I recently started using an Apple notebook as a development laptop. I realized that when I block the screen the WIFI connection goes down. This is a wanted behavior and can be changed using this command:
cd /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources sudo ./airport en1 prefs DisconnectOnLogout=NO
Obviously you need to replace “en1” with the identifier of your WIFI interface.