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Date: 5 Aug 91 14:04:00 EST
From: "EDWARD CRAGG" <ecragg@gmuvax.gmu.edu>
Subject: Re: Ada and Unix--Blocked Tasks
Message-ID: <9108051811.AA04163@ajpo.sei.cmu.edu>
List-Id: <comp.lang.ada>

> 
> From:cis.ohio-state.edu!zaphod.mps.ohio-state.edu!sdd.hp.com!spool.mu.edu!cs.
umn.edu!sctc.com!stachour@ucbvax.Berkeley.EDU
> (Paul Stachour) 
> Subject: Re: Ada and Unix--Blocked Tasks
> Message-ID: <1991Aug2.181729.28061@sctc.com>
>
     [stuff deleted]
> 
>    The methods indicated here seem kind-of wierd to me.  After all,
> an Ada task is SUPPOSED to be an independent thread-of-control.
> And when I do something in Ada, I expect the run-time to arange to leave
> my other tasks alone, and only block the one needing the service.
> 
     [stuff deleted]
> 
>    Which leads us to the basic question:
> 
>      If the Ada system you are using can't do tasking "correctly"
> (i.e., in a non-blocking way) in its implementation, what is in
> error?
> 
>    Is it the OS (unix in this case)?
>    Your Ada compiler vendor (Don't know who)?
>    Your Ada run-time vendor?
>    Or something else?
> 
>    Yours, ...Paul
> 

    Paul,
          The factor which you are leaving out of your analysis is 
that Ada was designed for Embedded Systems using specialized 
computers (the ones I am most familiar with are the Navy's UYK-43 and 
UYK-44).  On these systems Ada tasking works "correctly" and is 
reasonably portable between systems.  The reason this that the Ada 
run-time *IS* the machine's OS.  (That incidently is one of the 
reasons that the ALS/N seems so expensive, in addition to developing
an Ada compiler, etc,  They also must develop two fourth generation
operating systems which will run on second generation architectures :-( 
On all other systems with which I am familiar you end up in a finger 
pointing exercise between the OS and the Ada Runtime and the blame 
gets spread around.

ed

 ............................................................
Edward E Cragg                Bitnet:   ECRAGG@GMUVAX
                              Internet: ECRAGG@GMUVAX.GMU.EDU