[libvirt] mingw: test-poll pipe part fails

Daniel P. Berrange berrange at redhat.com
Tue Jul 19 15:44:19 UTC 2011

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.

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