Reading second or following files from TChain returns broken data

ROOT
1

I have a set of root files with a tree and branches inside. Every branch is a class derived from TObject which contains a TClonesArray object where I store my final data.

If I use ROOT CLI to test it, eg:

TChain c("M").
c.Add("file1.root); c.Add("file2.root); c.Add("file3.root);
c.Draw("MGeantTrack.data.start.E")

all works fine and I see proper energy spectrum.

But when I try to use the same files from the application, where I read the chain using TChain::GetBranch() and TChain::SetAddress() and followed by getEntry(i), only data from the first file are OK. In my class I have function which can print all the members of the class, and when printing last two events of the first file the data are correct:

pos sta=(-63.860748,45.852509,-26.533522) sto=(-27.821383,43.458836,30.946054)
dir sta=(0.530840,-0.035504,0.846728) sto=(0.531200,-0.034308,0.846552)
start energy = 5382.276855, stop energy = 5082.808105
scat=0 process=
PID=1000110230 stop in det=1
num of sec=0

pos sta=(-66.399200,50.302349,16.030731) sto=(600.000000,-177.096909,-74.180840)
dir sta=(0.938943,-0.320097,-0.126192) sto=(0.938686,-0.320444,-0.127215)
start energy = 27827.259766, stop energy = 24863.156250
scat=0 process=
PID=1000150310 stop in det=0
num of sec=0

But every data from the second or later file gives always fixed data, always the same, like below:

pos sta=(-29.940292,91.304390,28.868572) sto=(462.300171,-327.365082,-600.000000)
dir sta=(0.545874,-0.464139,-0.697565) sto=(0.545903,-0.464326,-0.697417)
start energy = 84140.382812, stop energy = 83883.398438
scat=0 process=
PID=1000050110 stop in det=0
num of sec=0

Any idea where the difference in behaviour may come from?

2

Can you provide a small example of the problem you are experiencing?

3

It’s hard to provide one single file since the whole code is within a bigger framework I am working now. But here I extracted an essential part of the framework and analysis program and the input files. Please download this file:
http://rlalik.com/media/upload/mapt.tar.bz2
and extract in, then do following:

cd mapt
mkdir build
cd build
cmake … #(dot dot, markup language translates two dots into three…, the same line below)
make
./analysis/mapt_analysis …/files/CR_*_digi.root -e 20000

You will observe that the first 10k events will be processed slower than the following 10k.

After that, you can edit line 150 of analysis/analysis.cc and uncomment it. It will print out the information about each track,you will find the problem. I recommend to run the analysis program from line above with | less on the end.

Please ignore the exception error on the end. It’s irrelevant for this case.

4

Mostly likely you are not refreshing the TBranch pointer value when the file changed over. Use

Int_t TChain::SetBranchAddress 	( 	const char *  	bname,
		void *  	add,
		TBranch **  	ptr = 0 
	) 		
	virtual

Set branch address.

Parameters
    [in]	bname	is the name of a branch.
    [in]	add	is the address of the branch.
    [in]	ptr	Note: See the comments in TBranchElement::SetAddress() for a more detailed discussion of the meaning of the add parameter.

IMPORTANT REMARK:

In case TChain::SetBranchStatus is called, it must be called BEFORE calling this function.

See TTree::CheckBranchAddressType for the semantic of the return value.

Reimplemented from TTree.

Definition at line 2374 of file TChain.cxx.
5

i.e

TBranch *branchPtr = nullptr;

mychain->SetBranchAddress(branchname, pointerToDataPointer, branchPtr);
6

This was my thought as well. Didn’t have time to dig through your code though.

7

That was it. Before I had:

TBranch * br = tree->BetBranch(…);
br->SetAddress(…);

Now it works fine.

8

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