fix race on cb.lastFailureTime

struct ConsecCircuitBreaker{} cannot pass the race test below:
	go test ./client -race -run TestCircuitBreakerRace$

Split compond type value lastFailureTime (time.Time) to second and nano,
then we can use atomic.

client/circuit_breaker.go

@@ -13,7 +13,10 @@ var (
 
 // ConsecCircuitBreaker is window sliding CircuitBreaker with failure threshold.
 type ConsecCircuitBreaker struct {
-	lastFailureTime  time.Time
+	// time.Time is a compund type, split into second and nano for using atomic.
+	lastFailureTimeSecond int64
+	lastFailureTimeNano   int32
+
 	failures         uint64
 	failureThreshold uint64
 	window           time.Duration
@@ -64,7 +67,8 @@ func (cb *ConsecCircuitBreaker) Call(fn func() error, d time.Duration) error {
 }
 
 func (cb *ConsecCircuitBreaker) ready() bool {
-	if time.Since(cb.lastFailureTime) > cb.window {
+	lastFailureTime := cb.loadLastFailureTime()
+	if time.Since(lastFailureTime) > cb.window {
 		cb.reset()
 		return true
 	}
@@ -78,7 +82,7 @@ func (cb *ConsecCircuitBreaker) success() {
 }
 func (cb *ConsecCircuitBreaker) fail() {
 	atomic.AddUint64(&cb.failures, 1)
-	cb.lastFailureTime = time.Now()
+	cb.updateLastFailureTime(time.Now())
 }
 
 func (cb *ConsecCircuitBreaker) Success() {
@@ -94,5 +98,15 @@ func (cb *ConsecCircuitBreaker) Ready() bool {
 
 func (cb *ConsecCircuitBreaker) reset() {
 	atomic.StoreUint64(&cb.failures, 0)
-	cb.lastFailureTime = time.Now()
+	cb.updateLastFailureTime(time.Now())
+}
+
+func (cb *ConsecCircuitBreaker) updateLastFailureTime(cur time.Time) {
+	atomic.StoreInt64(&cb.lastFailureTimeSecond, cur.Unix())
+	atomic.StoreInt32(&cb.lastFailureTimeNano, int32(cur.UnixNano()))
+}
+func (cb *ConsecCircuitBreaker) loadLastFailureTime() time.Time {
+	nano := atomic.LoadInt32(&cb.lastFailureTimeNano)
+	second := atomic.LoadInt64(&cb.lastFailureTimeSecond)
+	return time.Unix(second, int64(nano))
 }

client/circuit_breaker_test.go

@@ -2,6 +2,7 @@ package client
 
 import (
 	"errors"
+	"math/rand"
 	"testing"
 	"time"
 )
@@ -51,3 +52,24 @@ func TestConsecCircuitBreaker(t *testing.T) {
 	}
 
 }
+
+func TestCircuitBreakerRace(t *testing.T) {
+	cb := NewConsecCircuitBreaker(2, 50*time.Millisecond)
+	routines := 100
+	loop := 100000
+
+	fn := func() error {
+		if rand.Intn(2) == 1 {
+			return nil
+		}
+		return errors.New("test error")
+	}
+
+	for r := 0; r < routines; r++ {
+		go func() {
+			for i := 0; i < loop; i++ {
+				cb.Call(fn, 100*time.Millisecond)
+			}
+		}()
+	}
+}