Lock-free tdb lookups

[Joe Seigh]

tridge at samba.org wrote:
> Joe,
> 
>  > I can't see any way of making things lock-free without infringing,
>  > in part at least, on patent application 20050198030 "Efficient
>  > support of consistent cyclic search with read-copy-update" by Paul
>  > McKenney, file in March 2004,
> 
> I'd be pretty surprised if Paul's employer (IBM) wasn't happy to allow
> that patent to be used in tdb. In Paul's talk at LCA last year I think
> he specifically mentioned tdb as a possible use.

I'll check with Paul then.

> 
> So I think the main impediment would be someone implementing it, and
> proving its safe on all the architectures we care about. We'd also
> have to decide if the extra complexity is worth it. If we find its
> only a small gain then I'd rather keep the simple approach we have
> now.

The transactional stuff does raise the cost somewhat.  Simple 
read/write locking is a lot easier to plug read lock-free into.

--
Joe Seigh