SO_KEEPALIVE on existing java application

Question

I need to activate SO_KEEPALIVE on an existing commercial java application because my firewall drops the connections after some inactivity. I do not own the source code so i can't change it (it would be rather easy when i had the source, just adding socket.setKeepAlive(true) ). So i was looking for some alternatives:

• first i tried to work with libkeepalive.so ( http://libkeepalive.sourceforge.net/ ), putting this in de LD_PRELOAD seems to work for things like telnet & nc, but when i use it with my jrockit jvm, this LD_PRELOAD is totally ignored and every socket object is still being created without SO_KEEPALIVE

• then i tried to search on the OS level if there was an option to activate this SO_KEEPALIVE per default for all TCP connections: unfortunately on redhat 6 enterprise there isn't such an option, although i found one for freebsd (net.inet.tcp.always_keepalive)

• patching the linux kernel for adding this feature was a big no for my sysadmin ;)

• searching for any java command line argument was unsuccessful

• so last option: patching the existing JVM's java.net.PlainSocketImpl by adding setOption(SocketOptions.SO_KEEPALIVE, Boolean.valueOf(true)); in the protected synchronized void create(boolean stream) method and putting it before rt.jar via -Xbootclasspath/p

This last option works so far, but i'am a bit frustrated because i had to change a JVM for this! Anyone knows other / better ways to deal with such a problem? Why isn't there another simple way to activate SO_KEEPALIVE per default on all (java) applications?

Last question: why doesn't the java API let you set the keepAlive on serverSockets objects? It's only possible on Socket objects but in fact it also works on serverSockets

Answer 1

I run over the same problem and wondered why libkeepalive does not work. After some investigation I found, that libkeepalive has some 'limitations' (maybe somebody would call them bugs). Because of the strange license (it comes with GPL), I decided to start over. The result is the libdontdie. You can find a small Java test program there that works with (at least) openjdk7.