95 lines
2.3 KiB
Go
95 lines
2.3 KiB
Go
/*
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Copyright 2016 The Kubernetes Authors.
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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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http://www.apache.org/licenses/LICENSE-2.0
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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 storage
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import (
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"sync"
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"time"
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)
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const (
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refreshPerSecond = 50 * time.Millisecond
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maxBudget = 250 * time.Millisecond
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)
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// timeBudget implements a budget of time that you can use and is
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// periodically being refreshed. The pattern to use it is:
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// budget := newTimeBudget(...)
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// ...
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// timeout := budget.takeAvailable()
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// // Now you can spend at most timeout on doing stuff
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// ...
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// // If you didn't use all timeout, return what you didn't use
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// budget.returnUnused(<unused part of timeout>)
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//
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// NOTE: It's not recommended to be used concurrently from multiple threads -
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// if first user takes the whole timeout, the second one will get 0 timeout
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// even though the first one may return something later.
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type timeBudget struct {
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sync.Mutex
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budget time.Duration
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refresh time.Duration
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maxBudget time.Duration
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}
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func newTimeBudget(stopCh <-chan struct{}) *timeBudget {
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result := &timeBudget{
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budget: time.Duration(0),
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refresh: refreshPerSecond,
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maxBudget: maxBudget,
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}
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go result.periodicallyRefresh(stopCh)
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return result
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}
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func (t *timeBudget) periodicallyRefresh(stopCh <-chan struct{}) {
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ticker := time.NewTicker(time.Second)
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defer ticker.Stop()
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for {
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select {
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case <-ticker.C:
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t.Lock()
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if t.budget = t.budget + t.refresh; t.budget > t.maxBudget {
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t.budget = t.maxBudget
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}
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t.Unlock()
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case <-stopCh:
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return
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}
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}
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}
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func (t *timeBudget) takeAvailable() time.Duration {
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t.Lock()
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defer t.Unlock()
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result := t.budget
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t.budget = time.Duration(0)
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return result
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}
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func (t *timeBudget) returnUnused(unused time.Duration) {
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t.Lock()
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defer t.Unlock()
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if unused < 0 {
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// We used more than allowed.
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return
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}
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if t.budget = t.budget + unused; t.budget > t.maxBudget {
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t.budget = t.maxBudget
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}
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}
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