Scope system threads (was Re: PS_BLOCKED)

[Robert Watson]

On Thu, 10 Apr 2003, Craig Rodrigues wrote:

> FreeBSD lacks POSIX real-time signals, which was very troublesome when I
> was trying to get the ACE Proactor to work properly, because the
> Proactor uses POSIX AIO + POSIX RT signals.  I would really like to see
> POSIX RT signals on FreeBSD. 

There was some earlier work done by Juli Mallett to introduce reliable
signals, which supported some of the elements of the POSIX realtime signal
requirements.  However, there were a fair number of implementation details
that hadn't been addressed at that point that really needed to be
addressed before the changes could be merged (largely related to
reliability and stability concerns).  I'd be interested in seeing that
work brought back to life, perhaps on a Perforce branch.  One of the
concerns with the reliable signalling bits was that it required more
kernel memory allocation, often while holding locks -- I suspect things
can be reworked to avoid that burden without too much difficulty.
Interestingly, it looked like on some other operating systems the
introduction of reliable signaling actually resulted in the potential loss
of signals in low memory scenarios :-).

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert at fledge.watson.org      Network Associates Laboratories