Tornado HTTPServer that adds objects to a queue upon receiving a POST request

Question

I want to create a web server, that automatically handles "orders" when receiving a POST request.

My code so far looks like this:

from json import loads
from tornado.httpserver import HTTPServer
from tornado.ioloop import IOLoop
from tornado.web import Application, url, RequestHandler


order_list = list()


class MainHandler(RequestHandler):  

    def get(self):
        pass

    def post(self):
        if self.__authenticate_incoming_request():
            payload = loads(self.request.body)
            order_list.append(payload)
        else:
            pass

    def __authenticate_incoming_request(self) -> bool:
        # some request authentication code
        return True


def start_server():
    application = Application([
        url(r"/", MainHandler)
    ])

    server = HTTPServer(application)
    server.listen(8080)

    IOLoop.current().start()


if __name__ == '__main__':
    start_server()

Here is what I want to achieve:

1. Receive a POST request with information about incoming "orders"
2. Perform an action A n-times based on a value defined in the request.body (concurrently, if possible)

Previously, to perform action A n-times, I have used a threading.ThreadPoolExecutor, but I am not sure, how I should handle this correctly with a web server running in parallel.

My idea was something like this:

start_server()

tpe = ThreadPoolExecutor(max_workers=10)
while True:
     if order_list:
         new_order = order_list.pop(0)
         tpe.submit(my_action, new_order)         # my_action is my desired function

     sleep(5)

Now this piece of code is of course blocking, and I was hoping that the web server would continue running in parallel, while I am running my while-loop.

Is a setup like this possible? Do I maybe need to utilize other modules? Any help greatly appreciated!

Answer 1

It's not working as expected because time.sleep is a blocking function.

Instead of using a list and a while loop and sleeping to check for new items in a list, use Tornado's queues.Queue which will allow you to check for new items asynchronously.

from tornado.queues import Queue

order_queue = Queue()
tpe = ThreadPoolExecutor(max_workers=10)

async def queue_consumer():
    # The old while-loop is now converted into a coroutine
    # and an async for loop is used instead
    async for new_order in order_queue:
        # run your function in threadpool
        IOLoop.current().run_in_executor(tpe, my_action, new_order)


def start_server():
   # ...
   # run queue_consumer function before starting the loop
   IOLoop.current().spawn_callback(queue_consumer)
   IOLoop.current().start()

Put items in the queue like this:

order_queue.put(payload)