Module: Axn::Extras::Strategies::Vernier

Defined in:
lib/axn/extras/strategies/vernier.rb

Class Method Summary collapse

Class Method Details

.configure(if: nil, sample_rate: 0.1, output_dir: nil) ⇒ Module

Returns A configured module that adds profiling to the action.

Parameters:

  • if (Proc, Symbol, #call, nil) (defaults to: nil) —

    Optional condition to determine when to profile

  • sample_rate (Float) (defaults to: 0.1) —

    Sampling rate (0.0 to 1.0, default: 0.1)

  • output_dir (String, Pathname) (defaults to: nil) —

    Output directory for profile files (default: Rails.root/tmp/profiles or tmp/profiles)

Returns:

  • (Module) —

    A configured module that adds profiling to the action



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# File 'lib/axn/extras/strategies/vernier.rb', line 14

def self.configure(if: nil, sample_rate: 0.1, output_dir: nil)
  condition = binding.local_variable_get(:if)
  sample_rate_value = sample_rate
  output_dir_value = output_dir || _default_output_dir

  Module.new do
    extend ActiveSupport::Concern

    included do
      class_attribute :_vernier_condition, default: condition
      class_attribute :_vernier_sample_rate, default: sample_rate_value
      class_attribute :_vernier_output_dir, default: output_dir_value

      around do |hooked|
        _with_vernier_profiling { hooked.call }
      end
    end

    private

    def _with_vernier_profiling(&)
      return yield unless _should_profile?

      _profile_with_vernier(&)
    end

    def _profile_with_vernier(&)
      _ensure_vernier_available!

      class_name = self.class.name.presence || "AnonymousAction"
      profile_name = "axn_#{class_name}_#{Time.now.to_i}"

      # Ensure output directory exists (only once per instance)
      _ensure_output_directory_exists

      # Build output file path
      output_dir = self.class._vernier_output_dir || _default_output_dir
      output_file = File.join(output_dir, "#{profile_name}.json")

      # Configure Vernier with our settings
      collector_options = {
        out: output_file,
        allocation_sample_rate: (self.class._vernier_sample_rate * 1000).to_i,
      }

      ::Vernier.profile(**collector_options, &)
    end

    def _ensure_output_directory_exists
      return if @_vernier_directory_created

      output_dir = self.class._vernier_output_dir || _default_output_dir
      FileUtils.mkdir_p(output_dir)
      @_vernier_directory_created = true
    end

    def _should_profile?
      # Fast path: no condition means always profile
      return true unless self.class._vernier_condition

      # Slow path: evaluate condition (only when needed)
      Axn::Core::Flow::Handlers::Invoker.call(
        action: self,
        handler: self.class._vernier_condition,
        operation: "determining if profiling should run",
      )
    end

    def _ensure_vernier_available!
      return if defined?(::Vernier) && ::Vernier.is_a?(Module)

      begin
        require "vernier"
      rescue LoadError
        raise LoadError, <<~ERROR
          Vernier profiler is not available. To use profiling, add 'vernier' to your Gemfile:

            gem 'vernier', '~> 1.0'

          Then run: bundle install
        ERROR
      end
    end

    def _default_output_dir
      if defined?(Rails) && Rails.respond_to?(:root)
        Rails.root.join("tmp", "profiles")
      else
        Pathname.new("tmp/profiles")
      end
    end
  end
end