require 'java'
 
class AsyncPriorityQueue < java.util.PriorityQueue
  def initialize(*args)
    super
    @popq = []
  end
  def add(o)
    super unless contains?(o)
  end
  def push(o)
    if add(o) and !@popq.empty?
      @popq.shift.call(self.poll)
    end
  end
  def pop(prc=nil, &blk)
    raise ArgumentError, 'block or proc required' unless blk ||= prc
 
    if empty?
      @popq << blk
    else
      blk.call(self.poll)
    end
  end
end