TBufferMerger is a class to facilitate writing data in parallel from multiple threads, while writing to a single output file.

A TBufferMergerFile is similar to a TMemFile, but when data is written to it, it is appended to the TBufferMerger queue.

Its purpose is similar to TParallelMergingFile, but instead of using processes that connect to a network socket, TBufferMerger uses threads that each write to a TBufferMergerFile, which in turn push data into a queue managed by the TBufferMerger.

The TBufferMerger merges all data into the output file on disk.

Definition at line 41 of file TBufferMerger.hxx.

Public Member Functions
	TBufferMerger (const char name, Option_t option="RECREATE", Int_t compress=ROOT::RCompressionSetting::EDefaults::kUseCompiledDefault)
	Constructor. More...

	TBufferMerger (std::unique_ptr< TFile > output)
	Constructor. More...

virtual	~TBufferMerger ()
	Destructor. More...

size_t	GetAutoSave () const
	Returns the current value of the auto save setting in bytes (default = 0). More...

size_t	GetBuffered () const
	Returns the number of bytes currently buffered (i.e. More...

Bool_t	GetCompressTemporaryKeys () const
	Returns whether to compressed the TKey in the TMemFile for the object held by the TDirectories. More...

std::shared_ptr< TBufferMergerFile >	GetFile ()
	Returns a TBufferMergerFile to which data can be written. More...

const char *	GetMergeOptions ()
	Returns the current merge options. More...

Bool_t	GetNotrees () const
	Returns whether the the file has been marked as not containing any TTree objects and thus that steps that are specific to TTree can be skipped. More...

size_t	GetQueueSize () const
	Returns the number of buffers currently in the queue. More...

void	SetAutoSave (size_t size)
	By default, TBufferMerger will call TFileMerger::PartialMerge() for each buffer pushed onto its merge queue. More...

void	SetCompressTemporaryKeys (Bool_t request_compression=true)
	Indicates that the temporary keys (corresponding to the object held by the directories of the TMemFile) should be compressed or not. More...

void	SetMergeOptions (const TString &options)
	Sets the merge options. More...

void	SetNotrees (Bool_t notrees=kFALSE)
	Indicates that any TTree objects in the file should be skipped and thus that steps that are specific to TTree can be skipped. More...

Private Member Functions
	TBufferMerger ()
	TBufferMerger has no default constructor. More...

	TBufferMerger (const TBufferMerger &)
	TBufferMerger has no copy constructor. More...

void	Init (std::unique_ptr< TFile >)

void	Merge ()

void	MergeImpl ()

TBufferMerger &	operator= (const TBufferMerger &)
	TBufferMerger has no copy operator. More...

void	Push (TBufferFile *buffer)

bool	TryMerge (TBufferMergerFile *memfile)

Private Attributes
std::vector< std::weak_ptr< TBufferMergerFile > >	fAttachedFiles

size_t	fAutoSave {0}

std::atomic< size_t >	fBuffered {0}

bool	fCompressTemporaryKeys {false}

std::mutex	fMergeMutex

TFileMerger	fMerger {false, false}

std::queue< TBufferFile * >	fQueue

std::mutex	fQueueMutex

Friends
class	TBufferMergerFile

#include <ROOT/TBufferMerger.hxx>

Constructor & Destructor Documentation

◆ TBufferMerger() [1/4]

ROOT::Experimental::TBufferMerger::TBufferMerger	(	const char *	name,
		Option_t *	option = `"RECREATE"`,
		Int_t	compress = `ROOT::RCompressionSetting::EDefaults::kUseCompiledDefault`
	)

Constructor.

Parameters

name	Output file name
option	Output file creation options
compression	Output file compression level

Definition at line 24 of file TBufferMerger.cxx.

◆ TBufferMerger() [2/4]

ROOT::Experimental::TBufferMerger::TBufferMerger ( std::unique_ptr< TFile > output )

Constructor.

Parameters

output Output TFile

Definition at line 32 of file TBufferMerger.cxx.

◆ ~TBufferMerger()

ROOT::Experimental::TBufferMerger::~TBufferMerger ( )

virtual

Destructor.

Definition at line 45 of file TBufferMerger.cxx.

