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minio/pkg/dsync/retry.go

142 lines
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/*
* Minio Cloud Storage, (C) 2017 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 dsync
import (
"math/rand"
"sync"
"time"
)
// lockedRandSource provides protected rand source, implements rand.Source interface.
type lockedRandSource struct {
lk sync.Mutex
src rand.Source
}
// Int63 returns a non-negative pseudo-random 63-bit integer as an
// int64.
func (r *lockedRandSource) Int63() (n int64) {
r.lk.Lock()
n = r.src.Int63()
r.lk.Unlock()
return
}
// Seed uses the provided seed value to initialize the generator to a
// deterministic state.
func (r *lockedRandSource) Seed(seed int64) {
r.lk.Lock()
r.src.Seed(seed)
r.lk.Unlock()
}
// 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
// Global random source for fetching random values.
var globalRandomSource = rand.New(&lockedRandSource{
src: rand.NewSource(time.Now().UTC().UnixNano()),
})
// newRetryTimerJitter 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 newRetryTimerWithJitter(unit time.Duration, cap time.Duration, jitter float64, doneCh <-chan struct{}) <-chan int {
attemptCh := make(chan int)
// normalize jitter to the range [0, 1.0]
if jitter < NoJitter {
jitter = NoJitter
}
if jitter > MaxJitter {
jitter = MaxJitter
}
// 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
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(globalRandomSource.Float64() * float64(sleep) * jitter)
}
return sleep
}
go func() {
defer close(attemptCh)
nextBackoff := 0
// Channel used to signal after the expiry of backoff wait seconds.
var timer *time.Timer
for {
select { // Attempts starts.
case attemptCh <- nextBackoff:
nextBackoff++
case <-doneCh:
// Stop the routine.
return
}
timer = time.NewTimer(exponentialBackoffWait(nextBackoff))
// wait till next backoff time or till doneCh gets a message.
select {
case <-timer.C:
case <-doneCh:
// stop the timer and return.
timer.Stop()
return
}
}
}()
// Start reading..
return attemptCh
}
// Default retry constants.
const (
defaultRetryUnit = time.Second // 1 second.
defaultRetryCap = 1 * time.Second // 1 second.
)
// newRetryTimer creates a timer with exponentially increasing delays
// until the maximum retry attempts are reached. - this function provides
// resulting retry values to be of maximum jitter.
func newRetryTimer(unit time.Duration, cap time.Duration, doneCh <-chan struct{}) <-chan int {
return newRetryTimerWithJitter(unit, cap, MaxJitter, doneCh)
}
// newRetryTimerSimple 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 newRetryTimerSimple(doneCh <-chan struct{}) <-chan int {
return newRetryTimerWithJitter(defaultRetryUnit, defaultRetryCap, MaxJitter, doneCh)
}