app.py

from tornado.options import define, options
import tornado.ioloop
import tornado.web
import tornado.httpserver


class MainHandler(tornado.web.RequestHandler):
 @tornado.web.asynchronous
 def get(self):
 self._async_callback()

 def _async_callback(self):
 self.write("Hello, world!")
 self.finish()

app = tornado.web.Application([
 (r"/", MainHandler),
])

define("port", default="5555", help="Port to listen on")

if __name__ == "__main__":
 tornado.options.parse_command_line()
 server = tornado.httpserver.HTTPServer(app)
 server.bind(options.port)
 # autodetect cpu cores and fork one process per core
 try:
 server.start(0)
 tornado.ioloop.IOLoop.instance().start()
 except KeyboardInterrupt:
 tornado.ioloop.IOLoop.instance().stop()