[Interest] QTimer priority

[Edward Sutton]

On Jan 8, 2016, at 4:11 AM, Etienne Sandré-Chardonnal <etienne.sandre at m4x.org<mailto:etienne.sandre at m4x.org>> wrote:

Dear all,

In a recent stress test, where I created 5 sub-processes, each one starting idealThreadCount() fully working threads (ie they never sleep), I found that a QTimer responsible for sending some information messages to the sub-process stdout was stuck until the working threads stopped.

The QTimer is created and lives in the main thread, and the main event loop is alive and responds to event. But the slot to which timeout() is called is never called until the worker threads finish.

Could it be that the QTimer is using a different thread, that gets stuck due to the high system load?

The platform is Windows


While possible, I doubt issue is caused by system load.

Slots will not get called unless the main event loop gets to run.  You can force this to happen by calling processEvents.  If you find yourself calling processEvents you may need to analyze your code for “bad smells”.


    QCoreApplication::processEvents();


If you are emitting signals from threads and need to receive them on a slot in your MainWindow for example, you can use a QueuedConnection


    // Use QueuedConnection because readyRead signal is called from a thread that uses WINSOCK to listen for Bluetooth receive data

    connect(&m_bufferReceiveWriter, SIGNAL(readyRead()),

            this,   SIGNAL(readyRead()),

            Qt::ConnectionType(Qt::QueuedConnection | Qt::UniqueConnection));

I would recommend to analyze where you create your QTimer, where you emit the QTimer signals, and where is your slot located.

-Ed



Thanks!
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