forked from mirror/backoff
115 lines
2.5 KiB
Go
115 lines
2.5 KiB
Go
// Package backoff provides an exponential-backoff implementation.
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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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// 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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//
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// Backoff is not generally concurrent-safe, but the ForAttempt method can
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// be used concurrently.
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type Backoff struct {
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attempt uint64
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// Factor is the multiplying factor for each increment step.
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//
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// Defaults to 2.
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Factor float64
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// Jitter eases contention by randomizing backoff steps.
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//
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// Defaults to false.
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Jitter bool
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// Minimum value of the counter.
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//
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// Defaults to 100 milliseconds.
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Min time.Duration
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// Maximum value of the counter.
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//
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// Defaults to 10 seconds.
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Max time.Duration
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}
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// Duration returns the duration for the current attempt before incrementing
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// the attempt counter. See ForAttempt.
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func (b *Backoff) Duration() time.Duration {
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d := b.ForAttempt(float64(atomic.AddUint64(&b.attempt, 1) - 1))
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return d
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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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//
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// ForAttempt is concurrent-safe.
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func (b *Backoff) ForAttempt(attempt float64) time.Duration {
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// Zero-values are nonsensical, so we use
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// them to apply defaults
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min := b.Min
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if min <= 0 {
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min = 100 * time.Millisecond
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}
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max := b.Max
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if max <= 0 {
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max = 10 * time.Second
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}
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if min >= max {
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// short-circuit
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return max
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}
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factor := b.Factor
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if factor <= 0 {
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factor = 2
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}
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//calculate this duration
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minf := float64(min)
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durf := minf * math.Pow(factor, attempt)
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if b.Jitter {
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durf = rand.Float64()*(durf-minf) + minf
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}
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//ensure float64 wont overflow int64
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if durf > maxInt64 {
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return max
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}
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dur := time.Duration(durf)
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//keep within bounds
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if dur < min {
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return min
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}
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if dur > max {
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return max
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}
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return dur
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}
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// Reset restarts the current attempt counter at zero.
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func (b *Backoff) Reset() {
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atomic.StoreUint64(&b.attempt, 0)
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}
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// Attempt returns the current attempt counter value.
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func (b *Backoff) Attempt() float64 {
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return float64(atomic.LoadUint64(&b.attempt))
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}
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// Copy returns a backoff with equals constraints as the original
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func (b *Backoff) Copy() *Backoff {
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return &Backoff{
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Factor: b.Factor,
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Jitter: b.Jitter,
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Min: b.Min,
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Max: b.Max,
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}
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}
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