render_benchmark.rb

# frozen_string_literal: true

require "active_record"
require "active_record/railties/collection_cache_association_loading"
require "action_controller"
require "action_view"
require "tmpdir"
require "benchmark/ips"

ActionView::PartialRenderer.prepend(ActiveRecord::Railties::CollectionCacheAssociationLoading)

class TestController < ActionController::Base
  def _prefixes; ["."]; end # Search the current directory rather than "test/"
end

class Neat
  def to_partial_path; "thing"; end
end

class NoYield
  def to_partial_path; "no_yield"; end
end

def recurse(cv, depth)
  if depth == 0
    cv.render("thing") { "World" }
  else
    cv.render("thing") { recurse(cv, depth - 1) }
  end
end

def recurse_with_object(cv, obj, depth)
  if depth == 0
    cv.render(obj) { "World" }
  else
    cv.render(obj) { recurse_with_object(cv, obj, depth - 1) }
  end
end

def allocs
  x = GC.stat(:total_allocated_objects)
  yield
  GC.stat(:total_allocated_objects) - x
end

Dir.mktmpdir do |dir|
  TestController.view_paths = dir

  File.write File.join(dir, "_thing.html.erb"), "Hello <%= yield %>"
  File.write File.join(dir, "_no_yield.html.erb"), "Hello World"

  cv = TestController.new.view_context

  obj              = Neat.new
  collection       = [NoYield.new] * 50
  yield_collection = [Neat.new] * 50

  # heat
  cv.render("thing") { "World" }
  cv.render(obj)     { "World" }
  cv.render(collection)

  puts "Allocations for partial rendering with object"
  10.times do |i|
    p i => allocs { recurse_with_object(cv, obj, i) }
  end

  puts "Allocations for partial rendering"
  10.times do |i|
    p i => allocs { recurse(cv, i) }
  end

  puts "Allocations for collection rendering"
  p 0 => allocs { cv.render(collection) }

  Benchmark.ips do |x|
    x.report("shallow render") { cv.render("thing") { "World" } }
    x.report("deep render")    { recurse(cv, 30) }

    x.report("shallow render obj") { cv.render(obj) { "World" } }
    x.report("deep render obj")    { recurse_with_object(cv, obj, 30) }

    x.report("collection render")  { cv.render(collection) }
  end
end