baseimage-tutorial-framework/lib/tfw/decorators/rate_limiter.py

# Copyright (C) 2018 Avatao.com Innovative Learning Kft.
# All Rights Reserved. See LICENSE file for details.

from functools import wraps, partial
from time import time, sleep

from tfw.decorators.lazy_property import lazy_property


class RateLimiter:
    """
    Decorator class for rate limiting, blocking.

    When applied to a function this decorator will apply rate limiting
    if the function is invoked more frequently than rate_per_seconds.

    By default rate limiting means sleeping until the next invocation time
    as per __init__ parameter rate_per_seconds.

    Note that this decorator BLOCKS THE THREAD it is being executed on,
    so it is only acceptable for stuff running on a separate thread.

    If this is no good for you please refer to AsyncRateLimiter in this module,
    which is designed not to block and use the IOLoop it is being called from.
    """
    def __init__(self, rate_per_second):
        """
        :param rate_per_second: max frequency the decorated method should be
                                invoked with
        """
        self.min_interval = 1 / float(rate_per_second)
        self.fun = None
        self.last_call = time()

    def action(self, seconds_to_next_call):
        if seconds_to_next_call:
            sleep(seconds_to_next_call)
        self.fun()

    def __call__(self, fun):
        @wraps(fun)
        def wrapper(*args, **kwargs):
            self.fun = partial(fun, *args, **kwargs)
            limit_seconds = self._limit_rate()
            self.action(limit_seconds)
        return wrapper

    def _limit_rate(self):
        seconds_since_last_call = time() - self.last_call
        seconds_to_next_call = self.min_interval - seconds_since_last_call

        if seconds_to_next_call > 0:
            return seconds_to_next_call
        self.last_call = time()
        return 0


class AsyncRateLimiter(RateLimiter):
    """
    Decorator class for rate limiting, non-blocking.

    The semantics of the rate limiting:
        - unlike RateLimiter this decorator never blocks, instead it adds an async
          callback version of the decorated function to the IOLoop
          (to be executed after the rate limiting has expired).
        - the timing works similarly to RateLimiter
    """
    def __init__(self, rate_per_second, ioloop_factory):
        """
        :param rate_per_second: max frequency the decorated method should be
                                invoked with
        :param ioloop_factory: callable that should return an instance of the
                               IOLoop of the application
        """
        self._ioloop_factory = ioloop_factory
        self._ioloop = None
        self._last_callback = None

        self._make_action_thread_safe()
        super().__init__(rate_per_second=rate_per_second)

    def _make_action_thread_safe(self):
        self.action = partial(self.ioloop.add_callback, self.action)

    @lazy_property
    def ioloop(self):
        return self._ioloop_factory()

    def action(self, seconds_to_next_call):
        if self._last_callback:
            self.ioloop.remove_timeout(self._last_callback)

        self._last_callback = self.ioloop.call_later(
            seconds_to_next_call,
            self.fun_with_debounce
        )

    def fun_with_debounce(self):
        self.last_call = time()
        self.fun()