QNetworkAccessManager delete later while requests are added

Question

I have one QNetworkAccessManager to handle all my requests. The manager can receive an action to send a post request at anytime the application is running. I noticed there is almost a 70s timeout time before a QNetworkReply finishes when there is no internet.

In the constructor of the class I create the manager with:

mgr = new QNetworkAccessManager(this);
connect(mgr,SIGNAL(finished(QNetworkReply*)),this,SLOT(requestFinished(QNetworkReply*)));
connect(mgr,SIGNAL(sslErrors(QNetworkReply *, const QList<QSslError> &)),this,SLOT(handleSSLErrors(QNetworkReply *, const QList<QSslError> &)));

The request are created with:

QNetworkReply * reply = mgr->post(request, payload);
connect(reply, SIGNAL(error(QNetworkReply::NetworkError)), this, 
SLOT(slotError(QNetworkReply::NetworkError)));

For the networkreplies I have a signal slot:

connect(mgr,SIGNAL(finished(QNetworkReply*)),this,SLOT(requestFinished(QNetworkReply*)));

I delete the QNetworkReply rep in the requestFinished method with rep->deleteLater();.

With this I expect all QNetworkReply to be deleted automatically.

In the desctructor of the class I run

delete mngr

my thoughts: 0:00 I send a request. 0:01 I delete the mngr (which automatically deletes the onfinished slot) 1:10 the request finishes, there is no longer a slot so deleteLater() is not called.

What is the proper way to delete the 'QNetworkAccessManager', It is possible my appliation send a request every 60 seconds that timeouts for 70 seconds (meaning there is always an ongoing request). How can I delete the qnetworkmanager without creating memory leaks?

Maybe call the class deleteLater() in the slot of requestFinished? — wthung
@wthung I have but that does not cover the scenario where the mngr is deleted before the request finishes because at that point the slot does not exist anymore — Sven van den Boogaart
Is "0:01 I delete the mngr" necessary? Looks that the class got deleted very quickly but I think the class should be deleted after requestFinished slot has been called. Since the class is also a QObject derived class, just call deleteLater() in the slot of requestFinished — wthung
@wthung Thats just an example of a timeline that would couse the problem. How can I get the reply removed if the slot does not exist. and if the slot still exists the mngr is not removed right? — Sven van den Boogaart
Maybe an ugly way to store the pointer to a global one can solve the problem, but I don't recommend this. I recommend keep the class alive until it's not used anymore. In this way you won't suffer from the problem you asked. — wthung

T3 H40 T3 H40 · Accepted Answer · 2020-06-17T10:55:09

connect(mgr, &QNetworkAccessManager::destroyed, reply, &QNetworkReply::deleteLater);

QObjects offer the destroyed() signal. So you can connect your managers destroyed() with the open replys deleteLater(). When your manager is destroyed all open replies will be deleted. In case the reply finishes with the manager still alive, you explicitly call the deleteLater() as you already do, which will prevent the reply from lingering until you destroy the manager.

QNetworkAccessManager delete later while requests are added

1 Answers