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

From: Alexandros Attikis <attikis_at_cern.ch>
Date: Tue, 31 Aug 2010 17:48:24 +0200

So,

unsurprisingly at the moment it seems that the code is running much further than the crashing point! So I guess the array size was very much related. I only hope it finishes running without any problem.

In any case, thanx again for the tip!

Cheers,
Alexandros

---

                       Alexandros Attikis
                       Ph.D. Student 
                       HEP Group
                       Department of Physics
                       University of Cyprus
____________________________________

On 31 Aug 2010, at 17:28, Alexandros Attikis wrote:

> 
> 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 - 17:48:37 CEST