line 78 of file TTreeProcessorMT.hxx.

◆ fTreeView

ROOT::TThreadedObject<ROOT::Internal::TTreeView> ROOT::TTreeProcessorMT::fTreeView {TNumSlots{ROOT::GetThreadPoolSize()}}

private

Thread-local TreeViews.

Definition at line 86 of file TTreeProcessorMT.hxx.

Libraries for ROOT::TTreeProcessorMT:

[legend]

The documentation for this class was generated from the following files:

tree/treeplayer/inc/ROOT/TTreeProcessorMT.hxx
tree/treeplayer/src/TTreeProcessorMT.cxx

Public Member Functions

Static Public Member Functions

Private Member Functions

Private Attributes

Static Private Attributes

Constructor & Destructor Documentation

◆ TTreeProcessorMT() [1/4]

◆ TTreeProcessorMT() [2/4]

◆ TTreeProcessorMT() [3/4]

◆ TTreeProcessorMT() [4/4]

Member Function Documentation

◆ FindTreeNames()

◆ GetTasksPerWorkerHint()

◆ Process()

◆ SetTasksPerWorkerHint()

Member Data Documentation

◆ fEntryList

◆ fFileNames

◆ fFriendInfo

◆ fgTasksPerWorkerHint

◆ fPool

◆ fTreeNames

◆ fTreeView