88 lines
1.8 KiB
Go
88 lines
1.8 KiB
Go
package shadow
|
|
|
|
import (
|
|
"errors"
|
|
"sync"
|
|
)
|
|
|
|
// ErrClosed is returned by any closed values.
|
|
//
|
|
// A "closed value" is when the shadow has been notified that the real
|
|
// side is complete and any blocking values will _never_ be satisfied
|
|
// in the future. In this case, this error is returned. If a value is already
|
|
// available, that is still returned.
|
|
var ErrClosed = errors.New("shadow closed")
|
|
|
|
// Value is a struct that coordinates a value between two
|
|
// parallel routines. It is similar to atomic.Value except that when
|
|
// Value is called if it isn't set it will wait for it.
|
|
//
|
|
// The Value can be closed with Close, which will cause any future
|
|
// blocking operations to return immediately with ErrClosed.
|
|
type Value struct {
|
|
lock sync.Mutex
|
|
cond *sync.Cond
|
|
value interface{}
|
|
valueSet bool
|
|
}
|
|
|
|
func (v *Value) Lock() {
|
|
v.lock.Lock()
|
|
}
|
|
|
|
func (v *Value) Unlock() {
|
|
v.lock.Unlock()
|
|
}
|
|
|
|
// Close closes the value. This can never fail. For a definition of
|
|
// "close" see the struct docs.
|
|
func (w *Value) Close() error {
|
|
w.lock.Lock()
|
|
set := w.valueSet
|
|
w.lock.Unlock()
|
|
|
|
// If we haven't set the value, set it
|
|
if !set {
|
|
w.SetValue(ErrClosed)
|
|
}
|
|
|
|
// Done
|
|
return nil
|
|
}
|
|
|
|
// Value returns the value that was set.
|
|
func (w *Value) Value() interface{} {
|
|
w.lock.Lock()
|
|
defer w.lock.Unlock()
|
|
|
|
// If we already have a value just return
|
|
for !w.valueSet {
|
|
// No value, setup the condition variable if we have to
|
|
if w.cond == nil {
|
|
w.cond = sync.NewCond(&w.lock)
|
|
}
|
|
|
|
// Wait on it
|
|
w.cond.Wait()
|
|
}
|
|
|
|
// Return the value
|
|
return w.value
|
|
}
|
|
|
|
// SetValue sets the value.
|
|
func (w *Value) SetValue(v interface{}) {
|
|
w.lock.Lock()
|
|
defer w.lock.Unlock()
|
|
|
|
// Set the value
|
|
w.valueSet = true
|
|
w.value = v
|
|
|
|
// If we have a condition, clear it
|
|
if w.cond != nil {
|
|
w.cond.Broadcast()
|
|
w.cond = nil
|
|
}
|
|
}
|