2023-05-29 21:03:29 +00:00
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/*
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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 promise
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import (
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"context"
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2023-05-29 21:03:29 +00:00
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"sync"
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)
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// promise implements the WriteOnce interface.
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type promise struct {
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doneCtx context.Context
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doneVal interface{}
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setCh chan struct{}
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onceler sync.Once
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value interface{}
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}
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var _ WriteOnce = &promise{}
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// NewWriteOnce makes a new thread-safe WriteOnce.
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//
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// If `initial` is non-nil then that value is Set at creation time.
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//
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// If a `Get` is waiting soon after the channel associated with the
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// `doneCtx` becomes selectable (which never happens for the nil
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// channel) then `Set(doneVal)` effectively happens at that time.
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func NewWriteOnce(initial interface{}, doneCtx context.Context, doneVal interface{}) WriteOnce {
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p := &promise{
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doneCtx: doneCtx,
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doneVal: doneVal,
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setCh: make(chan struct{}),
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}
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if initial != nil {
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p.Set(initial)
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}
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return p
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}
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func (p *promise) Get() interface{} {
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select {
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case <-p.setCh:
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case <-p.doneCtx.Done():
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p.Set(p.doneVal)
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}
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return p.value
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}
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func (p *promise) Set(value interface{}) bool {
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var ans bool
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p.onceler.Do(func() {
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p.value = value
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close(p.setCh)
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ans = true
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})
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return ans
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}
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