137 lines
4.2 KiB
Python
137 lines
4.2 KiB
Python
import threading
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import time
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from voussoirkit import sentinel
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REJECT = sentinel.Sentinel('reject mode')
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SLEEP = sentinel.Sentinel('sleep mode')
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class Ratelimiter:
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'''
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The Ratelimiter class is used to limit how often you perform some other
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action. Just create a Ratelimiter object with the allowance you need, then
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call `limit()` before doing the thing you wish to ratelimit.
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Example:
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download_limiter = Ratelimiter(allowance=1, period=3)
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for file_url in file_urls:
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download_limiter.limit()
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download(file_url)
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'''
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def __init__(
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self,
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allowance,
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*,
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mode=SLEEP,
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operation_cost=1,
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period=1,
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starting_balance=None,
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):
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'''
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allowance:
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Our spending balance per `period` seconds.
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mode:
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SLEEP:
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If we do not have the balance for an operation, sleep until we
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do. Then return True every time.
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REJECT:
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If we do not have the balance for an operation, do nothing and
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return False. Otherwise subtract the cost and return True.
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operation_cost:
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The default amount to remove from our balance after each operation.
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Pass a `cost` parameter to `self.limit` to use a nondefault value.
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period:
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The number of seconds over which we can perform `allowance`
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operations.
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starting_balance:
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With a value of None, the limiter will be given a starting balance
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of `operation_cost` so that you can perform a single operation as
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soon as you instantiate the object. You can provide another starting
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balance here.
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Although (allowance=1, period=1) and (allowance=30, period=30) can both
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be described as "once per second", the latter allows for much greater
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burstiness of operation. You could spend the whole allowance in a
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single second, then relax for 29 seconds, for example.
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'''
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def positive(x, name):
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if not isinstance(x, (int, float)):
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raise TypeError(f'{name} should be int or float, not {type(x)}.')
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if x <= 0:
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raise ValueError(f'{name} should be > 0, not {x}.')
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return x
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self.allowance = positive(allowance, 'allowance')
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self.period = positive(period, 'period')
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self.operation_cost = positive(operation_cost, 'operation_cost')
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if starting_balance is None:
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self.balance = operation_cost
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else:
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self.balance = positive(starting_balance, 'starting_balance')
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mode = {
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'reject': REJECT,
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'sleep': SLEEP,
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}.get(mode, mode)
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if mode is not SLEEP and mode is not REJECT:
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raise ValueError(f'mode should be SLEEP or REJECT, not {repr(mode)}.')
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self.mode = mode
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self.lock = threading.Lock()
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self.last_operation = time.monotonic()
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def __repr__(self):
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return f'{self.__class__.__name__}(allowance={self.allowance}, period={self.period})'
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@property
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def gain_rate(self):
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return self.allowance / self.period
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def _limit(self, cost):
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now = time.monotonic()
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time_diff = now - self.last_operation
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self.balance += time_diff * self.gain_rate
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self.balance = min(self.balance, self.allowance)
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self.last_operation = now
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if self.mode is REJECT and self.balance < cost:
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success = False
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sleep_needed = 0
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return (success, sleep_needed)
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self.balance -= cost
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success = True
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if self.balance >= 0:
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sleep_needed = 0
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else:
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sleep_needed = abs(self.balance) / self.gain_rate
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return (success, sleep_needed)
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def limit(self, cost=None):
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'''
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See the main class docstring for info about cost and mode behavior.
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'''
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if cost is None:
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cost = self.operation_cost
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with self.lock:
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(success, sleep_needed) = self._limit(cost)
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if sleep_needed > 0:
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time.sleep(sleep_needed)
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return success
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