Re: futex for Mach?

> I am worried about L4, though.

I don't think anything is lost by not worrying about L4 now.  If a
different kind of port is desireable later on whatever kernel, we can do it
later.  If later we want a port similar to Neal's libpthread, we can reuse
some of that code.  

> In other words:  We are adding a new requirement to the underlying kernel,
> instead working with the minimal set of primitives.

No, this is an implementation detail of one of the existing requirements,
which is "libpthread implementation appropriate for the underlying kernel".

The only potentially wasted effort is that of adding futex to Mach and
working on NPTL.  The user-level stuff for using new Mach futex interfaces
per se will be small, and the other stuff that needs to be done with NPTL
and glibc is the tight integration with glibc and revamp of some hurdish
glibc innards that we need eventually to do one way or the other.

As to the kernel work, I think I can do that pretty quickly especially if
we are not worried to begin with about it being especially fast.