[Halld-offline] HDGeant4 Meeting Minutes, June 30, 2020

[Mark Ito]

Folks,

Please find the minutes here 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_June_30,_2020#Minutes> 
and below.

   -- Mark


    HDGeant4 Meeting, June 30, 2020, Minutes

Present: Alex Austregesilo, Sean Dobbs, Colin Gleason, Mark Ito (chair), 
Igal Jaegle, Richard Jones, Simon Taylor, Nilanga Wickramaarachchi

There is a recording of this meeting <https://bluejeans.com/s/Ghdjw/> on 
the BlueJeans site. Use your JLab credentials to get access.


      Announcement: Version Set with Upgraded Geant4

A new version set with upgrade to Geant4: version_4.21.3.xml 
<https://mailman.jlab.org/pipermail/halld-offline/2020-June/004104.html> 
was released today. Mark described it and attendant caveats. This led to 
a discussion of upgrading compilers.

  * We did not go further with Geant4 versions because of limitations
    with the CentOS7 native compiler.
  * Similar issues may arise with ROOT.
  * There are three options to address the issue:
     1. Do nothing and accept the limitations imposed by the default GCC
        4.8.5 compiler
     2. Require users to use a container for all software-dependent
        functions where the container has a non-CentOS7-default version
        of the compiler installed.
     3. Require users to implement advanced compilers on their systems
        either by
         1. using a system like Software Collections
            <https://www.softwarecollections.org/en/>
         2. or installing more modern compiler versions natively

There are various use cases that may (or may not) need support going 
forward, e.g., farm user at JLab, developer on a private desktop or 
laptop machine, maintainer of a university cluster, etc.

We will have to return to this discussion at some point.


      Review of minutes from the last Meeting

We went over the minutes from June 16 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_June_16,_2020#Minutes> 
without extensive comment.


      Issues on GitHub

We reviewed the issues <https://github.com/JeffersonLab/HDGeant4/issues>.


        Energy deposition in TOF mismatch in data & MC #159
        <https://github.com/JeffersonLab/HDGeant4/issues/159>

Sean cross-posted this issue from the halld_sim repository to hdgeant4.


        BCAL reconstructed energy sometimes broken on startup: multicore
        only #143 <https://github.com/JeffersonLab/HDGeant4/issues/143>

Richard reported progress on non-reproducible BCAL energy results when 
running hdgeant4 with multiple threads. He has discovered a pathology 
with the "division" technique of Geant4 to create multiple sensitive 
detector channels. HDGeant4 uses this feature ubiquitously, not only in 
the BCAL but also in the CDC, FCAL, TOF, etc. The implementation of 
divisions turns to be manifestly non-thread-safe. Another technique, the 
Geant4 "replica" feature, does have thread safety built in and Richard 
has followed that code as a model for how to implement thread safety for 
divisions.

In the process, Richard identified a separate issue where results from 
one events depend on details of how processing proceed with previous 
events, an effect he is calling hysteresis. This leads to 
non-reproducibility in repeated execution of the code starting with the 
same random number seeds each time. He believes the problem lies in the 
code to do charged particle propagation through magnetic fields.

He concludes that all results to date of multi-threaded running of 
HDGeant4 are suspect. Luckily, the running we have been doing on the OSG 
has always been single-threaded.


      Pull Requests on GitHub

We looked over the pull requests 
<https://github.com/JeffersonLab/HDGeant4/pulls>. Igal submitted changes 
to simulate the lead tungstate insert 
<https://github.com/JeffersonLab/HDGeant4/pull/158> for FCAL2. He based 
his changes on work done by Simon. Simon explained that, in terms of 
material, the insert is implemented as a single block, but sub-divided 
to give individual read-out channels following the scheme used in the 
FCAL. The pull request has been merged.


      Action Item Review

 1. Continue work on the BCAL multi-threading problem (Richard)
 2. Structure a discussion on advanced compiler versions (Mark)
 3. Try out the bcal_nolight_heavy_rtj branch. (Colin)
 4. Merge issues #93 and #111 (Mark)

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  * This page was last modified on 30 June 2020, at 17:23.

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