70 lines
1.9 KiB
Go
70 lines
1.9 KiB
Go
package backoff
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import (
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"math"
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"math/rand"
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"time"
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)
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//Backoff is a time.Duration counter. It starts at Min.
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//After every call to Duration() it is multiplied by Factor.
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//It is capped at Max. It returns to Min on every call to Reset().
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//Used in conjunction with the time package.
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//
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// Backoff is not threadsafe, but the ForAttempt method can be
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// used concurrently if non-zero values for Factor, Max, and Min
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// are set on the Backoff shared among threads.
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type Backoff struct {
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//Factor is the multiplying factor for each increment step
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attempts, Factor float64
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//Jitter eases contention by randomizing backoff steps
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Jitter bool
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//Min and Max are the minimum and maximum values of the counter
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Min, Max time.Duration
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}
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//Returns the current value of the counter and then
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//multiplies it Factor
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func (b *Backoff) Duration() time.Duration {
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d := b.ForAttempt(b.attempts)
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b.attempts++
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return d
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}
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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 threadsafe iff non-zero values for Factor, Max, and Min
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// are set before any calls to ForAttempt are made.
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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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if b.Min == 0 {
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b.Min = 100 * time.Millisecond
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}
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if b.Max == 0 {
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b.Max = 10 * time.Second
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}
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if b.Factor == 0 {
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b.Factor = 2
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}
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//calculate this duration
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dur := float64(b.Min) * math.Pow(b.Factor, attempt)
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if b.Jitter == true {
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dur = rand.Float64()*(dur-float64(b.Min)) + float64(b.Min)
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}
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//cap!
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if dur > float64(b.Max) {
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return b.Max
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}
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//return as a time.Duration
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return time.Duration(dur)
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}
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//Resets the current value of the counter back to Min
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func (b *Backoff) Reset() {
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b.attempts = 0
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}
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