class Vines::TokenBucket
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.
Public Class Methods
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.
# File lib/vines/token_bucket.rb, line 18 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
Public Instance Methods
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.
# File lib/vines/token_bucket.rb, line 34 def take(tokens) raise ArgumentError.new('tokens must be > 0') unless tokens > 0 tokens <= fill ? @tokens -= tokens : false end
Private Instance Methods
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.
# File lib/vines/token_bucket.rb, line 45 def fill if @tokens < @capacity now = Time.new @tokens += (@rate * (now - @timestamp)).round @tokens = @capacity if @tokens > @capacity @timestamp = now end @tokens end