Independent TTree/TFile in different threads

ROOT
1

Hi,

I am trying to build a threaded program that would basically fill histograms from quite a big number of different TTree’s (of drastically different size).

I’d like to use multithreading. The idea is to have two queues (based on the size of the trees) to feed a certain number of threads. I’ve come up with this attached example to test the basic concept of threaded TFile/TTree access. The code works fine some times, some times not. So please run it a couple of times if it doesn’t crash at first. One of the main errors I have is, with usually with >= 5 threads (the only parameter of the function)

R__unzip: error -5 in inflate (zlib)
Error in <TBasket::ReadBasketBuffers>: fNbytes = 27421, fKeylen = 73, fObjlen = 31924, noutot = 0, nout=0, nin=27348, nbuf=31924
Error in <TBranch::GetBasket>: File: f0.root at byte:210, branch:rnd0, entry:-1, badread=1, nerrors=1, basketnumber=0
R__unzip: error -5 in inflate (zlib)
Error in <TBasket::ReadBasketBuffers>: fNbytes = 27421, fKeylen = 73, fObjlen = 31924, noutot = 0, nout=0, nin=27348, nbuf=31924
Error in <TBranch::GetBasket>: File: f0.root at byte:210, branch:rnd0, entry:-1, badread=1, nerrors=2, basketnumber=0

which makes me think the issue is when I try to read the root files. So where should my locks go (hopefully they won’t defeat the purpose of threads). I am sure I miss some stuff (I’m new to threads).

Also, I tried at first to open the TFile/TTree in the individual threads, which lead to complete disaster. Therefore I now open my files before launching the threads (which ideally should close it once their job is done). While not most effective, I guess I could live with that. Does the current ROOT setup allow to run such a case ?

The attached code simply does generate TTrees and fills them randomly (works usually fine). Then, I try to read the files and extract the content in histograms. All this in threaded mode. This is supposed to mimic what I would like.

The code runs inside root as well as compiled with the usual g++ root-config --cflags --libs -lThread root_threads_test.cxx

I’ve got the impression that running as ‘root file.cxx+’ is crashing less often than the g++ compiled one. Any reason for this to happen ?

Thanks for you help.

Karolos

P.S. I was unable to find a tutorial or something with what I’m trying to do.
root_thread_test.cxx (3.25 KB)

2

Hi,

Which version of ROOT are you using?

Philippe.

3

Hi,

With v5.25/05, I have been unable to reproduce your problem.

Cheers,
Philippe.

4

Hi Philippe,

I’m using ROOT 5.25/04 (trunk@31401, Nov 23 2009, 23:28:12 on macosx64)

The problem does not always appear. I’d say one on four times or so. I will try with the latest release though.

However, it’s more something like

that causes errors.

Karolos

5

Hi Philippe,

Indeed, it is MUCH more stable on 5.25/05.

It takes way more iterations for the program to crash. At this point, I cannot be certain it’s an issue with ROOT.

Thanks to the whole team for the continuing support to make ROOT thread-safe.

Karolos