Reducing TCP/IP connection timeouts

P_Shep · 09-15-2004, 04:47 AM

Hi there.

I'm looking for a way of reducing the time taken to move on after attempting to connect to a non-existant server.

I've had a couple of thoughts:
Test for server first
Reduce the timeout time
reduced the number of re-tries
multi-thread the app

The latter of which i'd prefer not to do since it'll probably require the most re-programming.

I'm using RH 7.0 and programming in C (whatever GCC version it on there!)

Can anyone point me in the direction of info on how to do the former three?

TIA.

itsme86 · 09-15-2004, 10:31 AM

Your best bet is to make your connection socket non-blocking. Then you can use select() to create whatever timeout you'd like.

Check out the man page for fcntl().

P_Shep · 09-20-2004, 09:52 AM

Cheers

P_Shep · 09-27-2004, 09:13 AM

OK done that
create socket
turn socket into non-blocking
add socket to FDSET
connect
Select
if FDSET complete connect

Question is now, how do I test to see if the connection is still being attempted?
If i wait say 10s and no connection is completed in that time, I'll try and re-connect, but i'm pretty sure taht would cause problems, no?

TIA

itsme86 · 09-27-2004, 09:40 AM

This is from 'man connect':

Quote:

EINPROGRESS
The socket is non-blocking and the connection can-
not be completed immediately. It is possible to
select(2) or poll(2) for completion by selecting
the socket for writing. After select indicates
writability, use getsockopt(2) to read the SO_ERROR
option at level SOL_SOCKET to determine whether
connect completed successfully (SO_ERROR is zero)
or unsuccessfully (SO_ERROR is one of the usual
error codes listed here, explaining the reason for
the failure).

Is that helpful?

P_Shep · 09-27-2004, 09:46 AM

Can you make it a bit more obvious?

Doh! Brain not working properly.

Cheers again.

itsme86 · 09-27-2004, 09:47 AM

Here's a tiny section of code that I wrote once for an email plugin that does what you're trying to do:

Code:

  for(e = pending_email_list;e;e = enext)
  {
    enext = e->next;

    if(!FD_ISSET(e->socket, &writeset))
      continue;

    getsockopt(e->socket, SOL_SOCKET, SO_ERROR, (void *)&err, &len);
    if(err)    /* connect() failed */
    {
      while((rv = try_next_server(e)) == 0);   /* Whole loop */
      if(rv == -1)
      {
        notifyf(e->player, "I couldn't send email to %s.",
          (e->victim)?name(e->victim):e->send_to);
        del_email_send(e);
      }
      continue;
    }

    blocking_flags = fcntl(e->socket, F_GETFL);
    blocking_flags &= ~O_NONBLOCK;
    fcntl(e->socket, F_SETFL, blocking_flags);
    send_email(e);
    del_email_send(e);
  }