On Mon, Aug 02, 2010 at 03:19:26PM -0500, Justin Santa Barbara wrote: > A) Do I change the interface so that the method returns a deferred > even in the providers that are synchronous? If so, we should just > have all interfaces return a deferred on all methods, so that the > interface doesn't expose the implementation. However, this would make > everything messy...
The fact that e.g. libvirt.get_info() is synchronous is, IMO, a bug. It calls out to libvirt and hangs the entire process until libvirt decides to respond. Until libvirt becomes async itself, we need make these calls in a separate thread or process so that we can carry on while waiting for libvirt to get back to us. > B) Should I type-check the result of the call and synchronously wait > on it if it is deferred? As Vish pointed out, that's what maybeDeferred is for. > (And can anyone point me at some code that can do a sync-wait?) Using standard Twisted, no. I doubt it's possible. You need threads or coroutines or something to pull that off and Twisted uses neither. > As an aside, and to borrow from the Wizard of Oz, "Twisted, I've a > feeling we're not in Python any more". Every method is preceded by > @defer.inlineCallbacks, return x becomes returnValue(x), and there are > yields scattered throughout the code based on whether the called > method returns a deferred or not. Yup. inlineCallbacks is a bit of an acquired taste. I'm not entirely there yet myself. > Perhaps we can clarify the Twisted vs Eventlet discussion: would > Eventlet solve this particular problem? The inlineCallbacks thing? Yes. The libvirt thing? Not as far as I know. eventlet has this patching mechanism, but as I understand it, it relies on the particular module using Python's socket module to work, which python-libvirt doesn't, AFAIK. -- Soren Hansen Systems Architect The Rackspace Cloud _______________________________________________ Mailing list: https://launchpad.net/~nova Post to : [email protected] Unsubscribe : https://launchpad.net/~nova More help : https://help.launchpad.net/ListHelp
