_[netbsd][unix]connect - connect a socketはバックグラウンド動作する

んですね。 全く知りませんでしたよ。。。

If connect() is interrupted by a signal that is caught while blocked 
waiting to establish a connection, connect() shall fail and set
errno to [EINTR], but the connection request shall not be aborted,
and the connection shall be established asynchronously.
 
If the connection cannot be established immediately and O_NONBLOCK 
is set for the file descriptor for the socket, connect() shall fail 
and set errno to [EINPROGRESS], but the connection request shall not 
be aborted, and the connection shall be established asynchronously.