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Asked: 2026-06-02T13:05:51+00:00

Have an application where I have QOBJects which all contain an QNetworkAccessManager. I am

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Have an application where I have QOBJects which all contain an QNetworkAccessManager. I am aware of that it’s suggested to only have on per application but since I’m making a lot more that 6 calls at the same time, I needed to have it like this. So, this is how I start the threads. 

FileUploader *fileUploader = new FileUploader(_fileList);
QThread *fileUploaderThread = new QThread();
fileUploader->moveToThread(fileUploaderThread);

// uploader > model
connect(fileUploader, SIGNAL(progressChangedAt(int)), _model, SLOT(reportProgressChanged(int)), Qt::QueuedConnection);
connect(fileUploader, SIGNAL(statusChangedAt(int)), _model, SLOT(reportStatusChanged(int)), Qt::QueuedConnection);
// uploader > its thread
connect(fileUploader, SIGNAL(canceled()), fileUploaderThread, SLOT(quit()), Qt::QueuedConnection);
connect(fileUploader, SIGNAL(finished()), fileUploaderThread, SLOT(quit()), Qt::QueuedConnection);
// uploader > this
connect(fileUploader, SIGNAL(canceled()), this, SLOT(deleteFinishedUploader()), Qt::QueuedConnection);
connect(fileUploader, SIGNAL(finished()), this, SLOT(deleteFinishedUploader()), Qt::QueuedConnection);
connect(fileUploader, SIGNAL(finishedCurrentUpload()), this, SLOT(uploadNextFileOrFinish()), Qt::QueuedConnection);
// thread > this
connect(fileUploaderThread, SIGNAL(finished()), this, SLOT(checkIfAllThreadsAreFinished()), Qt::QueuedConnection);
connect(fileUploaderThread, SIGNAL(finished()), this, SLOT(deleteFinishedThread()), Qt::QueuedConnection);
// this > uploader
connect(this, SIGNAL(cancel()), fileUploader, SLOT(cancel()), Qt::QueuedConnection);

fileUploaderThread->start();
QMetaObject::invokeMethod(fileUploader, "init", Qt::QueuedConnection);
QMetaObject::invokeMethod(fileUploader, "uploadAt", Qt::QueuedConnection, Q_ARG(int, startIndex));

QMutexLocker locker(&_mutex);
_threadCount++;

Every thread starts out with an index to a list so that they can fetch the thing they need to upload and proceed about 5 steps (calls with the QNetworkAccessManager). When there’s no more items to upload, the fileUploader signals “finished()” which calls the deleteFinishedThread and deleteFinishedUploader where I do:

QThread *thread = qobject_cast<QThread*>(sender());

if(thread != NULL) thread->deleteLater();

or 

FileUploader *fileUploader = qobject_cast<FileUploader*>(sender());

if(fileUploader != NULL) fileUploader->deleteLater();

These are suppose to delete the threads when they are done.

The issue is that every time I start (for example) 3 threads that have 1 file to upload and handle each, the thread count gets increased by 8-10. This means that the thread count goes from about 5 to 100 if I restart the uploading process a few times.

What am I doing wrong? Or is my biggest issue that I use “Windows Task Manager” to control this? I am handeling all replies from the QNAM which I delete and everything seems to get deleted, but still I scratching my head when the threadcount keeps increasing…

EDIT:
In my fileuploader I create an object(Manager) on the heap which has a QNetworkAccessManager on the stack. When the fileuploader gets deleted it calls “deleteLater()” on the Manager but it never gets deleted. We tried to delete the Manager and set it to NULL but that gave us an access violation since the Manager wasn’t done yet (the QNetwork.dll reported the issue so it must be something inside the QNAM that is running still). The times when we didnt get access violation, the object was deleted and the thread count went back to normal. What can live inside the QNAM and prevent me from deleting it when it goes out of scope? Should I create the QNAM on the heap instead? At this stage non of the destructors are being called even when calling deleteLater()…

Also, how do I reduce the handle-count?

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1 Answer

  1. Editorial Team

    After a lot of "almost giving up" I came up with a solution for the threads. It is true what Synxis said about the order of the slots.

    I still however have some issue with the filehandles, and if someone has a better answer that mine I’m happy to accept that.

    I changed my code to:

    ...
// uploader > this
connect(fileUploader, SIGNAL(canceled()), this, SLOT(deleteFinishedUploader()), Qt::QueuedConnection);
connect(fileUploader, SIGNAL(finished()), this, SLOT(deleteFinishedUploader()), Qt::QueuedConnection);
// uploader > its thread
connect(fileUploader, SIGNAL(destroyed()), fileUploaderThread, SLOT(quit()));

    This means that the thread gets stopped (quit()) when the object is getting deleted. This actually works even though the documentation states:

    This signal is emitted immediately before the object obj is destroyed, and can not be blocked.

    All the objects’s children are destroyed immediately after this signal is emitted.

    Which means that this signals gets emitted just BEFORE anything gets destroyed (which would mean that I would quit the thread before the uploader in it got deleted)? Not really good enough and it might be a better way. HOWEVER, atm, my thread count goes down quite a bit every time the uploader finishes and back to normal after a 20sec or so (a few "watcher-threads" must be killed by windows etc).

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