Add an exponential backoff helper

p2p/backoff.go

@@ -0,0 +1,60 @@
+package p2p
+
+import "time"
+
+// Backoff is a backoff sleeper.
+type Backoff interface {
+	Reset()
+	Sleep()
+	Backoff()
+}
+
+// BackoffBase is the base implementation of backoff sleeper.  It handles the
+// minimum/current/maximum backoff logic.  If maximum backoff is 0, there is no
+// maximum.
+type BackoffBase struct {
+	Min, Cur, Max time.Duration
+}
+
+func NewBackoffBase(min, max time.Duration) *BackoffBase{
+	return &BackoffBase{min, min, max}
+}
+
+// Reset the current sleep duration to its minimum value.
+func (b *BackoffBase) Reset() {
+	b.Cur = b.Min
+}
+
+// Sleep for the current duration, then adjust the duration.
+func (b *BackoffBase) Sleep() {
+	if b.Cur < b.Min {
+		b.Cur = b.Min
+	}
+	time.Sleep(b.Cur)
+	b.Backoff()
+	if b.Max != 0 && b.Cur > b.Max {
+		b.Cur = b.Max
+	}
+	if b.Cur < b.Min {
+		b.Cur = b.Min
+	}
+}
+
+// Adjust the duration.  Subtypes shall implement this.
+func (b *BackoffBase) Backoff() {
+	// default implementation does not backoff
+}
+
+// Exponential backoff.
+type ExpBackoff struct {
+	BackoffBase
+	Factor float64
+}
+
+func NewExpBackoff(min, max time.Duration, factor float64) *ExpBackoff {
+	return &ExpBackoff{*NewBackoffBase(min, max), factor}
+}
+
+func (b *ExpBackoff) Backoff() {
+	b.Cur = time.Duration(float64(b.Cur) * b.Factor)
+}