threads.rb

races = Race.where(runs_at: (Date.today - 12.months)..Date.today)
variants_queue = # big queue!

workers = []
results = []
best_strike_rate = [0, nil]
best_avg = [100, nil]

mutex = Mutex.new

8.times do |i|
  workers << Thread.new do
    ActiveRecord::Base.connection_pool.with_connection do
      loop do
        break if variants_queue.empty?
        v = variants_queue.pop
        puts "Worker #{i+1} processing variant: #{v} (#{(variants.index(v).fdiv(variants.size)*100).round(2)}%). "
        variant_results = []
        
        races.each do |r|
          prediction = predict(r)
          result = r.results.find{|res| res.runner.name == predicted_winner}
          variant_results << result.pos if result
        end
        
        strike_rate = variant_results.count{|j| j == "1"}.fdiv(variant_results.size)
        finish_r = variant_results.reject(&:nil?).map(&:to_i).reject(&:zero?)
        avg = finish_r.reduce(:+).fdiv(finish_r.length) rescue nil
        mutex.synchronize do
          best_avg = [avg, v] if avg < best_avg[0]
          best_strike_rate = [strike_rate, v] if strike_rate > best_strike_rate[0]
          results << [v, strike_rate, avg]
        end
      end
    end
  end
end
workers.each { |c| c.join }