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package sync
import "sync"
// OnceErr wraps the behavior of recording an error
// once and signal on a channel when this has occurred.
// Signaling is done by closing of the channel.
//
// Type is safe for concurrent usage.
type OnceErr struct {
mu sync.RWMutex
err error
ch chan struct{}
}
// NewOnceErr return a new OnceErr
func NewOnceErr() *OnceErr {
return &OnceErr{
ch: make(chan struct{}, 1),
}
}
// Err acquires a read-lock and returns an
// error if one has been set.
func (e *OnceErr) Err() error {
e.mu.RLock()
err := e.err
e.mu.RUnlock()
return err
}
// SetError acquires a write-lock and will set
// the underlying error value if one has not been set.
func (e *OnceErr) SetError(err error) {
if err == nil {
return
}
e.mu.Lock()
if e.err == nil {
e.err = err
close(e.ch)
}
e.mu.Unlock()
}
// ErrorSet returns a channel that will be used to signal
// that an error has been set. This channel will be closed
// when the error value has been set for OnceErr.
func (e *OnceErr) ErrorSet() <-chan struct{} {
return e.ch
}
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