Re: TCP connect in Non Blocking Mode

On Apr 30, 1:00 pm, David Schwartz <dav...@xxxxxxxxxxxxx> wrote:
On Apr 29, 1:38 pm, Alan McKenney <alan_mckenn...@xxxxxxxxx> wrote:

This leaves unanswered the question: why does checking
only for writeability (assuming that the OP did this
-- the code is a bit sketchy) not work for the OP?

The OP had a bug in his code. If you look at his post closely, he
points out that he fixed the bug, and now his code works.

I'm pushing this point because I want to do more
or less the same thing the OP is trying to do.
Right now, the code I have (more or less copied
from its predecessor) doesn't do select() at all.
It just does connect() and sleep(1) in a loop
until connect() returns success or failure of
the connection. Since the old code uses select()
everywhere else, I can't help wondering if there
is a reason it doesn't use it here.

Probably cargo cult programming.

I would like to improve the code by using
something like select(), but the Solaris "man"
pages are not clear as to what Sun thinks
are read/write/exception events, especially
with sockets.

I have code that uses 'poll' to wait for asynchronous connections to
complete. It usually uses more sophisticated I/O mechanisms on
Solaris, but we test with those both enabled and disabled, and we've
never had a problem. We only check writability for pending
asynchronous connections.

For what it's worth, Stevens (_Unix_Network_Programming_,
vol. 1) recommends checking for both readability and
writability; he seems to be considered An
Authority, so I'm assuming this is based on
experience with a wide variety of implementations.

That is how cargo cult programming spreads. You see someone else do
it, don't understand why, and so you do it too. (This is not to say
that Stevens is wrong.)

DS

Setting the select for check for readability of sock descriptor didn't
help in my case. I now check for getsockopt(SO_ERROR) to determine the
status as shown below:

//
if(getsockopt(sd, SOL_SOCKET, SO_ERROR, (int*)&l_sock_optval,
(socklen_t*)&l_sock_optval_len) !=0)
{
return 0;
}

if(l_sock_optval == 0)
{
//connection sucess
break;
}
else if(l_sock_optval == ECONNREFUSED)
{
//connection refused. This condition comes true on
receiving RST from server.
return 0;
}

Thanks,
Prabhu. S
.

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