The prefetching mechanism uses two classes (TFilePrefetch and TFPBlock) to prefetch in advance a block of tree entries.

There is a thread which takes care of actually transferring the blocks and making them available to the main requesting thread. Therefore, the time spent by the main thread waiting for the data before processing considerably decreases. Besides the prefetching mechanisms there is also a local caching option which can be enabled by the user. Both capabilities are disabled by default and must be explicitly enabled by the user.

Definition at line 33 of file TFilePrefetch.h.

Public Member Functions
	TFilePrefetch (TFile *)
	Constructor.

	~TFilePrefetch () override
	Destructor.

void	AddPendingBlock (TFPBlock *)
	Safe method to add a block to the pendingList.

void	AddReadBlock (TFPBlock *)
	Safe method to add a block to the readList.

Bool_t	BinarySearchReadList (TFPBlock , Long64_t, Int_t, Int_t )
	Search for a requested element in a block and return the index.

Bool_t	CheckBlockInCache (char &, TFPBlock )
	Test if the block is in cache.

TFPBlock *	CreateBlockObj (Long64_t , Int_t , Int_t)
	Create a new block or recycle an old one.

char *	GetBlockFromCache (const char *, Int_t)
	Return a buffer from cache.

std::condition_variable &	GetCondNewBlock ()

TFPBlock *	GetPendingBlock ()
	Safe method to remove a block from the pendingList.

TThread *	GetThread () const
	Return reference to the consumer thread.

Long64_t	GetWaitTime ()
	Return the time spent wating for buffer to be read in microseconds.

TClass *	IsA () const override

Bool_t	IsPrefetchFinished () const

void	ReadAsync (TFPBlock *, Bool_t &)
	Read one block and insert it in prefetchBuffers list.

void	ReadBlock (Long64_t , Int_t , Int_t)
	Create a TFPBlock object or recycle one and add it to the prefetchBlocks list.

Bool_t	ReadBuffer (char *, Long64_t, Int_t)
	Return a prefetched element.

void	ReadListOfBlocks ()
	Get blocks specified in prefetchBlocks.

void	SaveBlockInCache (TFPBlock *)
	Save the block content in cache.

Bool_t	SetCache (const char *)
	Set the path of the cache directory.

void	SetFile (TFile *file, TFile::ECacheAction action=TFile::kDisconnect)
	Change the file.

void	Streamer (TBuffer &) override
	Stream an object of class TObject.

void	StreamerNVirtual (TBuffer &ClassDef_StreamerNVirtual_b)

Int_t	SumHex (const char *)
	Sum up individual hex values to obtain a decimal value.

Int_t	ThreadStart ()
	Used to start the consumer thread.

void	WaitFinishPrefetch ()
	Killing the async prefetching thread.

Public Member Functions inherited from TObject
	TObject ()
	TObject constructor.

	TObject (const TObject &object)
	TObject copy ctor.

virtual	~TObject ()
	TObject destructor.

void	AbstractMethod (const char *method) const
	Use this method to implement an "abstract" method that you don't want to leave purely abstract.

virtual void	AppendPad (Option_t *option="")
	Append graphics object to current pad.

virtual void	Browse (TBrowser *b)
	Browse object. May be overridden for another default action.

ULong_t	CheckedHash ()
	Check and record whether this class has a consistent Hash/RecursiveRemove setup (*) and then return the regular Hash value for this object.

virtual const char *	ClassName () const
	Returns name of class to which the object belongs.

virtual void	Clear (Option_t *="")

virtual TObject *	Clone (const char *newname="") const
	Make a clone of an object using the Streamer facility.

virtual Int_t	Compare (const TObject *obj) const
	Compare abstract method.

virtual void	Copy (TObject &object) const
	Copy this to obj.

virtual void	Delete (Option_t *option="")
	Delete this object.

virtual Int_t	DistancetoPrimitive (Int_t px, Int_t py)
	Computes distance from point (px,py) to the object.

