<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set_ioloop(self, ioloop=None):
 """Set the tornado ioloop to use Defaults to tornado.ioloop.IOLoop.current() if set_ioloop() is not called or if ioloop=None. Must be called before start() """

        ioloop = ioloop or tornado.ioloop.IOLoop.current()
        self.ioloop = ioloop
        for res in dict.values(self.children):
            res.set_ioloop(ioloop)