Slightly friendlier API for adding custom method traces to NewRelic

gistfile1.rb

require 'new_relic/agent/method_tracer'

class NR
  # Convenience method for adding NewRelic tracing around specific methods of interest.
  #
  # Note about performance:
  #
  #   " CAUTION - adding probes to your code adds overhead.
  #     Each probe burns about 20 microseconds of CPU.
  #     Be careful not to probe a method that's called frequently in a loop. "
  #   Source: http://newrelic.com/docs/ruby/ruby-agent-configuration
  #
  # Note about reporting:
  #
  #   > The :metric => false option tells the Ruby Agent to have this probe
  #   > only participate in transaction traces and not produce streams of
  #   > metric data, which would not be visible except in Custom Dashboards.
  #   Source: http://newrelic.com/docs/ruby/ruby-agent-configuration
  #
  #   However, when I tried this using :metric => false, the traces didn't show
  #   up in the Performance Breakdown view that NR gives for specific controller
  #   actions. So, the default here is :metric => true.
  #
  # More examples of adding tracing are available in the Ruby section at:
  #   http://newrelic.com/docs/docs/custom-metric-collection
  #
  # And the API documentation for add_method_tracer can be found at:
  #   http://newrelic.github.com/rpm/NewRelic/Agent/MethodTracer/ClassMethods.html#method-i-add_method_tracer
  #   (Possibly of interest:  it takes :code_header => '' and :code_footer => '' as Ruby strings and inserts
  #   them before or after calling the traced method.)
  #
  #
  #
  # Usage Examples (note the use of '.' and '#' to distinguish between class and instance methods):
  #
  #   NRInstrumentation.instrument 'Foo::Bar.baz'                   # add tracing to a class method on the Foo::Bar module
  #   NRInstrumentation.instrument 'Spam.new_tin'                   # add tracing to a class method on the Spam class
  #   NRInstrumentation.instrument 'Spam#temperature'               # add tracing to an instance method on the Spam class
  #
  def self.instrument(fully_qualified_method, options = {})
    new.instrument(fully_qualified_method, options)
  end

  DefaultOptions = {
    :metric => true,
    :deduct_call_time_from_parent => true,
  }

  def instrument(fully_qualified_method, options = {})
    target    = target_for_tracing(fully_qualified_method)
    teh_codez = code_for_eval(fully_qualified_method, options.reverse_merge(DefaultOptions))
    # puts '', target.name, teh_codez # uncomment if you're confused
    target.module_eval(teh_codez)
  end

protected

  def target_for_tracing(fully_qualified_method)
    unless fully_qualified_method.match(/^(.*)(?:[\.\#].*)$/)
      raise "Couldn't understand fully_qualified_method: #{fully_qualified_method.inspect}"
    end
    $1.constantize
  end

  def code_for_eval(fully_qualified_method, options)
    glyph, method = *fully_qualified_method.match(/^(?:.*)([\.\#])(.*)$/).captures
    lines = [
      enable_tracing_line,
      add_method_trace_line(fully_qualified_method, options)
    ]
    lines = go_meta(lines) if '.' == glyph
    lines.join('; ')
  end

  def go_meta(lines)
    # To enable tracing on class/module methods, we need to eval against the class's (metaclass/singleton class/eigenclass/whatever)
    ['class << self'] + lines + ['end']
  end

  def enable_tracing_line
    # Make sure the #add_method_tracer macro is available
    'include NewRelic::Agent::MethodTracer unless ancestors.include?(NewRelic::Agent::MethodTracer)'
  end

  def add_method_trace_line(fully_qualified_method, options)
    # Invoke the add_method_tracer macro
    method = *fully_qualified_method.match(/^(?:.*[\.\#])(.*)$/).captures
    metric_name = "Custom/#{fully_qualified_method}"
    'add_method_tracer %s, %s, %s' % [method.to_sym, metric_name, options].map(&:inspect)
  end

end


NR.instrument 'Brochure.find'
NR.instrument 'Brochure.liquid_render'
NR.instrument 'Platypus::CmsGateway.boc'
NR.instrument 'Platypus::CmsGateway::Remote#boc'
NR.instrument 'Platypus::CmsGateway::Remote#preview_boc'
NR.instrument 'Platypus::CmsGateway::Remote#get'
NR.instrument 'Platypus::CmsGateway::Remote#get_cached'
NR.instrument 'Platypus::CmsGateway::Remote#get_uncached'
NR.instrument 'Platypus::CmsGateway::Remote#parse_response'