We have run in-to following issue in our software:
We have 3 servers running mongodb in replicaset configuration. One servers runs our application and is loaded by testing software at rate of 50 requests pes second. Then we configure iptables on server running primary monga node to drop all packets from and to other servers. By this we emulate network probems which may occur.
In some small period of time (I think 20 seconds) secondary nodes understand, that link is broken and elect new primary. Server works fine. But not our application. C++ driver uses default network timeout for connection which on our system is 15 minutes. When netwok fails our application still tries to make queries and all available threas hang inside C++ driver waiting for network response. For next 15 minutes our service does not respond because all threads in thread pool are used out.
What we need is to set timeout for about 15 seconds instead of 15 minutes.

Attached patch adds ability to specify timeout to replica set. This patch breaks ABI, but API is backward compatible.