Qt 6, Qt.Future .then freezess app

[Dariusz]

Hey

More or less my code >

auto reply = mNetworkAccessManager->get(initialRequest);//, j.dump().c_str());
    
        auto o = QtFuture::connect(reply, &QNetworkReply::finished)
                .then(this, [this, reply] {
                    const auto data = icuj::getJsonFromRawString(reply->readAll());
                    qDebug() << data;
                    qDebug() << reply;
                    return reply;
                });

Intended to be returned from function as "backend-pre-process-logic" so that I can attach logic after it.

        o.then(this, [](QNetworkReply *reply) {
            qDebug() << "secondary callback?";
            return reply;
        });

However when I try to daisy chain second .then, from o, then the app freezes.
Any ideas? I'm a little lost.

I know I can do
.then()
.then()
.then()
But I want to do thens, in different functions/handlers...

Edit, ok I take it back, I cant do .then().then().then(), second then freezes app o.o

[Dariusz]

Ok seems like the issue was thread... passing context > this, caused it to somehow self lock o.O

[Pl45m4]

@Dariusz said in Qt 6, Qt.Future .then freezess app:

    o.then(this, [](QNetworkReply *reply) {
        qDebug() << "secondary callback?";
        return reply;
    });

What if you chain them directly?
Maybe o.then() is the problem?!

auto reply = mNetworkAccessManager->get(initialRequest);//, j.dump().c_str());
    
        auto o = QtFuture::connect(reply, &QNetworkReply::finished)
                .then(this, [this, reply] {
                    const auto data = icuj::getJsonFromRawString(reply->readAll());
                    qDebug() << data;
                    qDebug() << reply;
                    return reply;
              }).then(this, [](QNetworkReply *reply) {           
                    qDebug() << "secondary callback?";           
                    return reply;           
              });

@Dariusz said in Qt 6, Qt.Future .then freezess app:

.then()
.then()
.then()

and then? aaaand then? :D

[Dariusz]

@Pl45m4 For some reason passing this as context caused mutex lock!
I'm now trying to figure out how to perform multiple/nested "then's"....

Like >

QFuture<int> networkInit() {
    QNetworkRequest initialRequest(QUrl("some fancy url"));
    auto reply = mNetworkAccessManager->get(initialRequest);//, j.dump().c_str());
    auto o = QtFuture::connect(reply, &QNetworkReply::finished)
            .then([reply] {
                auto data = reply->readAll()
                return data;
            }).then([](QByteArray reply) {
        return 1;
    })
    QObject::connect(reply, &QNetworkReply::finished, reply, QNetworkReply::deleteLater, Qt::QueuedConnection);
    return o
}
///This func breaks :- ) 
QFuture<QNetworkReply *> requestData(QString adr) {
    return networkInit().then([this, adr](int status) {
        if (status == 0) {
            QNetworkRequest initialRequest(QUrl(adr));
            auto reply = mNetworkAccessManager->get(initialRequest);
            auto futReply= QtFuture::connect(reply, &QNetworkReply::finished)
                    .then([reply] {
                        return reply;
                    });
            return futReply;
        }
        // raise Exception ???
    });
}

/// But if the one above works then I get >

Adding a continuation to a future which already has a continuation. The existing continuation is overwritten.		
(C:\Users\qt\work\qt\qtbase\src\corelib\thread\qfutureinterface.cpp:940, void __cdecl QFutureInterfaceBase::setContinuation(class std::function<void __cdecl(class QFutureInterfaceBase const &)>,class QFutureInterfaceBasePrivate *))

int main() {
    auto future = requestData("someFancyDat")
    future.then([](QNetworkReply *reply) {
        qDebug() << reply->readAll();
    });
}

@Pl45m4 said in Qt 6, Qt.Future .then freezess app:

and then? aaaand then? :D

lolz that's hilarious XDDD

[SGaist]

Hi,

One issue with your main function is that it does not create any QCoreApplication object hence Qt's internal state is not properly setup.

[Dariusz]

@SGaist I have QApplication - gui one. ah yes the int main() is just a quick hack/example... there full widget app with buttons running :- )

Also I got it to work, I ended up getting nested futures, and the path to fix that is .unwrap()>https://doc.qt.io/qt-6/qfuture.html#unwrap
Seems to work! :D

Threading and linking to context still seem to be broken tho o.o