quickie_parallel.rb

class QuickieParallel
  attr_accessor :results
  def initialize(args)
    @num_procs = args.fetch(:num_processes, 4)
    @using_db = args.fetch(:using_db, false)
    @debug = args.fetch(:debug, false)
    @results = {}
  end

  def finish_callback(val, index, result)
    @results[index] = result
  end

  def each(batch)
    log_with_time("total time for batch", 0.0) do
      Parallel.each_with_index(batch, in_processes: @num_procs, finish: method(:finish_callback)) do |value, index|
        ActiveRecord::Base.connection.reconnect! if @num_procs > 1 && @using_db

        log_with_time("yield ##{index}", 0.0) do
          yield(value, index) if block_given?
        end

      end
    end
  end

  private

  def log_with_time(txt=nil, thld=100, &block)
    start = Time.now
    result = yield

    taken = ((Time.now - start) * 1000).round(1)
    dbg = ["===="]
    dbg << txt.to_s.ljust(50) if txt
    dbg << "(#{taken}ms)"
    puts dbg.join(' ') if @debug && taken > thld
    result
  end
end

def fibonacci_r(a, b, n)
  n == 0 ? a : fibonacci_r(b, a + b, n - 1)
end

def fibonacci(n)
  fibonacci_r(0, 1, n)
end

# processes | time
# 0         | (7892.3ms)
# 2         | (6069.9ms)
# 4         | (4878.0ms)
processor = QuickieParallel.new(num_processes: 4, debug: true)
processor.each(5_000.times) do |val, index|
  fibonacci(val)
end

processor.results.sort
# => [
#      [0, 0],
#      [1, 1],
#      [2, 1],
#      [3, 2],
#      [4, 3],
#      [5, 5],
#      [6, 8],
#      ...