sketch of a ProcessUtilization rework

01_process_stats.rb

class ProcessStats
  include Singleton
  
  def add_source(source)
    @sources << source
  end
  
  def snapshot
    Snapshot.new(@sources)
  end

  def measure
    before = snapshot
    yield
    snapshot - before
  end
  
  class Snapshot
    attr_reader :data

    def initialize(sources)
      @data = sources.each_with_object({}) { |source, hash|
        hash.update(source.sample)
      }.freeze
    end
    
    def -(other)
      (data.keys | other.keys).each_with_object({}) { |key, hash|
        hash[key] = data.fetch(key, 0) - other.fetch(key, 0)
      }.freeze
    end
  end
end

02_process_clock_stats_source.rb

class ProcessClockStatsSource
  def sample
    times = Process.times
    cpu = times.utime + times.stime
    {
      :cpu_time => cpu,
      :real_time => times.real,
      :idle_time => times.real - cpu,
    }.freeze
  end
  
  ProcessStats.instance.add_source(self.new)
end

03_process_utilization.rb

class ProcessUtilization
  def call(env)
    result = nil
    diff = ProcessStats.instance.measure {
      result = @app.call(env)
    }

    record_request(diff)
    result
  end
  
  private
  
  def record_request(snapshot_diff)
    snapshot_diff.each do |key, value|
      stats.histogram("request.#{key}", value)
    end
  end
end

04_graphql.rb

class GraphQL
  def execute(query)
    result = nil
    diff = ProcessStats.instance.measure {
      result = inner_execute(query)
    }
    # save diff somewhere for later (e.g., rendering in a performance dump)
    result
  end
end