tornado multiple thread workers

import time

from tornado.concurrent import run_on_executor
from concurrent.futures import ThreadPoolExecutor   # `pip install futures` for python2

MAX_WORKERS = 4


class Handler(tornado.web.RequestHandler):
    executor = ThreadPoolExecutor(max_workers=MAX_WORKERS)

    @run_on_executor
    def background_task(self, i):
        """ This will be executed in `executor` pool. """
        time.sleep(10)
        return i

    @tornado.gen.coroutine
    def get(self, idx):
        """ Request that asynchronously calls background task. """
        res = yield self.background_task(idx)
        self.write(res)