Super call creates the mutex

super_created.rb

require 'benchmark'

module SuperMutex
 
  attr_reader :bar

  def initialize
    @mutex = Mutex.new
  end
  
  def threadsafe_mutex
    @mutex
  end

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

end

class Foo
  include SuperMutex
end

threads = []
thread_count = 700
Thread.abort_on_exception
Benchmark.bmbm(7) do |x|
  x.report do 
    # it takes about half a second to create all of the threads so wait a full second to make sure they're all done being created
    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