CODEWITHSUNDEEP
c++multithreadingqt
Gabriel Chaves Becchi
Gabriel Chaves Becchi

Reputation: 423

Problems Calling a Thread from another GUI Thread in QT

I am using QT to run a Traffic Project. In one point, i create a thread who has to set some variables, wait sometime, set the variables to another value and die; While this thread is waiting, other threads must keep running. This is the thread class

//CLASS FOR CHANGING DYNAMIC LANE
class change_lane : public QThread
{
private:
    lane* dynamic_lane;
    lane_marking *lm_A;
    lane_marking *lm_B;
    time_t change_time;
    direction_way new_dir;
public:
    change_lane(lane *dl, time_t ct, direction_way new_dir) :
        dynamic_lane(dl), lm_A(dl->get_mark_A()), lm_B(dl->get_mark_B()), change_time(ct), new_dir(new_dir) {}
    void run()
    {
        QMutex mux;
        mux.lock();
        cout << "CHANGING DYNAMIC LANE" << endl;
        switch(new_dir)
        {
        case A:
            lm_A->change_status(changing_sw);
            lm_B->change_status(changing_df);
            break;
        case B:
            lm_A->change_status(changing_df);
            lm_B->change_status(changing_sw);
            break;
        }
        sleep(change_time);
        switch(new_dir)
        {
        case A:
            lm_A->change_status(same_way);
            lm_B->change_status(different_way);
            break;
        case B:
            lm_A->change_status(different_way);
            lm_B->change_status(same_way);
            break;
        }
        dynamic_lane->setDirection(new_dir);
        cout << "DONE: CHANGING DYNAMIC LANE" << endl;
        mux.unlock();
    }
};

This is how I call the thread;

This is inside another thread who is running in a while(true) loop;

The Thread is only called once because it sets the w->changing_lane to false;

//CHECKING IF DYNAMIC ROAD MUST CHANGE
    if(w->changing_lane == true)
    {
        direction_way temp_dirway = w->dyn_lane->getDirection();

         switch(temp_dirway)
         {
             case (A):
             {
                 change_lane cl_A(w->dyn_lane,5,B);
                 cl_A.start();
                 break;
             }
             case (B):
             {
                 change_lane cl_B(w->dyn_lane,5,A);
                 cl_B.start();
                 break;
             }
         }
        w->changing_lane = false;
    }

When I Press the button, I get this error:

QThread Error

And the program just stop responding.

In the Application Output, I get this error:

QThread: Destroyed while thread is still running QMutex: destroying locked mutex ASSERT failure in QThread::setTerminationEnabled(): "Current thread was not started with QThread.", file thread\qthread_win.cpp, line 641

Please help

Upvotes: 0

Views: 458

Answers (1)

Stuart Fisher
Stuart Fisher

Reputation: 91

The parent thread controls child threads through the QThread object.Consequently the lifetime of the QThread object should be greater than the lifetime of the thread. After starting a thread you should wait for the thread to finish before deleting it. Call QThread::wait() to do this.

The mutex you've declared in the thread doesn't do anything as it is local to the thread. The point of a mutex is to use it from different threads to protect the data that is shared between them (so a mutex has to be accessible to more than one thread to be of any use).

Upvotes: 1

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