[Qt-interest] QNetworkProxyFactory::setUseSystemConfiguration(true) slows down network access, even though proxy not used

[Tony Rietwyk]

> Sent: Friday, 23 September 2011 10:17 AM
> 
> Hi Everybody,
> 
> My application uses QNAM.post to communicate with a server.  I had
> assumed that QNAM would automatically use the system proxy settings if
> they were required.  I have no idea how to setup an Apache proxy server to
> test this, though.  The sales guy asked if we supported clients using
proxies.
> Looking at the docs, I get the impression that proxies are NOT supported
by
> default.
> So I changed the startup code to add a call to
> setUseSystemConfiguration(true) anyway.  Now every network access is
> much slower - at least 1 second.  (The code shows a progress popup after a
1
> second timeout, and it is constantly popping up, then disappearing).  I do
not
> have a proxy set on my system.
> 
> I'm using 4.6.0 commercial downloads on Win 7 64-bit,  MS Visual Studio
2008.
> 
> The application has been around for over 15 years (previously as Delphi),
and
> no-one has ever needed proxy settings - so at this stage, we just want to
be
> able to tick the proxy box if a new client needs it.
> 
> I do appreciate that we may need to add proxy username/password settings
> similar to Skype.  I also understand that there are several different
types of
> proxies with differing authentication requirements.  All the more reason
to
> be able to just use the default browser settings.
> 
> Has anybody experienced a similar slow-down?  Is there something else that
> I need to do to use the default settings efficiently?  Is there a way to
detect if
> a proxy will be required during startup and only make the call in those
cases?
> 
> Thanks for any tips or help!
> 
> Tony.

Further to the information above...

The progress popup has an animated graphic.  With
setUseSystemConfiguration(true) the animation was frozen.  So whatever the
call does to the subsequent network accesses, it is blocking the event loop
as well.  

Tony.