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breaker.go
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breaker.go
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package breaker
import (
"sync/atomic"
"time"
"github.com/cuigh/auxo/errors"
"github.com/cuigh/auxo/log"
)
const PkgName = "auxo.apm.breaker"
var (
// ErrMaxConcurrency occurs when too many of the same named command are executed at the same time.
ErrMaxConcurrency = errors.New("breaker: max concurrency")
// ErrCircuitOpen returns when an execution attempt "short circuits". This happens due to the circuit being measured as unhealthy.
ErrCircuitOpen = errors.New("breaker: circuit open")
// ErrTimeout occurs when the provided function takes too long to execute.
ErrTimeout = errors.New("breaker: timeout")
)
// Valid CircuitState values.
const (
Closed int32 = iota
Open
HalfOpen
)
type Action func() error
type Fallback func(error) error
// Options holds options of Breaker
type Options struct {
// Window is how long to wait for state switched to half-open from open.
Window time.Duration
// Timeout is how long to wait for action to complete.
Timeout time.Duration
// Concurrency is how many actions can execute at the same time. If concurrency is zero, no limitation is set.
Concurrency int32
}
type Breaker struct {
name string
cond Condition
opts Options
logger log.Logger
state int32
expiry time.Time
active int32
stat statistics
}
func NewBreaker(name string, cond Condition, opts Options) *Breaker {
if opts.Window <= 0 {
opts.Window = time.Second * 5
}
//if opts.Timeout <= 0 {
// opts.Timeout = time.Second
//}
return &Breaker{
name: name,
cond: cond,
opts: opts,
logger: log.Get(PkgName),
}
}
func (b *Breaker) State() int32 {
return b.state
}
func (b *Breaker) Summary() Summary {
return b.stat.summary
}
func (b *Breaker) Try(action Action, fallback ...Fallback) error {
switch b.state {
case HalfOpen:
return b.fail(ErrCircuitOpen)
case Open:
if time.Now().Before(b.expiry) {
return b.fail(ErrCircuitOpen)
}
return b.test(action, fallback...)
default: // Closed
if b.opts.Concurrency > 0 {
active := atomic.AddInt32(&b.active, 1)
defer atomic.AddInt32(&b.active, -1)
if active > b.opts.Concurrency {
return b.fallback(ErrMaxConcurrency, fallback...)
}
}
return b.call(action, fallback...)
}
}
func (b *Breaker) call(action Action, fb ...Fallback) error {
err := b.execute(action)
if err == nil {
b.stat.update(nil, nil, false)
return nil
}
return b.fallback(err, fb...)
}
// let one action passing for testing
func (b *Breaker) test(action Action, fb ...Fallback) error {
if !atomic.CompareAndSwapInt32(&b.state, Open, HalfOpen) {
if b.state == Closed {
return b.call(action, fb...)
}
return b.fail(ErrCircuitOpen)
}
b.logger.Info("breaker > half-open circuit: ", b.name)
err := b.call(action, fb...)
if err == nil {
b.state = Closed
b.stat.reset(false, true)
b.logger.Info("breaker > close circuit: ", b.name)
} else {
b.state = Open
b.expiry = time.Now().Add(b.opts.Window)
b.logger.Warn("breaker > open circuit: ", b.name)
}
return err
}
func (b *Breaker) execute(action Action) error {
if b.opts.Timeout > 0 {
errs := make(chan error)
go func() {
errs <- action()
}()
timer := time.NewTimer(b.opts.Timeout)
defer timer.Stop()
select {
case err := <-errs:
return err
case <-timer.C:
return ErrTimeout
}
}
return action()
}
func (b *Breaker) fail(err error) error {
b.stat.update(ErrCircuitOpen, nil, false)
return ErrCircuitOpen
}
// try call fallback function if any.
func (b *Breaker) fallback(err error, fb ...Fallback) error {
var final error
if len(fb) == 0 {
final = err
b.stat.update(err, nil, false)
} else {
final = fb[0](err)
b.stat.update(final, err, true)
}
if final != nil && b.cond(b.stat.counter) && atomic.CompareAndSwapInt32(&b.state, Closed, Open) {
b.expiry = time.Now().Add(b.opts.Window)
b.stat.reset(false, true)
b.logger.Warn("breaker > open circuit: ", b.name)
}
return final
}
//func (b *Breaker) Allow() bool {
// switch b.state {
// case HalfOpen:
// return false
// case Open:
// if time.Now().Before(b.expiry) {
// return false
// }
//
// if atomic.CompareAndSwapInt32(&b.state, Open, HalfOpen) {
// return true
// } else if b.state == Closed {
// return true
// }
// return false
// default: // Closed
// return true
// }
//}
//
//func (b *Breaker) Succeed() {
// b.stat.update(nil, nil, false)
// switch b.state {
// case HalfOpen:
// b.state = Closed
// }
//}
//
//func (b *Breaker) Fail(err error) {
// b.stat.update(err, nil, false)
// switch b.state {
// case HalfOpen:
// b.state = Open
// case Closed:
// if b.cond(b.stat.counter) && atomic.CompareAndSwapInt32(&b.state, Closed, Open) {
// b.stat.reset(false, true)
// }
// }
//}