aio_connect ?

[Christopher M. Sedore]

> From: Igor Sysoev [mailto:is at rambler-co.ru] 
> Subject: RE: aio_connect ?
> 
> On Wed, 20 Oct 2004, Christopher M. Sedore wrote:
> 
> > > While the developing my server nginx, I found the POSIX aio_*
> > > operations
> > > uncomfortable. I do not mean a different programming style, I mean
> > > the aio_read() and aio_write() drawbacks - they have no 
> scatter-gather
> > > capabilities (aio_readv/aio_writev) and they require too many
> > > syscalls.
> > > E.g, the reading requires
> > > *) 3 syscalls for ready data: aio_read(), aio_error(), 
> aio_return()
> > > *) 5 syscalls for non-ready data: aio_read(), aio_error(),
> > >    waiting for notification, then aio_error(), aio_return(),
> > >    or if timeout occuired - aio_cancel(), aio_error().
> >
> > This is why I added aio_waitcomplete().  It reduces both 
> cases to two
> > syscalls.
> 
> As I understand aio_waitcomplete() returns aiocb of any complete AIO
> operation but I need to know the state of the exact AIO, 
> namely the last
> aio_read().

Correct, it won't poll, but what state can you get from calling
aio_error() that you don't already know from aio_waitcomplete().  The
operation has either completed (successfully or unsuccessfully) or it
hasn't.  If it hasn't you haven't "gotten it back" via aio_waitcomplete,
and if it has, you did.  I may be missing something, but how does
aio_error() tell you something that you don't already know?

> I use kqueue to get AIO notifications. If AIO operation would fail
> at the start, will kqueue return notificaiton about this operation ?

I don't think so--IIRC, if you have a parameter problem or the operation
can't be queued, you'll get an error return from aio_read and no kqueue
result. If it is queued, you'll get a kqueue notification.

-Chris