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Select on channels (again)
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Date: -- (:)
From: Nathaniel Gray <n8gray@g...>
Subject: Re: [Caml-list] Re: Select on channels (again)
On 8/22/06, Olivier Andrieu <oandrieu@nerim.net> wrote:
>  Nathaniel Gray [Monday 21 August 2006] :
>  >
>  > On 8/21/06, Jonathan Roewen <jonathan.roewen@gmail.com> wrote:
>  > > Why can't you just use the unix file opening functions since you're
>  > > using unix select? And if you need the ocaml in/out channels, convert
>  > > the unix file descriptors to ocaml ones instead of the other way
>  > > around. Seems simple enough to me.
>  >
>  > It sounds simple but doesn't work.  If select tells you a file
>  > descriptor doesn't have data waiting you can't be sure there isn't
>  > still data in the corresponding channel's buffer.  See the thread that
>  > I referenced for a good discussion of why this is annoying.  For one
>  > thing, it makes it impossible to use Marshal.from_channel without
>  > potentially blocking.
>
> Indeed, Marshal.from_channel would block, but it's not the only way to
> read a marshalled value: cf. Marshal.header_size and
> Marshal.data_size.
>
> With these, you can read your marshalled value from file_descr into a
> buffer in a non-blocking, select-compatible way and then use
> Marshal.from_string.

Yes, as I said, it's possible to work around this limitation by
creating yet another implementation of buffered I/O.  My point is that
there's already a good buffered I/O implementation in ocaml that could
suit many (but not all) needs -- channels.  Adding channel_select
would make channels a lot more useful at very little expense.  Heck, I
would be satisfied with in/out_channel_is_ready, which would be even
easier!

Cheers,
-n8

-- 
>>>-- Nathaniel Gray -- Caltech Computer Science ------>
>>>-- Mojave Project -- http://mojave.cs.caltech.edu -->