On Mon, Jun 10, 2013 at 12:22:47AM +0200, Daniel Stenberg wrote:
> On Fri, 7 Jun 2013, Richard W.M. Jones wrote:
>
> >I'll try to look into the items below when I have time, but it'd
> >be great if you could just skip over the code here:
> >
> >http://git.qemu.org/?p=qemu.git;a=blob;f=block/curl.c;h=b8935fd9916363640df142d303b93756c8acf167;hb=HEAD
> >
> >and tell us if there's anything obviously broken about how it's
> >using the API. (Note I didn't write any of it.)
>
> Following such an event-triggered logic is a bit tricky and would
> require me to spend some time to fully understand the reasoning
> behind what's going on. But I gave it a quick look and found a few
> things:
>
> I'll start with seconding Kamil's remark about setting options for a
> handle that a few lines later gets killed. That seems like an
> indidication of things not being entirely right. Also, doing an
> easy-inteface call in there when you use the non-blocking
> event-based API everywhere else seems like perhaps something to
> reconsider as well at some point.
>
> Then I noticed two peculiarities which may contribute to what you're
> experiencing:
>
> 1 - The code uses the multi_socket API but without
> CURLMOPT_TIMERFUNCTION. That's highly unusual and I usually strongly
> advice against it unless you're perfectly aware of what side-effects
> it brings ... This can in fact be a reason for your problem.
>
> 2 - its use of curl_multi_socket_all() (which is documented as
> deprecated and "do not use") in curl_multi_do() probably mostly
> hides the problems (1) causes. Still, it seems to only get called on
> socket activity, and for example in the case of a libcurl with a
> threaded-resolver, there will very certainly be reasons to call
> libcurl again without any registered socket activity.

Thanks, this was all helpful.

I suspect that (1) is not fixable in current qemu. See my reasoning
here:
https://bugzilla.redhat.com/show_bug.cgi?id=971790#c21

Re (2) I tried to replace curl_multi_socket_all with
curl_multi_perform, however that does not work AFAICT. It could be
related to the other problem.

Rich.

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