On Thu, Dec 18, 2008 at 07:24:34PM +0100, Isidor Zeuner wrote:
> when looking into the implementations of the timeouts with millisecond
> resolution added in 2007, I stumbled upon the current status that there
> are three different time sources configurable to measure accurately
> enough so they are useful, but practically they still don't provide
> higher resolution, because the interaction of the timing with the
> networking code is done using sleep and poll system calls with 1 second
> resolution.

I don't follow this--both poll and select allow timeouts with millisecond
resolution (I assume you meant select and not sleep since the latter isn't
called in libcurl). The only timeout limited to second resolution that I can
think of is the name resolve on systems configured to use the synchronous
resolver.

> I found that the new timout interfaces can be made useful
> rather quickly by employing setitimer system calls and using a higher
> resolution in the polls. Attached is a proof of concept patch which
> integrates these changes. It may need some cleanup, especially to avoid
> breakage using more exotic combinations of preprocessor defines, but
> maybe it's already interesting for some people willing to experiment
> with the timing behavior. I'd be glad to receive comments if someone
> finds it useful or interesting.

I still don't see the point of the patch on the connect call since that
uses select/poll with millisecond resolution already, and switching to a
signal/longjmp approach has some serious down sides. But the patch to
use setitimer on the resolve is certainly welcome (it's TODO item #1.4).

I have a couple comments on that part. One is that we can't use C99-style
named structure initializers since we aim for C89 compatibility. Another
is that the use of the do{}while(0) construct in functions is a bit unusual
for libcurl. Otherwise, I think it's a good idea.

>>> Dan

-- 
http://www.MoveAnnouncer.com              The web change of address service
          Let webmasters know that your web site has moved