internal

var Caller = func(skip int, fast bool) (file string, line int) {

	if !fast {
		_, file, line, _ = runtime.Caller(skip + 1)
		return
	}

	rpc := make([]uintptr, 1)
	n := runtime.Callers(skip+2, rpc[:])
	if n < 1 {
		return
	}
	pc := rpc[0]
	if v, ok := frameMap.Load(pc); ok {
		e := v.(*runtime.Frame)
		return e.File, e.Line
	}
	frame, _ := runtime.CallersFrames(rpc).Next()
	frameMap.Store(pc, &frame)
	return frame.File, frame.Line
}