rate_limiter.py

"""
Copyright 2021 Google LLC

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

 https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
"""

importasyncio
fromtypingimportOptional


classAsyncRateLimiter(object):
"""An asyncio-compatible rate limiter which uses the Token Bucket algorithm
 (https://en.wikipedia.org/wiki/Token_bucket) to limit the number
 of function calls over a time interval using an event queue.

 Args:
 max_capacity (int): The maximum capacity of tokens the bucket
 will store at any one time. Default: 1
 rate (float): The number of tokens that should be added per second.
 loop (asyncio.AbstractEventLoop): The event loop to use.
 If not provided, the default event loop will be used.
 """

def__init__(
self,
max_capacity: int=1,
rate: float=1/60,
loop: Optional[asyncio.AbstractEventLoop] =None,
 ) ->None:
self.rate=rate
self.max_capacity=max_capacity
self._loop=looporasyncio.get_event_loop()
self._tokens: float=max_capacity
self._last_token_update=self._loop.time()
self._lock=asyncio.Lock()

def_update_token_count(self) ->None:
"""
 Calculates how much time has passed since the last leak and removes the
 appropriate amount of events from the queue.
 Leaking is done lazily, meaning that if there is a large time gap between
 leaks, the next set of calls might be a burst if burst_size > 1
 """
now=self._loop.time()
time_elapsed=now-self._last_token_update
new_tokens=time_elapsed*self.rate
self._tokens=min(new_tokens+self._tokens, self.max_capacity)
self._last_token_update=now

asyncdef_wait_for_next_token(self) ->None:
"""
 Wait until enough time has elapsed to add another token.
 """
token_deficit=1-self._tokens
iftoken_deficit>0:
wait_time=token_deficit/self.rate
awaitasyncio.sleep(wait_time)

asyncdefacquire(self) ->None:
"""
 Waits for a token to become available, if necessary, then subtracts token and allows
 request to go through.
 """
asyncwithself._lock:
self._update_token_count()
ifself._tokens<1:
awaitself._wait_for_next_token()
self._update_token_count()
self._tokens-=1