Job queue implementation example using Tornado coroutines

This is a memo when I made a job queue with Tornado's coroutine.

Queue jobs (functions and arguments) with the WorkerQueue put method. As soon as the currently running job is finished, the jobs in the queue will be executed one by one, starting with the oldest one.

I am using the Queue implemented in version 4.2 of Tornado. Tornado queues are similar to the Python standard library synchronous queue (queue.Queue), except that put and get return tornado.concurrent.Future.

filename

from concurrent.futures import ProcessPoolExecutor
import time

from tornado import ioloop, gen, process
from tornado.queues import Queue


class WorkerQueue(object):
    def __init__(self):
        self.queue = Queue()
        self.current_worker_id = None
        self.current_worker = None
        self.queued_ids = []
        self._dispatcher()

    def put(self, id_, func, args):
        worker = Worker(func, args)
        self.queued_ids.append(id_)
        self.queue.put_nowait((id_, worker))
        print("Put: {}".format(id_))

    def status(self, id_):
        if id_ in self.queued_ids:
            return "Queued"
        elif id_ == self.current_worker_id:
            return "Running"
        else:
            return "Ready"

    @gen.coroutine
    def _dispatcher(self):
        while 1:
            id_, worker = yield self.queue.get()
            self.queued_ids.remove(id_)
            self.current_worker_id = id_
            self.current_worker = worker
            print("Start: {}".format(id_))
            res = yield self.current_worker.execute()
            self.current_worker_id = None
            self.current_worker = None
            print("{} is {}.".format(id_, res))


class Worker(object):
    def __init__(self, func, args):
        self.func = func
        self.args = args

    @gen.coroutine
    def execute(self):
        with ProcessPoolExecutor(process.cpu_count()) as exec_:
            res = yield exec_.submit(self.func, *self.args)
        return res


def job(sec):
    time.sleep(sec)
    return "done"


@gen.coroutine
def run():
    q = WorkerQueue()
    q.put("Job1", job, (2,))
    q.put("Job2", job, (2,))
    print("Job1 <{}>".format(q.status("Job1")))
    print("Job2 <{}>".format(q.status("Job2")))
    yield gen.sleep(1)
    print("Job1 <{}>".format(q.status("Job1")))
    print("Job2 <{}>".format(q.status("Job2")))
    yield gen.sleep(2)
    print("Job1 <{}>".format(q.status("Job1")))
    print("Job2 <{}>".format(q.status("Job2")))
    yield gen.sleep(2)
    print("Job1 <{}>".format(q.status("Job1")))
    print("Job2 <{}>".format(q.status("Job2")))


if __name__ == "__main__":
    ioloop.IOLoop.current().run_sync(run)

Execution result

Put: Job1
Put: Job2
Job1 <Queued>
Job2 <Queued>
Start: Job1
Job1 <Running>
Job2 <Queued>
Job1 is done
Start: Job2
Job1 <Ready>
Job2 <Running>
Job2 is done
Job1 <Ready>
Job2 <Ready>

(Added on 2015.11.7) When dealing with a large amount of data, memory usage becomes a problem, so it is necessary to take measures such as limiting the queue length and making the producer wait.