Re: "write()" semantics

On 06/13/2011 02:51 PM, Don Y wrote:
Hi,

[I have nothing at all like a POSIX API! :> ]

My "write()" semantics essentially say, "Once invoked,
you forfeit the contents of 'buffer[]' -- even in asynchronous
mode."

This makes it a lot easier for my OS to move data around
as *it* sees fit. And, imposes minimal constraints on the
caller.

In "write()"'s case, it just means you *use* the buffer[]
contents, if necessary, *before* "write()"-ing them!

But, this means I can't take advantage of true parallelism
and/or I/O device scheduling delays. E.g., I can't start
an async write, get things enqueued for processing, and
*then* do a few last minute things with buffer[].

There is some cost to adding this support -- though I think
I already have most of the mechanisms necessary to do so in place.

So, the question is, how do *you* use write() and the data it
is called upon to process? E.g., if the de rigeur form is:

while (ALWAYS) {
...
fill(buffer);
...
write(buffer, device, mode);
}

then you *don't* need this proposed functionality.

Well, if I read your semantics correctly and unwind that loop, I get

fill(buffer) // with stuff to write it
....
write(buffer, device, mode); // write it
....
fill(buffer) // Aw crap!!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
.

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