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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Palatable Windows IO using Ada
Newsgroups: comp.lang.ada
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Date: Fri, 7 Apr 2006 20:51:01 +0200
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Date: 2006-04-07T20:50:59+02:00
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On 7 Apr 2006 09:30:23 -0700, Le wrote:

> Your attempt at a tutorial is in error in a couple of places. Stating
> that an application "should know" what will be returned is
> presumptuous. Note this is a legacy application, so obviously there are
> some devices out there which give varying responses. These are raw byte
> sequences - no blocks or lines.

If you mean a byte stream, then it is *byte* you (or application) should
know of. You cannot read any device not knowing the size of input. You
might have a higher level communication protocol which build something out
of these bytes, for example, "a valid Ada program encoded in ASCII." But
how an OS driver might know about it?

> The ReadFile interface *is* blocking.  Overlap allows an app to come
> back and see if it is done.

Then it is rather a strange definition of "blocking." In my world blocking
operation means that the execution thread gets blocked until its completes.
The thread cannot go anywhere it that state.

> With respect to buffering, my point was that doing byte at a time IO to
> get around the blocking nature of the API defeats the efficiencies
> presumably provided by the driver's internal buffering.

How so? Byte-wise reading just does not do any extra and unnecessary
buffering, because OS already did it. One could argue that OS API are
expensive to call. This a different issue. I don"t have any figures
concerning Windows, but in my experience that was never a problem. At least
when reading from sockets and serial devices.

As for overlapping ReadFile, your argument does not apply either, because
it gets *all available* bytes the buffer provided in its argument can take.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de