virtual void	Draw (Option_t *option="")
	Default Draw method for all objects.

virtual void	DrawClass () const
	Draw class inheritance tree of the class to which this object belongs.

virtual TObject *	DrawClone (Option_t *option="") const
	Draw a clone of this object in the current selected pad with: `gROOT->SetSelectedPad(c1)`.

virtual void	Dump () const
	Dump contents of object on stdout.

virtual void	Error (const char method, const char msgfmt,...) const
	Issue error message.

virtual void	Execute (const char method, const char params, Int_t *error=nullptr)
	Execute method on this object with the given parameter string, e.g.

virtual void	Execute (TMethod method, TObjArray params, Int_t *error=nullptr)
	Execute method on this object with parameters stored in the TObjArray.

virtual void	ExecuteEvent (Int_t event, Int_t px, Int_t py)
	Execute action corresponding to an event at (px,py).

virtual void	Fatal (const char method, const char msgfmt,...) const
	Issue fatal error message.

virtual TObject *	FindObject (const char *name) const
	Must be redefined in derived classes.

virtual TObject *	FindObject (const TObject *obj) const
	Must be redefined in derived classes.

virtual Option_t *	GetDrawOption () const
	Get option used by the graphics system to draw this object.

virtual const char *	GetIconName () const
	Returns mime type name of object.

virtual const char *	GetName () const
	Returns name of object.

virtual char *	GetObjectInfo (Int_t px, Int_t py) const
	Returns string containing info about the object at position (px,py).

virtual Option_t *	GetOption () const

virtual const char *	GetTitle () const
	Returns title of object.

virtual UInt_t	GetUniqueID () const
	Return the unique object id.

virtual Bool_t	HandleTimer (TTimer *timer)
	Execute action in response of a timer timing out.

virtual ULong_t	Hash () const
	Return hash value for this object.

Bool_t	HasInconsistentHash () const
	Return true is the type of this object is known to have an inconsistent setup for Hash and RecursiveRemove (i.e.

virtual void	Info (const char method, const char msgfmt,...) const
	Issue info message.

virtual Bool_t	InheritsFrom (const char *classname) const
	Returns kTRUE if object inherits from class "classname".

virtual Bool_t	InheritsFrom (const TClass *cl) const
	Returns kTRUE if object inherits from TClass cl.

virtual void	Inspect () const
	Dump contents of this object in a graphics canvas.

void	InvertBit (UInt_t f)

Bool_t	IsDestructed () const
	IsDestructed.

virtual Bool_t	IsEqual (const TObject *obj) const
	Default equal comparison (objects are equal if they have the same address in memory).

virtual Bool_t	IsFolder () const
	Returns kTRUE in case object contains browsable objects (like containers or lists of other objects).

R__ALWAYS_INLINE Bool_t	IsOnHeap () const

virtual Bool_t	IsSortable () const

R__ALWAYS_INLINE Bool_t	IsZombie () const

virtual void	ls (Option_t *option="") const
	The ls function lists the contents of a class on stdout.

void	MayNotUse (const char *method) const
	Use this method to signal that a method (defined in a base class) may not be called in a derived class (in principle against good design since a child class should not provide less functionality than its parent, however, sometimes it is necessary).

virtual Bool_t	Notify ()
	This method must be overridden to handle object notification (the base implementation is no-op).

void	Obsolete (const char method, const char asOfVers, const char *removedFromVers) const
	Use this method to declare a method obsolete.

void	operator delete (void *ptr)
	Operator delete.

void	operator delete (void ptr, void vp)
	Only called by placement new when throwing an exception.

void	operator delete[] (void *ptr)
	Operator delete [].

void	operator delete[] (void ptr, void vp)
	Only called by placement new[] when throwing an exception.

void *	operator new (size_t sz)

void *	operator new (size_t sz, void *vp)

void *	operator new[] (size_t sz)

void *	operator new[] (size_t sz, void *vp)

