Sleep call in qthread blocks UI thread

Question

Hi i am implementing a simple threaded GUI application in QT 4.6.2. I am using QThread without subclassing it. I have made a call to the usleep() function in my start() function this however results in freezing of the GUI. How do i get around this. Below is the code

#ifndef ECGREADER_H
#define ECGREADER_H
#include<QObject>
class ecgreader : public QObject
{
    Q_OBJECT

public:
    ecgreader(QObject *parent=0);
    ~ecgreader();
public Q_SLOTS:
    void start();
Q_SIGNALS:
    void finished();
};
#endif // ECGREADER_H

Below is the start() function

void ecgreader::start()
{
   int i= system("ls>output.txt");
   SLEEP(10000);
   if(i==0)
   {
       emit finished();
   }
}

finally the call to start is made here

void Application::onbtnclicked()
{
    QThread* thread=new QThread;
    ecgreader* reader=new ecgreader;
    reader->moveToThread(thread);
    connect(thread,SIGNAL(started()),reader,SLOT(start()));
    connect(reader,SIGNAL(finished()),thread,SLOT(quit()));
    connect(reader,SIGNAL(finished()),reader,SLOT(deleteLater()));
    connect(reader,SIGNAL(finished()),thread,SLOT(deleteLater()));
    reader->start();
}

Please help

Answer 1

You have two problems: first you created the thread, but you never started it. Second you are directly calling start() on your reader instead of emiting a signal.

I think what you meant was to call thread->start() instead of reader->start():

void Application::onbtnclicked()
{
    QThread* thread=new QThread;
    ecgreader* reader=new ecgreader;
    reader->moveToThread(thread);
    connect(thread,SIGNAL(started()),reader,SLOT(start()));
    connect(reader,SIGNAL(finished()),thread,SLOT(quit()));
    connect(reader,SIGNAL(finished()),reader,SLOT(deleteLater()));
    connect(reader,SIGNAL(finished()),thread,SLOT(deleteLater()));
    thread->start();
}