You’re thinking of the kernel and urcu implementations. The RCU implementation that I linked here isn’t exotic at all. It creates a duplicate structure and atomically swaps pointers. If the swap fails because another update occurred, it tries creating a new duplicate structure running your RCU closure and swapping again. Forward progress is eventually made although it scales poorly if you have a lot of concurrent updaters.

So not quite as performant but in terms of having a writer and lots of concurrent readers, it achieves that requirement. And it’s data structure agnostic and you only need to pay this cost if you really have concurrency.