bench_atomic.rb

require 'benchmark'
require 'rbconfig'
require 'thread'
require 'concurrent'
Thread.abort_on_exception = true

$go = false # for synchronizing parallel threads

# number of updates on the value
N = ARGV[1] ? ARGV[1].to_i : 100_000

# number of threads for parallel test
M = ARGV[0] ? ARGV[0].to_i : 10

# list of platform-specific implementations
ATOMICS = [
  'MutexAtomic',
  'CAtomic',
  'JavaAtomic',
  'RbxAtomic',
]

puts "Testing with #{RbConfig::CONFIG['ruby_install_name']} #{RUBY_VERSION}"

puts
puts '*** Sequential updates ***'
Benchmark.bm(10) do |x|
  value = 0
  x.report 'no lock' do
    N.times do
      value += 1
    end
  end

  @lock = Mutex.new
  x.report 'mutex' do
    value = 0
    N.times do
      @lock.synchronize do
        value += 1
      end
    end
  end

  ATOMICS.each do |clazz|
    if Concurrent.const_defined? clazz
      @atom = Concurrent.const_get(clazz).new(0)
      x.report clazz do
        N.times do
          @atom.update{|x| x += 1}
        end
      end
    end
  end
end

def para_setup(num_threads, count, &block)
  if num_threads % 2 > 0
    raise ArgumentError, 'num_threads must be a multiple of two'
  end
  raise ArgumentError, 'need block' unless block_given?

  # Keep those threads together
  tg = ThreadGroup.new

  num_threads.times do |i|
    diff = (i % 2 == 0) ? 1 : -1

    t = Thread.new do
      nil until $go
      count.times do
        yield diff
      end
    end

    tg.add(t)
  end

  # Make sure all threads are started
  while tg.list.find{|t| t.status != 'run'}
    Thread.pass
  end

  # For good measure
  GC.start

  tg
end

def para_run(tg)
  $go = true
  tg.list.each{|t| t.join}
  $go = false
end

puts
puts '*** Parallel updates ***'
Benchmark.bm(10) do |bm|
  # This is not secure
  value = 0
  tg = para_setup(M, N/M) do |diff|
    value += diff
  end
  bm.report('no lock'){ para_run(tg) }

  value = 0
  @lock = Mutex.new
  tg = para_setup(M, N/M) do |diff|
    @lock.synchronize do
      value += diff
    end
  end
  bm.report('mutex'){ para_run(tg) }
  raise unless value == 0

  ATOMICS.each do |clazz|
    if Concurrent.const_defined? clazz
      @atom = Concurrent.const_get(clazz).new(0)
      tg = para_setup(M, N/M) do |diff|
        @atom.update{|x| x + diff}
      end
      bm.report(clazz){ para_run(tg) }
      raise unless @atom.value == 0
    end
  end
end