1package libkb
2
3// from here:
4// https://blog.gopheracademy.com/advent-2014/backoff/
5
6import (
7	"math/rand"
8	"time"
9)
10
11// BackoffPolicy implements a backoff policy, randomizing its delays
12// and saturating at the final value in Millis.
13type BackoffPolicy struct {
14	Millis []int
15}
16
17// BackoffDefault is a backoff policy ranging up to 5 seconds.
18var BackoffDefault = BackoffPolicy{
19	[]int{0, 10, 10, 100, 100, 500, 500, 3000, 3000, 5000},
20}
21
22// Duration returns the time duration of the n'th wait cycle in a
23// backoff policy. This is b.Millis[n], randomized to avoid thundering
24// herds.
25func (b BackoffPolicy) Duration(n int) time.Duration {
26	if n >= len(b.Millis) {
27		n = len(b.Millis) - 1
28	}
29
30	return time.Duration(jitter(b.Millis[n])) * time.Millisecond
31}
32
33// jitter returns a random integer uniformly distributed in the range
34// [0.5 * millis .. 1.5 * millis]
35func jitter(millis int) int {
36	if millis == 0 {
37		return 0
38	}
39
40	return millis/2 + rand.Intn(millis)
41}
42