Hallo all,
I wrote a little test program to do some poll() benchmarks.
I changed the host address to localhost and observed that
connect() always returns EINPROGRESS when used with non-blocking
sockets.
>From the man page:
EINPROGRESS
The socket is non-blocking and the connection cannot be completed
immediately. It is possible to select(2) or poll(2) for completion by
selecting the socket for writing.
So my question is:
What is meant by 'cannot be completed immediately' ?
I thought that connections to localhost would complete
without any delay when the application listens ?
thanks for your answers,
Patrick
Patrick Mau <[email protected]> writes:
> I wrote a little test program to do some poll() benchmarks.
> I changed the host address to localhost and observed that
> connect() always returns EINPROGRESS when used with non-blocking
> sockets.
>
> >From the man page:
>
> EINPROGRESS
> The socket is non-blocking and the connection cannot be completed
> immediately. It is possible to select(2) or poll(2) for completion by
> selecting the socket for writing.
>
> So my question is:
>
> What is meant by 'cannot be completed immediately' ?
> I thought that connections to localhost would complete
> without any delay when the application listens ?
Probably the accept()ing process hasn't been scheduled yet.
EINPROGRESS is a perfectly reasonable response in such a case.
-Doug
--
Let us cross over the river, and rest under the shade of the trees.
--T. J. Jackson, 1863
> Patrick Mau <[email protected]> writes:
>
> > I wrote a little test program to do some poll() benchmarks.
> > I changed the host address to localhost and observed that
> > connect() always returns EINPROGRESS when used with non-blocking
> > sockets.
> >
> > >From the man page:
> >
> > EINPROGRESS
> > The socket is non-blocking and the connection cannot be completed
> > immediately. It is possible to select(2) or poll(2) for completion by
> > selecting the socket for writing.
> >
> > So my question is:
> >
> > What is meant by 'cannot be completed immediately' ?
> > I thought that connections to localhost would complete
> > without any delay when the application listens ?
>
> Probably the accept()ing process hasn't been scheduled yet.
> EINPROGRESS is a perfectly reasonable response in such a case.
You have to be prepared to handle both immediate and delayed
connection, especially if you want to be portable. (Solaris behaves
a bit differently than Linux in this regard.) See
http://www.kegel.com/dkftpbench/dkftpbench-0.37/ftp_client_pipe.cc
for an example of how to handle nonblocking connects more or less portably.
(You have to wade through quite a bit of code, tabstops 4, to find
all the connect-handling stuff -- sorry.)
- Dan
On Sun, Oct 21, 2001 at 04:18:10PM -0700, Dan Kegel wrote:
> > Patrick Mau <[email protected]> writes:
> >
[Snip]
> You have to be prepared to handle both immediate and delayed
> connection, especially if you want to be portable. (Solaris behaves
> a bit differently than Linux in this regard.) See
> http://www.kegel.com/dkftpbench/dkftpbench-0.37/ftp_client_pipe.cc
> for an example of how to handle nonblocking connects more or less portably.
> (You have to wade through quite a bit of code, tabstops 4, to find
> all the connect-handling stuff -- sorry.)
> - Dan
Hallo Dan,
thnaks for the pointer and your remarks, but I really
wondered if linux _never_ immediatly accept()'s connections.
I never saw a connect() call returning 0 (connected) on a
non-blocking socket. Always EINPROGRESS. I guess I have to
look at the kernel to see scheduling effects ...
thanks,
Patrick