cmssw: how to skip events which throw a `cms::Exception`

In particular what does it mean that an output module depends on a module that throws an exception ? Does it mean that it has a matching keep statement ?

Yes. It also means any modules needed by those modules which created the data products to ‘keep’.

Does it mean that it has a SelectEvents entry for a Path that includes that module ?

Not exactly. A Path which sees an exception (either because a module on the Path throws the exception OR an unscheduled module needed by the module on the Path throws an exception) will be marked as having an ‘error’ status. The OutputModule will only run if at least one of its Paths doesn’t see the exception and the Path succeeds as normal.

To illustrate, I’ve put together a small program using some dummy test modules. (NOTE: I modified AddIntsProducer so that it would ignore any data products which are missing from the Event).

The following is a trivialized representation of the HLT.

• It only have ‘Track’ and ‘Calo’ related paths.
• There is a ‘globalTrigger’ data product which records to output of the Filters at the end of the two paths. This is marked as shouldTryToContinue() so that even if one of the filters dependent on a module that fails, the globalTrigger will still run.
• The outputs consist of
  • one dependent only on trackPath
  • one dependent only on caloPath
  • one dependent on either trackPath or caloPath
  • one that doesn’t care about Paths and only cares about globalTrigger (to show how that work with exceptions)
  • one that only runs if there was an exception
• The ‘Track’ path has an exception happen early on as part of the ‘track hits’.

import FWCore.ParameterSet.Config as cms

process = cms.Process("TEST")

process.source = cms.Source("EmptySource")

process.maxEvents.input = 3
#this is the type thrown by FailingProducer
process.options.TryToContinue = ["NotFound"]
process.options.wantSummary = True

process.trackingHits = cms.EDProducer("FailingProducer")
process.tracks = cms.EDProducer("AddIntsProducer", labels = cms.VInputTag("trackingHits"))
process.trackFilter = cms.EDFilter("IntProductFilter",
   label = cms.InputTag("tracks"),
   threshold = cms.int32(0),
   shouldProduce = cms.bool(True)
)

process.caloClusters = cms.EDProducer("IntProducer", ivalue = cms.int32(1))
process.caloFilter = cms.EDFilter("IntProductFilter",
   label = cms.InputTag("caloClusters"),
   threshold = cms.int32(0),
   shouldProduce = cms.bool(True)
)

process.globalTrigger = cms.EDProducer("AddIntsProducer", labels = cms.VInputTag("trackFilter","caloFilter"))
process.globalTrigger.shouldTryToContinue()

process.trackPath = cms.Path(process.trackingHits+process.tracks+process.trackFilter)
process.caloPath = cms.Path(process.caloClusters+process.caloFilter)
process.globalTriggerPath = cms.Path(process.globalTrigger)

outputTemplate_ = cms.OutputModule("AsciiOutputModule",
                                        outputCommands = cms.untracked.vstring("drop *", "keep edmTriggerResults_*_*_*"),
                                        SelectEvents = cms.untracked.PSet(SelectEvents = cms.vstring()))

process.trackOut = outputTemplate_.clone(SelectEvents = dict(SelectEvents=["trackPath"]))
process.caloOut = outputTemplate_.clone(SelectEvents = dict(SelectEvents=["caloPath"]))
process.trackAndCaloOut = outputTemplate_.clone(SelectEvents=dict(SelectEvents=["trackPath","caloPath"]))
process.globalTriggerOut = outputTemplate_.clone(outputCommands = ["drop *", "keep edmTriggerResults_*_*_*","keep *_globalTrigger__TEST"])
process.exceptionOut = outputTemplate_.clone(SelectEvents=dict(SelectEvents=["exception@*"]))

process.out = cms.EndPath(process.trackOut+process.caloOut+process.trackAndCaloOut+process.exceptionOut+process.globalTriggerOut)

when run, all the OutputModules write the 3 events except for the ‘trackOut’ which writes no events as the only path it depends upon never succeeds (i.e. trackPath is set to the error state for each Event).

From the summary we see

TrigReport ---------- Path   Summary ------------
TrigReport  Trig Bit#   Executed     Passed     Failed      Error Name
TrigReport     1    0          3          0          0          3 trackPath
TrigReport     1    1          3          3          0          0 caloPath
TrigReport     1    2          3          3          0          0 globalTriggerPath

TrigReport ---------- Module Summary ------------
TrigReport    Visited   Executed     Passed     Failed      Error Name
TrigReport          3          3          3          0          0 TriggerResults
TrigReport          3          3          3          0          0 caloClusters
TrigReport          3          3          3          0          0 caloFilter
TrigReport          3          3          3          0          0 caloOut
TrigReport          3          3          3          0          0 caloPath
TrigReport          3          3          3          0          0 exceptionOut
TrigReport          3          3          3          0          0 globalTrigger
TrigReport          3          3          3          0          0 globalTriggerOut
TrigReport          3          3          3          0          0 globalTriggerPath
TrigReport          3          3          3          0          0 out
TrigReport          3          3          3          0          0 trackAndCaloOut
TrigReport          3          0          0          0          3 trackFilter
TrigReport          3          3          3          0          0 trackOut
TrigReport          3          3          3          0          0 trackPath
TrigReport          3          3          0          0          3 trackingHits
TrigReport          3          0          0          0          3 tracks