How Tornado gen.Task making Sync into Async function?

Tornado-async-maker

from tornado import gen, ioloop
import urllib2
import re
tre = re.compile('\<title\>(?P<title>[^<]+)',re.IGNORECASE)
from pprint import pformat
@gen.coroutine
def sleep_bug(url):
    print 'fetch:'+url
    r = yield gen.Task(ioloop.IOLoop.current().add_callback)
    print "callback "+ str(r)
    title = tre.findall(urllib2.urlopen(url).read())[0].decode('utf-8')
    print 'got from:'+url
    raise gen.Return(title)

@gen.coroutine
def make_sleepy_bug(sec=3):
    print "making..."
    re = yield [sleep_bug('http://www.baidu.com'),
                sleep_bug('http://www.google.com'), 
                sleep_bug('http://mengzhuo.org')]
    raise gen.Return(re)

if __name__ == '__main__':
    loop = ioloop.IOLoop.instance()
    #print make_sleepy_bug()
    print "done...\n"+pformat([unicode(x) for x in loop.run_sync(make_sleepy_bug)])