class Concurrent::IVar

def add_observer(observer = nil, func = :update, &block)
  raise ArgumentError.new('cannot provide both an observer and a block') if observer && block
  direct_notification = false
  if block
    observer = block
    func = :call
  end
  mutex.synchronize do
    if event.set?
      direct_notification = true
    else
      observers.add_observer(observer, func)
    end
  end
  observer.send(func, Time.now, self.value, reason) if direct_notification
  observer
end

def complete(success, value, reason)
  mutex.synchronize do
    raise MultipleAssignmentError.new('multiple assignment') if [:fulfilled, :rejected].include? @state
    set_state(success, value, reason)
    event.set
  end
  time = Time.now
  observers.notify_and_delete_observers{ [time, self.value, reason] }
  self
end

def fail(reason = StandardError.new)
  complete(false, nil, reason)
end

def initialize(value = NO_VALUE, opts = {})
  init_obligation
  self.observers = CopyOnWriteObserverSet.new
  set_deref_options(opts)
  if value == NO_VALUE
    @state = :pending
  else
    set(value)
  end
end

def set(value)
  complete(true, value, nil)
end