I am doing an exercise qt console application on threading, here is the code:

Qt Code: 
  1. // make two thread, one checking on the state of the other
  2.  
  3.  
  4.     //////////////////////////////////////
  5.     // main.cpp
  6.  
  7.     #include "mytimer.h"
  8.     #include "mythread.h"
  9.     #include "checkthread.h"
  10.     #include <QCoreApplication>
  11.     #include <QString>
  12.     #include <QFile>
  13.     #include <QDebug>
  14.  
  15.  
  16.     int main(int argc, char *argv[])
  17.     {
  18.         QCoreApplication a(argc, argv);
  19.         MyThread mThread1;
  20.         mThread1.name = "thread 1";
  21.         mThread1.start(QThread::HighestPriority);
  22.         CheckThread mCheck(&mThread1);
  23.         mCheck.start();
  24.  
  25.         return a.exec();
  26.     }
  27.  
  28.     ///////////////////////////////////////
  29.     // mythread.h
  30.  
  31.     #ifndef MYTHREAD_H
  32.     #define MYTHREAD_H
  33.  
  34.     #include <QThread>
  35.     #include <QtCore>
  36.  
  37.     class MyThread : public QThread
  38.     {
  39.     public:
  40.         MyThread();
  41.         void run();
  42.         QString name;
  43.         bool stop;
  44.         int sum;
  45.     };
  46.  
  47.     #endif // MYTHREAD_H
  48.  
  49.     //////////////////////////////////////
  50.     // mythread.cpp
  51.  
  52.     #include "mythread.h"
  53.  
  54.     MyThread::MyThread()
  55.     {
  56.         sum = 0;
  57.     }
  58.  
  59.     void MyThread::run()
  60.     {
  61.         qDebug() << this->name << " running...";
  62.         for(int i=0; i<1000; i++) {
  63.             this->sum += i;
  64.             qDebug() << this->name << " counting " << sum;
  65.             this->sleep(1);
  66.             if(this->stop) {
  67.                 break;
  68.             }
  69.         }
  70.     }
  71.  
  72.     //////////////////////////////////////
  73.     // checkthread.h
  74.  
  75.  
  76.     #ifndef CHECKTHREAD_H
  77.     #define CHECKTHREAD_H
  78.  
  79.     #include <QThread>
  80.     #include "mythread.h"
  81.  
  82.     class CheckThread : public QThread
  83.     {
  84.         Q_OBJECT
  85.     public:
  86.         explicit CheckThread(QObject *parent = 0);
  87.         explicit CheckThread(MyThread *tocheck);
  88.         void run();
  89.         MyThread *tocheck_;
  90.     };
  91.  
  92.     #endif // CHECKTHREAD_H
  93.  
  94.     //////////////////////////////////////
  95.     // checkthread.cpp
  96.  
  97.  
  98.     #include "checkthread.h"
  99.  
  100.     CheckThread::CheckThread(QObject *parent) :
  101.         QThread(parent)
  102.     {
  103.     }
  104.  
  105.     CheckThread::CheckThread(MyThread *tocheck) :
  106.         tocheck_(tocheck)
  107.     {
  108.     }
  109.  
  110.     void CheckThread::run() {
  111.         while(true) {
  112.             this->sleep(1);
  113.             if(tocheck_->sum > 15) {
  114.                 tocheck_->stop = true;
  115.             }
  116.         }
  117.     }
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The expected behavior is that mThread1 shoud count to 15 and then stop,
but instead it is stuck at 0.

Interestingly (strangely, i mean), if I add the following code into the main.cpp file, then it runs
ok:


Qt Code: 
  1. void Write(QString Filename)
  2.     {
  3.         QFile fh(Filename);
  4.         if(!fh.open(QFile::WriteOnly | QFile::Text))
  5.         {
  6.             qDebug() << "Could not open file for writing";
  7.             return;
  8.         }
  9.         QTextStream out(&fh);
  10.         out << "hi world";
  11.         fh.flush();
  12.         fh.close();
  13.     }
  14.  
  15.     void Read(QString Filename)
  16.     {
  17.         QFile fh(Filename);
  18.         if(!fh.open(QFile::ReadOnly | QFile::Text))
  19.         {
  20.             qDebug() << "Could not open file for writing";
  21.             return;
  22.         }
  23.         QTextStream in(&fh);
  24.         QString mtext = in.readAll();
  25.         qDebug() << mtext;
  26.     }
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I am using qt 4.8 on a kubuntu 13.10 machine, and the ide is qt creator 3.0.1