Re: Tasking performance between Ada83 and Ada95

[fjh@mundook.cs.mu.OZ.AU (Fergus Henderson)]

kilgallen@eisner.decus.org (Larry Kilgallen) writes:

>Geert Bosch <geert@gonzo.sun3.iaf.nl> writes:
>
>> IMO the best solution would be to start X system level threads and
>> implement a user-level threads package on top of it.
>
>That is the method used by Alpha VMS.  The kernel thread primitives
>in fact are not documented for public consumption.  The documented
>interface is the DECthreads library (which has a couple different
>APIs matching varying styles and standards).  DECthreads creates the
>user-mode lightweight threads which then get scheduled onto some
>number of kernel threads (typically numbering on the order of the
>number of CPUs).

What happens with blocking I/O?  Does DECthreads implement blocking
I/O operations using asynchronous kernel I/O operations, so that it 
will avoid blocking a whole kernel thread when all that really needs
to be blocked is a user thread?

If not, then choosing the right number of kernel threads may be a bit
tricky -- you want one for each CPU, to get multiprocessing, but
you also need one for every user-level thread that might get blocked
on I/O, so that you background compute threads don't get paused
when your foreground threads are doing blocking I/O.

--
Fergus Henderson <fjh@cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
PGP: finger fjh@128.250.37.3         |     -- the last words of T. S. Garp.