◆ TBufferMerger() [3/4]

ROOT::Experimental::TBufferMerger::TBufferMerger ( )

private

TBufferMerger has no default constructor.

◆ TBufferMerger() [4/4]

ROOT::Experimental::TBufferMerger::TBufferMerger ( const TBufferMerger & )

private

TBufferMerger has no copy constructor.

Member Function Documentation

◆ GetAutoSave()

size_t ROOT::Experimental::TBufferMerger::GetAutoSave ( ) const

Returns the current value of the auto save setting in bytes (default = 0).

Definition at line 87 of file TBufferMerger.cxx.

◆ GetBuffered()

size_t ROOT::Experimental::TBufferMerger::GetBuffered ( ) const

inline

Returns the number of bytes currently buffered (i.e.

in the queue).

Definition at line 74 of file TBufferMerger.hxx.

◆ GetCompressTemporaryKeys()

Bool_t ROOT::Experimental::TBufferMerger::GetCompressTemporaryKeys ( ) const

inline

Returns whether to compressed the TKey in the TMemFile for the object held by the TDirectories.

See TBufferMerger::SetCompressTemporaryKeys for more details.

Definition at line 135 of file TBufferMerger.hxx.

◆ GetFile()

std::shared_ptr< TBufferMergerFile > ROOT::Experimental::TBufferMerger::GetFile ( )

Returns a TBufferMergerFile to which data can be written.

At the end, all TBufferMergerFiles get merged into the output file. The user is responsible to "cd" into the file to associate objects such as histograms or trees to it.

After the creation of this file, the user must reset the kMustCleanup bit on any objects attached to it and take care of their deletion, as there is a possibility that a race condition will happen that causes a crash if ROOT manages these objects.

Definition at line 60 of file TBufferMerger.cxx.

◆ GetMergeOptions()

const char * ROOT::Experimental::TBufferMerger::GetMergeOptions ( )

Returns the current merge options.

Definition at line 92 of file TBufferMerger.cxx.

◆ GetNotrees()

Bool_t ROOT::Experimental::TBufferMerger::GetNotrees ( ) const

inline

Returns whether the the file has been marked as not containing any TTree objects and thus that steps that are specific to TTree can be skipped.

Definition at line 111 of file TBufferMerger.hxx.

◆ GetQueueSize()

size_t ROOT::Experimental::TBufferMerger::GetQueueSize ( ) const

Returns the number of buffers currently in the queue.

Definition at line 69 of file TBufferMerger.cxx.

◆ Init()

void ROOT::Experimental::TBufferMerger::Init ( std::unique_ptr< TFile > output )

private

Definition at line 37 of file TBufferMerger.cxx.

◆ Merge()

void ROOT::Experimental::TBufferMerger::Merge ( )

private

Definition at line 108 of file TBufferMerger.cxx.

◆ MergeImpl()

void ROOT::Experimental::TBufferMerger::MergeImpl ( )

private

Definition at line 116 of file TBufferMerger.cxx.

◆ operator=()

TBufferMerger & ROOT::Experimental::TBufferMerger::operator= ( const TBufferMerger & )

private

TBufferMerger has no copy operator.

◆ Push()

void ROOT::Experimental::TBufferMerger::Push ( TBufferFile * buffer )

private

Definition at line 75 of file TBufferMerger.cxx.

◆ SetAutoSave()

void ROOT::Experimental::TBufferMerger::SetAutoSave ( size_t size )

By default, TBufferMerger will call TFileMerger::PartialMerge() for each buffer pushed onto its merge queue.

This function lets the user change this behaviour by telling TBufferMerger to accumulate at least size bytes in memory before performing a partial merge and flushing to disk. This can be useful to avoid an excessive amount of work to happen in the output thread, as the number of TTree headers (which require compression) written to disk can be reduced.

Definition at line 98 of file TBufferMerger.cxx.

◆ SetCompressTemporaryKeys()

void ROOT::Experimental::TBufferMerger::SetCompressTemporaryKeys ( Bool_t request_compression = true )

inline

Indicates that the temporary keys (corresponding to the object held by the directories of the TMemFile) should be compressed or not.

