TBufferMerger fails to write histograms to output file for Alma Linux

[crafter312]

Continuing the discussion from Multi-threaded output of TH* histograms via TBufferMerger:

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ROOT Version: 6.36.10
Platform: Alma Linux 8.10 (linuxx8664gcc)
Compiler: c++ (GCC) 8.5.0 20210514 (Red Hat 8.5.0-28)

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Details about this issue, along with a small code to reproduce, are contained in the original linked discussion. The original issue was never resolved, and this has become a crucial issue for me that now needs to be fixed. The gist is as follows:

@crafter312

I am writing a program which uses TTreeProcessorMT for multi-threaded processing of an input tree and TBufferMerger for output in this multi-threaded context. I can easily create a TTree and fill it from multiple threads. This works, and I have done this a few different times already.

However, when I try to create and fill a TH1I histogram alongside the tree, it fails to appear in the output file. As far as I’m aware, I should just be able to create and fill the histogram in the same way as I do for the tree, at least this is what I would do for a normal TFile:

auto f = merger.GetFile();
TTree t(“t”, “t”);
t.Branch(“whatever”, &whatever);

TH1I h(“h”, “h”, 100, -1., 1.);

I have tried all manner of different ways of writing a histogram to the thread-local file, with no success.

Crucially: The writing of histograms in this manner works just fine on other versions of Linux.

Mainly, I have tested and verified that this works on Rocky Linux for the same version 6.36.10 of ROOT. However, for some unexplicable reason, it fails to work on Alma Linux 8.10.

I have a data analysis code which relies on this functionality, and this issue needs to be resolved before I can continue with my work. I am so incredibly confused by this problem, and have made absolutely no progress in fixing it.

[devajith]

Hi @crafter312, thanks for your question. @pcanal might be able to help here.