TObject &	operator= (const TObject &rhs)
	TObject assignment operator.

virtual void	Paint (Option_t *option="")
	This method must be overridden if a class wants to paint itself.

virtual void	Pop ()
	Pop on object drawn in a pad to the top of the display list.

virtual void	Print (Option_t *option="") const
	This method must be overridden when a class wants to print itself.

virtual Int_t	Read (const char *name)
	Read contents of object with specified name from the current directory.

virtual void	RecursiveRemove (TObject *obj)
	Recursively remove this object from a list.

void	ResetBit (UInt_t f)

virtual void	SaveAs (const char filename="", Option_t option="") const
	Save this object in the file specified by filename.

virtual void	SavePrimitive (std::ostream &out, Option_t *option="")
	Save a primitive as a C++ statement(s) on output stream "out".

void	SetBit (UInt_t f)

void	SetBit (UInt_t f, Bool_t set)
	Set or unset the user status bits as specified in f.

virtual void	SetDrawOption (Option_t *option="")
	Set drawing option for object.

virtual void	SetUniqueID (UInt_t uid)
	Set the unique object id.

void	StreamerNVirtual (TBuffer &ClassDef_StreamerNVirtual_b)

virtual void	SysError (const char method, const char msgfmt,...) const
	Issue system error message.

R__ALWAYS_INLINE Bool_t	TestBit (UInt_t f) const

Int_t	TestBits (UInt_t f) const

virtual void	UseCurrentStyle ()
	Set current style settings in this object This function is called when either TCanvas::UseCurrentStyle or TROOT::ForceStyle have been invoked.

virtual void	Warning (const char method, const char msgfmt,...) const
	Issue warning message.

virtual Int_t	Write (const char *name=nullptr, Int_t option=0, Int_t bufsize=0)
	Write this object to the current directory.

virtual Int_t	Write (const char *name=nullptr, Int_t option=0, Int_t bufsize=0) const
	Write this object to the current directory.

Static Public Member Functions
static TClass *	Class ()

static const char *	Class_Name ()

static constexpr Version_t	Class_Version ()

static const char *	DeclFileName ()

Static Public Member Functions inherited from TObject
static TClass *	Class ()

static const char *	Class_Name ()

static constexpr Version_t	Class_Version ()

static const char *	DeclFileName ()

static Longptr_t	GetDtorOnly ()
	Return destructor only flag.

static Bool_t	GetObjectStat ()
	Get status of object stat flag.

static void	SetDtorOnly (void *obj)
	Set destructor only flag.

static void	SetObjectStat (Bool_t stat)
	Turn on/off tracking of objects in the TObjectTable.

Static Private Member Functions
static TThread::VoidRtnFunc_t	ThreadProc (void *)
	Execution loop of the consumer thread.

Private Attributes
TThread *	fConsumer
	consumer thread

TFile *	fFile
	reference to the file

std::mutex	fMutexPendingList
	mutex for the pending list

std::mutex	fMutexReadList
	mutex for the list of read blocks

std::condition_variable	fNewBlockAdded
	signal the addition of a new pending block

TString	fPathCache
	path to the cache directory

TList *	fPendingBlocks
	list of pending blocks to be read

std::atomic< Bool_t >	fPrefetchFinished
	true if prefetching is over

std::condition_variable	fReadBlockAdded
	signal the addition of a new red block

TList *	fReadBlocks
	list of blocks read

TSemaphore *	fSemChangeFile
	semaphore used when changing a file in TChain

Bool_t	fThreadJoined
	mark if async thread was joined

TStopwatch	fWaitTime
	time waiting to prefetch a buffer (in usec)

