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QDebug prevents 100% CPU usage on boost::thread



  • In code blocks , if I have no QDebug or printf on threads I get Figure 1, with QDebug I get sinusoid diagram on Figure 2. But I want to CPU usage like Figure 1, what caused this unexpected CPU usage , how can I prevent sinusoid CPU usage.

    0_1537336339261_printf.png
    Figure 1.

    0_1537336352928_printfw.png
    Figure 2.

    Thanks Regards..

    boost::mutex mtx;
    static int i =0;
    
    void tFunc()
    {
        while(true)
        {
            mtx.lock();
            ++i;
            mtx.unlock();
            // qDebug() = comment => CPU  %100?
            qDebug() << i;
    
        }
    }
    void tFunc2()
    {
        while(true)
        {
            mtx.lock();
            ++i;
            mtx.unlock();        
            qDebug() << i;
        }
    }
    int main(int argc, char *argv[])
    {
        QCoreApplication a(argc, argv);
    
        cpu_set_t set;
        // cpu_set_t : Data structure represents a set of CPUs.
        CPU_ZERO(&set);
        //CPU_ZERO : Clears set, so that it contains no CPUs.
        CPU_SET(0,&set); // CPU 1
        //CPU_SET : Add CPU to cpu set.  
    
        sched_setaffinity(0,sizeof(cpu_set_t),&set);
    
        boost::thread *tP2 = new boost::thread(tFunc);
        boost::thread *tP3 = new boost::thread(tFunc2);
    
     
        return a.exec();
    }
    
    

  • Lifetime Qt Champion

    Hi,

    It's not unexpected, printing something from your thread requires a lot more instructions and IO than just incrementing a counter that will happen in memory.

    So if you want to maximise your CPU usage, don't print.


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