Merge pull request #16 from borgstrom/concurrent

Make Duration safe for concurrent use

backoff.go

@@ -4,6 +4,7 @@ package backoff
 import (
 	"math"
 	"math/rand"
+	"sync/atomic"
 	"time"
 )
 
@@ -14,8 +15,9 @@ import (
 // Backoff is not generally concurrent-safe, but the ForAttempt method can
 // be used concurrently.
 type Backoff struct {
+	attempt uint64
 	// Factor is the multiplying factor for each increment step
-	attempt, Factor float64
+	Factor float64
 	// Jitter eases contention by randomizing backoff steps
 	Jitter bool
 	// Min and Max are the minimum and maximum values of the counter
@@ -25,8 +27,7 @@ type Backoff struct {
 // Duration returns the duration for the current attempt before incrementing
 // the attempt counter. See ForAttempt.
 func (b *Backoff) Duration() time.Duration {
-	d := b.ForAttempt(b.attempt)
+	d := b.ForAttempt(float64(atomic.AddUint64(&b.attempt, 1) - 1))
-	b.attempt++
 	return d
 }
 
@@ -80,12 +81,12 @@ func (b *Backoff) ForAttempt(attempt float64) time.Duration {
 
 // Reset restarts the current attempt counter at zero.
 func (b *Backoff) Reset() {
-	b.attempt = 0
+	atomic.StoreUint64(&b.attempt, 0)
 }
 
 // Attempt returns the current attempt counter value.
 func (b *Backoff) Attempt() float64 {
-	return b.attempt
+	return float64(atomic.LoadUint64(&b.attempt))
 }
 
 // Copy returns a backoff with equals constraints as the original

backoff_test.go

@@ -2,6 +2,7 @@ package backoff
 
 import (
 	"reflect"
+	"sync"
 	"testing"
 	"time"
 )
@@ -120,7 +121,28 @@ func TestCopy(t *testing.T) {
 	equals(t, b, b2)
 }
 
+func TestConcurrent(t *testing.T) {
+	b := &Backoff{
+		Min:    100 * time.Millisecond,
+		Max:    10 * time.Second,
+		Factor: 2,
+	}
+
+	wg := &sync.WaitGroup{}
+
+	test := func() {
+		time.Sleep(b.Duration())
+		wg.Done()
+	}
+
+	wg.Add(2)
+	go test()
+	go test()
+	wg.Wait()
+}
+
 func between(t *testing.T, actual, low, high time.Duration) {
+	t.Helper()
 	if actual < low {
 		t.Fatalf("Got %s, Expecting >= %s", actual, low)
 	}
@@ -130,6 +152,7 @@ func between(t *testing.T, actual, low, high time.Duration) {
 }
 
 func equals(t *testing.T, v1, v2 interface{}) {
+	t.Helper()
 	if !reflect.DeepEqual(v1, v2) {
 		t.Fatalf("Got %v, Expecting %v", v1, v2)
 	}