Class level mutex

class_mutex.rb

require 'benchmark'

module SuperMutex
 
  attr_reader :bar

  def self.included(base)
    base.extend(ThreadSafeClassMethods)
    base.threadsafe_class_mutex = Mutex.new
  end

  module ThreadSafeClassMethods
    attr_accessor :threadsafe_class_mutex
  end
  
  def threadsafe_mutex
    self.class.threadsafe_class_mutex.synchronize {
      @mutex ||= Mutex.new
    }
  end

  def some_method
    threadsafe_mutex.synchronize {
      @bar ||= 0
      @bar += 1
    }
  end

end

class Foo
  include SuperMutex
end

threads = []
Thread.abort_on_exception
thread_count = 700
Benchmark.bmbm(7) do |x|
  x.report do 
    # it takes about half a second to create 1,000 threads so a full second is plenty to wait
    start = Time.now + 1.0
    thread_count.times do 
      threads << Thread.new{sleep (start - Time.now); foo = Foo.new; 1000.times{foo.some_method} }
    end
    threads.each { |t| t.join }
  end
end