Add Attack constant to pacer

pacer/pacer.go

@@ -15,6 +15,7 @@ type Pacer struct {
 	minSleep           time.Duration // minimum sleep time
 	maxSleep           time.Duration // maximum sleep time
 	decayConstant      uint          // decay constant
+	attackConstant     uint          // attack constant
 	pacer              chan struct{} // To pace the operations
 	sleepTime          time.Duration // Time to sleep for each transaction
 	retries            int           // Max number of retries
@@ -58,11 +59,12 @@ type Paced func() (bool, error)
 // New returns a Pacer with sensible defaults
 func New() *Pacer {
 	p := &Pacer{
-		minSleep:      10 * time.Millisecond,
-		maxSleep:      2 * time.Second,
-		decayConstant: 2,
-		retries:       fs.Config.LowLevelRetries,
-		pacer:         make(chan struct{}, 1),
+		minSleep:       10 * time.Millisecond,
+		maxSleep:       2 * time.Second,
+		decayConstant:  2,
+		attackConstant: 1,
+		retries:        fs.Config.LowLevelRetries,
+		pacer:          make(chan struct{}, 1),
 	}
 	p.sleepTime = p.minSleep
 	p.SetPacer(DefaultPacer)
@@ -116,7 +118,7 @@ func (p *Pacer) SetMaxConnections(n int) *Pacer {
 // This is the speed the time falls back to the minimum after errors
 // have occurred.
 //
-// bigger for slower decay, exponential
+// bigger for slower decay, exponential. 1 is halve, 0 is go straight to minimum
 func (p *Pacer) SetDecayConstant(decay uint) *Pacer {
 	p.mu.Lock()
 	defer p.mu.Unlock()
@@ -124,6 +126,19 @@ func (p *Pacer) SetDecayConstant(decay uint) *Pacer {
 	return p
 }
 
+// SetAttackConstant sets the attack constant for the pacer
+//
+// This is the speed the time grows from the minimum after errors have
+// occurred.
+//
+// bigger for slower attack, 1 is double, 0 is go straight to maximum
+func (p *Pacer) SetAttackConstant(attack uint) *Pacer {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	p.attackConstant = attack
+	return p
+}
+
 // SetRetries sets the max number of tries for Call
 func (p *Pacer) SetRetries(retries int) *Pacer {
 	p.mu.Lock()
@@ -185,7 +200,11 @@ func (p *Pacer) beginCall() {
 func (p *Pacer) defaultPacer(retry bool) {
 	oldSleepTime := p.sleepTime
 	if retry {
-		p.sleepTime *= 2
+		if p.attackConstant == 0 {
+			p.sleepTime = p.maxSleep
+		} else {
+			p.sleepTime = (p.sleepTime << p.attackConstant) / ((1 << p.attackConstant) - 1)
+		}
 		if p.sleepTime > p.maxSleep {
 			p.sleepTime = p.maxSleep
 		}

pacer/pacer_test.go

@@ -27,6 +27,9 @@ func TestNew(t *testing.T) {
 	if p.decayConstant != 2 {
 		t.Errorf("decayConstant")
 	}
+	if p.attackConstant != 1 {
+		t.Errorf("attackConstant")
+	}
 	if cap(p.pacer) != 1 {
 		t.Errorf("pacer 1")
 	}
@@ -85,6 +88,58 @@ func TestSetDecayConstant(t *testing.T) {
 	}
 }
 
+func TestDecay(t *testing.T) {
+	p := New().SetMinSleep(time.Microsecond).SetPacer(DefaultPacer).SetMaxSleep(time.Second)
+	for _, test := range []struct {
+		in             time.Duration
+		attackConstant uint
+		want           time.Duration
+	}{
+		{8 * time.Millisecond, 1, 4 * time.Millisecond},
+		{1 * time.Millisecond, 0, time.Microsecond},
+		{1 * time.Millisecond, 2, (3 * time.Millisecond) / 4},
+		{1 * time.Millisecond, 3, (7 * time.Millisecond) / 8},
+	} {
+		p.sleepTime = test.in
+		p.SetDecayConstant(test.attackConstant)
+		p.defaultPacer(false)
+		got := p.sleepTime
+		if got != test.want {
+			t.Errorf("bad sleep want %v got %v", test.want, got)
+		}
+	}
+}
+
+func TestSetAttackConstant(t *testing.T) {
+	p := New().SetAttackConstant(19)
+	if p.attackConstant != 19 {
+		t.Errorf("didn't set")
+	}
+}
+
+func TestAttack(t *testing.T) {
+	p := New().SetMinSleep(time.Microsecond).SetPacer(DefaultPacer).SetMaxSleep(time.Second)
+	for _, test := range []struct {
+		in             time.Duration
+		attackConstant uint
+		want           time.Duration
+	}{
+		{1 * time.Millisecond, 1, 2 * time.Millisecond},
+		{1 * time.Millisecond, 0, time.Second},
+		{1 * time.Millisecond, 2, (4 * time.Millisecond) / 3},
+		{1 * time.Millisecond, 3, (8 * time.Millisecond) / 7},
+	} {
+		p.sleepTime = test.in
+		p.SetAttackConstant(test.attackConstant)
+		p.defaultPacer(true)
+		got := p.sleepTime
+		if got != test.want {
+			t.Errorf("bad sleep want %v got %v", test.want, got)
+		}
+	}
+
+}
+
 func TestSetRetries(t *testing.T) {
 	p := New().SetRetries(18)
 	if p.retries != 18 {