Module: Greenroom::ExperimentBehavior

Defined in:
lib/greenroom/experiment_behavior.rb

Overview

The two behaviours Scientist::Experiment requires from its includer, plus a non-raising override of raised.

A module, not a concrete class: Scientist::Experiment has exactly one registration slot per process (Scientist::Experiment.set_default), and a later include silently steals it from an earlier one. If this gem shipped a class for a host to include, requiring this gem at all would risk taking over that slot from the host's own experiment class. A host includes both Scientist::Experiment and this module into its own class instead, keeping the registration decision with the host.

A host that wants an experiment to run outside a census (for example, sampling live traffic) overrides enabled? in its own class; that is why publish still works when no recorder is installed.

Instance Method Summary collapse

Instance Method Details

#enabled? ⇒ Boolean

True exactly while a census job has a recorder installed on this thread. The recorder's presence is what turns an experiment on, so there is only one mechanism to reason about, not two that could drift out of sync.

Returns:

  • (Boolean) 


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# File 'lib/greenroom/experiment_behavior.rb', line 23

def enabled?
  !Recorder.current.nil?
end

#publish(result) ⇒ Object

A recorder installed on this thread means a census is in progress: hand it the result to tally instead of sending an event per comparison. With no recorder installed, an experiment that a host enabled outside a census (see the module documentation) still gets a single event per comparison, sent directly.



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# File 'lib/greenroom/experiment_behavior.rb', line 32

def publish(result)
  recorder = Recorder.current
  if recorder
    recorder.record(result)
  else
    publish_comparison(result)
  end
end

#raised(operation, error) ⇒ Object

Scientist's default raised re-raises, which would let a failure in this gem's own instrumentation (a bad clean block, a reporter outage) break the host's actual call. Recording the failure and returning nil keeps that failure from ever reaching the caller.



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# File 'lib/greenroom/experiment_behavior.rb', line 45

def raised(operation, error)
  begin
    Greenroom.reporter.record("GreenroomInternalError", {
      experiment: name,
      operation: operation,
      error: error.class.name
    })
  rescue
    # Recording the failure must never itself fail the call that
    # triggered it -- a reporter outage would otherwise take down the
    # very requests this gem exists to observe, in a way that a broken
    # bit of measurement code has no business doing.
  end
  nil
end