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98 lines
3.4 KiB
Python
98 lines
3.4 KiB
Python
# Implementation of Token Bucket Algorithm
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# Token `rate` is added to the bucket every `frequency` in seconds.
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# The bucket can hold tokens up to `capacity` (full).
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# The bucket starts full.
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# Each request consume one token.
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# If a token arrives when the bucket is full, token is discarded.
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# If a request arrives when bucket is empty, request will be discarded.
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# If bucket has tokens available, requests will pass.
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# https://en.wikipedia.org/wiki/Token_bucket
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import threading
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import time
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class TokenBucketRateLimiter:
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def __init__(self, rate: int, capacity: int, frequency: int) -> None:
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"""
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Initialize a Token Bucket rate limiter.
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:param rate: Number of tokens added to the bucket per refill
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:param capacity: Maximum number of tokens the bucket can hold.
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:param frequency: Frequency of refill in seconds
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>>> bucket = TokenBucketRateLimiter(4, 4, 60)
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>>> bucket.tokens
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4
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>>> bucket.capacity
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4
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>>> bucket.frequency
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60
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"""
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self.rate = rate # Tokens added per refill
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self.capacity = capacity # Maximum capacity of the bucket
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self.frequency = frequency # Frequency tokens are refilled
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self.tokens = capacity # Current tokens in the bucket
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self.last_checked = time.time() # Time when tokens were last checked
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self.lock = threading.Lock() # To make the rate limiter thread-safe
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def _add_tokens(self) -> None:
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"""
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Refill tokens only when a full minute has passed.
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>>> bucket = TokenBucketRateLimiter(1, 4, 60)
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>>> bucket.tokens # Initially has 4 token (rate)
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4
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>>> bucket._add_tokens()
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>>> bucket.tokens # Bucket already full
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4
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"""
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current_time = time.time()
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elapsed_time = current_time - self.last_checked
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if elapsed_time >= self.frequency:
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minutes_passed = int(elapsed_time // self.frequency)
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# Add tokens based on rate
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added_tokens = minutes_passed * self.rate
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self.tokens = min(self.capacity, self.tokens + added_tokens)
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# Update the last checked time
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self.last_checked += minutes_passed * self.frequency
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def allow_request(self) -> bool:
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"""
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Check if a request is allowed.
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If there are enough tokens, it consumes one token.
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:return: True if the request is allowed, False otherwise.
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>>> bucket = TokenBucketRateLimiter(1, 2, 60)
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>>> bucket.allow_request() # Token is available, request passes
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True
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>>> bucket.allow_request() # Token is available, request passes
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True
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>>> bucket.allow_request() # No token left, request is dropped
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False
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"""
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with self.lock:
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self._add_tokens()
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if self.tokens >= 1:
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self.tokens -= 1
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return True
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return False
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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print("Allow 4 requests per minute, capacity of 4")
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bucket = TokenBucketRateLimiter(4, 4, 60)
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total_requests = 10
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delay_in_seconds = 10
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print("Simulate 1 request per 10 seconds...")
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for i in range(total_requests):
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result = "pass" if bucket.allow_request() else "dropped"
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print(
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f"Request {i+1}/{total_requests} \
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timeline: {i*delay_in_seconds} seconds = {result}"
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)
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time.sleep(delay_in_seconds)
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