96 lines
2.4 KiB
Go
96 lines
2.4 KiB
Go
/*
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Copyright 2019 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 lockingpromise
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import (
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"sync"
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"k8s.io/apiserver/pkg/util/flowcontrol/counter"
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"k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/promise"
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)
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// lockingPromise implementss the promise.LockingWriteOnce interface.
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// This implementation is based on a condition variable.
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// This implementation tracks active goroutines:
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// the given counter is decremented for a goroutine waiting for this
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// varible to be set and incremented when such a goroutine is
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// unblocked.
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type lockingPromise struct {
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lock sync.Locker
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cond sync.Cond
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activeCounter counter.GoRoutineCounter // counter of active goroutines
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waitingCount int // number of goroutines idle due to this being unset
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isSet bool
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value interface{}
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}
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var _ promise.LockingWriteOnce = &lockingPromise{}
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// NewWriteOnce makes a new promise.LockingWriteOnce
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func NewWriteOnce(lock sync.Locker, activeCounter counter.GoRoutineCounter) promise.LockingWriteOnce {
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return &lockingPromise{
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lock: lock,
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cond: *sync.NewCond(lock),
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activeCounter: activeCounter,
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}
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}
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func (p *lockingPromise) Get() interface{} {
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p.lock.Lock()
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defer p.lock.Unlock()
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return p.GetLocked()
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}
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func (p *lockingPromise) GetLocked() interface{} {
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if !p.isSet {
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p.waitingCount++
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p.activeCounter.Add(-1)
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p.cond.Wait()
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}
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return p.value
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}
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func (p *lockingPromise) IsSet() bool {
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p.lock.Lock()
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defer p.lock.Unlock()
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return p.IsSetLocked()
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}
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func (p *lockingPromise) IsSetLocked() bool {
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return p.isSet
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}
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func (p *lockingPromise) Set(value interface{}) bool {
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p.lock.Lock()
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defer p.lock.Unlock()
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return p.SetLocked(value)
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}
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func (p *lockingPromise) SetLocked(value interface{}) bool {
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if p.isSet {
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return false
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}
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p.isSet = true
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p.value = value
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if p.waitingCount > 0 {
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p.activeCounter.Add(p.waitingCount)
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p.waitingCount = 0
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p.cond.Broadcast()
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}
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return true
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}
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