server simply get `value` from querystring and returns it, request simply pass `value` in querystring and tests if the return value equals `value`

request.py

# coding: utf-8

import random
import requests
import multiprocessing

def request_once():
    randint = random.randint(1, 10000)
    url = 'http://localhost:8000?value=%s' % randint
    r = requests.get(url)
    if r.content != str(randint):
        print 'expect %s, got %s' % (randint, r.content)
    else:
        print '-------------------'

def m():
    for i in range(10):
        request_once()

pool = multiprocessing.Pool(processes=30)
[pool.apply_async(m) for _ in range(30)]
pool.close()
pool.join()

server.py

# coding: utf-8

import tornado
import tornado.web
from tornado import ioloop, gen, httpclient
from tornado.web import RequestHandler

class Holder(object):
    pass

holder = Holder()

@gen.engine
def outside_function(callback, value):
    holder.value = value
    yield gen.Task(httpclient.AsyncHTTPClient().fetch, 'https://www.google.com')
    callback(value)

class MasterHandler(RequestHandler):

    @gen.coroutine
    def get(self):
        holder.value = self.get_argument('value', 'default')
        yield gen.Task(outside_function, value=holder.value)
        self.finish(str(holder.value))

urls = [
    (r'/', MasterHandler),
]

app = tornado.web.Application(urls)
app.listen(8000)
ioloop.IOLoop().instance().start()