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// Copyright (c) The EfficientGo Authors.
// Licensed under the Apache License 2.0.
// Initially copied from Cortex project.
// Package backoff implements backoff timers which increases wait time on every retry, incredibly useful
// in distributed system timeout functionalities.
package backoff
import (
"context"
"fmt"
"math/rand"
"time"
)
// Config configures a Backoff.
type Config struct {
Min time.Duration `yaml:"min_period"` // Start backoff at this level
Max time.Duration `yaml:"max_period"` // Increase exponentially to this level
MaxRetries int `yaml:"max_retries"` // Give up after this many; zero means infinite retries
}
// Backoff implements exponential backoff with randomized wait times.
type Backoff struct {
cfg Config
ctx context.Context
numRetries int
nextDelayMin time.Duration
nextDelayMax time.Duration
}
// New creates a Backoff object. Pass a Context that can also terminate the operation.
func New(ctx context.Context, cfg Config) *Backoff {
return &Backoff{
cfg: cfg,
ctx: ctx,
nextDelayMin: cfg.Min,
nextDelayMax: doubleDuration(cfg.Min, cfg.Max),
}
}
// Reset the Backoff back to its initial condition.
func (b *Backoff) Reset() {
b.numRetries = 0
b.nextDelayMin = b.cfg.Min
b.nextDelayMax = doubleDuration(b.cfg.Min, b.cfg.Max)
}
// Ongoing returns true if caller should keep going.
func (b *Backoff) Ongoing() bool {
// Stop if Context has errored or max retry count is exceeded.
return b.ctx.Err() == nil && (b.cfg.MaxRetries == 0 || b.numRetries < b.cfg.MaxRetries)
}
// Err returns the reason for terminating the backoff, or nil if it didn't terminate.
func (b *Backoff) Err() error {
if b.ctx.Err() != nil {
return b.ctx.Err()
}
if b.cfg.MaxRetries != 0 && b.numRetries >= b.cfg.MaxRetries {
return fmt.Errorf("terminated after %d retries", b.numRetries)
}
return nil
}
// NumRetries returns the number of retries so far.
func (b *Backoff) NumRetries() int {
return b.numRetries
}
// Wait sleeps for the backoff time then increases the retry count and backoff time.
// Returns immediately if Context is terminated.
func (b *Backoff) Wait() {
// Increase the number of retries and get the next delay.
sleepTime := b.NextDelay()
if b.Ongoing() {
select {
case <-b.ctx.Done():
case <-time.After(sleepTime):
}
}
}
func (b *Backoff) NextDelay() time.Duration {
b.numRetries++
// Handle the edge case the min and max have the same value
// (or due to some misconfig max is < min).
if b.nextDelayMin >= b.nextDelayMax {
return b.nextDelayMin
}
// Add a jitter within the next exponential backoff range.
sleepTime := b.nextDelayMin + time.Duration(rand.Int63n(int64(b.nextDelayMax-b.nextDelayMin)))
// Apply the exponential backoff to calculate the next jitter
// range, unless we've already reached the max.
if b.nextDelayMax < b.cfg.Max {
b.nextDelayMin = doubleDuration(b.nextDelayMin, b.cfg.Max)
b.nextDelayMax = doubleDuration(b.nextDelayMax, b.cfg.Max)
}
return sleepTime
}
func doubleDuration(value, maxValue time.Duration) time.Duration {
value = value * 2
if value <= maxValue {
return value
}
return maxValue
}
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