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Re^4: Windows: AnyEvent -> HTTP -> DNS - > Blocking for minutes

by sectokia (Pilgrim)
on Oct 20, 2022 at 04:26 UTC ( #11147529=note: print w/replies, xml ) Need Help??

in reply to Re^3: Windows: AnyEvent -> HTTP -> DNS - > Blocking for minutes
in thread Windows: AnyEvent -> HTTP -> DNS - > Blocking for minutes

Yes for me I get attempts to and ::1 as well

Setting tcp_timeout and udp_timeout changed nothing for me. Having a look in _udp_send the timeout used for can_read is made from the 'retrans' and 'retry' settings. Based on the default values (5 and 4) with the DNS timeout of 2.5s doubling, this results in a timeouts of: 2.5,2.5,5,5,10,10,20,20 for both servers (total 150 seconds).

This reduced the issue to 2.5 seconds:

Net::DNS::Resolver->tcp_timeout(1); Net::DNS::Resolver->udp_timeout(1);

But then I noticed that the local host name servers are in the defaults as well! So this 'fixes' it by setting the default nameservers to nothing:

Net::DNS::Resolver->nameserver4([]); Net::DNS::Resolver->nameserver6([]);

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Re^5: Windows: AnyEvent -> HTTP -> DNS - > Blocking for minutes
by NERDVANA (Chaplain) on Oct 20, 2022 at 23:12 UTC
    Well it sounds like you have enough info now that your problem is solved? If so, wonderful :-)

    ...but your post still leaves *me* with all kinds of questions, like why you need AnyEvent DNS to work if you don't have any network adapters in the first place, or how you're going to use a name server by host name if you don't have an initial default nameserver to resolve that with :-) I'll point back to my first post here about how if you know what name servers you want to use (like Cloudflare or google you can just pass those directly to AnyEvent::DNS and skip messing with Net::DNS::Resolver. Then if your network is connected, you can reach, and if it isn't, it should time out within AnyEvent rather than Net::DNS::Resolver.

      The problem wasn't that I need to make HTTP requests when there is no DNS, its about behavior of my Perl programs when networks are disconnected.

      For instance: If the PC disconnects from all networks, then any time the code attempts to do a AnyEvent HTTP request - it would block for 150 seconds - a complete block with the event loop no longer running. In that event loop I could be running things like AnyEvent:HTTPD to handle requests from a localhost user GUI, or I could have scheduled timers that I expect to occur within that 150 seconds, also AnyEvent Signal handlers can't run. So essentially the entire program 'freezes' for 150s trying to do the syncronous call to a non existent DNS server on localhost.

      The correct 'fix' here is probably for AnyEvent::DNS to use AnyEvent::DNS::Resolver as per my solution - with the DNS default nameservers removed - to ensure the constructor can never go down a code path of making a DNS call via AnyEvent::DNS::Resolver.

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