Data race for lambda with Qt::QueuedConnection

Seems like data race for lambda with Qt::QueuedConnection

env:

• Windows
• Qt 5, Qt 6, both tested
• VS2019
• MinGW 11.2

Lets take a look at code snippet:

void Controller::doWork()
{
    for (size_t ix = 0; ix < 2; ++ix) {
        QObject* ctx = new QObject;
        QObject::connect(this, &Controller::finished, ctx, [this, ctx] (QString id) {
            this->disconnect(ctx);
            ctx->deleteLater();

            qDebug() << "Received value " << ctx << " :";
            qDebug() << id;
        }, Qt::QueuedConnection);

        qDebug() << "Passed value: " << QString::number(ix);
        work(QString::number(ix));
    }
}

void Controller::work(QString id)
{
    [[maybe_unused]] auto future = QtConcurrent::run([this, id] () {
        qDebug() << "Replied:  " << id;
        QThread::msleep(300);
        emit finished(id);
    });
}

EB:

• lambda was called twice (see attachment)

AB:

• lambda was called 4 times, sometimes twice (see attachment)

Minimal sample to test in attach.

Detailed descrition.

• In my main project i had issue that on such call i got EB from above. But, second call was with cached arguments from first call arguments.
  Example output:
  Passed value: "0"
  Passed value: "1"
  Replied: "0"
  Replied: "1"
  Received value "0"
  Received value "0"
• I tried to reproduce argument caching on this code snippet, but i couldn`t, while i could steel reproduce it in main project env.
• I could not reproduce AB in main project env while code architecture literally same.