Vendor libs

vendor/github.com/jpillora/backoff/backoff.go

@@ -0,0 +1,69 @@
+package backoff
+
+import (
+	"math"
+	"math/rand"
+	"time"
+)
+
+//Backoff is a time.Duration counter. It starts at Min.
+//After every call to Duration() it is  multiplied by Factor.
+//It is capped at Max. It returns to Min on every call to Reset().
+//Used in conjunction with the time package.
+//
+// Backoff is not threadsafe, but the ForAttempt method can be
+// used concurrently if non-zero values for Factor, Max, and Min
+// are set on the Backoff shared among threads.
+type Backoff struct {
+	//Factor is the multiplying factor for each increment step
+	attempts, Factor float64
+	//Jitter eases contention by randomizing backoff steps
+	Jitter bool
+	//Min and Max are the minimum and maximum values of the counter
+	Min, Max time.Duration
+}
+
+//Returns the current value of the counter and then
+//multiplies it Factor
+func (b *Backoff) Duration() time.Duration {
+	d := b.ForAttempt(b.attempts)
+	b.attempts++
+	return d
+}
+
+// ForAttempt returns the duration for a specific attempt. This is useful if
+// you have a large number of independent Backoffs, but don't want use
+// unnecessary memory storing the Backoff parameters per Backoff. The first
+// attempt should be 0.
+//
+// ForAttempt is threadsafe iff non-zero values for Factor, Max, and Min
+// are set before any calls to ForAttempt are made.
+func (b *Backoff) ForAttempt(attempt float64) time.Duration {
+	//Zero-values are nonsensical, so we use
+	//them to apply defaults
+	if b.Min == 0 {
+		b.Min = 100 * time.Millisecond
+	}
+	if b.Max == 0 {
+		b.Max = 10 * time.Second
+	}
+	if b.Factor == 0 {
+		b.Factor = 2
+	}
+	//calculate this duration
+	dur := float64(b.Min) * math.Pow(b.Factor, attempt)
+	if b.Jitter == true {
+		dur = rand.Float64()*(dur-float64(b.Min)) + float64(b.Min)
+	}
+	//cap!
+	if dur > float64(b.Max) {
+		return b.Max
+	}
+	//return as a time.Duration
+	return time.Duration(dur)
+}
+
+//Resets the current value of the counter back to Min
+func (b *Backoff) Reset() {
+	b.attempts = 0
+}