Add exponential backoff implementation and tests

autopaho/backoff.go

@@ -16,6 +16,7 @@
 package autopaho
 
 import (
+	"math/rand"
 	"time"
 )
 
@@ -72,3 +73,121 @@ func NewConstantBackoffStrategy(duration time.Duration) *ConstantBackoffStrategy
 func (c *ConstantBackoffStrategy) GetBackoff() Backoff {
 	return c._Backoff
 }
+
+////////////////////////////////////////////////////////////////////////////////
+// implementation for an exponential backoff strategy
+////////////////////////////////////////////////////////////////////////////////
+
+// The ExponentialBackoff implements the Backoff interface and provides a backoff duration that increases exponentially up to a specied max value.
+// The backoff duration is computed as a random value between the min and the current max value.
+// The current max is updated by multiplying the current max with the factor up the the max value
+// Implementaion note: For simplicity the backoff uses numbers instead of duration.
+type ExponentialBackoff struct {
+	Backoff
+	_Min       int64
+	_Max       int64
+	_MovingMax int64
+	_Factor    float32
+}
+
+func NewExponentialBackoff(
+	min time.Duration,
+	max time.Duration,
+	initialMax time.Duration,
+	factor float32,
+) *ExponentialBackoff {
+	return &ExponentialBackoff{
+		_Min:       min.Milliseconds(),
+		_Max:       max.Milliseconds(),
+		_MovingMax: initialMax.Milliseconds(),
+		_Factor:    factor,
+	}
+}
+
+func (eb *ExponentialBackoff) Next() time.Duration {
+	backoff := eb._computeDuration()
+	defer eb._updateRange()
+
+	return backoff
+}
+
+// Computes the next backoff duration which will have a random value between the min and the current max value.
+func (eb *ExponentialBackoff) _computeDuration() time.Duration {
+	normalizedRangeInMillis := eb._MovingMax - eb._Min
+	randomMillisInRange := rand.Int63n(normalizedRangeInMillis) + eb._Min
+	randomDurationInRange := time.Duration(randomMillisInRange) * time.Millisecond
+
+	return randomDurationInRange
+}
+
+// Updates the current max value by multiplying it with the factor and does not exceed the configured max value.
+func (eb *ExponentialBackoff) _updateRange() {
+	nextMax := int64(float32(eb._MovingMax) * eb._Factor)
+
+	// ensure we stay in range
+	// overflow of range OR  numerical overflow
+	if eb._Max < nextMax || nextMax < eb._MovingMax {
+		nextMax = eb._Max
+	}
+
+	eb._MovingMax = nextMax
+}
+
+type ExponentialBackoffStrategy struct {
+	BackoffStrategy
+	_Min        time.Duration
+	_Max        time.Duration
+	_InitialMax time.Duration
+	_Factor     float32
+}
+
+func (ebs *ExponentialBackoffStrategy) GetBackoff() Backoff {
+	return NewExponentialBackoff(
+		ebs._Min,
+		ebs._Max,
+		ebs._InitialMax,
+		ebs._Factor,
+	)
+}
+
+func NewExponentialBackoffStrategy(
+	min time.Duration,
+	max time.Duration,
+	initialMax time.Duration,
+	factor float32,
+) *ExponentialBackoffStrategy {
+	if min <= 0 {
+		panic("min Duration must not be lower than or equal to: 0")
+	}
+	if max <= min {
+		panic("max Duration must not be less than or equal to min Duration")
+	}
+	if initialMax < min || max < initialMax {
+		panic("initial max Duration must be in range ]min, max[")
+	}
+	if factor <= 1 {
+		panic("factor must not be less than or equal to: 1")
+	}
+
+	return &ExponentialBackoffStrategy{
+		_Min:        min,
+		_Max:        max,
+		_InitialMax: initialMax,
+		_Factor:     factor,
+	}
+}
+
+// DefaultExponentialBackoffStrategy returns a new ExponentialBackoffStrategy with default values.
+// The default values are:
+// - min:          5 seconds
+// - max:         10 minutes
+// - initial max: 10 seconds
+// - factor:       1.5
+func DefaultExponentialBackoffStrategy() *ExponentialBackoffStrategy {
+	return &ExponentialBackoffStrategy{
+		_Min:        5 * time.Second,
+		_Max:        10 * time.Minute,
+		_InitialMax: 10 * time.Second,
+		_Factor:     1.5,
+	}
+}

autopaho/backoff_test.go

@@ -51,3 +51,77 @@ func TestConstantBackoffStrategyRandomValue(t *testing.T) {
 		}
 	}
 }
+
+// tests for the exponential backoff strategy implementation
+
+func TestRandomExponentialBackoff(t *testing.T) {
+	for i := 0; i < 20; i++ {
+		doSetupAndTestRandomExponentialBackoff(t)
+	}
+}
+
+func doSetupAndTestRandomExponentialBackoff(t *testing.T) {
+	// set up a partially random min backoff time
+	minBackoffInMillisLowerBound := 500                                    // 500ms
+	minBackoffInMillisUpperBound := minBackoffInMillisLowerBound + 5*1_000 // +
+	minBackoffInMillis := RandInt(
+		minBackoffInMillisLowerBound,
+		minBackoffInMillisUpperBound,
+	)
+
+	minBackoff := time.Duration(minBackoffInMillis) * time.Millisecond
+
+	// set up a partially random initial max backoff time
+	initialMaxBackoffInMillisLowerBound := minBackoffInMillis + 500                       // +500ms
+	initialMaxBackoffInMillisUpperBound := initialMaxBackoffInMillisLowerBound + 30*1_000 // +30s
+	initialMaxBackoffInMillis := RandInt(
+		initialMaxBackoffInMillisLowerBound,
+		initialMaxBackoffInMillisUpperBound,
+	)
+
+	initialMaxBackoff := time.Duration(initialMaxBackoffInMillis) * time.Millisecond
+
+	// set up a partially random max backoff time
+	maxBackoffInMillisLowerBound := minBackoffInMillis + 30*60*1_000           // +30min
+	maxBackoffInMillisUpperBound := maxBackoffInMillisLowerBound + 60*60*1_000 // +60min
+	maxBackoffInMillis := RandInt(
+		maxBackoffInMillisLowerBound,
+		maxBackoffInMillisUpperBound,
+	)
+
+	maxBackoff := time.Duration(maxBackoffInMillis) * time.Millisecond
+
+	// set up factor for the next variation
+	const factor = 2.0
+
+	exponentialBackoffStrategy := NewExponentialBackoffStrategy(
+		minBackoff,
+		maxBackoff,
+		initialMaxBackoff,
+		factor,
+	)
+
+	exponentialBackoff := exponentialBackoffStrategy.GetBackoff()
+
+	// create many backof and test they are within constraints
+	for i := 0; i < 50; i++ {
+		actual := exponentialBackoff.Next()
+		if i == 0 {
+			if initialMaxBackoff < actual {
+				t.Fatalf("Actual backoff value: `%s` was higher than configured initial maximum: `%s`", actual, initialMaxBackoff)
+			}
+		}
+		if actual < minBackoff {
+			t.Fatalf("Actual backoff value: `%s` was less than configured minimum: `%s`", actual, minBackoff)
+		}
+		if maxBackoff < actual {
+			t.Fatalf("Actual backoff value: `%s` was higher than configured maximum: `%s`", actual, maxBackoff)
+		}
+	}
+}
+
+func RandInt(min int, max int) int {
+	normalizedRange := max - min
+
+	return rand.Intn(normalizedRange) + max
+}