QNetworkAccessManager and QRunnable issue

Hello,

I have the such code architecture. For each request I am creating Worker class, which is QRunnable object and it should be started in a new QThread by QThreadPool.
This Worker has the following code:

Code:

---

#include "Worker.h"
#include <QString>
 
Worker::Worker(const WorkerData& data) :
    _reader()
    _writer(),
    _sender()
{
}
 
void Worker::run()
{
    _reader.readFile();
}
 
void Worker::sendData(const DataToSend& data)
{
    _writer.write(data);
    _sender.send(data);
}

---

The Sender header code:

Code:

---

#include <QObject>
#include <QtNetwork/QNetworkAccessManager>
 
class DataSender : public QObject
{
    Q_OBJECT
public:
    DataSender();
 
    void send(const DataToSend& data);
 
private:
    QNetworkAccessManager _networkMgr;
};

---

The Sender.cpp code:

Code:

---

#include <QUrl>
#include <QJsonObject>
#include <QJsonDocument>
#include <QtNetwork/QNetworkReply>
DataSender::DataSender() : _networkMgr()
{
 
}
 
void DataSender::send(const DataToSend& data)
{
    qDebug() << "\tINFO: [DataSender::send] sending data to endpoint: " << data;
 
    QUrl serviceUrl = QUrl("http://someUrl.com");
    QNetworkRequest request(serviceUrl);
    QJsonObject json;
    json.insert("data", data.first());
    QJsonDocument jsonDoc(json);
    QByteArray jsonData= jsonDoc.toJson();
    request.setHeader(QNetworkRequest::ContentTypeHeader,"application/json");
    request.setHeader(QNetworkRequest::ContentLengthHeader,QByteArray::number(jsonData.size()));
    QNetworkReply *reply = _networkMgr.post(request, jsonData);
}

---

As you know, the only run() method in QRunnable object is running in a new thread. Based on that, all my QNetworkAccessManager is created in the old thread, because it is not created in run method, am I right?

I am asking about that, because i got the following error:

Quote:

---

QObject: Cannot create children for a parent that is in a different thread.
(Parent is QNetworkAccessManager(0xda5a74c), parent's thread is QThread(0xdb14e0), current thread is QThread(0xda579a0)

---

Do you have any idea why I get this error?
I do not see the cause of the problem...

Why do you want to create the request in a separate thread at all? It's not needed: https://doc.qt.io/qt-5/qnetworkacces...r.html#details

Quote:

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Originally Posted by ChristianEhrlicher

Why do you want to create the request in a separate thread at all? It's not needed: https://doc.qt.io/qt-5/qnetworkacces...r.html#details

---

..because there will be a lot of requests to my main app and I would like to dispatch them to many threads, thus I use QThreadPool with Workers for each request.

So did you actually read the link? Then you would see that your idea will not work.

Quote:

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Originally Posted by ChristianEhrlicher

So did you actually read the link? Then you would see that your idea will not work.

---

Yes, I saw it. Network manager must be run in the same thread it was created. Based on that I create it in worker, but Worker itself is not in the new thread. In the new thread is Worker::run() method only, am I right?

I meant this:

"Note: QNetworkAccessManager queues the requests it receives. The number of requests executed in parallel is dependent on the protocol. Currently, for the HTTP protocol on desktop platforms, 6 requests are executed in parallel for one host/port combination."

So there is no real need to create a thread and when then you need to create on QNAM per thread.

Quote:

---

Originally Posted by ChristianEhrlicher

I meant this:

"Note: QNetworkAccessManager queues the requests it receives. The number of requests executed in parallel is dependent on the protocol. Currently, for the HTTP protocol on desktop platforms, 6 requests are executed in parallel for one host/port combination."

So there is no real need to create a thread and when then you need to create on QNAM per thread.

---

I see, but presence of QNAM is not the main factor to using QThreadPool class. Each request processes files (read/write one file) and based on that the application architecture is better and more flexible.

Quote:

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based on that the application architecture is better and more flexible.

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I have a square peg. I do not care if the hole is round. I will make it fit. I just need to use a bigger hammer.

Maybe you should consider threading the file processing after the network requests are complete, and not combine the two and attempt to thread the whole thing.