waiting for a signal

Question

I am working on an application which uploads the content of the file to server.

To upload the file to server I am using ‘QNetworkAccessManager’ class. Since it works as asynchronous way, I changed it to work as synchronous way by using QEventLoop.

Class FileTransfer
{
Public : 
     QNetworkAccessManager mNetworkManager;
     Void Upload(QNetworkRequest request, QIODevice *data)
     {
           responce = mNetworkManager.put(request, data);
           EventLoop.exec();
           ReadResponce(responce);
      }

      Void Stop()
      {
            responce ->close();
      }
}

In my sample application I have 2 windows. 1st to select the files and 2nd to show the progress.

When user click on upload button in the first window, the 2nd window will be displayed and then I create the FileTransfer object and start uploading.

While uploading the file if user closes the form then in the destructor of the window I call the stop of ‘FileTransfer’ after that I delete the ‘FileTransfer’ object.

But here the Upload() function is not yet completed so it will crash.

Please help me to: How to wait in 'stop()' function until the Upload() function is completed

Answer 1

From what I can see from your code, you're executing a QEventLoop but you're not actually connecting its "quit" slot to any signal. Take the below as an example, login is a QHttp - and the code is taken from something different - but the principle applies.

/* Create the QEventLoop */
QEventLoop pause;
/* connect the QHttp.requestFinished() Signal to the QEventLoop.quit() Slot */
connect(&login, SIGNAL(requestFinished( int, bool )), &pause, SLOT(quit()));
/* The code that will run during the QEventLoop */
login.request(header,&logmein,&result);
/* Execute the QEventLoop - it will quit when the above finished due to the connect() */
pause.exec();

This could be applied to your code, if I'm not mistaken, like this...

/* connect the signal to the relevant slot */
connect(&mNetworkManager, SIGNAL(finished( QNetworkReply )), &EventLoop, SLOT(quit()));
/* Execute the code that will run during QEventLoop */
responce = mNetworkManager.put(request, data);
/* Execute the QEventLoop */
EventLoop.exec();

Apologies if I've mistaken your query! I'm only getting to grips with qt again after a break, but I believe this is what you mean! Good luck!

Answer 2

I think you need to add something like that in your upload function:

if (upf->openFile())
{
    reply = manager->post(request, upf);
    connect(reply, SIGNAL(uploadProgress(qint64,qint64)), this, SIGNAL(progress(qint64,qint64)));
    connect(reply, SIGNAL(finished()), this, SLOT(replyFinished()));
    isInProgress = true;
    emit started();
} else
{
    emit finished(true, false, tr("Error: can't open file %1").arg(filename));
}

Here is the full text code: datacod-qt-tools

Hope it help.

Answer 3

Personally, I would recommend to not use any of these answers. It would be sufficient to connect a countdown latch to the signal.

So you could write:

Latch latch( 1 );
QObject::connect( reply, SIGNAL(finished()),
                  &latch, SLOT(countDown()) );

latch.wait();

For this you would need a wrapper:

class Latch : public QObject {
    Q_OBJECT
public:
    Latch( uint count );
    void wait();
public slots:
    void countDown();
private:
    gcl::countdown_latch _latch;
};