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Rate-limited Queue

Project description

A slower queue implementation, guaranteeing that tasks are processsed at a maximum rate. SlowQueue aims to be directly comparable with the Queue API so that it can be dropped in as an alternative implementation, as with LIFOQueue and PriorityQueue, but currently (as this needn’t be the case) will raise additional ValueErrors if you try to pass block=False or timeout > 0 to get methods. Some slamming is possible and is controllable using the max_slam keyword argument on the TokenBucket or SlowQueue instance.

See following example (taken from demo_sloq.py) or the unit tests for more:

from argparse import ArgumentParser
from threading import Thread, current_thread
import logging
import time

from sloq import SlowQueue


def main(args=None):
    prog = ArgumentParser()
    prog.add_argument("-n", type=int, default=10, metavar="TASK_COUNT",
                      help="The number of tasks")
    prog.add_argument("-t", type=float, default=1, metavar="TASK_INTERVAL",
                      help="The tick: seconds between tasks being released")
    prog.add_argument("-w", type=int, default=3, metavar="WORKER_COUNT",
                      help="Number of workers")
    prog.add_argument("-d", type=float, default=0, metavar="TASK_DURATION",
                      help="Duration of a single task")
    prog.add_argument("-s", type=float, default=0, metavar="MAX_SLAM",
                      help="The maximum amount of slam to allow")
    args = prog.parse_args(args)

    logger = logging.getLogger(__name__)
    logger.setLevel(logging.INFO)
    logger.addHandler(logging.StreamHandler())

    test_queue(logger, args.t, args.n, args.d, args.w, args.s)


def test_queue(logger, tick=1, tasks=10, task_duration=0, worker_count=3,
               slam=0):
    start_time = time.time()
    sloq = SlowQueue(release_tick=tick, max_slam=slam)

    # Begin the workers
    for w in xrange(0, worker_count):
        Thread(target=test_worker, args=(logger, start_time, sloq)).start()

    # Populate the queue
    for task in xrange(0, tasks):
        sloq.put((task, task_duration))
    for w in xrange(0, worker_count):
        sloq.put((None, None))

    sloq.join()


def test_worker(logger, start_time, queue):
    while True:
        task, sleep = queue.get()
        if task is None:
            logger.info("%s, Done" % current_thread().name)
            queue.task_done()
            return
        else:
            logger.info("%s, Elapsed time: %0.2f, Task: %r",
                        current_thread().name, time.time() - start_time, task)
            if sleep:
                time.sleep(sleep)
            queue.task_done()


if __name__ == "__main__":
    main()

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