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|
# frozen_string_literal: true
module HTTPX
module Plugins::CircuitBreaker
#
# A circuit is assigned to a given absoolute url or origin.
#
# It sets +max_attempts+, the number of attempts the circuit allows, before it is opened.
# It sets +reset_attempts_in+, the time a circuit stays open at most, before it resets.
# It sets +break_in+, the time that must elapse before an open circuit can transit to the half-open state.
# It sets +circuit_breaker_half_open_drip_rate+, the rate of requests a circuit allows to be performed when in an half-open state.
#
class Circuit
def initialize(max_attempts, reset_attempts_in, break_in, circuit_breaker_half_open_drip_rate)
@max_attempts = max_attempts
@reset_attempts_in = reset_attempts_in
@break_in = break_in
@circuit_breaker_half_open_drip_rate = circuit_breaker_half_open_drip_rate
@attempts = 0
total_real_attempts = @max_attempts * @circuit_breaker_half_open_drip_rate
@drip_factor = (@max_attempts / total_real_attempts).round
@state = :closed
end
def respond
try_close
case @state
when :closed
nil
when :half_open
@attempts += 1
# do real requests while drip rate valid
if (@real_attempts % @drip_factor).zero?
@real_attempts += 1
return
end
@response
when :open
@response
end
end
def try_open(response)
case @state
when :closed
now = Utils.now
if @attempts.positive?
# reset if error happened long ago
@attempts = 0 if now - @attempted_at > @reset_attempts_in
else
@attempted_at = now
end
@attempts += 1
return unless @attempts >= @max_attempts
@state = :open
@opened_at = now
@response = response
when :half_open
# open immediately
@state = :open
@attempted_at = @opened_at = Utils.now
@response = response
end
end
def try_close
case @state
when :closed
nil
when :half_open
# do not close circuit unless attempts exhausted
return unless @attempts >= @max_attempts
# reset!
@attempts = 0
@opened_at = @attempted_at = @response = nil
@state = :closed
when :open
if Utils.elapsed_time(@opened_at) > @break_in
@state = :half_open
@attempts = 0
@real_attempts = 0
end
end
end
end
end
end
|
