Logo 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 85 of file TTreeProcessorMT.hxx.

Public Member Functions

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

Static Public Member Functions

static unsigned int GetMaxTasksPerFilePerWorker ()
 Sets the maximum number of tasks created per file, per worker. More...
 
static void SetMaxTasksPerFilePerWorker (unsigned int m)
 Sets the maximum number of tasks created per file, 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...
 
Internal::FriendInfo GetFriendInfo (TTree &tree)
 Get and store the names, aliases and file names of the friends of the tree. More...
 

Private Attributes

const 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 Internal::FriendInfo fFriendInfo
 
const std::vector< std::string > fTreeNames
 TTree names (always same size and ordering as fFileNames) More...
 
ROOT::TThreadedObject< ROOT::Internal::TTreeViewfTreeView
 ! Thread-local TreeViews More...
 

Static Private Attributes

static unsigned int fgMaxTasksPerFilePerWorker = 24U
 

#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]filenameName of the file containing the tree to process.
[in]treenameName 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.

Definition at line 403 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]filenamesCollection of the names of the files containing the tree to process.
[in]treenameName 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.

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 430 of file TTreeProcessorMT.cxx.

◆ TTreeProcessorMT() [3/4]

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

Constructor based on a TTree and a TEntryList.

Parameters
[in]treeTree or chain of files containing the tree to process.
[in]entriesList of entry numbers to process.

Definition at line 468 of file TTreeProcessorMT.cxx.

◆ TTreeProcessorMT() [4/4]

TTreeProcessorMT::TTreeProcessorMT ( TTree tree)

Constructor based on a TTree.

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

Definition at line 477 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 371 of file TTreeProcessorMT.cxx.

◆ GetFriendInfo()

Internal::FriendInfo TTreeProcessorMT::GetFriendInfo ( TTree tree)
private

Get and store the names, aliases and file names of the friends of the tree.

Parameters
[in]treeThe main tree whose friends to

Note that "friends of friends" and circular references in the lists of friends are not supported.

Definition at line 328 of file TTreeProcessorMT.cxx.

◆ GetMaxTasksPerFilePerWorker()

unsigned int TTreeProcessorMT::GetMaxTasksPerFilePerWorker ( )
static

Sets the maximum number of tasks created per file, per worker.

Returns
The maximum number of tasks created per file, per worker

Definition at line 557 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

// Select branches to read
while (readerSubRange.Next()) {
// Use content of current entry
}
});
void Process(std::function< void(TTreeReader &)> func)
Process the entries of a TTree in parallel.
A simple, robust and fast interface to read values from ROOT columnar datasets such as TTree,...
Definition: TTreeReader.h:43
Bool_t Next()
Move to the next entry (or index of the TEntryList if that is set).
Definition: TTreeReader.h:182

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]funcUser-defined function that processes a subrange of entries

Definition at line 496 of file TTreeProcessorMT.cxx.

◆ SetMaxTasksPerFilePerWorker()

void TTreeProcessorMT::SetMaxTasksPerFilePerWorker ( unsigned int  maxTasksPerFile)
static

Sets the maximum number of tasks created per file, per worker.

Parameters
[in]maxTasksPerFileName of the file containing the tree to process.

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.

Definition at line 569 of file TTreeProcessorMT.cxx.

Member Data Documentation

◆ fEntryList

const TEntryList ROOT::TTreeProcessorMT::fEntryList
private

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

Definition at line 90 of file TTreeProcessorMT.hxx.

◆ fFileNames

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

Names of the files.

Definition at line 87 of file TTreeProcessorMT.hxx.

◆ fFriendInfo

const Internal::FriendInfo ROOT::TTreeProcessorMT::fFriendInfo
private

Definition at line 91 of file TTreeProcessorMT.hxx.

◆ fgMaxTasksPerFilePerWorker

unsigned int ROOT::TTreeProcessorMT::fgMaxTasksPerFilePerWorker = 24U
staticprivate

Definition at line 97 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 88 of file TTreeProcessorMT.hxx.

◆ fTreeView

ROOT::TThreadedObject<ROOT::Internal::TTreeView> ROOT::TTreeProcessorMT::fTreeView
private

! Thread-local TreeViews

Definition at line 93 of file TTreeProcessorMT.hxx.

Libraries for ROOT::TTreeProcessorMT:
[legend]

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