Additional Inherited Members
Public Types inherited from TObject
enum	{ kIsOnHeap = 0x01000000 , kNotDeleted = 0x02000000 , kZombie = 0x04000000 , kInconsistent = 0x08000000 , kBitMask = 0x00ffffff }

enum	{ kSingleKey = (1ULL << ( 0 )) , kOverwrite = (1ULL << ( 1 )) , kWriteDelete = (1ULL << ( 2 )) }

enum	EDeprecatedStatusBits { kObjInCanvas = (1ULL << ( 3 )) }

enum	EStatusBits { kCanDelete = (1ULL << ( 0 )) , kMustCleanup = (1ULL << ( 3 )) , kIsReferenced = (1ULL << ( 4 )) , kHasUUID = (1ULL << ( 5 )) , kCannotPick = (1ULL << ( 6 )) , kNoContextMenu = (1ULL << ( 8 )) , kInvalidObject = (1ULL << ( 13 )) }

Protected Types inherited from TObject
enum	{ kOnlyPrepStep = (1ULL << ( 3 )) }

Protected Member Functions inherited from TObject
virtual void	DoError (int level, const char location, const char fmt, va_list va) const
	Interface to ErrorHandler (protected).

void	MakeZombie ()

#include <TFilePrefetch.h>

Inheritance diagram for TFilePrefetch:

[legend]

Constructor & Destructor Documentation

◆ TFilePrefetch()

TFilePrefetch::TFilePrefetch ( TFile * file )

Constructor.

Definition at line 54 of file TFilePrefetch.cxx.

◆ ~TFilePrefetch()

TFilePrefetch::~TFilePrefetch ( )

override

Destructor.

Definition at line 72 of file TFilePrefetch.cxx.

Member Function Documentation

◆ AddPendingBlock()

void TFilePrefetch::AddPendingBlock ( TFPBlock * block )

Safe method to add a block to the pendingList.

Definition at line 223 of file TFilePrefetch.cxx.

◆ AddReadBlock()

void TFilePrefetch::AddReadBlock ( TFPBlock * block )

Safe method to add a block to the readList.

Definition at line 259 of file TFilePrefetch.cxx.

◆ BinarySearchReadList()

Bool_t TFilePrefetch::BinarySearchReadList	(	TFPBlock *	blockObj,
		Long64_t	offset,
		Int_t	len,
		Int_t *	index
	)

Search for a requested element in a block and return the index.

Definition at line 144 of file TFilePrefetch.cxx.

◆ CheckBlockInCache()

Bool_t TFilePrefetch::CheckBlockInCache	(	char *&	path,
		TFPBlock *	block
	)

Test if the block is in cache.

Definition at line 395 of file TFilePrefetch.cxx.

◆ Class()

static TClass * TFilePrefetch::Class ( )

static

Returns: TClass describing this class

◆ Class_Name()

static const char * TFilePrefetch::Class_Name ( )

static

Returns: Name of this class

◆ Class_Version()

static constexpr Version_t TFilePrefetch::Class_Version ( )

inlinestaticconstexpr

Returns: Version of this class

Definition at line 84 of file TFilePrefetch.h.

◆ CreateBlockObj()

TFPBlock * TFilePrefetch::CreateBlockObj	(	Long64_t *	offset,
		Int_t *	len,
		Int_t	noblock
	)

Create a new block or recycle an old one.

Definition at line 281 of file TFilePrefetch.cxx.

◆ DeclFileName()

static const char * TFilePrefetch::DeclFileName ( )

inlinestatic

Returns: Name of the file containing the class declaration

Definition at line 84 of file TFilePrefetch.h.

◆ GetBlockFromCache()

char * TFilePrefetch::GetBlockFromCache	(	const char *	path,
		Int_t	length
	)

Return a buffer from cache.

Definition at line 441 of file TFilePrefetch.cxx.

◆ GetCondNewBlock()

std::condition_variable & TFilePrefetch::GetCondNewBlock ( )

inline

Definition at line 80 of file TFilePrefetch.h.

