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once.go (946B)

      1 package errors
      2 
      3 import (
      4 	"sync/atomic"
      5 	"unsafe"
      6 )
      7 
      8 // OnceError is an error structure that supports safe multi
      9 // threaded usage and setting only once (until reset).
     10 type OnceError struct{ err unsafe.Pointer }
     11 
     12 // NewOnce returns a new OnceError instance.
     13 func NewOnce() OnceError {
     14 	return OnceError{
     15 		err: nil,
     16 	}
     17 }
     18 
     19 // Store will safely set the OnceError to value, no-op if nil.
     20 func (e *OnceError) Store(err error) {
     21 	// Nothing to do
     22 	if err == nil {
     23 		return
     24 	}
     25 
     26 	// Only set if not already
     27 	atomic.CompareAndSwapPointer(
     28 		&e.err,
     29 		nil,
     30 		unsafe.Pointer(&err),
     31 	)
     32 }
     33 
     34 // Load will load the currently stored error.
     35 func (e *OnceError) Load() error {
     36 	return *(*error)(atomic.LoadPointer(&e.err))
     37 }
     38 
     39 // IsSet returns whether OnceError has been set.
     40 func (e *OnceError) IsSet() bool {
     41 	return (atomic.LoadPointer(&e.err) != nil)
     42 }
     43 
     44 // Reset will reset the OnceError value.
     45 func (e *OnceError) Reset() {
     46 	atomic.StorePointer(&e.err, nil)
     47 }