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Subject: Re: readv/writev
From: Robert Collins <rbcollins AT cygwin DOT com>
To: Conrad Scott <Conrad DOT Scott AT dsl DOT pipex DOT com>
Cc: cygwin-developers AT cygwin DOT com
In-Reply-To: <025401c24a0d$1c996380$6132bc3e@BABEL>
References: 
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	<025401c24a0d$1c996380$6132bc3e AT BABEL>
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Date: 23 Aug 2002 09:48:06 +1000
Message-Id: <1030060087.8462.14.camel@lifelesswks>
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On Fri, 2002-08-23 at 04:52, Conrad Scott wrote:
> There's no comparison possible right now since the existing code
...

K.
=20
> I've looked at putting in readv/writev directly for disk files
> etc. (pipes and raw devices would benefit as well) but a general
> solution doesn't fit very well w/ the current structure of the
> fhandler classes: for example, the text-mode vs binary-mode code
> and something else I can't quite remember just now :-)

Yah. One thing I've been pondering for a while - strip out all the
text/binary translation for non FILE calls. I have done *any* research
to see if there are text-dependent apps using fd based IO, but there
probably are :p.

> I'd have thought that overlapped was the reverse of the Posix
> select/poll model.  That is, in NT you issue your IO operation and
> got told when it has completed, which allows for zero-copy IO and
> for queues of operations (shades of VMS indeed);=20

Overlapped refers to capability for Win32 to have 'overlapping' IO's
outstanding, not to a specific notification mechanism. The
ReadFile/WSARecv interfaces support 3 interfaces I'm aware of:
un-notified (select)
notified via an event object (poll)
notified via a completion port.

> while the
> select/poll model is the opposite: you get told when a read/write
> would succeed if you were to do it.  You can't, w/ select/poll,
> issue a nonblocking IO operation and be told when it has completed
> (except for the strange cases of accept and connect).  And it's
> not clear to me how to bridge that gap.

USe WSAAsyncSelect and register for FD_WRITE and FD_READ. These get sent
when a socket is ready for writing/reading. We then keep a table of the
sockets we own, and update their state when we recieve the messages.

Select and poll then become trivial querys into our state table.

(If I misunderstood, and you wanted to emulate overlapped with
select/poll - sorry :]).

Rob

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