This gist compares the use of Threaded and non-Threaded Ruby code to perform IO(Read/Write) on a shared file.

ruby_multi_threading.rb

gem 'thread' # gem install thread

require 'thread/pool'

@semaphore = Mutex.new

LOOPS_COUNT = (ENV['LOOPS_COUNT'] || 100).to_i
POOL_SIZE = (ENV['POOL_SIZE'] || LOOPS_COUNT).to_i

def with_thread_without_mutex!(num_loops = 100)
  executions = num_loops.times.map do |i|
    Thread.new do
      count = (File.read('test.txt') || 0).to_i

      File.open('test.txt', 'wb') do |file|
        file.write((count + 1).to_s)
      end
    end
  end

  executions.map(&:join)
end

def with_thread_mutex!(num_loops = 100)
  executions = num_loops.times.map do |i|
    Thread.new do
      @semaphore.synchronize do
        count = (File.read('test.txt') || 0).to_i

        File.open('test.txt', 'wb') do |file|
          # puts "Current count = #{count} | Next count = #{count + 1}"
          file.write((count + 1).to_s)
        end
      end
    end
  end

  executions.map(&:join)
end

def with_thread_pool!(pool_size = 100, num_loops = 100)
  pool = Thread.pool(num_loops)

  num_loops.times do |i|
    pool.process do
      @semaphore.synchronize do
        count = (File.read('test.txt') || 0).to_i

        File.open('test.txt', 'wb') do |file|
          # puts "Current count = #{count} | Next count = #{count + 1}"
          file.write((count + 1).to_s)
        end
      end
    end
  end

  pool.shutdown
end


def without_thread!(num_loops = 100)
  num_loops.times do |i|
    count = (File.read('test.txt') || 0).to_i

    File.open('test.txt', 'wb') do |file|
      file.write((count + 1).to_s)
    end
  end
end

def test!(label, value)
  if File.read('test.txt').to_i != value
    puts "Error for \"#{label}\". The file 'test.txt' must have the exact value 200"
  end
end

def truncate!
  File.truncate('test.txt', 0)
end

def with_time(label, &block)
  start_time = Time.now
  yield block if block_given?
  end_time = Time.now

  puts "Total time for \"#{label}\" ==> #{((end_time - start_time) * 100).round(2)} ms"
end

with_time("with_thread_pool!") do
  truncate!
  with_thread_pool!(POOL_SIZE, LOOPS_COUNT)
  test!("with_thread_pool!", LOOPS_COUNT)
end

sleep(2)

with_time("with_thread_mutex!") do
  truncate!
  with_thread_mutex!(LOOPS_COUNT)
  test!("with_thread_mutex!", LOOPS_COUNT)
end

sleep(2)

with_time("without_thread!") do
  truncate!
  without_thread!(LOOPS_COUNT)
  test!("without_thread!", LOOPS_COUNT)
end

➜ ruby test.rb 
Total time for "with_thread_pool!" ==> 13.1 ms [fastest]
Total time for "with_thread_mutex!" ==> 20.57 ms
Total time for "without_thread!" ==> 34.13 ms [slowest]

➜ LOOPS_COUNT=250 ruby test.rb 
Total time for "with_thread_pool!" ==> 96.6 ms
Total time for "with_thread_mutex!" ==> 90.64 ms [fastest]
Total time for "without_thread!" ==> 122.73 ms [slowest]

➜ LOOPS_COUNT=450 ruby test.rb 
Total time for "with_thread_pool!" ==> 169.74 ms
Total time for "with_thread_mutex!" ==> 175.59 ms [slowest]
Total time for "without_thread!" ==> 156.91 ms [fastest]

➜ LOOPS_COUNT=1000 ruby test.rb 
Total time for "with_thread_pool!" ==> 528.86 ms [slowest]
Total time for "with_thread_mutex!" ==> 423.94 ms 
Total time for "without_thread!" ==> 363.41 ms [fastest]

➜ LOOPS_COUNT=1000 ruby test.rb 
Total time for "with_thread_pool!" ==> 420.08 ms
Total time for "with_thread_mutex!" ==> 436.92 ms
Total time for "without_thread!" ==> 418.73 ms

➜ LOOPS_COUNT=1000 ruby test.rb 
Total time for "with_thread_pool!" ==> 416.59 ms 
Total time for "with_thread_mutex!" ==> 514.78 ms [slowest]
Total time for "without_thread!" ==> 389.42 ms [fastest]

➜ LOOPS_COUNT=1500 ruby test.rb 
Total time for "with_thread_pool!" ==> 699.17 ms [slowest]
Total time for "with_thread_mutex!" ==> 572.88 ms [fastest]
Total time for "without_thread!" ==> 632.88 ms