Harshavardhana
8 years ago
committed by
GitHub
parent
5a3c5aec31
commit
f1d7780167
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/* |
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* Minio Cloud Storage, (C) 2017 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 dsync |
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import ( |
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"math/rand" |
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"sync" |
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"time" |
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) |
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// lockedRandSource provides protected rand source, implements rand.Source interface.
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type lockedRandSource struct { |
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lk sync.Mutex |
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src rand.Source |
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} |
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// Int63 returns a non-negative pseudo-random 63-bit integer as an
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// int64.
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func (r *lockedRandSource) Int63() (n int64) { |
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r.lk.Lock() |
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n = r.src.Int63() |
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r.lk.Unlock() |
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return |
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} |
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// Seed uses the provided seed value to initialize the generator to a
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// deterministic state.
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func (r *lockedRandSource) Seed(seed int64) { |
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r.lk.Lock() |
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r.src.Seed(seed) |
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r.lk.Unlock() |
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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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// Global random source for fetching random values.
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var globalRandomSource = rand.New(&lockedRandSource{ |
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src: rand.NewSource(time.Now().UTC().UnixNano()), |
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}) |
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// newRetryTimerJitter 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 newRetryTimerWithJitter(unit time.Duration, cap time.Duration, jitter float64, doneCh chan struct{}) <-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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if jitter < NoJitter { |
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jitter = NoJitter |
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} |
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if jitter > MaxJitter { |
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jitter = MaxJitter |
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} |
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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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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(globalRandomSource.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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defer close(attemptCh) |
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nextBackoff := 0 |
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// Channel used to signal after the expiry of backoff wait seconds.
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var timer *time.Timer |
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for { |
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select { // Attempts starts.
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case attemptCh <- nextBackoff: |
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nextBackoff++ |
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case <-doneCh: |
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// Stop the routine.
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return |
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} |
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timer = time.NewTimer(exponentialBackoffWait(nextBackoff)) |
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// wait till next backoff time or till doneCh gets a message.
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select { |
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case <-timer.C: |
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case <-doneCh: |
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// stop the timer and return.
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timer.Stop() |
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return |
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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 = time.Second // 1 second.
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defaultRetryCap = 1 * time.Second // 1 second.
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) |
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// newRetryTimer creates a timer with exponentially increasing delays
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// until the maximum retry attempts are reached. - this function provides
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// resulting retry values to be of maximum jitter.
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func newRetryTimer(unit time.Duration, cap time.Duration, doneCh chan struct{}) <-chan int { |
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return newRetryTimerWithJitter(unit, cap, MaxJitter, doneCh) |
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} |
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// newRetryTimerSimple 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 newRetryTimerSimple(doneCh chan struct{}) <-chan int { |
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return newRetryTimerWithJitter(defaultRetryUnit, defaultRetryCap, MaxJitter, doneCh) |
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} |
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