Migrate Code to New Random Service Interface

[wddgit]

Migrate FastSimulation code to use the new interface
of the random number generator service designed to work
with the multithreaded Framework. The main interface
change is to require a StreamID or LuminosityBlockIndex
argument to the getEngine function. These objects are only
available during the event or beginLuminosityBlock method.

[cmsbuild]

A new Pull Request was created by @wddgit (W. David Dagenhart) for CMSSW_7_1_X.

Migrate Code to New Random Service Interface

It involves the following packages:

FastSimulation/MaterialEffects
FastSimulation/PileUpProducer
FastSimulation/Utilities

@cmsbuild, @Degano, @giamman, @lveldere, @nclopezo can you please review it and eventually sign? Thanks.
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@nclopezo, @ktf you are the release manager for this.
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[lveldere]

Hi again David

All looks sane, thanks a lot for your work!
There is just one thing that I'm wondering about:

RandomEngineAndDistribution random(lumi.index());

Does that mean that the lumi number is used as the seed for the random generator?
As far as I know, when events are generated, the luminumber in each simulation job is 0,
so the PU would be seeded identical in each simulation job. Do you know if my presumption is right?

Lukas

[wddgit]

Hi Lukas,

lumi.index() is a LuminosityBlockIndex. This is a new thing and not the same as the luminosity block number. In the Framework, this is a simple index that counts from 0 to one less than the number of LuminosityBlocks that can be processed concurrently. It is simply an index so the threaded Framework knows which currently active LuminosityBlock it is handling.

The argument to that function is not a seed. The argument is an index the service uses to find the correct engine. The service has constructed an engine for each possible value of the index. If you look at the code for this, look in the 7_1_THREADED_X branch. The new service is not in 7_1_X yet, although it is coming there also soon.

I hope that helps explain things, but ask again if not.

[cmsbuild]

+1
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-2620/284/summary.html

[lveldere]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes (tests are also fine). @nclopezo, @ktf can you please take care of it?