Parameterizing a factory

Overview

Teaching: 5 min
Exercises: 0 min

Questions

Objectives

Learn how to set parameters on a factory

Learn how to override factories via a generator

Learn how to override factories via the command line

Learn how to access services from a factory

Setting parameters on a factory

Parameters are also handled using registered members. JOmniFactory provides a Parameter class template which can hold its own value, but in EICrecon we prefer to use Config structs. Thus JOmniFactory provides ParameterRef, which stores a reference into the Config object.

    ParameterRef<double> m_samplingFraction {this, "samplingFraction", config().sampFrac};
    ParameterRef<std::string> m_energyWeight {this, "energyWeight", config().energyWeight};

Parameters are fetched immediately before Init() is called, so you may access them from any of the callbacks like so:

    void Process(int64_t run_number, uint64_t event_number) {
        logger()->debug( "Event {}: samplingFraction = {}", event_number, m_samplingFraction() );
    }

Because we are using ParameterRefs, we can also access the field the ref points to directly:

    void Process(int64_t run_number, uint64_t event_number) {
        logger()->debug( "Event {}: samplingFraction = {}", event_number, config().sampFrac );
    }

Config objects

We create a plain-old struct to hold our parameters. For now this config struct can live in the same header file as our factory, although eventually it should belong with the algorithm instead.

struct ReconstructedElectrons_config {
    double threshold = 0.9;
    int bucket_count = 4;
    // ...
}

By passing it in to the JOmniFactory base class, we can make it automatically available via the config() method.

class ReconstructedElectrons_factory : public JOmniFactory<ReconstructedElectrons_factory, ElectronReconstructionConfig> {
    ...
}

Overriding parameters via a generator

If you use a Config object for your parameters, you can pass it in directly to the factory generator:

    app->Add(new JOmniFactoryGeneratorT<BasicTestAlg>(
        "FunTest", {"MyHits"}, {"MyClusters"}, 
        {
          .threshold = 6.1,
          .bucket_count = 22
        },
        app));

Overriding parameters via the command line

We can override parameters on the command line like so:

eicrecon -PFunTest:threshold=12.0 in.root

Accessing services from a factory

Services are singletons that provide access to resources such as loggers, geometry, magnetic field maps, etc. Services need to be thread-safe because they are shared by different threads. The most relevant service right now is DD4hep_service. You obtain a service using a registered member like this:

    Service<DD4hep_service> m_geoSvc {this};

Oftentimes we want to retrieve a resource from a Service and refresh it whenever the run number changes. OmniFactory provides Resource for this purpose.

Exercise:

Give your factory a Config struct

Give your Config struct some parameters

Experiment with overriding parameter values in the generator and on the command line.

Key Points

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