Fine-grained locking for POSIX local sockets (UNIX domain sockets)

[Paul Allen]

>From Andrew Gallatin <gallatin at cs.duke.edu>, Fri, May 12, 2006 at 04:41:11PM -0400:
> In addition to this linux vsyscall, there is the MacOSX/Darwin
> commpage.  The map machine-specific implementations of atomic
> operations, bcopy, bzero, spinlocks, pthread_getspecific, etc into a
> common page mapped into userspace applications. The also do a (mostly)
> syscall-free gettimeoday this way.
> 
> See http://fxr.watson.org/fxr/source/osfmk/ppc/commpage/?v=xnu-792
> 
> Obviously, we could not take the code due to APSL infection (unless
> Apple were to donate it), but it is something else to look at.

I've often wondered why they release their code under such a verbose 
license.  What do they substantively gain relative to the BSD license?

Given Jordan Hubbard's position there why does the interaction between 
FreeBSD and Apple seem to be such an arms length affair?

                         Paul