Random seed policy moved back to per-event

[PetrilloAtWork]

The policy now uses random as fallback policy for per-event seeds.

This addresses issue #243.

The background: LArSoft provides a policy for providing seeds to the random number generators which ensures that the same event will always receive the same seeds, guaranteeing job reproducibility. Unfortunately that policy does not define what happens when seeds are required outside the event boundaries; a typical case is the LArSoft implementation of CORSIKA interface, CORSIKAGen, which at beginning of the job decides randomly which pool of pre-generated events to use in the job. This choice happens at a time when no event is being processed (no input file, in fact, has been opened yet). The undefined behaviour of the per-event policy was in fact to always use 0 as a seed, which would cause the same pool of cosmic ray events to be used for every job.

While LArSoft offers no real solution to this issue, it now provide a workaround in allowing to control which seeds are provided at that time. My choice here is to use a random policy, which does not guarantee reproducibility (e.g. rerunning a job on a certain input will pick a different CORSIKA event pool) but at least behaves as a random generator.

This pull request defines this new configuration, defines also an alias icarus_default_NuRandomService supposed to define the "default" random seed service configuration for ICARUS, and then it uses the latter wherever there is the need to configure that service.

This may be a breaking change for the simulation, since different random streams may be generated for some of the modules, but it will likely not be noticed by the integration tests, which fix the random seeds overriding the standard configuration settings.

This pull request has been tested running the unit tests, a prodcorsika_genie_standard_icarus.fcl job, a standard_g4_icarus.fcl job and a standard_detsim_icarus.fcl job.

[SFBayLaser]

I believe this is a good change to make. Thank you!

[rennney]

trigger build

[FNALbuild]

✔️ CI build for LArSoft Succeeded on slf7 for c7:prof -- details available through the CI dashboard

[FNALbuild]

✔️ CI build for LArSoft Succeeded on slf7 for e20:prof -- details available through the CI dashboard

[FNALbuild]

⚠️ CI build for ICARUS Warning at phase ci_tests ICARUS on slf7 for c7:prof - ignored warnings for build -- details available through the CI dashboard

🚨 For more details about the warning phase, check the ci_tests ICARUS phase logs

parent CI build details are available through the CI dashboard

[FNALbuild]

⚠️ CI build for ICARUS Warning at phase ci_tests ICARUS on slf7 for e20:prof - ignored warnings for build -- details available through the CI dashboard

🚨 For more details about the warning phase, check the ci_tests ICARUS phase logs

parent CI build details are available through the CI dashboard