Subj : Re: Hazard Pointers w/o memory barrier.
To   : comp.programming.threads
From : Chris Thomasson
Date : Thu May 05 2005 02:01 am

> Actually, thinking about it, I'd stay away from RCU until IBM makes its
> intentions a little more clear.  IBM does have this Linux strategy.  It's
> not a problem for me since I'm not going to publish any code, I'm just
> experimenting with it.  If you've been following any of the C++ smart
> pointer / shared pointer discussions, you'd realize that nothing short
> of a scheme that can GC everything with zero overhead in a multi-threaded
> environment with no scalability problems and can deal with untracked raw
> pointers will satisfy anyone.  Until everyone becomes more realistic, and
> I don't know how long that will take since most of them don't appear to
> have even started on their multi-threaded learning curves, there's not
> much use trying to create a general usage smart pointer.

:)




> Back to IBM again.  They don't seem to publicize any projects that are in
> the works, so it's hard to tell what they might be up to here.  I would
> guess they might try to put this in the Linux kernel since RCU is already
> in place and the hazard pointer stuff would solve some problems running
> with preemption enabled and some problems with resource granularity that
> a pure proxy GC method would have.  As far as user space is concerned,
> they might try to restrict it's usage to Linux as far as it fits in with
> their Linux strategy.

This could be point of contention for my Library. It runs on Windows and 
Linux... Yikes!




> That could be a problem however since a lot of
> open source projects are platform independent and aren't going to adopt
> non-portable api's.

Good point.




> You might run something by IBM's lawyers just to see what they might say.
> If you phrase the questions right, you might learn something about IBM's
> intentions but being lawyers they'd probably catch on pretty quick.  You'd
> have more of a chance if you restricted your stuff to Linux though I don't
> know if the GPL will allow patent restrictions of that kind.  I don't know
> how they got RCU in the Linux kernel in the first place like they did.

Good question. Does Linux really infringe on any active RCU patents? Linux 
uses multiple methods to detect quiescent states, I wonder if there is 
patent that describes Linux quiescent state detection algorithm.

.