Re: TChain->GetEntry(jentry) - Segmentation Fault

From: Alexandros Attikis <attikis_at_cern.ch>
Date: Tue, 31 Aug 2010 17:28:44 +0200

On 31 Aug 2010, at 16:36, Chris Schilling wrote:

> When you run makeClass ROOT automatically assigns leaf arrays to have a certain size. Probably this size is different for the qcd ntuple. In the .h file created by makeclass, try increasing the size of the arrays. I have run into this before and this seems to be the problem you are describing. >

Hm... that is a very interesting point! I think/hope this could be it! I will have a look now.

Thanx for the tip anyway, it should be useful for the near future if not with my current issue.

Cheers,
Alexandros

> Chris
> 
> On Aug 31, 2010, at 6:23 AM, Alexandros Attikis wrote:
> 
>> 
>> On 31 Aug 2010, at 14:53, Axel Naumann wrote:
>> 
>>> Hi Alexandros,
>>> 
>>> do you have a memory leak (check with e.g. ps, free,...)? Can you run
>>> with valgrind (see http://valgrind.org)?
>> I am already running with it. It should take quite a long time according to the link. 
>> Should I post here the result?
>>> Can you post the complete
>>> backtrace you got from GDB (the one ending with memset)? Can you reduce
>>> your code to something we can run, and give us the ROOT file so we can
>>> reproduce it?
>> I will put gdb on the side for now.
>> I guess I should finish off with valgrind and if I am still at a dead-end I can move to gdb.
>>  
>>> 
>>> Cheers, Axel.
>>> 
>>> On 8/31/10 2:48 PM, Alexandros Attikis wrote:

>>>> Hi ROOTers,
>>>>
>>>> I have a used "makeClass" to access an ntuple and manipulate it using
>>>> C++ code and ROOT. I compile the code with g++ and
>>>> have run on multiple samples including millions of events.
>>>>
>>>> Now, when trying to run on a specific QCD ntuple, I get a segmentation
>>>> fault after ~140k events, always at the same point if a start from zero.
>>>> I have tried to start 10 events before it and and runs smoothly up to
>>>> some other event later on where it crashes with the same error.
>>>> Obviously it is not
>>>> the specific event that is causing the seg. fault. I have also had a
>>>> look at the ROOT files (2) and they seem okay.
>>>>
>>>> I have used cout to pinpoint the error to right before I access the
>>>> specific entry of the TChain:
>>>> nb = fChain->GetEntry(jentry);
>>>>
>>>> I have tried to use gdb (beginner using this) but with no success of
>>>> finding something useful. The Crash when running gdb gives:
>>>> Program received signal SIGSEV, Segmentation fault.
>>>> 0x00000033c627ac4a in memset () from /lib64/libc.so.6
>>>>
>>>> Back-tracing hasn't been very useful, but as I said I am not experienced
>>>> in using gdb.
>>>>
>>>> Can someone direct as to how to locate/fix the problem?
>>>> Is it the aforementioned piece of code or is it possible that the
>>>> problem lies somewhere else?
>>>>
>>>>
>>>> Cheers,
>>>> Alexandros

>>> 
>> 
> 

Received on Tue Aug 31 2010 - 17:28:51 CEST