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