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Contents
# encoding: UTF-8
module Vines
# The token bucket algorithm is useful for rate limiting.
# Before an operation can be completed, a token is taken from
# the bucket. If no tokens are available, the operation fails.
# The bucket is refilled with tokens at the maximum allowed rate
# of operations.
class TokenBucket
# Create a full bucket with `capacity` number of tokens to be filled
# at the given rate of tokens/second.
#
# capacity - The Fixnum maximum number of tokens the bucket can hold.
# rate - The Fixnum number of tokens per second at which the bucket is
# refilled.
def initialize(capacity, rate)
raise ArgumentError.new('capacity must be > 0') unless capacity > 0
raise ArgumentError.new('rate must be > 0') unless rate > 0
@capacity = capacity
@tokens = capacity
@rate = rate
@timestamp = Time.new
end
# Remove tokens from the bucket if it's full enough. There's no way, or
# need, to add tokens to the bucket. It refills over time.
#
# tokens - The Fixnum number of tokens to attempt to take from the bucket.
#
# Returns true if the bucket contains enough tokens to take, false if the
# bucket isn't full enough to satisy the request.
def take(tokens)
raise ArgumentError.new('tokens must be > 0') unless tokens > 0
tokens <= fill ? @tokens -= tokens : false
end
private
# Add tokens to the bucket at the `rate` provided in the constructor. This
# fills the bucket slowly over time.
#
# Returns the Fixnum number of tokens left in the bucket.
def fill
if @tokens < @capacity
now = Time.new
@tokens += (@rate * (now - @timestamp)).round
@tokens = @capacity if @tokens > @capacity
@timestamp = now
end
@tokens
end
end
end
Version data entries
21 entries across 21 versions & 4 rubygems