On Apr 22, 5:19 pm, Jean-Paul Calderone <exar...@divmod.com> wrote: > On Wed, 22 Apr 2009 08:08:51 -0700 (PDT), marc wyburn > <marc.wyb...@googlemail.com> wrote: > >Hi, I am writing an asynchronous ping app to check if 1000s of hosts > >are alive very quickly. Everything works extremely quickly unless the > >host name doesn't have a DNS record. > > >when calling socket.gethostbyname if there is no record for the host > >the result seems to block all other threads. As an example I have 6 > >threads running and if I pass the class below a Queue with about 30 > >valid addresses with one invalid address in the middle the thread that > >the exception occurs in seems to block the others. > > If your system doesn't have the gethostbyname_r function, then you can > only make one gethostbyname_ex call at a time - a call to this function > will block any other calls to this function, since it is not safe to > call gethostbyname reentrantly. > > I'm not sure what the easiest way to determine whether Python has found > gethostbyname_r or not on your system is. The configure script used to > build Python will probably tell, but I doubt you have that lying around. > You could just assume this is the case, since you're observing behavior > consistent with it. ;) > > An alternate approach would be to use a DNS library which doesn't have > this restriction. For example, Twisted includes a DNS library which > is not implemented in terms of threads. There are also a couple other > Python DNS client libraries around. > > This isn't /quite/ the same as using gethostbyname, though, since > gethostbyname is controlled by system configuration in various ways, > and may do more than just DNS lookups (in fact, it may even be > configured not to use DNS at all!). But it's pretty close, and may > be close enough for your purposes. > > Jean-Paul
Thanks for the quick response. I'm using Win32, I don't think there is a non-blocking gethostbyname avail. I managed to find some info on the net but most of it was old and Nix related and I was hoping it was a bug that had been fixed and I was making a mistake with my threads. I wrote a simlar script that uses multiprocess and that seemed to have less problems but I will look at http://www.dnspython.org/. Thanks, Marc. -- http://mail.python.org/mailman/listinfo/python-list
