ROOT   Reference Guide
ROOT::TTreeProcessorMT Class Reference

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 81 of file TTreeProcessorMT.hxx.

## Public Member Functions

TTreeProcessorMT (const std::vector< std::string_view > &filenames, std::string_view treename="", UInt_t nThreads=0u, const std::pair< Long64_t, Long64_t > &globalRange={0, std::numeric_limits< Long64_t >::max()})

TTreeProcessorMT (std::string_view filename, std::string_view treename="", UInt_t nThreads=0u, const std::pair< Long64_t, Long64_t > &globalRange={0, std::numeric_limits< Long64_t >::max()})

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

TTreeProcessorMT (TTree &tree, UInt_t nThreads=0u, const std::pair< Long64_t, Long64_t > &globalRange={0, std::numeric_limits< Long64_t >::max()})

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

## Static Public Member Functions

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

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

## 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. More...

## Private Attributes

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

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

const ROOT::TreeUtils::RFriendInfo fFriendInfo

std::pair< Long64_t, Long64_tfGlobalRange {0, std::numeric_limits<Long64_t>::max()}

! Thread pool for processing. More...

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

## Static Private Attributes

static unsigned int fgTasksPerWorkerHint = 10U

#include <ROOT/TTreeProcessorMT.hxx>

## ◆ TTreeProcessorMT() [1/4]

 ROOT::TTreeProcessorMT::TTreeProcessorMT ( std::string_view filename, std::string_view treename = "", UInt_t nThreads = 0u, const std::pair< Long64_t, Long64_t > & globalRange = {0, std::numeric_limits< Long64_t >::max()} )

## ◆ TTreeProcessorMT() [2/4]

 ROOT::TTreeProcessorMT::TTreeProcessorMT ( const std::vector< std::string_view > & filenames, std::string_view treename = "", UInt_t nThreads = 0u, const std::pair< Long64_t, Long64_t > & globalRange = {0, std::numeric_limits< Long64_t >::max()} )

## ◆ 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 500 of file TTreeProcessorMT.cxx.

## ◆ TTreeProcessorMT() [4/4]

 ROOT::TTreeProcessorMT::TTreeProcessorMT ( TTree & tree, UInt_t nThreads = 0u, const std::pair< Long64_t, Long64_t > & globalRange = {0, std::numeric_limits< Long64_t >::max()} )

## ◆ 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 416 of file TTreeProcessorMT.cxx.

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 613 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

// Use content of current entry
}
});
Process the entries of a TTree in parallel.
A simple, robust and fast interface to read values from ROOT columnar datasets such as TTree,...
Bool_t Next()
Move to the next entry (or index of the TEntryList if that is set).

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 538 of file TTreeProcessorMT.cxx.

static

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

Parameters

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 626 of file TTreeProcessorMT.cxx.

## ◆ fEntryList

 TEntryList ROOT::TTreeProcessorMT::fEntryList
private

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

Definition at line 86 of file TTreeProcessorMT.hxx.

## ◆ fFileNames

 const std::vector ROOT::TTreeProcessorMT::fFileNames
private

Names of the files.

Definition at line 83 of file TTreeProcessorMT.hxx.

## ◆ fFriendInfo

 const ROOT::TreeUtils::RFriendInfo ROOT::TTreeProcessorMT::fFriendInfo
private

Definition at line 87 of file TTreeProcessorMT.hxx.

## ◆ fGlobalRange

 std::pair ROOT::TTreeProcessorMT::fGlobalRange {0, std::numeric_limits::max()}
private

Definition at line 97 of file TTreeProcessorMT.hxx.

staticprivate

Definition at line 95 of file TTreeProcessorMT.hxx.

## ◆ fPool

private

Definition at line 88 of file TTreeProcessorMT.hxx.

## ◆ fTreeNames

 const std::vector ROOT::TTreeProcessorMT::fTreeNames
private

TTree names (always same size and ordering as fFileNames)

Definition at line 84 of file TTreeProcessorMT.hxx.