TTree->Show()

ROOT
1

Dear Rooters,

Using the Show() method in TTree I obtain a “bus error”.

ROOT 5.22/00a (tags/v5-22-00a@27441, May 08 2009, 13:15:54 on macosx 10.4.11)
gcc version 4.0.1 (Apple Computer, Inc. build 5363)

I have a class (SamplePoint) inheriting from TObject containing only one Short_t so that a TClonesArray of type Short_t can be contained in another class (Signal).
(I had problems reading std vectors from a Tree and also memory leaks
with Int_t fNSamples; // # of sampled points
Short_t *thisSample; //[fNSamples]
contained within another class, so I went down the TClonesArray of Short_ts path)

If in a macro I do a simple
{
TFile *f = TFile::Open(“TestEvent.root”);

TTree testT = (TTree) f->Get(“testTree1”);

for(Int_t i = 0; i < 3; i++) {
testT->Show(i);
}
}

I get the obvious warnings :

Warning in TClass::TClass: no dictionary for class Signal is available
Warning in TClass::TClass: no dictionary for class SamplePoint is available

But, the N Short_t of the TClonesArray values are displayed.

However, when I try and read in the dictionary via gSystem->Load("./libTNT2Event.so");, or,
gROOT->ProcessLine(".L TNT2Event.cxx++"); then I get a bus error.

Included is a tar of the reduced problem.
sequence :

make TestEvent
./TestEvent
root -l CheckTree.C

within CheckTree.C are the readDict and showBusError flags to switch behaviour.

Probably related is the fact that when I try and read the size of the TClonesArray using

Signal *signal = new Signal();
…
TClonesArray *samplePoints = new TClonesArray();
samplePoints = signal->GetSamples();
Int_t nSamples = samplePoints->GetLast() + 1;

nSamples is always 0.

Many thanks,
Karl Hauschild
test5.tar.gz (78.5 KB)

2

Philippe will look at your problem once he will be back.

Rene

3

Hi,

The problems comes from the Signal destructor functions in your code that deletes the TClonesArray that is referred to by the static/global variable fgSamples but does not update that pointer … hence leading to the reuse of the ‘deleted’ TClonesArray. Use:Signal::~Signal() { Clear(); if(fSamples) { if (fSamples == fgSamples) { fgSamples = 0; } delete fSamples; } }or do not delete the TClonesArray or do no use a ‘static’ TClonesArray.

Cheers,
Philippe.

4

Hi and thanks for the help,

I followed the code change advice. Now I do get the correct number of
sample points stored in the TClonesArray. However, when I try and use
TTree->Show() I have a bus error.

(NB I used a static TClonesArray as the signal class is a member of
another class and I found, probably a fudge, that using static solved a memory leak problem)

In the previously included CheckTree.C macro I test the following cases :

Int_t readDict = 0; //Do not read in dictionary

and get the expected :

root [0]
Processing CheckTree.C…
Warning in TClass::TClass: no dictionary for class Signal is available
Warning in TClass::TClass: no dictionary for class SamplePoint is available

and testT-Show(3) gives :

======> EVENT:2
OscBranch = (Signal*)0x329dc40
fTriggerCounter = 2
fNSamples = 2000
fSamples = 2000
fSamples.fPoint = 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22

Int_t readDict = 1; //Read in the dict
Int_t showBusErorr = 0; //do not use TTree->Show()

I can get access the the class members I want and the number of samples is correctly obtained this time.

But when I try and combine 1 and 2 :
3)
Int_t readDict = 1; //Read in the dict
Int_t showBusErorr = 1; //try and use TTree->Show()

TTree->Show(i) works correctly, but now, the code in case 2 causes
a bus error when I try and use TTree->GetEntry()

Best regards
Karl

5

Hi,

The problem is still the static TClonesArray. Now you have 2 Signal objects are both pointing at the same TClonesArray[code]testT->Show(i); // Creation of a Signal object (let’s call it ‘SigOne’)
…
Signal *signal = new Signal(); // Creation of second Signal object (let’s call it SigTwo) which is connected with the same TClonesArray.
…
bSignals->SetAddress(&signal); // Induce the deletion of SigOne (no longer needed) which induce the deletion of the TClonesArray (which SigTwo still points to).

…
testT->GetEntry(i); // Using SigTwo and the deleted TClonesArray …
[/code]

Conclusion, the ~Signal destructor can not delete the static TClonesArray. (i.e. do no use a static TClonesArray and/or never delete it).

Cheers,
Philippe.

6

Sorry about the delay between posts [no longer fresh in the mind].

I now wish to add my previous two classes into an “event” class so that :

the event class [OscillogramEvt] contains a TClonesArray of Signal classes
and each Signal contains a TClonesArray of SamplePoints. In this simplified example the OscillogramEvt also contains a time-stamp field.

The small test code TestEvent.cxx illustrates the memory leak I have when I try to add a “Signal” to the OscillogramEvt.

Please could someone help me understand my mistake.

Thanks,
Karl Hauschild
test5b.tar.gz (6.63 KB)