mirror of
https://github.com/crazybber/go-pattern-examples.git
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110 lines
3.0 KiB
Go
110 lines
3.0 KiB
Go
/*
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* @Description: https://github.com/crazybber
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* @Author: Edward
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* @Date: 2020-05-22 12:42:34
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* @Last Modified by: Edward
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* @Last Modified time: 2020-05-22 16:48:56
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*/
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package circuit
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import (
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"context"
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"time"
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)
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////////////////////////////////
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//way 2 简单的函数式断路器
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// 一个func实例作为一个Breaker 允许多个worker(即goroutine)同时访问
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// 当前简单场景下，只考虑单个worker情况下的连续请求
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// 当前的设计思路，非常简单：
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// 1、不考虑三种状态之间的转换，只靠两种状态，电路打开与电路关闭
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// 2、当累计失败到达一定失败次数就端开请求(打开电路)，并延迟一定的时间再允许请求
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////////////////////////////////
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//states of CircuitBreaker
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//states: closed --->open ---> half open --> closed
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const (
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UnknownState OperationState = iota
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FailureState
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SuccessState
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)
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type simpleCounter struct {
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lastState OperationState
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lastActivity time.Time
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ConsecutiveSuccesses uint32
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ConsecutiveFailures uint32
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}
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func (c *simpleCounter) LastActivity() time.Time {
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return c.lastActivity
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}
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func (c *simpleCounter) Reset() {
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ct := &simpleCounter{}
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ct.lastActivity = c.lastActivity
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ct.lastState = UnknownState
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c = ct
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}
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//Count the failure and success
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func (c *simpleCounter) Count(statue OperationState) {
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switch statue {
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case FailureState:
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c.ConsecutiveFailures++
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case SuccessState:
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c.ConsecutiveSuccesses++
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}
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c.lastActivity = time.Now() //更新活动时间
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c.lastState = statue
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//handle status change
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}
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//Circuit of action stream,this is actually to do something.
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//Circuit hold the really action
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type Circuit func(context.Context) error
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//失败达到阈值后,过两秒重试
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var canRetry = func(cnt simpleCounter, failureThreshold uint32) bool {
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backoffLevel := cnt.ConsecutiveFailures - failureThreshold
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// Calculates when should the circuit breaker resume propagating requests
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// to the service
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shouldRetryAt := cnt.LastActivity().Add(time.Second << backoffLevel)
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return time.Now().After(shouldRetryAt)
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}
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//Breaker return a closure wrapper to hold Circuit Request
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func Breaker(c Circuit, failureThreshold uint32) Circuit {
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//闭包内部的全局计数器 和状态标志
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cnt := simpleCounter{}
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//ctx can be used hold parameters
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return func(ctx context.Context) error {
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//阻止请求
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if cnt.ConsecutiveFailures >= failureThreshold {
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if !canRetry(cnt, failureThreshold) {
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// Fails fast instead of propagating requests to the circuit since
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// not enough time has passed since the last failure to retry
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return ErrServiceUnavailable
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}
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//reset mark for failures
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cnt.ConsecutiveFailures = 0
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}
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// Unless the failure threshold is exceeded the wrapped service mimics the
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// old behavior and the difference in behavior is seen after consecutive failures
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if err := c(ctx); err != nil {
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//连续失败会增大backoff 时间
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cnt.Count(FailureState)
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return err
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}
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cnt.Count(SuccessState)
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return nil
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}
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}
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