Re: Language runtime requirements (was Re: DoD

[cis.ohio-state.edu!math.ohio-state.edu!cs.utexas.edu!utah-morgan!hellgate .utah.edu!peruvian.cs.utah.edu!matwood@ucbvax.Berkeley.EDU (Mark Atwood)]

In article <1993Aug12.224346.20541@scf.loral.com> bashford@srs.loral.com (Dave 
Bashford) writes:
>In article ... falis@ajpo.sei.cmu.edu (Edward Falis) writes:
>>...  For OS' that don't
>>provide lightweight processes, we generally map all tasks into a single
>>process.  ...
>
>So, why the problem with Unix ?  I've heard excuses like "it would be too
>inefficient."  But Unix/C has been using multi-tasking well for years.
>Besides, I'd take inefficient over useless any day.

I've used Alsys Ada on HPUX at work, and used a preemptive cthreads
on BSD at school for an OS class.  The problem I see with mapping Ada
tasks on UNIX processes is that UNIX processes are too independent.
Once a process starts, it doesn't share memory and doesn't have any
sync points with the parent that forked it until it exits.  Admittadly
it COULD be done using pipes and/or OS supplied shared memory or sync
resources, but it would be a major design pain.

Threads are a model of multiple tasks that are closely related.
Processes are a model of multiple virtual processors.

You could use one of the several Ada socket or distributed processing
packages to build a multi-process Ada system, but I don't think
tasks map to processes very well




-- 
Mark Atwood                  | My school and employer have too many problems
matwood@peruvian.cs.utah.edu | without being blamed for mine.