nptl refactoring; nacl port

[Petr Salinger]

> There is also lots of code that doesn't really assume Linux, but
> just assumes that there is a futex facility.  As NPTL is fundamentally
> based on the futex facility, I don't think there will ever be an attempt 
> to port it to a system without such a facility.  (NaCl has a futex 
> facility and the Hurd's GNU Mach might grow one someday.)

And FreeBSD kernel have similar capability. It provides basic futes-wake 
and futex-wait operations. By default they operate on long, but later API 
for int have been provided too. There is no FUTEX_CMP_REQUEUE, the 
condition have to be implemented differently.

In fact the NPTL-like implementation already exists and reasonably works.

See subdirectories fbtl/ and fbtl_db/ in
http://anonscm.debian.org/viewvc/glibc-bsd/trunk/glibc-ports/

http://anonscm.debian.org/viewvc/glibc-bsd/trunk/glibc-ports/fbtl/?view=log

Petr Salinger