Those object are stored in the TMemFile (and thus possibly compressed) when a thread push its data forward (by calling TBufferMergerFile::Write) and the queue is being processed by another. Once the TMemFile is picked (by any thread to be merged), after taking the TBufferMerger::fMergeMutex, those object are read back (and thus possibly uncompressed) and then used by merging. In order word, the compression of those objects/keys is only usefull to reduce the size in memory (of the TMemFile) and does not affect (at all) the compression factor of the end result.

Definition at line 127 of file TBufferMerger.hxx.

◆ SetMergeOptions()

void ROOT::Experimental::TBufferMerger::SetMergeOptions ( const TString & options )

Sets the merge options.

SetMergeOptions("fast") will disable recompression of input data into the output if they have different compression settings.

Parameters

options TFileMerger/TFileMergeInfo merge options

Definition at line 103 of file TBufferMerger.cxx.

◆ SetNotrees()

void ROOT::Experimental::TBufferMerger::SetNotrees ( Bool_t notrees = kFALSE )

inline

Indicates that any TTree objects in the file should be skipped and thus that steps that are specific to TTree can be skipped.

Definition at line 104 of file TBufferMerger.hxx.

◆ TryMerge()

bool ROOT::Experimental::TBufferMerger::TryMerge ( TBufferMergerFile * memfile )

private

Definition at line 135 of file TBufferMerger.cxx.

Friends And Related Function Documentation

◆ TBufferMergerFile

friend class TBufferMergerFile

friend

Definition at line 140 of file TBufferMerger.hxx.

Member Data Documentation

◆ fAttachedFiles

std::vector<std::weak_ptr<TBufferMergerFile> > ROOT::Experimental::TBufferMerger::fAttachedFiles

private

Definition at line 167 of file TBufferMerger.hxx.

◆ fAutoSave

size_t ROOT::Experimental::TBufferMerger::fAutoSave {0}

private

Definition at line 161 of file TBufferMerger.hxx.

◆ fBuffered

std::atomic<size_t> ROOT::Experimental::TBufferMerger::fBuffered {0}

private

Definition at line 162 of file TBufferMerger.hxx.

◆ fCompressTemporaryKeys

bool ROOT::Experimental::TBufferMerger::fCompressTemporaryKeys {false}

private

Definition at line 160 of file TBufferMerger.hxx.

◆ fMergeMutex

std::mutex ROOT::Experimental::TBufferMerger::fMergeMutex

private

Definition at line 164 of file TBufferMerger.hxx.

◆ fMerger

TFileMerger ROOT::Experimental::TBufferMerger::fMerger {false, false}

private

Definition at line 163 of file TBufferMerger.hxx.

◆ fQueue

std::queue<TBufferFile *> ROOT::Experimental::TBufferMerger::fQueue

private

Definition at line 166 of file TBufferMerger.hxx.

◆ fQueueMutex

std::mutex ROOT::Experimental::TBufferMerger::fQueueMutex

mutableprivate

Definition at line 165 of file TBufferMerger.hxx.

Libraries for ROOT::Experimental::TBufferMerger:

[legend]

Public Member Functions

Private Member Functions

Private Attributes

Friends

Constructor & Destructor Documentation

◆ TBufferMerger() [1/4]

◆ TBufferMerger() [2/4]

◆ ~TBufferMerger()

◆ TBufferMerger() [3/4]

◆ TBufferMerger() [4/4]

Member Function Documentation

◆ GetAutoSave()

◆ GetBuffered()

◆ GetCompressTemporaryKeys()

◆ GetFile()

◆ GetMergeOptions()

◆ GetNotrees()

◆ GetQueueSize()

◆ Init()

◆ Merge()

◆ MergeImpl()

◆ operator=()

◆ Push()

◆ SetAutoSave()

◆ SetCompressTemporaryKeys()

◆ SetMergeOptions()

◆ SetNotrees()

◆ TryMerge()

Friends And Related Function Documentation

◆ TBufferMergerFile

Member Data Documentation

◆ fAttachedFiles

◆ fAutoSave

◆ fBuffered

◆ fCompressTemporaryKeys

◆ fMergeMutex

◆ fMerger

◆ fQueue

◆ fQueueMutex