Linux socket released too slowly when program killed

Question

EDIT: tl;dr:

Don't open sockets with the wrong options, it's unlikely to work!

Original Question:

I'm working with a program which doesn't have a clean shutdown mechanism, it just relies on being killed to terminate it.

It opens a socket as follows:

(void) setsockopt(h, SOL_SOCKET, (SO_KEEPALIVE | SO_REUSEADDR), (int *) & optval, sizeof( optval ));

The re-use address option does seem to work, in that eventually the socket is released after the program dies. Eventually being anything from a couple of seconds up to maybe a minute.

This is quite tedious as I need to restart this program regularly. Making the program teminate properly would be a very big job, but I'm wondering if there's anything more local I can do to release the socket earlier?

Answer 1

Socket options are not bits and hence can not be or'ed like SO_KEEPALIVE | SO_REUSEADDR. To be pedantic, SO_KEEPALIVE | SO_REUSEADDR yields another socket option SO_NO_CHECK.

You don't notice this mistake because you don't check the return value of setsockopt. Now you know why ignoring return values is considered bad practice.