[Qt-interest] qtconcurrent::run() virtual member methods?

[Daniel Bowen]

I was just contemplating making a request to add a timeout for
QNetworkRequest/Reply to Qt itself.  What I'd like to see is at least one
timeout value, but ideally 2 new timeouts - a "connect timeout" and a
"read/write timeout".  Then, if a timeout is encountered, the reply's error
could be QNetworkReply::TimeoutError (which is already defined).  Connect
timeout would be how long before giving up on connecting to the resource,
and read/write timeout is how long to go before giving up on being able to
complete a read (on a get) or write (on a put or post).  It could be done
using QNetworkRequest::Attribute - QNetworkRequest::ConnectTimeout and
QNetworkRequest::ReadWriteTimeout.  Each of them could be a QVariant::Int.
If the QVariant is empty, or the value is -1, it could mean no timeout.
What's the best way to make that request formally?

 

In the meantime, here's one way to deal with timeouts.  I've attached two
files - NetworkRequestTimeout.h and NetworkRequestTimeout.cpp.  To use it,
you'd do something like this:

 

      QNetworkRequest networkRequest;

      // ... (Fill out the request)

 

      QEventLoop eventLoop;

 

      QNetworkReply* reply = networkManager.get(networkRequest);

      QObject::connect(reply, SIGNAL(finished()), &eventLoop, SLOT(quit()));

 

      // Request timeout

      NetworkRequestTimeout timeoutHandler(reply);

      timeoutHandler.Start(30 * 1000); // Have a 30-second timeout

 

      eventLoop.exec();

 

      // "completed" will be true if the request completed, and false if it
timed out.

      bool completed = timeoutHandler.Stop();

      if(completed)

      {

            QByteArray contents = reply->readAll();

 

            qDebug(contents.constData());

      }

 

-Daniel

 

From: qt-interest-bounces at trolltech.com
[mailto:qt-interest-bounces at trolltech.com] On Behalf Of Liam Staskawicz
Sent: Tuesday, June 09, 2009 3:46 PM
To: qt-interest at trolltech.com
Subject: [Qt-interest] qtconcurrent::run() virtual member methods?

 

Hi - I was taking the opportunity of adding timeout functionality to the
QNetworkAccessManager api to experiment with QtConcurrent a bit.  Since
there doesn't seem to be a built-in way to specify a timeout per request, I
thought I'd run each request in a thread via QtConcurrent and call
waitForReadyRead with my appropriate timeout value.  Code looks roughly
like:

 

QNetworkReply* reply = netAccess.get(QNetworkRequest(url));

QFuture<bool> future = QtConcurrent::run( reply,
&QNetworkReply::waitForReadyRead, REQUEST_TIMEOUT );

 

but I'm getting the following compile error:

 

 error: no matching function for call to 'run(QNetworkReply*&, bool
(QIODevice::*)(int), int)'

 

just for fun, I tried passing a method defined explicitly by QNetworkReply -
::manager() - and that seemed to compile happily.  Any chance this has
something to do with the fact that waitForReadyRead is provided by
QIODevice?  The doc for QtConcurrent::run() is mostly based on a few
examples so I wasn't able to glean too much more from it.

 

Secondarily, any other better timeout strategies for QNetworkAccessManager
would also be welcome!

 

Thanks,

Liam

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