◆ GetPendingBlock()

TFPBlock * TFilePrefetch::GetPendingBlock ( )

Safe method to remove a block from the pendingList.

Definition at line 235 of file TFilePrefetch.cxx.

◆ GetThread()

TThread * TFilePrefetch::GetThread ( ) const

Return reference to the consumer thread.

Definition at line 303 of file TFilePrefetch.cxx.

◆ GetWaitTime()

Long64_t TFilePrefetch::GetWaitTime ( )

Return the time spent wating for buffer to be read in microseconds.

Definition at line 170 of file TFilePrefetch.cxx.

◆ IsA()

TClass * TFilePrefetch::IsA ( ) const

inlineoverridevirtual

Returns: TClass describing current object

Reimplemented from TObject.

Definition at line 84 of file TFilePrefetch.h.

◆ IsPrefetchFinished()

Bool_t TFilePrefetch::IsPrefetchFinished ( ) const

inline

Definition at line 82 of file TFilePrefetch.h.

◆ ReadAsync()

void TFilePrefetch::ReadAsync	(	TFPBlock *	block,
		Bool_t &	inCache
	)

Read one block and insert it in prefetchBuffers list.

Definition at line 106 of file TFilePrefetch.cxx.

◆ ReadBlock()

void TFilePrefetch::ReadBlock	(	Long64_t *	offset,
		Int_t *	len,
		Int_t	nblock
	)

Create a TFPBlock object or recycle one and add it to the prefetchBlocks list.

Definition at line 214 of file TFilePrefetch.cxx.

◆ ReadBuffer()

Bool_t TFilePrefetch::ReadBuffer	(	char *	buf,
		Long64_t	offset,
		Int_t	len
	)

Return a prefetched element.

Definition at line 178 of file TFilePrefetch.cxx.

◆ ReadListOfBlocks()

void TFilePrefetch::ReadListOfBlocks ( )

Get blocks specified in prefetchBlocks.

Definition at line 128 of file TFilePrefetch.cxx.

◆ SaveBlockInCache()

void TFilePrefetch::SaveBlockInCache ( TFPBlock * block )

Save the block content in cache.

Definition at line 474 of file TFilePrefetch.cxx.

◆ SetCache()

Bool_t TFilePrefetch::SetCache ( const char * path )

Set the path of the cache directory.

Definition at line 526 of file TFilePrefetch.cxx.

◆ SetFile()

void TFilePrefetch::SetFile	(	TFile *	file,
		TFile::ECacheAction	action = `TFile::kDisconnect`
	)

Change the file.

When prefetching is enabled we also need to:

make sure the async thread is not doing any work
clear all blocks from prefetching and read list
reset the file pointer

Definition at line 317 of file TFilePrefetch.cxx.

◆ Streamer()

void TFilePrefetch::Streamer ( TBuffer & R__b )

overridevirtual

Stream an object of class TObject.

Reimplemented from TObject.

◆ StreamerNVirtual()

void TFilePrefetch::StreamerNVirtual ( TBuffer & ClassDef_StreamerNVirtual_b )

inline

Definition at line 84 of file TFilePrefetch.h.

◆ SumHex()

Int_t TFilePrefetch::SumHex ( const char * hex )

Sum up individual hex values to obtain a decimal value.

Definition at line 381 of file TFilePrefetch.cxx.

◆ ThreadProc()

TThread::VoidRtnFunc_t TFilePrefetch::ThreadProc ( void * arg )

staticprivate

Execution loop of the consumer thread.

Definition at line 365 of file TFilePrefetch.cxx.

◆ ThreadStart()

Int_t TFilePrefetch::ThreadStart ( )

Used to start the consumer thread.

Definition at line 349 of file TFilePrefetch.cxx.

◆ WaitFinishPrefetch()

void TFilePrefetch::WaitFinishPrefetch ( )

Killing the async prefetching thread.

Definition at line 88 of file TFilePrefetch.cxx.

