module EventMachine

def self.synchrony(blk=nil, tail=nil)

It detects whether EM is running or not.
paused and resumed based on IO scheduling.
a Ruby Fiber such that async operations can be transparently
A convenience method for wrapping a given block within 
def self.synchrony(blk=nil, tail=nil)
  # EM already running.
  if reactor_running?
    if block_given?
      Fiber.new { yield }.resume
    else
      Fiber.new { blk.call }.resume
    end
    tail && add_shutdown_hook(tail)
  # EM not running.
  else
    if block_given?
      run(nil, tail) { Fiber.new { yield }.resume }
    else
      run(Proc.new { Fiber.new { blk.call }.resume }, tail)
    end
  end
end