SlicedFriendElement

Description

A TFriendElement that remembers the list of files and slicing of a ChainSlice.

#include <FriendUtils.h>

Inheritance diagram for SlicedFriendElement:

Collaboration diagram for SlicedFriendElement:

Public Member Functions
	SlicedFriendElement ()
	SlicedFriendElement (TTree *parent, ChainSlice *friendChain, const char *alias)
virtual	~SlicedFriendElement ()
TTree *	GetTree () override
TFile *	GetFile () override
TList *	GetListOfTrees () const
Long64_t	GetBegin () const
Long64_t	GetEnd () const
bool	Notify () override
void	Print (Option_t *opt=0) const override
	SlicedFriendElement ()
	SlicedFriendElement (TTree *parent, ChainSlice *friendChain, const char *alias)
virtual	~SlicedFriendElement ()
TTree *	GetTree () override
TFile *	GetFile () override
TList *	GetListOfTrees () const
Long64_t	GetBegin () const
Long64_t	GetEnd () const
bool	Notify () override
void	Print (Option_t *opt=0) const override

Static Public Member Functions
static SlicedFriendElement *	AddTo (TTree *tree, ChainSlice *chain, const char *alias)
static SlicedFriendElement *	AddTo (TTree *tree, ChainSlice *chain, const char *alias)

Private Attributes
Long64_t	fBegin = 0
Long64_t	fEnd = -1
TList *	fTrees = nullptr
ChainSlice *	fChain = nullptr
bool	fOwnsChain = false
TNotifyLink< SlicedFriendElement >	fNotify

Constructor & Destructor Documentation

SlicedFriendElement() [1/4]

SlicedFriendElement ( )

inline

: fNotify(this) {}

SlicedFriendElement() [2/4]

SlicedFriendElement	(	TTree *	parent,
		ChainSlice *	friendChain,
		const char *	alias
	)

Constructs an SlicedFriendElement without attaching it to the parent.

See the corresponding TFriendElement constructor.

    : TFriendElement(parent, friendChain, alias)
    , fBegin(friendChain->GetBegin())
    , fEnd(friendChain->GetEnd())
    , fTrees(new TList)
    , fChain(friendChain)
    , fOwnsChain(false)
    , fNotify(this)
{
    for (const TObject * el : *friendChain->GetListOfFiles()) {
        // These are actually TChainElements, but we don't need to know
        auto named = dynamic_cast<const TNamed *>(el);
        if (!named)
            // If this throws, ROOT changed how chains work
            BOOST_THROW_EXCEPTION(
                std::logic_error("unexpected chain structure"));
 
        auto name = TString(el->GetTitle()) + "?#" + el->GetName();
        fTrees->Add(new TObjString(name));
    }
}

~SlicedFriendElement() [1/2]

~SlicedFriendElement ( )

virtual

Destructor.

{
    if (fOwnsChain)
        delete fChain;
    delete fTrees;
}

SlicedFriendElement() [3/4]

SlicedFriendElement ( )

inline

: fNotify(this) {}

SlicedFriendElement() [4/4]

SlicedFriendElement	(	TTree *	parent,
		ChainSlice *	friendChain,
		const char *	alias
	)

~SlicedFriendElement() [2/2]

virtual ~SlicedFriendElement ( )

virtual

Member Function Documentation

AddTo() [1/2]

SlicedFriendElement * AddTo ( TTree *  tree, ChainSlice *  chain, const char *  alias  )

static

Adds a ChainSlice as a friend to a TTree.

The chain is added to the list of friends of the tree. Entry 0 in the tree is matched to entry 0 in the chain, taking the offset into account. The chain offset must be set before using this function or it will not be stored correctly.

Todo:

ROOT does a few extra checks when adding a friend. Easier to do if upstreaming.

{
    // Make sure the tree has a list of friends. This requires some gymnastics
    // when it's not there yet.
    auto friends = tree->GetListOfFriends();
    if (!friends) {
        // Force the TTree to create its list of friends by adding one.
        TTree t;
        tree->AddFriend(&t);
        tree->RemoveFriend(&t);
        friends = tree->GetListOfFriends();
        if (!friends)
            // Normally the above will always work, but ROOT might change it at
            // some point
            BOOST_THROW_EXCEPTION(
                std::logic_error("could not create TTree list of friends"));
    }
 
    auto element = new SlicedFriendElement(tree, chain, alias);
    friends->Add(element);
 
    return element;
}

AddTo() [2/2]

static SlicedFriendElement* AddTo ( TTree *  tree, ChainSlice *  chain, const char *  alias  )

static

GetBegin() [1/2]

Long64_t GetBegin ( ) const

inline

Index of the first entry to use in the chain.

{ return fBegin; }

GetBegin() [2/2]

Long64_t GetBegin ( ) const

inline

Index of the first entry to use in the chain.

{ return fBegin; }

GetEnd() [1/2]

Long64_t GetEnd ( ) const

inline

Index of a past-the-end entry to use in the chain.

