[Info-vax] KP threads

[Arne Vajhøj]

On 12/23/2021 3:13 PM, John Dallman wrote:
> In article <61c49505$0$702$14726298 at news.sunsite.dk>, arne at vajhoej.dk
> (Arne Vajhøj) wrote:
>> They have been mentioned a few times, so I decided to take a look.
>>
>> And I am puzzled.
>>
>> Normally (pthreads, Win32, Boost/C++11, Java, .NET etc.) threads are
>> about starting a bunch of independent threads that does some work
>> in parallel.
> 
> It looks to me, from a bit of PDF-searching, as if the VMS idiom for that
> kind of threading is Kernel Threads, described in section 2.8 of VSI's
> Programming Concepts manual.

I have used pthreads before. Portable and standard paradigm. But I was
curious about what KP threads was all about.

>> But when I look at EXE$KP_START, EXE$KP_STALL_GENERAL,
>> EXE$KP_RESTART and EXE$KP_END then I do not see such capability.
>>
>> Instead it is easy to see how to do coroutines with two streams
>> of execution but only one executing at a time transferring control
>> forth and back between the two streams (pretty similar to Modula-2
>> ISO COROUTINES TRANSFER).
> 
> I agree. The KP_ routines seem, looking at the explanation in Appendix C
> of "Porting Applications from Alpha to IA64," to have been created to let
> applications' internal coroutine systems work on IA-64. The hardware
> stack implementation on that architecture is a lot more complicated than
> VAX, or Alpha, or x86-64. It's fairly transparent if you use the stack
> simplistically, but it isn't really designed for DIY coroutines, or other
> clever trickery.

OK.

Arne