- signal happens, triggers perl internals
 - flag for this signal is set by internals
 - systemcall is interrupted, $! set to EINTR
 - perl dispatcher sees flag, starts your signal code
    However, this code happens to change $!
 - The assign of undef to $conn happens
 - You check $conn, see its undef and then go look at $!,
   but you get the $! left by your signal handler, not the
   older one you really need.

##</code><code>##

local $!;