Hi all,

Since Emacs gained the capability to make asynchronous DNS lookups 
under GNU/Linux, I've been wishing for the same thing under OSX. 
Here is a little patch that I've hacked together, that I'd like 
some feedback on.  In particular:

1. In Fmake_network_process, there's an XXX comment about 
deallocating my CFStringRef.  I couldn't figure out from the 
documentation whether CFHostCreateWithName takes ownership of the 
string, or just copies it.

2. There is a callback function, host_client_callback, that writes 
error information into memory referred to by the process struct. 
There is a potential for a race condition here: what if the 
callback is called after the process has been deallocated?  I've 
tried to avoid that by cancelling name resolution before 
deallocating the memory (see free_dns_request), but I suspect 
that's not enough.  Is there a clever way to avoid that?

3. Unlike getaddrinfo_a, this CFHost thing doesn't resolve service 
names to port numbers.  Therefore, I arrange to call getservbyname 
in Fmake_network_process, and insert the port number into a copy 
of the sockaddr struct in check_for_dns.  I _think_ this should 
work for both IPv4 and IPv6, but I haven't tested IPv6.  Is there 
a nicer way to do this?

It took me a while to figure out the port number thing: before I 
added the port number, the process seemed to silently do nothing. 
That's because non-blocking connect would fail, and 
connect_network_socket would treat that as having to do a 
synchronous connect, which ended up not happening.  I'm not sure 
if this is a bug or a feature.

Any other comments are appreciated as well.  I'll have sporadic 
Internet access during the coming week or so, will probably look 
at this again after that time.

Regards,
Magnus