nonblocking connect and threads

I see that nonblocking connects are implemented using nonblocking I/O. I wonder if I should use threads instead, I'm not sure how portable threads are, are most implementations similar to Pthreads? I'm thinking of letting the timeout for hostconnect specify time- out for both resolving and connecting, I need to use threads then I think. If I go for threads, would I also need to implement nonblocking connect for systems without thread support? Any input welcome, Stig