Qt: qthread destroyed while thread is still running during closing

Question

I have a class:

class centralDataPool : public QObject
{
    Q_OBJECT
public:
    centralDataPool(QObject * parent = 0);
    ~centralDataPool();
    commMonitor commOverWatch;

private:
    QThread monitorThread;
    int totalNum;

signals:
    void createMonitor(int);
};

In its constructor I did:

centralDataPool::centralDataPool(QObject* parent) : QObject(parent),totalNum(0)
{
    connect(this, SIGNAL(createMonitor(int)), &commOverWatch, SLOT(createMonitor(int)));
    commOverWatch.moveToThread(&monitorThread);
    monitorThread.start();
}

when I called the destructor of this class I get the error message:

qthread destroyed while thread is still running

But when I tried to terminate the monitorThread in the destructor of class centralDataPool,

centralDataPool::~centralDataPool()
{
    monitorThread.terminate();
}

I get memory leakage.

What is the correct way to terminate a thread during the destruction of its owner object ?

You should not finish a thread like this. Look at the documentation: http://doc.qt.io/qt-5/qthread.html#terminate — Vinícius Gobbo A. de Oliveira, Feb 22 '15 at 17:35
@ViníciusGobboA.deOliveira, Hi, I have tried to add wait() or switch to quit(), but none of them works...Could you give more hints? — Nyaruko, Feb 22 '15 at 17:43
Have you called `monitorThread.setTerminationEnabled(true);` before calling `terminate();`? — Vinícius Gobbo A. de Oliveira, Feb 22 '15 at 17:47
Oh! I've missed that. It is a static protected method, so it is not possible to call it without inheriting from `QThread`. In this case, you must somehow signal the method being executed at the thread that it must end. Anyway, this is the most correct way to do this without leaking. — Vinícius Gobbo A. de Oliveira, Feb 22 '15 at 17:54
Try together: monitorThread.quit(); monitorThread.wait(); in destructor — Jablonski, Feb 22 '15 at 18:55
You should declare QThread as pointer because it is garbage collected as soon as it goes out of the scope. — Kahn, Feb 22 '15 at 20:16

score 15 · Accepted Answer · answered Feb 23 '15 at 05:10

You should note that if you have a loop running in a function of your thread, you should explicitly end it in order to properly terminate the thread.

You can have a member variable in your class named finishThread which should be set to true when the application is going to close. Just provide a slot in which you set the value for finishThread. When you want to terminate the thread emit a signal that is connected to that slot with a true value. finishThread should be provided in the loop condition to end it when it is set to true. After that wait for the thread to finish properly for some seconds and force it to terminate if it did not finish.

So you can have in your destructor :

emit setThreadFinished(true); //Tell the thread to finish
monitorThread->quit();
if(!monitorThread->wait(3000)) //Wait until it actually has terminated (max. 3 sec)
{
    monitorThread->terminate(); //Thread didn't exit in time, probably deadlocked, terminate it!
    monitorThread->wait(); //We have to wait again here!
}

I can call destructor via way? delete object; object.deleteLAter(); object->~Class(); — kien bui, May 30 '18 at 09:29

Qt: qthread destroyed while thread is still running during closing

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