[TUHS] man-page style

[Bakul Shah]

On Dec 4, 2018, at 1:34 PM, Larry McVoy <lm at mcvoy.com> wrote:
> 
> On Wed, Dec 05, 2018 at 08:26:29AM +1100, Dave Horsfall wrote:
>> On Sun, 2 Dec 2018, Larry McVoy wrote:
>> 
>>>>> And anyone who has not edited sendmail.cf (shudder!) is not a
>>>>> programmer.
>>> 
>>> As a systems guy I think if you have not written, or understood, swtch(),
>>> you are not a systems guy.
>> 
>> Ahh, line 2238...
> 
> I dunno what line it is, I'm guessing that's the # for the Lions book?
> 
> I learned swtch() because I wrote a userland thread library for Udi Manber
> as a grad student (yield based as I recall).  I'd never really thought
> about it hard, yeah, did all the CS toy OS stuff but I don't think they
> made us write that.  I loved writing it, I did a super minimal one that
> had the bulk of the work in C, just did the save/restore in asm.

I too built a coroutine library. We used it for simulating
some real h/w we were building. The nice thing about h/w
simulation is no recursion so your threads can work with as
little as 50-100 bytes of stack, so even on a 64MB machine 100K
threads was not a problem! There is no yield() here being a
simulation core. Thread switch occurs in wait(), signal() &
busy(n) -- the last one to simulate passage of time. I built
the very initial version in 1982-83 using setjmp/longjmp! We
used it to check if our 5.6Mhz bus could support ethernet
traffic while doing other things.

Of course, this is much simpler than a unix swtch().