Hi,
So, I reproduced the issue, albeit with one configuration change that
I'm not sure whether is common or not.
Basically, I could see that lookups to any host with a ".local" suffix
would use MDNS and if the local services are not active, then I see the
packets being sent on the wire, no responses and a delay of 5 seconds
before the lookup fails. Initially, this was not affecting localhost
lookups which still use normal DNS and even when DNS not available, that
was failing immediately and therefore no delay.
To make InetAddress.getLocalHost() fail with a 5 second delay, I had to
add ".local" to the DNS search path of the system. That has the effect
of attempting a MDNS lookup after the DNS lookup fails, and this delays
the failure for 5 seconds.
One question is if this is a common network configuration, or is there
some other way to cause it to happen?
Looking at the patch again, I think perhaps (assuming we want to make a
change here) a different approach might be better. Quite a lot of work
is happening in the lookupIfLocalhost() function and I think we should
try to limit this being called to only the local hostname lookup path.
This might require boolean flags being being passed down from the
InetAddress.getLocalHost() call to indicate whether this is a local
address lookup or not.
Thanks,
Michael
On 05/04/2019, 20:15, Nora Howard wrote:
Oh, another element is that to see the behavior, your local hostname
has to not have an entry in /etc/hosts. Adding it is one of the
workarounds. My /etc/hosts has a localhost entry that does not include
the name my machine ends up with after boot.
I'm also on 10.13, so I don't think that's the issue per se.
When I run scutil --dns. I get a resolver that points to en01 with
some names on my VPN, and a number of mdns registrations that all look
like this, where the resolver number, the domain and the order change,
but the rest of the fields stay the same.
resolver #2
domain : local
options : mdns
timeout : 5
flags : Request A records
reach : 0x00000000 (Not Reachable)
order : 300000
On Fri, Apr 5, 2019 at 10:14 AM Michael McMahon
<michael.x.mcma...@oracle.com <mailto:michael.x.mcma...@oracle.com>>
wrote:
I've spent some time trying to reproduce this on 10.13 but have
not been able.
I have disabled all the services as suggested (including some
additional)
such that the dns-sd command produces no output "records" and also by
disabling unicast DNS access.
I wonder if there has been a change in 10.13 to workaround this
problem
as I don't see any delay or external MDNS lookups happening.
.
Could you send me the output of "scutil --dns" of your laptop?
At the same time, I will ask some colleagues here who might be
running 10.12
to try it out.
Thanks,
Michael
On 04/04/2019, 18:38, Nora Howard wrote:
Here's the diff
http://cr.openjdk.java.net/~tonyp/8170910/webrev.0/
<http://cr.openjdk.java.net/%7Etonyp/8170910/webrev.0/>
To setup an env to reproduce the issue, on a OSX machine with >=
10.12, turn off services that register with mDNS. For my laptop,
I had to turn off iTunes and General System Preferences, disable
"Allow Handoff between this Mac and your iCloud services". You
might have to restart. The reporter on the ticket said to run
`dns-sd -lo -B _services._dns-sd._udp local` to see whether you
have any running.
The file I used for exercising the behavior looks like this
import java.net.InetAddress;
public class Test {
public static void main(String[] args) throws Exception {
for (int i=0;i<4;i++){
long start = System.currentTimeMillis();
InetAddress localHost = InetAddress.getLocalHost();
System.out.println(localHost);
System.out.println(System.currentTimeMillis() - start);
}}}
The output I get on my laptop when I've set things up this way
looks like this on JDK 13 EA. The first call takes the full 5
seconds and subsequent ones hit a cache.
nhoward.local/10.0.0.3 <http://10.0.0.3>
5044
nhoward.local/10.0.0.3 <http://10.0.0.3>
0
nhoward.local/10.0.0.3 <http://10.0.0.3>
0
nhoward.local/10.0.0.3 <http://10.0.0.3>
0
On JDK 8, each request takes 5 seconds. JDK 8's address lookup
cache works differently. It's localhost name cache expiry is 5
seconds.
On Thu, Apr 4, 2019 at 2:41 AM Michael McMahon
<michael.x.mcma...@oracle.com
<mailto:michael.x.mcma...@oracle.com>> wrote:
Hi Nora,
At first sight, the approach sounds reasonable to me. I'd
like to see the patch
and also do you have detailed instructions on how to
reproduce the issue (the 5 second delay)?
Thanks,
Michael.
On 03/04/2019, 17:46, Nora Howard wrote:
I'd initially sent this to jdk-dev, but I was asked to move
it to net-dev.
On OSX 10.12 or later, when no mDNS services are registered,
getaddrinfo fails on looking up localhost addresses[1]. The
jdk’s current implementation falls back to getifaddrs after
getaddrinfo fails[2]. When getaddrinfo fails in this way, it
takes 5 seconds to fail [3]. This means that calls to
InetAddress.getLocalHost() may take up to 5 seconds to run.
I’d like to change the jdk’s behavior in this instance so
that instead of falling back to calling getifaddrs after
getaddrinfo fails, it instead calls getifaddrs first if
we’re on OSX and the hostname is localhost’s.
Doing this will eliminate the 5 second delay looking up
localhost on machines with this network setup. When looking
up non-localhost addresses, it’ll add a call to
os:gethostname and a comparison.
I’d like to get some feedback about whether this approach
sounds reasonable, and some guidance about next steps. I’ve
read the “how to contribute” page[4], and the “code review”
guide[5].
I’ve put together a patch that I’ve tested locally by
turning off mDNS services on my local OSX machine and
exercising the behavior. I’d like to submit patches that
target dev trunk as well as the jdk 8 and 11 branches.
References
1.
On a Macintosh running 10.12 or later, if there are no
apps that have a mDNS services registered (for instance,
iTunes) and there are no services selected in the
Sharing System Preferences, then the getaddrinfo will fail.
(https://bugs.openjdk.java.net/browse/JDK-8170910)
2.
http://hg.openjdk.java.net/jdk/jdk/file/cd3b7ad53265/src/java.base/unix/native/libnet/Inet6AddressImpl.c#l252
http://hg.openjdk.java.net/jdk/jdk/file/cd3b7ad53265/src/java.base/unix/native/libnet/Inet4AddressImpl.c#l132
(The lookupIfLocalhost function checks the passed hostname
against os::get_host_name, and if they match, looks up via
getifaddrs.)
3. This comment describes how to reproduce the issue. I’ve
reproduced it locally on jdk 8, 11 and 13 ea.
https://bugs.openjdk.java.net/browse/JDK-8170910?focusedCommentId=14038262&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14038262
<https://bugs.openjdk.java.net/browse/JDK-8170910?focusedCommentId=14038262&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14038262>
4. https://openjdk.java.net/contribute/
5. https://openjdk.java.net/guide/codeReview.html
Thanks,
--
Nora
--
Nora
--
Nora
