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Date: 5 Aug 91 14:14:36 GMT
From: stanford.edu!msi.umn.edu!sctc.com!stachour@uunet.uu.net  (Paul Stachour)
Subject: Re: Ada and Unix--Blocked Tasks
Message-ID: <1991Aug5.141436.13559@sctc.com>
List-Id: <comp.lang.ada>

>I think it's important for designers & programmers of ANY language to remember
>what capabilities are controlled by language constructs, and either 
>(a) confine the solution to the "domain" of the language capability, or 
>(b) realize what portions of the solution are affected by "external controls"
>(relative to the language and it's run-time specific support) and act
>(implement) accordingly.

>Paul's questions are logical ones when trying to DETERMINE the domain of the
>implementation "problem", but we as software engineers should attempt to be as
>knowledgeable as possible regarding BOTH the language and the environment so
>that lengthy problem research/determination is avoided.

Thanks, Ray.  Indeed that was part of my question:

    What functions/features can we expect in an language, and
    what functions/features are deterimined by the environment,
       and not the language?

    Now, signals are part of unix, so I should expect that if
I write a an Ada program that uses signals that it will not be
portatable to another operating system, say VMS, or if I use
a VMS feature, it will not be portable to MS-DOS or unix or ...

    But tasking IS a part of Ada.  I should be able to expect
that any environment that that supports Ada, should be able to
support tasks.  Furthermore, that if I do ANYTHING in that task
(including a call on an OS-specific function) that could block,
that my task might block.  But I should be able to expect that
the other tasks DO NOT BLOCK just because the OS decides to block
one of the tasks.

    I would maintain that the designer/implementor of the Ada
compiler/run-time combination blew it; they got tasks "wrong".
I would maintain that the only time that they are allowed to
take the one-block-blocks-all behaviour is ONLY if they have
provided a copiler-option for that particular feature.  The general
form of the option is called "Not full language, feature xxxx",
and means:

    I, as the designer and builder of this program, declare to you,
to compilation system, that I do not plan to take advantage of
feature "xxxxx" in my programs.  If you, the compilation system,
can thus give me a more efficient program, I hereby request you
to do so.

    In the absense of such an option, it is my opinion that the
implmetor of the Ada compilation/run-time did it "wrong".  The
fact that it was done this was to get "reasonable efficiency"
on a particular operation system is no excuse.  ..Paul

-- 
Paul Stachour          SCTC, 1210 W. County Rd E, Suite 100           
stachour@sctc.com          Arden Hills, MN  55112-3739
                             [1]-(612) 482-7467