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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Standard Ada Preprocessor
Date: Wed, 28 Jan 2004 17:35:00 -0600
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Date: 2004-01-28T17:35:00-06:00
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"Warren W. Gay VE3WWG" <warren@ve3wwg.tk> wrote in message
news:a%ARb.52241$Kg6.386478@news20.bellglobal.com...
> Randy Brukardt wrote:
...
> > What is the point of having that functionality? Any code depending on it
is
> > by definition not portable.
>
> Performance!
>
> Some platforms for instance support asynchronous I/O.
> Some with bugs, others not at all. If you are writing
> servers, that BTW are very performance sensitive, then
> if you can determine that asynch I/O works properly
> (and well) on a given platform, then you're going to
> use it! Anything less is inferior.

Truly high-performance applications are by definition, not portable. The
parts that aren't high-performance might be sharable, but again, this is a
larger granularity than conditional compilation would be good for. Taking
your example, you need to use tasks to make asynch. I/O work. If you don't
have asynch. I/O, you probably don't want the tasks, either (because they
have a substantial overhead in most cases), especially as the I/O may very
well block all of the tasks. So large parts of the code will need to be
different.

...
> > What Claw does for features that aren't available on the current target
is
> > to raise Not_Supported_Error (which hopefully the caller can do
something
> > useful with, such as fall back to something that is supported).
>
> That will really help performance. Let's add some unnecessary
> exceptions!

Different problem. We're trying to get the code to run unmodified on as many
targets as possible. Having it being self-adapting is very valuable in that
aim. (Hopefully, even the binarys can run on most targets unmodified.)

                             Randy.