// It is called from the net package at init time to avoid
// loading ws2_32.dll when net is not used.
var InitWSA = sync.OnceFunc(func() {
	var d syscall.WSAData
	e := syscall.WSAStartup(uint32(0x202), &d)
	if e != nil {
		initErr = e
	}
	checkSetFileCompletionNotificationModes()
})

// operation contains superset of data necessary to perform all async IO.
type operation struct {