watch.rb for vernier - traps info signal to start/stop profiling

watch.rb

# put this inside vernier/lib/vernier/watch.rb
# to use with e.g. rails server: 
# $ 'RUBYOPT='-I/path-containing-vernier-repo/vernier/lib -rvernier/watch' rails server
# then sending the 'info' signal (shoult be Ctrl-T on macos terminal) will start/stop profiling

require "vernier"

class Null
  def self.record_interval name
    yield
  end
end

$collector = Null

def vernier
  $collector
end

trap(:INFO) do
  if $collector == Null
    puts "starting collector"
    $collector = Vernier::Collector.new(:wall)
    $collector.start
    puts "started collector"
  else
    puts "stopping collector"
    result = $collector.stop
    FIle.write("time_profile.json", Vernier::Output::Firefox.new(result).output)

    $collector = Null
    puts "stopped collector"
  end
end