On Mon, 30 Apr 2012, gokhansengun_at_gmail.com wrote:

> We need to get on the same page. In order to get a hard real time effect,
> you need operating system support, it has to provide you a real time TCP/IP
> stack. What I suggested can only work on the "best effort basis". It can
> only help you to avoid procesing a low priority jobs while high priority job
> is waiting for attention.

How does this "real time TCP/IP stack" let you do that in a way that a
"normal" stack doesn't?

> That is the whole point here. After returning from select, my code first
> checks whether high priority job needs action, if so action is provided and
> without doing any more work we are selecting again with the minimum expiry
> time.

Then you need to make your second select() exclude the low-priority sockets as
otherwise they will just trigger select() immediately again - and this is of
course not easily done with libcurl within a single multi handle and that's a
reason for you to use multiple ones.

With the multi_socket() API it would possibly be easier to do within a single
handle.

Hm, come to think about it. Perhaps your way can also be achieved with some
clever use of curl_easy_pause() on the low-prio transfers while there are
high-prio ones to deal with...

> This goes on until select wakes up with no higher priority job needs
> immediate attention, then we process low priority job.

Aah yes, that's how you can "sleep too long" since you then enforced a sleep
onto the low prio transfers that they didn't ask for.

> Why not utilizing the whole bandwidth for low priority jobs when there is no
> or low density of high priority jobs?

Your approach has the downside that it might completely ignore the low-prio
transfers while you have a few high speed important ones. Of course I
understand that you have things tested out and working for your case, but I'm
thinking if we would do something in a generic way for everyone.

Your way does indeed have the upside that it lets the low-prio connections
reach full speed if no high prio connections are used.

-- 
  / daniel.haxx.se
-------------------------------------------------------------------
List admin: http://cool.haxx.se/list/listinfo/curl-library
Etiquette:  http://curl.haxx.se/mail/etiquette.html