I think what Rein means is that the unix socket fd backing the windows socket handle is always non-blocking - and if he is, he may be correct:
http://source.winehq.org/source/server/sock.c#L578 && http://source.winehq.org/source/server/sock.c#L663
That's true, but it depends on whether the blocking state is transferred across a dup() call. The file descriptor used in a dll comes from wine_server_handle_to_fd: http://source.winehq.org/source/dlls/ntdll/server.c#L635
I confess I don't know whether it is. But the existence of the do_blocking call strongly implies that it is, doesn't it? --Juan