This is sample code about how to handle synchronous function as asynchronously in `tornado.web.RequestHandler` using `@tornado.gen.coroutine`.

async_request_handler

#!/usr/bin/python
# -*- coding:utf-8 -*-

"""
This is sample code about how to handle synchronous function 
as asynchronously in `tornado.web.RequestHandler` using `@tornado.gen.coroutine`.
Feel free to suggest idea or nicer python style code. 
I'm a newbie to python :-)

by somma (fixbrain@gmail.com)
"""

import time
import threading
import tornado.gen
import tornado.web
import tornado.httpclient
import concurrent.futures

thread_pool = concurrent.futures.ThreadPoolExecutor(4)

def very_slow_function(arg1):
    time.sleep(20)
    print 'very_slow_function() returned....'
    return arg1

def very_slow_function_async(arg1):
    return thread_pool.submit(very_slow_function, arg1)



def warp_async_and_return_future(func):
    """
    decorator wraps synchornous function and return future.
    """
    def ret_future(*args, **kwargs):
        return thread_pool.submit(func, *args, **kwargs)

    return ret_future

@warp_async_and_return_future
def very_slow_function_decorated(arg1):
    time.sleep(20)
    print 'very_slow_function_decorated() returned....'
    return arg1



class RootHandlerAsync(tornado.web.RequestHandler):
    @tornado.gen.coroutine
    def get(self):
        result = yield very_slow_function_async(100)        
        self.write("very_slow_function_async(), ret_value = {0}".format(result))
        
class RootHandlerAsync2(tornado.web.RequestHandler):
    @tornado.gen.coroutine
    def get(self):        
        result = yield very_slow_function_decorated(100)        
        self.write("very_slow_function_decorated(), ret_value = {0}".format(result))

class GetFullPageAsyncHandler(tornado.web.RequestHandler):
    @tornado.gen.coroutine
    def get(self):
        http_client = tornado.httpclient.AsyncHTTPClient()
        http_response = yield http_client.fetch("http://www.drdobbs.com/web-development")
        response = http_response.body.decode().replace(
            "Most Recent Premium Content", "Most Recent Content")
        self.write(response)
        self.set_header("Content-Type", "text/html")
        
class FetchHandler(tornado.web.RequestHandler):
    @tornado.gen.coroutine
    def get(self, url_to_fetch):
        http_client = tornado.httpclient.AsyncHTTPClient()
        http_response = yield http_client.fetch(url_to_fetch)        
        self.write(http_response.body)        
        self.set_header("Content-Type", "text/html")


if __name__ == "__main__":    
    application = tornado.web.Application([
                                tornado.web.url(r"/", RootHandlerAsync),
                                tornado.web.url(r"/2", RootHandlerAsync2),
                                tornado.web.url(r"/async", GetFullPageAsyncHandler),
                                tornado.web.url(r"/fetch/(.+)", FetchHandler),
                                ])
    application.listen(8080)
    tornado.ioloop.IOLoop.instance().start()