select() timeout of 3s even on ICMP port unreachable

When I try to connect to a server with a non blocking socket (so that i can use select() with a timeout parameter) i realized that on a connect to a port which is blocked by iptables with -j REJECT the select() waits up to the timeout parameter but at a maximum of 3s.. it doesn't matter that the ICMP port unreachable packet is really quick.

fcntl(sockfd, F_SETFL, O_NONBLOCK);
connect(sockfd,(struct sockaddr *) &开发者_如何学运维amp;serv_addr,sizeof(serv_addr));
if (select(sockfd + 1, NULL, &fdset, NULL, NULL) == 1) {...}

In the above example the select() blocks until 3s if the connect goes to localhost:1234 and the port is blocked like described above.

Does anyone know why this timeout of 3s to get a "connection refused"? How could I tweak it (because I got an ICMP port unreachable after 0.02ms)?

The socket will only become "writable" if connect succeeds. If you also want select to return on failure, you should also check for "error/exceptional" condition on the socket, i.e. pass the set as the third fd_set * argument to select too.