[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]
Re: pserialized reader/writer locks
Taylor R Campbell <riastradh%NetBSD.org@localhost> wrote:
> While reading the fstrans(9) code a few months ago and trying to
> understand what it does, I threw together a couple of simple
> pserialize(9)-based reader/writer locks -- one recursive for nestable
> transactions like fstrans(9), the other non-recursive.
> Unlike rwlock(9), frequent readers do not require interprocessor
> synchronization: they use pool_cache(9) to manage per-CPU caches of
> in-use records which writers wait for. Writers, in contrast, are very
> The attached code is untested and just represents ideas that were
> kicking around in my head. Thoughts? Worthwhile to experiment with?
I would expect a better problem statement even if it is a brain dump (one
sentence would have been enough). Are you trying to solve sleepable reader
problem? In such case, messing up pserialize(9) with somewhat read-write
lock semantics in ad-hoc way is a wrong approach. If you are building a
read-optimised *lock*, then it should be designed and implemented as such
mechanism rather than built as an ad-hoc wrapper.
Basically, there are two approaches:
a) Implement read-optimised / read-mostly lock. Years ago ad@ wrote an
implementation of rdlock(9). It was not published, but he added a BSD
license so I guess it is okay to post here:
Alternatively, there is FreeBSD's rmlock(9):
b) Implement grace-period based synchronisation mechanism which allows
readers to sleep, such as SRCU. There are some dangers here:
However, it can provide less expensive writer side and more granular
garbage collection of objects. I think it is worth to consider this way.
Main Index |
Thread Index |