118 lines
2.6 KiB
Go
118 lines
2.6 KiB
Go
// Package backoff provides an exponential-backoff implementation partially
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// taken from jpillora/backoff.
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package backoff
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import (
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"math"
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"math/rand"
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"sync/atomic"
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"time"
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)
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const (
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factor = 2
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jitter = true
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)
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func init() {
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rand.Seed(time.Now().UnixNano())
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}
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// Timer is a backoff timer.
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type Timer struct {
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backoff Backoff
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timer *time.Timer
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}
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// NewTimer returns a new uninitialized timer.
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func NewTimer(min, max time.Duration) Timer {
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return Timer{
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backoff: NewBackoff(min, max),
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}
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}
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// Next initializes the timer if needed and returns a timer channel that fires
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// when the backoff timeout is reached.
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func (t *Timer) Next() <-chan time.Time {
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if t.timer == nil {
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t.timer = time.NewTimer(t.backoff.Next())
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} else {
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t.timer.Stop() // ensure drained
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t.timer.Reset(t.backoff.Next())
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}
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return t.timer.C
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}
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// Stop stops the internal timer and frees its resources. It does nothing if the
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// timer is uninitialized.
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func (t *Timer) Stop() {
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if t.timer == nil {
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return
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}
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if !t.timer.Stop() {
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<-t.timer.C // drain
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}
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}
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// Backoff is a time.Duration counter, starting at Min. After every call to
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// the Duration method the current timing is multiplied by Factor, but it
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// never exceeds Max.
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type Backoff struct {
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min, max float64 // seconds
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attempt int32 // negative == max uint32
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}
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// NewBackoff creates a new backoff time.Duration counter.
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func NewBackoff(min, max time.Duration) Backoff {
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return Backoff{
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min: min.Seconds(),
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max: max.Seconds(),
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}
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}
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// Next returns the next backoff duration.
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func (b *Backoff) Next() time.Duration {
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return b.forAttempt(atomic.AddInt32(&b.attempt, 1) - 1)
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}
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const maxInt64 = float64(math.MaxInt64 - 512)
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// forAttempt returns the duration for a specific attempt. This is useful if
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// you have a large number of independent Backoffs, but don't want use
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// unnecessary memory storing the Backoff parameters per Backoff. The first
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// attempt should be 0.
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func (b *Backoff) forAttempt(attempt int32) time.Duration {
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if b.min >= b.max {
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// short-circuit
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return duration(b.max)
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}
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// Ensure attempt never overflows.
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if attempt < 0 {
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attempt = math.MaxInt32
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}
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// Calculate this duration.
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dur := b.min * math.Pow(factor, float64(attempt))
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if jitter {
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dur = rand.Float64()*(dur-b.min) + b.min
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}
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if dur < b.min {
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return duration(b.min)
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}
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if dur > b.max {
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return duration(b.max)
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}
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return duration(dur)
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}
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// duration converts a seconds float64 to time.Duration without losing accuracy.
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func duration(secs float64) time.Duration {
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int, frac := math.Modf(secs)
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return (time.Duration(int) * time.Second) + time.Duration(frac*float64(time.Second))
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}
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