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future.go
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future.go
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package future
import (
"context"
"go.uber.org/atomic"
)
type Value interface{}
type SetFunc func(Value, error)
// Thread-safe facility to obtain/wait for a value from a single producer in
// multiple goroutines
type Future struct {
value Value
err error
ready chan struct{}
blockSet atomic.Bool // block repeated calls of set
}
// New constructs new Future.
//
// Use return setter to set value of the future and unblock all routines waiting
// on the future. The setter will succeed only once, repeated calls of set do nothing.
func New() (*Future, SetFunc) {
f := &Future{ready: make(chan struct{})}
return f, f.set
}
// Get returns value when it is set.
func (f *Future) Get(ctx context.Context) (Value, error) {
if f.Ready() {
return f.value, f.err
}
select {
case <-f.ready:
return f.value, f.err
case <-ctx.Done():
return nil, ctx.Err()
}
}
// Set value or error of the future and change state to ready.
func (f *Future) set(value Value, err error) {
if !f.blockSet.CAS(false, true) {
return
}
f.value = value
f.err = err
close(f.ready)
}
// Ready checks whether value is set
func (f *Future) Ready() bool {
select {
case <-f.ready:
return true
default:
return false
}
}