Re: Improved implementation of *env(3) functions in "libc"

[Andrew Doran <ad%homeworld.netbsd.org@localhost>]

On Thu, Nov 18, 2010 at 11:07:51AM -0500, Steven Bellovin wrote:
> 
> On Nov 18, 2010, at 10:47 37AM, Andrew Doran wrote:
> 
> > My concern with using a tree is that it makes a concurrent getenv() very
> > hard to implement, and threaded programs like to make use of getenv().
> > 
> > Reader-writer locks don't scale on multi-core systems, and applications
> > like this one (getenv) may give you single threaded or worse behaviour.
> > 
> > 
> I don't think this is a serious issue for getenv().  Most applications make
> very little use of it; when they do, it's generally at initialization time.
> Nor, I suspect, is single-threading a huge concern, since the lock will be
> held for a very short time.

Unfortunately it's not about hold time, but cache writebacks to main memory
causing effective single threading.