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minio/pkg/retry/retry.go

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/*
* Minio Cloud Storage, (C) 2020 MinIO, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package retry
import (
"context"
"math"
"math/rand"
"time"
)
// MaxJitter will randomize over the full exponential backoff time
const MaxJitter = 1.0
// NoJitter disables the use of jitter for randomizing the
// exponential backoff time
const NoJitter = 0.0
// defaultTimer implements Timer interface using time.Timer
type defaultTimer struct {
timer *time.Timer
}
// C returns the timers channel which receives the current time when the timer fires.
func (t *defaultTimer) C() <-chan time.Time {
return t.timer.C
}
// Start starts the timer to fire after the given duration
// don't use this code concurrently.
func (t *defaultTimer) Start(duration time.Duration) {
if t.timer == nil {
t.timer = time.NewTimer(duration)
} else {
t.timer.Reset(duration)
}
}
// Stop is called when the timer is not used anymore and resources may be freed.
func (t *defaultTimer) Stop() {
if t.timer != nil {
t.timer.Stop()
}
}
// NewTimerWithJitter creates a timer with exponentially increasing delays
// until the maximum retry attempts are reached. - this function is a fully
// configurable version, meant for only advanced use cases. For the most part
// one should use newRetryTimerSimple and newRetryTimer.
func NewTimerWithJitter(ctx context.Context, unit time.Duration, cap time.Duration, jitter float64) <-chan int {
attemptCh := make(chan int)
// normalize jitter to the range [0, 1.0]
jitter = math.Max(NoJitter, math.Min(MaxJitter, jitter))
// computes the exponential backoff duration according to
// https://www.awsarchitectureblog.com/2015/03/backoff.html
exponentialBackoffWait := func(attempt int) time.Duration {
// 1<<uint(attempt) below could overflow, so limit the value of attempt
const maxAttempt = 30
if attempt > maxAttempt {
attempt = maxAttempt
}
//sleep = random_between(0, min(cap, base * 2 ** attempt))
sleep := unit * time.Duration(1<<uint(attempt))
if sleep > cap {
sleep = cap
}
if jitter != NoJitter {
sleep -= time.Duration(rand.Float64() * float64(sleep) * jitter)
}
return sleep
}
go func() {
nextBackoff := 0
t := &defaultTimer{}
defer func() {
t.Stop()
}()
defer close(attemptCh)
// Channel used to signal after the expiry of backoff wait seconds.
for {
select {
case attemptCh <- nextBackoff:
nextBackoff++
case <-ctx.Done():
return
}
t.Start(exponentialBackoffWait(nextBackoff))
select {
case <-ctx.Done():
return
case <-t.C():
}
}
}()
// Start reading..
return attemptCh
}
// Default retry constants.
const (
defaultRetryUnit = 50 * time.Millisecond // 50 millisecond.
defaultRetryCap = 500 * time.Millisecond // 500 millisecond.
)
// NewTimer creates a timer with exponentially increasing delays
// until the maximum retry attempts are reached. - this function is a
// simpler version with all default values.
func NewTimer(ctx context.Context) <-chan int {
return NewTimerWithJitter(ctx, defaultRetryUnit, defaultRetryCap, MaxJitter)
}