Instrumentation for methods

instrumentor.rb

module Instrumenter
  class Instrumentation < Module
    def initialize(method, label)
      @method = method
      @label = label

      define_method(method) do |*args|
        start_time = Time.now
        super(*args).tap do
          end_time = Time.now
          puts "#{label}: #{end_time - start_time}s"
        end
      end
    end

    def inspect
      klass = self.class.name || self.class.inspect
      "#<#{klass}: method=#{@method.inspect} label=#{@label.inspect}>"
    end
  end

  module_function

  def instrument_method(klass, method, label: "#{klass.name}##{method}")
    klass.prepend(Instrumentation.new(method, label))
  end

  def instrument_class_method(klass, method, label: "#{klass.name}.#{method}")
    instrument_method(klass.singleton_class, method, label: label)
  end
end

__END__
## Example usage

class Foo
  def foo
    sleep 1
  end

  def self.bar
    sleep 2
  end
end

Instrumenter.instrument_method(Foo, :foo)
Instrumenter.instrument_class_method(Foo, :bar)

Foo.bar
# (STDOUT) Foo.bar: 2.000576s
# => 2

Foo.new.foo
# (STDOUT) Foo#foo: 1.005025s
# => 1