Member Data Documentation

◆ fConsumer

TThread* TFilePrefetch::fConsumer

private

consumer thread

Definition at line 39 of file TFilePrefetch.h.

◆ fFile

TFile* TFilePrefetch::fFile

private

reference to the file

Definition at line 36 of file TFilePrefetch.h.

◆ fMutexPendingList

std::mutex TFilePrefetch::fMutexPendingList

private

mutex for the pending list

Definition at line 40 of file TFilePrefetch.h.

◆ fMutexReadList

std::mutex TFilePrefetch::fMutexReadList

private

mutex for the list of read blocks

Definition at line 41 of file TFilePrefetch.h.

◆ fNewBlockAdded

std::condition_variable TFilePrefetch::fNewBlockAdded

private

signal the addition of a new pending block

Definition at line 42 of file TFilePrefetch.h.

◆ fPathCache

TString TFilePrefetch::fPathCache

private

path to the cache directory

Definition at line 45 of file TFilePrefetch.h.

◆ fPendingBlocks

TList* TFilePrefetch::fPendingBlocks

private

list of pending blocks to be read

Definition at line 37 of file TFilePrefetch.h.

◆ fPrefetchFinished

std::atomic<Bool_t> TFilePrefetch::fPrefetchFinished

private

true if prefetching is over

Definition at line 48 of file TFilePrefetch.h.

◆ fReadBlockAdded

std::condition_variable TFilePrefetch::fReadBlockAdded

private

signal the addition of a new red block

Definition at line 43 of file TFilePrefetch.h.

◆ fReadBlocks

TList* TFilePrefetch::fReadBlocks

private

list of blocks read

Definition at line 38 of file TFilePrefetch.h.

◆ fSemChangeFile

TSemaphore* TFilePrefetch::fSemChangeFile

private

semaphore used when changing a file in TChain

Definition at line 44 of file TFilePrefetch.h.

◆ fThreadJoined

Bool_t TFilePrefetch::fThreadJoined

private

mark if async thread was joined

Definition at line 47 of file TFilePrefetch.h.

◆ fWaitTime

TStopwatch TFilePrefetch::fWaitTime

private

time waiting to prefetch a buffer (in usec)

Definition at line 46 of file TFilePrefetch.h.

Libraries for TFilePrefetch:

[legend]

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

io/io/inc/TFilePrefetch.h
io/io/src/TFilePrefetch.cxx

Public Member Functions

Static Public Member Functions

Static Private Member Functions

Private Attributes

Additional Inherited Members

Constructor & Destructor Documentation

◆ TFilePrefetch()

◆ ~TFilePrefetch()

Member Function Documentation

◆ AddPendingBlock()

◆ AddReadBlock()

◆ BinarySearchReadList()

◆ CheckBlockInCache()

◆ Class()

◆ Class_Name()

◆ Class_Version()

◆ CreateBlockObj()

◆ DeclFileName()

◆ GetBlockFromCache()

◆ GetCondNewBlock()

◆ GetPendingBlock()

◆ GetThread()

◆ GetWaitTime()

◆ IsA()

◆ IsPrefetchFinished()

◆ ReadAsync()

◆ ReadBlock()

◆ ReadBuffer()

◆ ReadListOfBlocks()

◆ SaveBlockInCache()

◆ SetCache()

◆ SetFile()

◆ Streamer()

◆ StreamerNVirtual()

◆ SumHex()

◆ ThreadProc()

◆ ThreadStart()

◆ WaitFinishPrefetch()

Member Data Documentation

◆ fConsumer

◆ fFile

◆ fMutexPendingList

◆ fMutexReadList

◆ fNewBlockAdded

◆ fPathCache

◆ fPendingBlocks

◆ fPrefetchFinished

◆ fReadBlockAdded

◆ fReadBlocks

◆ fSemChangeFile

◆ fThreadJoined

◆ fWaitTime