Cleanup initialisation of Geant4

[civanch]

PR description:

Clean-up of Geant4 initialisation inspired by DD4HeP developments:

1. do not instantiate magnetic field for master thread
2. add optional magnetic field dump to the first worker thread
3. initialise G4 world volume not in unique DDWorld class but in WorkerMTRunManager per thread
4. code clean-up, removed few class members and not used headers

Correctness of this PR should be in identical results

PR validation:

private test on identity of hits for MinBias events

if this PR is a backport please specify the original PR:

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• verify that the PR is really intended for the chosen branch
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[cmsbuild]

The code-checks are being triggered in jenkins.

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-27442/10752

• This PR adds an extra 28KB to repository

[cmsbuild]

A new Pull Request was created by @civanch (Vladimir Ivantchenko) for master.

It involves the following packages:

SimG4Core/Application
SimG4Core/Geometry

@cmsbuild, @civanch, @mdhildreth can you please review it and eventually sign? Thanks.
@makortel this is something you requested to watch as well.
@davidlange6, @slava77, @fabiocos you are the release manager for this.

cms-bot commands are listed here

[civanch]

please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-run-pr-tests/1329/console Started: 2019/07/04 18:27

[cmsbuild]

+1
Tested at: 19c36e9
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-04fb2d/1329/summary.html

[cmsbuild]

Comparison job queued.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-04fb2d/1329/summary.html

Comparison Summary:

• No significant changes to the logs found
• Reco comparison results: 4 differences found in the comparisons
• DQMHistoTests: Total files compared: 33
• DQMHistoTests: Total histograms compared: 3160399
• DQMHistoTests: Total failures: 2
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 3160063
• DQMHistoTests: Total skipped: 334
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 32 files compared)
• Checked 137 log files, 14 edm output root files, 33 DQM output files

[civanch]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next master IBs (tests are also fine). This pull request will now be reviewed by the release team before it's merged. @davidlange6, @slava77, @smuzaffar, @fabiocos (and backports should be raised in the release meeting by the corresponding L2)

[fabiocos]

@civanch from a quick test and comparing JobReports it seems to me that there is no significant change in performances at initialization expected

[civanch]

@fabiocos , there is a small advantage: we do not create magnetic field object in the master thread (it is an useless object) but this should not be a big value.

[fabiocos]

+1