First draft of circuit-breaker

breaker/breaker.go

@@ -0,0 +1,110 @@
+package breaker
+
+import (
+	"errors"
+	"fmt"
+	"sync"
+	"time"
+)
+
+var BreakerOpen = errors.New("circuit breaker is open")
+
+type Panic struct {
+	Value interface{}
+}
+
+func (p Panic) Error() string {
+	return fmt.Sprint("panic:", p.Value)
+}
+
+type state int
+
+const (
+	closed state = iota
+	open
+	halfOpen
+)
+
+type Breaker struct {
+	errorThreshold, successThreshold int
+	timeout                          time.Duration
+
+	lock              sync.RWMutex
+	state             state
+	errors, successes int
+}
+
+func New(errorThreshold, successThreshold int, timeout time.Duration) *Breaker {
+	return &Breaker{
+		errorThreshold:   errorThreshold,
+		successThreshold: successThreshold,
+		timeout:          timeout,
+	}
+}
+
+func (b *Breaker) Run(x func() error) error {
+	b.lock.RLock()
+	state := b.state
+	b.lock.RUnlock()
+
+	if state == open {
+		return BreakerOpen
+	}
+
+	result := func() (err error) {
+		defer func() {
+			if val := recover(); val != nil {
+				err = Panic{Value: val}
+			}
+		}()
+		return x()
+	}()
+
+	b.lock.Lock()
+	defer b.lock.Unlock()
+
+	if result == nil {
+		if b.state == halfOpen {
+			b.successes++
+			if b.successes == b.successThreshold {
+				b.closeBreaker()
+			}
+		}
+	} else {
+		switch b.state {
+		case closed:
+			b.errors++
+			if b.errors == b.errorThreshold {
+				b.openBreaker()
+			}
+		case halfOpen:
+			b.openBreaker()
+		}
+	}
+
+	return result
+}
+
+func (b *Breaker) openBreaker() {
+	b.changeState(open)
+	go b.timer()
+}
+
+func (b *Breaker) closeBreaker() {
+	b.changeState(closed)
+}
+
+func (b *Breaker) timer() {
+	time.Sleep(b.timeout)
+
+	b.lock.Lock()
+	defer b.lock.Unlock()
+
+	b.changeState(halfOpen)
+}
+
+func (b *Breaker) changeState(newState state) {
+	b.errors = 0
+	b.successes = 0
+	b.state = newState
+}