fix filling of pythia userhooks

[agrohsje]

PR is a back-port of this pull request from steve mrenna: #34068
we need a back-port to the current run 3 cmssw release which is still 11_2.
the original PR was to fix a segmentation fault of P8 when using userhooks. the code crashed at the start of a new lumisection.
I tested that the PR helps to avoid the crash and TSG-Run3Winter21GS-00071 runs fine. More tests already done for the master PR.

[agrohsje]

please test

[cmsbuild]

A new Pull Request was created by @agrohsje for CMSSW_11_2_X.

It involves the following packages:

GeneratorInterface/Pythia8Interface

@SiewYan, @alberto-sanchez, @agrohsje, @mkirsano, @GurpreetSinghChahal can you please review it and eventually sign? Thanks.
@alberto-sanchez, @mkirsano this is something you requested to watch as well.
@silviodonato, @dpiparo, @qliphy you are the release manager for this.

cms-bot commands are listed here

[agrohsje]

@smrenna backport to 11_2 FYI.

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-34f80e/16107/summary.html
COMMIT: 4105be3
CMSSW: CMSSW_11_2_X_2021-06-18-1100/slc7_amd64_gcc900
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week1/cms-sw/cmssw/34184/16107/install.sh to create a dev area with all the needed externals and cmssw changes.

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 7 differences found in the comparisons
• DQMHistoTests: Total files compared: 36
• DQMHistoTests: Total histograms compared: 2537235
• DQMHistoTests: Total failures: 12
• DQMHistoTests: Total nulls: 1
• DQMHistoTests: Total successes: 2537200
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.004 KiB( 35 files compared)
• DQMHistoSizes: changed ( 312.0 ): 0.004 KiB MessageLogger/Warnings
• Checked 151 log files, 37 edm output root files, 36 DQM output files
• TriggerResults: no differences found

[agrohsje]

+generators

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_11_2_X IBs (tests are also fine) and once validation in the development release cycle CMSSW_12_0_X is complete. This pull request will now be reviewed by the release team before it's merged. @silviodonato, @dpiparo, @qliphy (and backports should be raised in the release meeting by the corresponding L2)

[qliphy]

+1