promises.rb

require 'concurrent'
require 'benchmark'

class Request
  class << self
    def make(num)
      @body = Faraday.get("https://jsonplaceholder.typicode.com/todos/#{num}").body

      self
    end

    def to_json
      JSON(@body)
    end
  end
end

class PromisesExecutor
  def initialize(amount)
    @amount = amount
  end

  def call
    promises = @amount.times.map { |i| Concurrent::Promises.future(i) { |i| Request.make(i).to_json } }

    Concurrent::Promises.zip(*promises).value!
  end
end

class SeqExecutor
  def initialize(amount)
    @amount = amount
  end

  def call
    @amount.times.map { |i| Request.make(i).to_json }
  end
end

class WorkerPool
  TERMINATOR = :abort

  def initialize(amount)
    @amount = amount

    @jobs = Queue.new
    @results = Concurrent::Array.new

    @pool = @amount.times.map do |i|
      Thread.new(i) do |num|
        Thread.current.name = "worker-#{num}"

        loop do
          job, args = @jobs.pop
          break if args.first == TERMINATOR

          @results << job.call(*args)
        end
      end
    end
  end

  def schedule(*args, &block)
    @jobs << [block, args]
  end

  def shutdown
    @amount.times { schedule TERMINATOR }

    @pool.map(&:join)
  end
end

pool_4 = WorkerPool.new(4)
pool_8 = WorkerPool.new(8)
pool_10 = WorkerPool.new(10)
pool_16 = WorkerPool.new(16)
pool_32 = WorkerPool.new(32)

def run_thread_pool(pool)
  30.times { |i| pool.schedule(i) { |i| Request.make(i).to_json } }
  pool.shutdown
  pool.instance_variable_get(:@results)
end

Benchmark.bm do |experiment|
  experiment.report('custom threadpool: (4)') { run_thread_pool(pool_4) }
  experiment.report('custom threadpool: (8)') { run_thread_pool(pool_8) }
  experiment.report('custom threadpool: (10)') { run_thread_pool(pool_10) }
  experiment.report('custom threadpool: (16)') { run_thread_pool(pool_16) }
  experiment.report('custom threadpool: (32)') { run_thread_pool(pool_32) }
end

Benchmark.bm do |experiment|
  experiment.report('seq:') { SeqExecutor.new(30).call }
  experiment.report('async via promises:') { PromisesExecutor.new(30).call }
  experiment.report('custom threadpool:') { run_thread_pool(pool_32) }
end

       user     system      total        real
seq:  0.144788   0.030441   0.175229 (  4.008818)
async via promises:  0.085559   0.020963   0.106522 (  0.655998)
custom threadpool:  0.100604   0.017977   0.118581 (  0.403523)

       user     system      total        real
custom threadpool: (4)  0.139250   0.031637   0.170887 (  1.237397)
custom threadpool: (8)  0.135445   0.032640   0.168085 (  0.641248)
custom threadpool: (10)  0.121258   0.027308   0.148566 (  0.492202)
custom threadpool: (16)  0.110450   0.026344   0.136794 (  0.403192)
custom threadpool: (32)  0.074541   0.019488   0.094029 (  0.219029)

Intel(R) Core(TM) i5-8257U CPU @ 1.40GHz