threaddemo.cpp

// threaddemo.cpp: Thread demonstration program.
#include "threaddemo.h"

ThreadDemo::ThreadDemo(QWidget *) {
   QRect rec = QApplication::primaryScreen()->geometry();
   int scrW = rec.width(), scrH = rec.height();
   setGeometry(scrW / 8, scrH / 6, 6 * scrW / 8, 4 * scrH / 6);
   setWindowTitle("Thread demo: GUI responsive during computing");
   thread.setParent(this);
   repaint();
}

void ThreadDemo::calculate() {
   qreal sum = 0;
   for (int i = 1; i <= n; i++) {
      if (thread.isInterruptionRequested()) {
         return;
      }
      qreal i2 = i * i;
      for (int j = 1; j <= n; j++) {
         qreal j2 = j * j;
         for (int k = 1; k <= n; k++)
            sum += sqrt(i2 + j2 + k * k);
      }
   }
   if (n > 0) {
      average = sum / (n * n * n);
      resultAvailable = true;
   }
}

void ThreadDemo::onFinished() {
   QApplication::restoreOverrideCursor();
   repaint();
}

void ThreadDemo::paintEvent(QPaintEvent *) {
   QPainter pnt(this);
   pnt.drawText(30, 100,
      "Click the mouse button to start a new computation.");
   if (resultAvailable) {
      pnt.drawText(30, 150,
         "For i, j, k running independently from 1 to " +
         QString::number(n) +
         ", the average of all values sqrt(i^2 + j^2 + k^2) is " +
         QString::number(average));
   }
}

void ThreadDemo::mousePressEvent(QMouseEvent *) {
   if (thread.isRunning()) { // in case of impatience...
      thread.requestInterruption();
      QApplication::restoreOverrideCursor();
   }
   bool ok;
   int n1 = QInputDialog::getInt(this, "Thread demo",
      "Enter n  to compute n x n x n calculations",
      1, 1, 1000000000, 1, &ok);
   if (!ok)   // Cancel button used?
      return; // n, average and resultAvailable not changed.
   resultAvailable = false;
   n = n1;
   connect(&thread, SIGNAL(finished()), this, SLOT(onFinished()));
   QApplication::setOverrideCursor(Qt::WaitCursor);
   thread.start();
}

void ThreadDemo::closeEvent(QCloseEvent *event) {
   thread.terminate();
   event->accept();
}

void MyThread::run() {
   ThreadDemo *p = (ThreadDemo*)(parent());
   p->calculate();
}