Benchmark of Rake::FileTask#out_of_date? for https://github.com/ruby/rake/pull/224

rake-out_of_date-benchmark.rb

# This attempts to reproduce the performance regression caused by #183
# 
# We basically go wide with a bottleneck file and then go wide again. This
# causes the "downstream" part (after the bottleneck) to be queried over and
# over again with #183

require 'rake'

MAX_SIZE = 100
MAX_SIZE.times do |i|
    FileUtils.touch "down#{i}"
end
sleep 0.1
MAX_SIZE.times do |i|
    FileUtils.touch "up#{i}"
end
sleep 0.1
MAX_SIZE.times do |i|
    FileUtils.touch "root#{i}"
end

def setup(size)
    app = Rake::Application.new
    downstream = (0...size).map do |i|
        app.define_task(Rake::FileTask, "down#{i}")
    end
    upstream   = (0...size).map do |i|
        app.define_task(Rake::FileTask, "up#{i}")
    end
    roots = (0...size).map do |i|
        app.define_task(Rake::FileTask, "root#{i}")
    end

    roots.each do |root_t|
        root_t.enhance upstream.map(&:name)
    end
    upstream.each do |upstream_t|
        upstream_t.enhance downstream.map(&:name)
    end

    tic = Time.now
    roots.each { |t| t.send(:out_of_date?, Time.now + 1) }
    Time.now - tic
end

[10, 20, 30, 40, 50, 60, 70, 80, 90, 100].each do |size|
    10.times do
        duration = setup(size)
        puts "#{size} #{duration}"
    end
end

task :default