Re: Concurrency in Gnat 3.05?

[cosc19z5@Bayou.UH.EDU (Spasmo)]

Michael Feldman (mfeldman@seas.gwu.edu) wrote:
: In article <4sjqte$3mu@masala.cc.uh.edu>, Spasmo <cosc19z5@Bayou.UH.EDU> wrote:
: >Hey all.
: >
: >Is Gnat 3.05 (for DOS) truly concurrent when executing tasks?  I'm
: >asking because I've written some tasking code (finally got it
: >to link) and when I ran the code, the tasks didn't run
: >concurrently at all.  I'm running in a Win95 DOS box.  One task
: >runs to completion before the other task starts up.  I've also
: >tried some sample code including Feldman's Twotasks program
: >and they exhibit the same behavior.  Is there a way to get
: >tasks to run concurrently, or would I have to look for a
: >GNAT that's native to something like WinNT/95 that can
: >handle multi-tasking?

: Hmmm - since you have access to my Two_Tasks program, you oughta try
: Two_Cooperating_Tasks in the same distribution (or book) in which
: DELAY is used to cause the tasks to cooperatively swap control.

Well I've more or less got a grip on things and am implementing
my own scheduling as folks suggested which is actually a blessing
in disguise IMHO, but I'd love to see your Two_Cooperating_Tasks
program indeed.  I've got a subdirectory chock full of your stuff
so I'll look for it imemdiately.


: The term "multitasking" seems to be one of the least well understood
: by the most people, especially in the Ada context.

While I do understand multitasking I'm as guilty as they get for
misusing that term in the most gruesome of ways.


: _Preemptive_ multitasking is NOT required in the Ada 95 core language,
: nor is time-slicing. 

At this point I know :).  I just saw tasks and immediately a synapse
fired and said "pre-emptive multi-tasking".  I suppose the reason
I assumed time slicing was because I had assumed that tasking was
similar to the fork() system call in UNIX C.  My mistake indeed!



: Further, "truly" concurrent is possible only if you have
: multiple processors. A typical single processor can execute only one 
: instruction at a time (maybe with some I/O overlap), so "true" concurrency
: is simply not possible. _All_ concurrency on a single processor is
: "logical" (sometimes called pseudo-) concurrency.

Well "truly" is another gruesome error on my behalf.  Why I even
said "truly" I will never know, especially since I should know
better.


: Your question then can be re-phrased as,

: "Will the OS, or the runtime system, manage my logical concurrency
: automatically, or is it up to me to write cooperative tasks?" In Ada, 
: the answer is "sometimes." :-)

Perfect!  Hey maybe next time I'll just send you a poorly worded
post and you can write it up for me :)


: Mike Feldman

--
Spasmo
"Here's a present just for you
When you open it, you'll be through"
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