k8s.io/apiserver@v0.31.1/pkg/util/flowcontrol/fairqueuing/promise/promise.go (about)

     1  /*
     2  Copyright 2019 The Kubernetes Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package promise
    18  
    19  import (
    20  	"context"
    21  	"sync"
    22  )
    23  
    24  // promise implements the WriteOnce interface.
    25  type promise struct {
    26  	doneCtx context.Context
    27  	doneVal interface{}
    28  	setCh   chan struct{}
    29  	onceler sync.Once
    30  	value   interface{}
    31  }
    32  
    33  var _ WriteOnce = &promise{}
    34  
    35  // NewWriteOnce makes a new thread-safe WriteOnce.
    36  //
    37  // If `initial` is non-nil then that value is Set at creation time.
    38  //
    39  // If a `Get` is waiting soon after the channel associated with the
    40  // `doneCtx` becomes selectable (which never happens for the nil
    41  // channel) then `Set(doneVal)` effectively happens at that time.
    42  func NewWriteOnce(initial interface{}, doneCtx context.Context, doneVal interface{}) WriteOnce {
    43  	p := &promise{
    44  		doneCtx: doneCtx,
    45  		doneVal: doneVal,
    46  		setCh:   make(chan struct{}),
    47  	}
    48  	if initial != nil {
    49  		p.Set(initial)
    50  	}
    51  	return p
    52  }
    53  
    54  func (p *promise) Get() interface{} {
    55  	select {
    56  	case <-p.setCh:
    57  	case <-p.doneCtx.Done():
    58  		p.Set(p.doneVal)
    59  	}
    60  	return p.value
    61  }
    62  
    63  func (p *promise) Set(value interface{}) bool {
    64  	var ans bool
    65  	p.onceler.Do(func() {
    66  		p.value = value
    67  		close(p.setCh)
    68  		ans = true
    69  	})
    70  	return ans
    71  }