[adding libvirt] On 06/04/2011 12:24 AM, Paolo Bonzini wrote: > On Sat, Jun 4, 2011 at 00:37, Matthias Bolte > <matthias.bolte(a)googlemail.com&gt; wrote: >> After testing a while and reading MSDN docs the problem seems to be >> that MsgWaitForMultipleObjects doesn't work on pipes. It doesn't >> actually wait but just returns immediately. Digging MSDN and googling >> about this suggest that there is no simple solution to this. > > Yes, Windows pipes are that broken. :( > > Using socketpair is a possibly good idea, but I would do it on > libvirtd only. I don't know exactly how libvirtd uses this pipe, but > perhaps it can be changed to an eventfd-like abstraction that can be > used with both Windows and Unix. This is similar to Eric's > suggestion, but without the pipe at all. It would also be a > libvirtd-specific suggestion. I'm wondering if the problem here is that libvirt is trying to use the pipe-to-self mechanism as a fundamental event loop idiom. That is, the reason libvirt is calling poll is in order to minimize CPU until something interesting happens, where interesting includes needing to wake up a helper thread to do an action inside locks in response to the receipt of a signal. Maybe you are on to something, and replacing all uses of pipe() with virPipeToSelf() (which uses pipe() for efficiency on Linux, but socketpair() on mingw), would allow libvirt to continue to use the pipe-to-self idiom while also using fds that can actually be poll'd on mingw.

On 07/19/2011 09:30 AM, Daniel P. Berrange wrote: >>I'm wondering if the problem here is that libvirt is trying to use the >>pipe-to-self mechanism as a fundamental event loop idiom. That is, the >>reason libvirt is calling poll is in order to minimize CPU until >>something interesting happens, where interesting includes needing to >>wake up a helper thread to do an action inside locks in response to the >>receipt of a signal. >> >>Maybe you are on to something, and replacing all uses of pipe() with >>virPipeToSelf() (which uses pipe() for efficiency on Linux, but >>socketpair() on mingw), would allow libvirt to continue to use the >>pipe-to-self idiom while also using fds that can actually be poll'd on >>mingw. > >IIRC, we never resolved this for the last release. I think we should >do as you suggest and just use socketpair() on Win32. Given the way >in which libvirt uses these capabilities, I don't think the overheads >of socketpair() vs pipe() are so onerous that we need worry about an >even more fancy Win32 impl or eventfd for linux. Of course if someone >wants todo a full job for gnulib meawhile, we won't complain... Well, right now, we don't even have socketpair() for Win32. We'd have to wire up some other native APIs for this to work.

I have some code if you want that work. If you could test, I wil lsend you. I have no time to create m4 and proper gnulib integration. It is up to you

Bastien On Tue, Jul 19, 2011 at 5:44 PM, Daniel P. Berrange <berrange(a)redhat.com&gt; wrote: > On Tue, Jul 19, 2011 at 09:31:59AM -0600, Eric Blake wrote: >> On 07/19/2011 09:30 AM, Daniel P. Berrange wrote: >> >>I'm wondering if the problem here is that libvirt is trying to use the >> >>pipe-to-self mechanism as a fundamental event loop idiom.  That is, the >> >>reason libvirt is calling poll is in order to minimize CPU until >> >>something interesting happens, where interesting includes needing to >> >>wake up a helper thread to do an action inside locks in response to the >> >>receipt of a signal. >> >> >> >>Maybe you are on to something, and replacing all uses of pipe() with >> >>virPipeToSelf() (which uses pipe() for efficiency on Linux, but >> >>socketpair() on mingw), would allow libvirt to continue to use the >> >>pipe-to-self idiom while also using fds that can actually be poll'd on >> >>mingw. >> > >> >IIRC, we never resolved this for the last release. I think we should >> >do as you suggest and just use socketpair() on Win32. Given the way >> >in which libvirt uses these capabilities, I don't think the overheads >> >of socketpair() vs pipe() are so onerous that we need worry about an >> >even more fancy Win32 impl or eventfd for linux. Of course if someone >> >wants todo a full job for gnulib meawhile, we won't complain... >> >> Well, right now, we don't even have socketpair() for Win32.  We'd >> have to wire up some other native APIs for this to work. > > Oh I read your mail above as indicating we did have socketpair() > on Mingw32. A quick look through google, suggests most people > go down the route of creating a TCP socket bound to localhost > for this purpose. > > Daniel > -- > |: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :| > |: http://libvirt.org              -o-             http://virt-manager.org :| > |: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :| > |: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :| > >