{ return fEnd; }

GetEnd() [2/2]

Long64_t GetEnd ( ) const

inline

Index of a past-the-end entry to use in the chain.

{ return fEnd; }

GetFile() [1/2]

TFile* GetFile ( )

override

GetFile() [2/2]

TFile * GetFile ( )

override

Always returns nullptr, as ChainSlice cover multiple files.

{
    return nullptr;
}

GetListOfTrees() [1/2]

TList* GetListOfTrees ( ) const

inline

Returns the list of trees in the associated chain.

The list contains strings in a format suitable for TChain::AddFileInfoList.

{ return fTrees; }

GetListOfTrees() [2/2]

TList* GetListOfTrees ( ) const

inline

Returns the list of trees in the associated chain.

The list contains strings in a format suitable for TChain::AddFileInfoList.

{ return fTrees; }

GetTree() [1/2]

TTree * GetTree ( )

override

See TFriendElement::GetTree.

This returns a ChainSlice.

{
    if (!fChain) {
        fChain = new ChainSlice(GetName(), GetBegin(), GetEnd(), GetTitle());
        fChain->RegisterExternalFriend(this);
        fOwnsChain = true;
        if (fTrees)
            fChain->AddFileInfoList(fTrees);
    } else {
        // See the HACK section below.
        ResetUpdated();
    }
 
    // HACK: Ask the parent tree to notify us when a new tree is loaded.
    //
    // This is necessary when our parent is in a TChain. It allows us to work
    // around a ROOT bug and force trigger internal TChain code to update
    // branch addresses.
    //
    // If the parent is a simple TTree and we are the only friend, fNotify
    // fires in two cases:
    //
    // * Upon loading of the parent TTree. This only ever happens once.
    // * When *our* chain switches to another tree. This is what we need to
    //   catch.
    //
    // The sequence of events for the second case is as follows:
    //
    // 1. Our chain loads a new tree and calls MarkUpdated().
    // 2. The parent tree checks IsUpdated() then ResetUpdated().
    // 3. If IsUpdated() returned true, call our Notify().
    // 4. Our Notify() calls MarkUpdated() again.
    // 5. The parent's chain checks IsUpdated() then calls ResetUpdated(). If
    //    we hadn't marked ourselves as updated, IsUpdated() would return false
    //    here and nothing else would happen.
    // 6. The parent's chain, seeing IsUpdated() == true, updates its branch
    //    addresses. This is the logic we need to trigger.
    //
    // If our parent tree isn't in a TChain, IsUpdated() will never get reset
    // externally. We do it above to avoid Notify being called at every event
    // (this function gets called for every event).
    //
    // We do not do this when the parent is a TChain because direct friends of
    // a TChain update branches in step 2 above.
    if (!fNotify.IsLinked() && !dynamic_cast<TChain *>(GetParentTree())) {
        fNotify.PrependLink(*GetParentTree());
    }
 
    return fChain;
}

GetTree() [2/2]

TTree* GetTree ( )

override

Notify() [1/2]

bool Notify ( )

override

Gets notification about modified TTrees.

{
    // If the parent tree is part of a TChain, the chain may look at us next if
    // configured properly.  Even then it doesn't always do it, so we may stay
    // in updated state for too long, triggering extraneous branch updates.
    // Fixing the behaviour in ROOT would allow removing this hack.
    //
    // See the explanation in GetTree() for why we do this.
    MarkUpdated();
 
    return true;
}

Notify() [2/2]

bool Notify ( )

override

Print() [1/2]

void Print ( Option_t *  opt = 0 ) const

override

Print() [2/2]

void Print ( Option_t *  opt = 0 ) const

override

Prints information about the trees in this friend element.

{
    TNamed::Print(opt);
    if (fTrees) {
        Printf("Contains %d trees, slice [%lld:%lld):", fTrees->GetSize(), fBegin, fEnd);
        for (const TObject * tree : *fTrees)
            Printf("- %s", tree->GetName());
    } else
        Printf("Contains no trees, slice [%lld:%lld)", fBegin, fEnd);
}

Member Data Documentation

fBegin

Long64_t fBegin = 0

private

Begin parameter of the ChainSlice.

fChain

ChainSlice * fChain = nullptr

private

! The loaded chain.

fEnd

Long64_t fEnd = -1

private

End parameter of the ChainSlice.

fNotify

TNotifyLink< SlicedFriendElement > fNotify

private

! See comment in GetTree().

fOwnsChain

bool fOwnsChain = false

private

! Whether we own the tree.

fTrees

TList * fTrees = nullptr

private

The list of trees in the chain.

The list contains strings in a format suitable for TChain::AddFileInfoList. We keep track of this separately from the chain because fChain isn't saved. This list does get saved.

---

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

• /builds/cms-analysis/general/DasAnalysisSystem/Core/Installer/Darwin/interface/FriendUtils.h
• /builds/cms-analysis/general/DasAnalysisSystem/Core/Installer/Darwin/src/FriendUtils.cc