gethostbyname blocking

[marc wyburn]

On Apr 23, 2:16 pm, Piet van Oostrum <p... at cs.uu.nl> wrote:
> >>>>> marc wyburn <marc.wyb... at googlemail.com> (MW) wrote:
> >MW> Hi, I am writing anasynchronousping app to check if 1000s of hosts
> >MW> are alive very quickly.  Everything works extremely quickly unless the
> >MW> host name doesn't have a DNS record.
> >MW> when calling socket.gethostbynameif there is no record for the host
> >MW> the result seems to block all other threads.  As an example I have 6
> >MW> threads running and if I pass the class below a Queue with about 30
> >MW> valid addresses with one invalid address in the middle the thread that
> >MW> the exception occurs in seems to block the others.
>
> What you could do is have two Queues, one with host names, and one with
> results fromgethostbyname. And an additional thread which gets from the
> first queue, callsgethostbynameand puts the results in the second queue.
> The ping threads then should get from the second queue. The lookup
> thread could even do caching of the results if you often have to repeat
> the pings for thew same host.
> --
> Piet van Oostrum <p... at cs.uu.nl>
> URL:http://pietvanoostrum.com[PGP 8DAE142BE17999C4]
> Private email: p... at vanoostrum.org

Hi, I did try this but the socket blocked for so long that this was a
real bottleneck.  It also seemed that whilst the DNS lookup thread was
blocking the other threads were also blocked.  I guess this may have
something to do with the GIL but I'm still fairly new to threading.  I
ended up using DNSPython which flys along.  I have a thread creating
the ping packets and pinging them and another performing a select and
logging + filtering any ICMP replies.  I may put the DNS code into
another thread but the whole script runs faster than I need it to as
it is, I've got time.sleeps in the ping thread as I'm scared of
saturating the local LAN during work hours.