CODEWITHSUNDEEP
c++multithreadingqt
JadziaMD
JadziaMD

Reputation: 2740

Process Signals & Slots Using a Thread

I need to be able make a request GET request, which requires the use of signals to process the replies, and return the reply back in a a processed form. I've structured the code as described in Threading Wihtout the Headache, but when I run the reply is never received or processed.

// Set-up request
QNetworkAccessManager* pConnection(new QNetworkAccessManager());
connect(pConnection,
       SIGNAL(finished(QNetworkReply*)),
       this,
       SLOT(process(QNetworkReply*)));
QUrl url;
url.setUrl(HOST);
url.addQueryItem("P1", "Hi");
url.addQueryItem("P2", "Bob");

// Send request
QNetworkRequest request(url);
pConnection->get(request);

// Wait for reply
QThread* pResponce(new QThread(this));
connect(this,
        SIGNAL(processingFinished()),
        pResponce,
        SLOT(quit()));
pConnection->moveToThread(pResponce);
pResponce->start();
pResponce->wait();
pConnection->deleteLater();
pResponce->deleteLater();
return this->processedReply;

Obviously I'm missing something, but what? It works when I'm not using the threads (and the deletes), so it's not the URL or server.

Upvotes: 2

Views: 175

Answers (1)

ypnos
ypnos

Reputation: 52317

Only the main/gui thread receives signals if you don't set up an event loop in the other threads.

If no event loop is running, events won't be delivered to the object. For example, if you create a QTimer object in a thread but never call exec(), the QTimer will never emit its timeout() signal. Calling deleteLater() won't work either. (These restrictions apply to the main thread as well.)

Source: http://doc.qt.digia.com/4.6/threads-qobject.html

See QThread::exec(). That's why in the example you're linking the QThreadEx class is introduced, and used (not in your code snipplet, though!)...

Upvotes: 4

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