go-pattern-examples/resiliency/06_circuit_breaker/circuit_func_closure.go

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/*
* @Description: https://github.com/crazybber
* @Author: Edward
* @Date: 2020-05-22 12:42:34
* @Last Modified by: Edward
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* @Last Modified time: 2020-05-22 17:21:40
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*/
package circuit
import (
"context"
"time"
)
////////////////////////////////
//way 2 简单的函数式断路器
// 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:
// 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
// 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
//states: closed --->open ---> half open --> closed
const (
UnknownState OperationState = iota
FailureState
SuccessState
)
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type simpleCounter struct {
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lastOpResult OperationState
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lastActivity time.Time
ConsecutiveSuccesses uint32
ConsecutiveFailures uint32
}
func (c *simpleCounter) LastActivity() time.Time {
return c.lastActivity
}
func (c *simpleCounter) Reset() {
ct := &simpleCounter{}
ct.lastActivity = c.lastActivity
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ct.lastOpResult = UnknownState
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c = ct
}
//Count the failure and success
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func (c *simpleCounter) Count(lastState OperationState) {
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switch lastState {
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case FailureState:
c.ConsecutiveFailures++
case SuccessState:
c.ConsecutiveSuccesses++
}
c.lastActivity = time.Now() //更新活动时间
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c.lastOpResult = lastState
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//handle status change
}
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//Circuit of action stream,this is actually to do something.
//Circuit hold the really action
type Circuit func(context.Context) error
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//失败达到阈值后,过两秒重试
var canRetry = func(cnt simpleCounter, failureThreshold uint32) bool {
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backoffLevel := cnt.ConsecutiveFailures - failureThreshold
// Calculates when should the circuit breaker resume propagating requests
// to the service
shouldRetryAt := cnt.LastActivity().Add(time.Second << backoffLevel)
return time.Now().After(shouldRetryAt)
}
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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
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
// not enough time has passed since the last failure to retry
return ErrServiceUnavailable
}
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//reset mark for failures
cnt.ConsecutiveFailures = 0
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}
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// Unless the failure threshold is exceeded the wrapped service mimics the
// 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)
return err
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}
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cnt.Count(SuccessState)
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return nil
}
}