terraform/helper/shadow/value.go

52 lines
953 B
Go

package shadow
import (
"sync"
)
// 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.
type Value struct {
lock sync.Mutex
cond *sync.Cond
value interface{}
valueSet bool
}
// 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
}
}