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future.go
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future.go
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// Copyright 2018 ko Build Authors All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package build
import (
"sync"
)
func newFuture(work func() (Result, error)) *future {
// Create a channel on which to send the result.
ch := make(chan *result)
// Initiate the actual work, sending its result
// along the above channel.
go func() {
img, err := work()
ch <- &result{img: img, err: err}
}()
// Return a future for the above work. Callers should
// call .Get() on this result (as many times as needed).
// One of these calls will receive the result, store it,
// and close the channel so that the rest of the callers
// can consume it.
return &future{
promise: ch,
}
}
type result struct {
img Result
err error
}
type future struct {
m sync.RWMutex
result *result
promise chan *result
}
// Get blocks on the result of the future.
func (f *future) Get() (Result, error) {
// Block on the promise of a result until we get one.
result, ok := <-f.promise
if ok {
func() {
f.m.Lock()
defer f.m.Unlock()
// If we got the result, then store it so that
// others may access it.
f.result = result
// Close the promise channel so that others
// are signaled that the result is available.
close(f.promise)
}()
}
f.m.RLock()
defer f.m.RUnlock()
return f.result.img, f.result.err
}