still using cache when fetching content

[Jean-Christophe Petit]

Hello,

Is it possible to make Varnish sending the cache content at the same 
time it is fetching from the backend ?
It will be more efficient for slow dynamic content ;)
For example, I have a php page taking up to 5sec to run. If Varnish was 
able to get it while still sending the old cache page, it would be 
really great.
No more unlucky visitor hitting it to update the cache..

Thanks,

-- 
Jean-Christophe Petit
VP R&D et DSI

GROUPE SYSPARK