Processing opticalphoton event info into ROOT file via multithreading mode

Particles, Track, Event, Run and Biasing
1

Dear Geant4 Experts

I am facing problem while processing the opticalphoton info into a ROOT file when I am processing the events in multi thread mode. Here is a situation: I am shooting gamma rays over a scintillator bar, and the resulting optical photons attributes I am storing into a ROOT file. The situation is fine with a single thread, but when I am running in multi-thread, then, the output file is not reproduced as that of a single thread case for the same no. of gamma-ray shoots. I have the feeling that in multi-thread mode, the gamma-ray energy deposition is catered by one thread while the optical photon processing is done by another thread, so when I am creating the ROOT file, it leaves the useful events. I don’t know how to tackle this situation. I came to know the example OpNovice but I don’t exactly got the concept of G4Run::Merge(run).

I also notices that no. of event starts and stop print outputs are not equal in single and multi thread?
I am attaching the output files (for 190 gamma-ray shoots) of my terminal in case of single and two thread runs files for closer inspection to the experts.

Please tell me the relevant files of my geant4 code I will upload that.

output_singleThread.txt (40.0 KB)
output_TwoThreads.txt (41.7 KB)

2

Are you doing all of the ROOT I/O stuff yourself? TFile, TTree, AddBranch, blah blah blah? Or are you using G4AnalysisManager to produce a ROOT-format output file? ROOT is quite thread-unsafe when used by non-ROOT applications; for CDMS, we had to make our ROOT output manager a singleton, and wrap all of the ROOT calls in mutexes (G4AutoLock).

G4AnalysisManager handles everything in a natively Geant4 way, and produces an output file that ROOT can read, without using any ROOT libraries. It may be a better option for you.

You asked,

Nope! Each whole event is handled by a single thread. You are most likely seeing the cross-thread collisions that we saw, and which required mutexing to avoid.

3

Thank you for the response

Yes all the ROOT I/O I am doing by myself and not using the G4AnalysisManager, can you please help me how to wrap all the ROOT calls in mutex (G4AutoLock)? and how do I avoid the cross-thread collisions. I am attaching my EventAction and RunAction files. Please help me out.

This is a old piece of code which I edited for another detector configuration, initially I was not using multi-thread, but now I seriously required.

Also provide the Geant4 directory example to understand G4AnalysisManager further.

Thanks !
SinglePlasticEventAction.cc (13.1 KB)
SinglePlasticRunAction.cc (5.8 KB)

4

Hello,

Please, take a look at the basic example B4/B4a and also the Analysis section in the Geant4 Guide For Application Developers.

Best regards,

5

Thanks for the suggestions, Can you please tell how to implement G4Autolock in my eventaction code?

6

The overall documentation for multithreading, including discussions of shared vs. local memory, singletons, etc., is in the Toolkit Guide (which is aimed at the G4 developers, not end users): Parallelism in Geant4: multi-threading capabilities — Geant4 Documentation 11.3 documentation. The discussion of mutexes is towards the end, Parallelism in Geant4: multi-threading capabilities — Geant4 Documentation 11.3 documentation. In the Application Developers’ Guide, there’s a discussion of G4AutoLock in the Analysis section cited above, Analysis Manager Classes — Book For Application Developers 11.3 documentation