Hi Jayson,
On Sep 8, 2009, at 4:51 PM, Jayson Adams wrote:
On Sep 8, 2009, at 3:31 PM, Marc Krochmal wrote:
Hi Brent,
I may have been one of those appalled Apple engineers. In general,
[NSHost currentHost] is the worst API on the system and people
should avoid it like the plague.
Hi Marc,
Can you tell why this is so?
[NSHost currentHost] as currently written, iterates over all available
IP addresses on the system and does reverse DNS lookups on each
address. It actually does this twice for each address. This includes
loopback and link-local addresses, IPv4 and IPv6. This results in
packets hitting the network. If DNS servers are slow to respond, this
call will block and your application will SPOD. If DNS happens to be
down or temporarily misconfigured, each individual query will take 30
seconds to timeout. All the queries are performed serially so the
timeouts start to add up.
If you're just looking for the mDNS Local Hostname, it's MUCH more
efficient to use SCDynamicStoreCopyLocalHostName, which is just a Mach
message over to configd running on the local machine. No network
delays.
If you just want to know the list of IP addresses, instead of doing
[[NSHost currentHost] addresses], it's much more efficient to use
getifaddrs, which doesn't require any DNS queries.
So in general people should avoid calling this API, or make sure to
call it async, either on a separate thread or on a concurrent GCD queue.
Of course, given that we're aware of the performance issues, don't be
surprised if [NSHost currentHost] performs better in future releases.
-Marc
Best,
__jayson
Circus Ponies NoteBook - Organization for a Creative Mind
www.circusponies.com
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