118 lines
3.2 KiB
Go
118 lines
3.2 KiB
Go
package retry
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import (
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"context"
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"math/rand"
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"time"
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)
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// Jitter should return a new wait duration optionally with some time added or
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// removed to create some randomness in wait time.
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type Jitter func(baseTime time.Duration) time.Duration
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// NewJitter returns a new random Jitter that is up to percent longer than the
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// original wait time.
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func NewJitter(percent int64) Jitter {
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if percent < 0 {
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percent = 0
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}
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return func(baseTime time.Duration) time.Duration {
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if percent == 0 {
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return baseTime
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}
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max := (int64(baseTime) * percent) / 100
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if max < 0 { // overflow
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return baseTime
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}
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return baseTime + time.Duration(rand.Int63n(max))
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}
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}
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// Waiter records the number of failures and performs exponential backoff when
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// when there are consecutive failures.
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type Waiter struct {
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// MinFailures before exponential backoff starts. Any failures before
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// MinFailures is reached will wait MinWait time.
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MinFailures uint
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// MinWait time. Returned after the first failure.
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MinWait time.Duration
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// MaxWait time applied before Jitter. Note that the actual maximum wait time
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// is MaxWait + MaxWait * Jitter.
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MaxWait time.Duration
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// Jitter to add to each wait time. The Jitter is applied after MaxWait, which
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// may cause the actual wait time to exceed MaxWait.
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Jitter Jitter
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// Factor is the multiplier to use when calculating the delay. Defaults to
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// 1 second.
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Factor time.Duration
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failures uint
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}
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// delay calculates the time to wait based on the number of failures
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func (w *Waiter) delay() time.Duration {
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if w.failures <= w.MinFailures {
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return w.MinWait
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}
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factor := w.Factor
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if factor == 0 {
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factor = time.Second
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}
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shift := w.failures - w.MinFailures - 1
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waitTime := w.MaxWait
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if shift < 31 {
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waitTime = (1 << shift) * factor
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}
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// apply MaxWait before jitter so that multiple waiters with the same MaxWait
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// do not converge when they hit their max.
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if w.MaxWait != 0 && waitTime > w.MaxWait {
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waitTime = w.MaxWait
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}
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if w.Jitter != nil {
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waitTime = w.Jitter(waitTime)
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}
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if waitTime < w.MinWait {
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return w.MinWait
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}
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return waitTime
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}
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// Reset the failure count to 0.
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// Reset must be called if the operation done after Wait did not fail.
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func (w *Waiter) Reset() {
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w.failures = 0
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}
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// Failures returns the count of consecutive failures.
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func (w *Waiter) Failures() int {
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return int(w.failures)
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}
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// Wait increases the number of failures by one, and then blocks until the context
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// is cancelled, or until the wait time is reached.
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//
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// The wait time increases exponentially as the number of failures increases.
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// Every call to Wait increments the failures count, so Reset must be called
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// after Wait when there wasn't a failure.
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//
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// Wait will return ctx.Err() if the context is cancelled.
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func (w *Waiter) Wait(ctx context.Context) error {
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w.failures++
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timer := time.NewTimer(w.delay())
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select {
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case <-ctx.Done():
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timer.Stop()
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return ctx.Err()
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case <-timer.C:
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return nil
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}
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}
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// NextWait returns the period the next call to Wait with block for assuming
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// it's context is not cancelled. It's useful for informing a user how long
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// it will be before the next attempt is made.
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func (w *Waiter) NextWait() time.Duration {
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return w.delay()
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}
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