mirror of
https://github.com/crazybber/go-pattern-examples.git
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158 lines
3.3 KiB
Go
158 lines
3.3 KiB
Go
package circuit
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/*
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* @Description: https://github.com/crazybber
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* @Author: Edward
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* @Date: 2020-05-10 22:00:58
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* @Last Modified by: Edward
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* @Last Modified time: 2020-05-11 11:57:21
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*/
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import (
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"context"
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"errors"
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"sync"
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"time"
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)
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////////////////////////////////
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///使用HTTP请求的例子
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//每个搜索引擎时时刻刻都会遇到超大规模的请求的流量.
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//这里演示一个复杂一点的例子，同时使用Option 模式
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//ErrServiceUnavailable for error
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var (
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ErrTooManyRequests = errors.New("too many requests")
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ErrServiceUnavailable = errors.New("service unavailable")
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FailureThreshold = 10
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)
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//StateCheckerHandler check state
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type StateCheckerHandler func(counts counters) bool
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//StateChangedEventHandler set event handle
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type StateChangedEventHandler func(name string, from State, to State)
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//Option set Options
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type Option func(opts *Options)
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//RequestBreaker for protection
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type RequestBreaker struct {
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options Options
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mutex sync.Mutex
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state State
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generation uint64
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counts Counter
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}
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//NewRequestBreaker return a breaker
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func NewRequestBreaker(opts ...Option) *RequestBreaker {
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defaultOptions := Options{
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Name: "defaultBreakerName",
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Expiry: time.Now().Add(time.Second * 20),
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Interval: time.Second * 2,
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Timeout: time.Second * 5,
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MaxRequests: 5,
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ReadyToTrip: func(counts counters) bool { return true },
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OnStateChanged: func(name string, from State, to State) {},
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}
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for _, setOption := range opts {
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setOption(&defaultOptions)
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}
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return &RequestBreaker{
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options: defaultOptions,
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counts: nil,
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generation: 0,
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}
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}
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//State of current switch
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type State int
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//states of CircuitBreaker
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const (
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UnknownState State = iota
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FailureState
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SuccessState
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)
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//Circuit of action stream
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type Circuit func(context.Context) error
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//Counter interface
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type Counter interface {
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Count(State)
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ConsecutiveFailures() uint32
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LastActivity() time.Time
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Reset()
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}
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type counters struct {
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state State
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lastActivity time.Time
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counts uint32 //counts of failures
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}
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func (c *counters) Count(state State) {
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}
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func (c *counters) ConsecutiveFailures() uint32 {
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return 0
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}
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func (c *counters) LastActivity() time.Time {
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return c.lastActivity
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}
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func (c *counters) Reset() {
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}
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//NewCounter New Counter for Circuit Breaker
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func NewCounter() Counter {
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return &counters{}
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}
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//Breaker of circuit
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func Breaker(c Circuit, failureThreshold uint32) Circuit {
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cnt := NewCounter()
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return func(ctx context.Context) error {
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if cnt.ConsecutiveFailures() >= failureThreshold {
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canRetry := func(cnt Counter) 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 * 2 << backoffLevel)
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return time.Now().After(shouldRetryAt)
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}
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if !canRetry(cnt) {
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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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}
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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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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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