add protection for rare infinite loop in ecal multifit (76X)

[bendavid]

This protects against a rare infinite loop observed to occur when updating ecal pulse shape templates to those derived from 2015 low pileup data.

Should have zero effect on MC (or data with existing db conditions)

Will be backported to 74x and 75x asap as well. (And in fact this change is needed both for HLT and prompt reco before updated multifit pulse conditions can safely be deployed)

@emanueledimarco @lgray

[cmsbuild]

A new Pull Request was created by @bendavid (Josh Bendavid) for CMSSW_7_6_X.

add protection for rare infinite loop in ecal multifit (76X)

It involves the following packages:

RecoLocalCalo/EcalRecAlgos

@cmsbuild, @cvuosalo, @slava77 can you please review it and eventually sign? Thanks.
@argiro this is something you requested to watch as well.
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@Degano you are the release manager for this.
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[slava77]

@cmsbuild please test
[ Josh, you could request the tests, I guess.]

Josh, please post here (or in another PR) how to reproduce the infinite loop condition to test this PR.

[bendavid]

The infinite loop is rare and never occurs with the current conditions. You can reproduce it with the work-in-progress tag for 2015 data

process.GlobalTag.toGet = cms.VPSet(
cms.PSet(record = cms.string("EcalPulseShapesRcd"),
tag = cms.string("EcalPulseShapes_data"),
connect = cms.untracked.string("sqlite_file:/afs/cern.ch/work/e/emanuele/public/ecal/pulseshapes_db/ecaltemplates_popcon_data_Run2015C_lowPU.db")
)
)

And it occurs in the 829th event of
/store/data/Run2015C/DoubleEG/RAW-RECO/ZElectron-PromptReco-v1/000/254/833/00000/8CF44CF6-094B-E511-AD5A-02163E014439.root

[bendavid]

Existing tests were in CMSSW_7_4_11 starting from the global tag "74X_dataRun2_Prompt_v1"

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: ef9303b
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-11204/7984/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-11204/7984/summary.html

[lgray]

These two *prev variables should be made const to ensure the compiler optimizes them out.

[cvuosalo]

+1

For #11204 ef9303b

Bug fix for rare infinite loop in ECAL multifit. There should be no change in monitored quantities. #11205 is the 74X version of this PR, and it has already been approved by Reco.

The fixed code is satisfactory, and Jenkins tests against baseline CMSSW_7_6_X_2015-09-08-2300 show no significant differences, as expected. The bug fix was verified for #11205.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_6_X IBs (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[davidlange6]

@bendavid - could you comment on @lgray suggestion?

[lgray]

@davidlange6 If Jenkins tests show no significant differences any change is likely in the noise. I am simply being picky. :-)

[bendavid]

I'm skeptical there will be a meaningful difference in the generated code either way :)

[davidlange6]

+1