The Posix AIO calls that john implememted are the best way of doing this.
On Thu, 9 Sep 1999, Luigi Rizzo wrote:
> Hi,
>
> please redirect to the appropriate forum if appropriate.
>
> There is one thing i don't completely understand with non-blocking
> FS operation.
>
> Is there any way to guarantee (more or less strictly, see below)
> that when i issue a read() on a file (a real file coming from a
> UFS i mean) such read will not block because data from the disk is
> not in memory yet, yet avoid that i end up in a busy loop.
>
> The app i have in mind is squid-like, which, if i understand well, is a
> single process looping around a select. If i get things right, select()
> on a file descriptor will return the read bit set if i am not at the
> end of file, yet the block might not be in memory yet even if the UFS
> seems to do readahead. Maybe i can turn NONBLOCK on for these
> descriptors, but still would have select returning essentially useless
> info as I'd need to try the read() to be sure...
>
> Maybe poll() has some way to indicate "yes you can read and the page is
> in memory" ? I can tolerate some occasional failures when because of
> memory shortage the readahead page is discarded after the select/poll
> in favour of some other one...
>
> Any suggestion ? Would async I/O help in a case like this, considering
> the possible overhead for handling signals when a transfer is
> complete ?
>
> thanks
> luigi
> -----------------------------------+-------------------------------------
> Luigi RIZZO, [EMAIL PROTECTED] . Dip. di Ing. dell'Informazione
> http://www.iet.unipi.it/~luigi/ . Universita` di Pisa
> TEL/FAX: +39-050-568.533/522 . via Diotisalvi 2, 56126 PISA (Italy)
>
> http://www.iet.unipi.it/~luigi/ngc99/
> ==== First International Workshop on Networked Group Communication ====
> -----------------------------------+-------------------------------------
>
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