func (b *AtomicFixedSizeRingBuf) BytesTwo() TwoBuffers {
	b.tex.Lock()
	defer b.tex.Unlock()
	return b.unatomic_BytesTwo()
}
func (b *AtomicFixedSizeRingBuf) BytesTwo() TwoBuffers {
	b.tex.Lock()
	defer b.tex.Unlock()
	return b.unatomic_BytesTwo()
}
// BytesTwo returns all readable bytes, but in two separate slices,
// to avoid copying. The two slices are from the same buffer, but
// are not contiguous. Either or both may be empty slices.