emit qt signal is very slow how it can be optimized?

I have a such peace of code.

thread that reeds the file

Code:

---

#include <QThread>
#include <QString>
class openner : public QThread
{
	Q_OBJECT
 
public:	
	openner(QString);
	~openner();
	void run();
private:
	QString file;
signals:
	void onStart(int);
	void on(int);
	void onEnd(int);
};

---

Code:

---

#include "openner.h"
#include <QFile>
#include <QTextStream>
openner::openner(QString f)
	: QThread(0)
{
	file=f;
}
void openner::run()
{
	QString str;
	QFile f(file);	
	f.open(QIODevice::ReadOnly | QIODevice::Text);		
	QTextStream in(&f);
	emit onStart(f.size());
	while(!in.atEnd())
	{
		str=in.readLine();		
		emit on(in.pos());
	}
	emit onEnd(f.size());
	f.close();
}
openner::~openner()
{
 
}

---

main form

Code:

---

#include <QtGui/QMainWindow>
#include <QProgressBar>
#include "openner.h"
class progressTest : public QMainWindow
{
	Q_OBJECT
private:
	openner *o;
	QProgressBar *pb;
public:
	progressTest(QWidget *parent = 0, Qt::WFlags flags = 0);
	~progressTest();
protected slots:
	void onStart(int);
	void onProgres(int);
	void onEnd(int);
};

---

Code:

---

#include "progresstest.h"
 
progressTest::progressTest(QWidget *parent, Qt::WFlags flags)
	: QMainWindow(parent, flags)
{
	pb=new QProgressBar(this);
	pb->resize(200,20);
	o=new openner("C:\\projects\\umc\\UMC_invoice_.28532.00.00.100000_id_0793918_part_1.csv");
	QObject::connect(o,SIGNAL(onStart(int)),this,SLOT(onStart(int)));
	QObject::connect(o,SIGNAL(on(int)),this,SLOT(onProgres(int)));
	QObject::connect(o,SIGNAL(onEnd(int)),this,SLOT(onEnd(int)));
	o->start();
}
void progressTest::onStart(int m)
{	
	pb->setMaximum(m);
 
}
void progressTest::onProgres(int l)
{
	pb->setValue(l);
}
void progressTest::onEnd(int l)
{	
	pb->setValue(0);
}
progressTest::~progressTest()
{
 
}

---

When I use my program with emit on(in.pos()); then it takes for about three hours to read file. But then I use it without emit on(in.pos()); file is read in the minutes. the size of file is 3000 kb
How the emit of signal can be optimised?
OS - windows XP
IDE - Microsoft Visual Studio 2008?

What happens if u use Qt::DirectConnection as last argument with connect ?

it's bad idea to use Qt:: DirectConnection between threads, Qt::QueuedConnection must be used.

I tried Qt::QueuedConnection and nothing changed.

yes, because by default last parameter in 'connect' is Qt::AutoConnection, which means

Quote:

---

If the signal is emitted from the thread in which the receiving object lives, the slot is invoked directly, as with Qt:: DirectConnection; otherwise the signal is queued, as with Qt::QueuedConnection.

---

try to use customs events, but I think result will not change.
ps. if you use thread just for loading information and don't transform it then you can you only main thread and use qApp->processEvents() in long time operations.

a) Qt::QueuedConnection is the default for threads. So explicitly specifying it won't change anything.

b) simple solutions might be

1. emit the signal not every time but only every 100th time (or so)
2. just open the file in a normal function call, update the gui and call QCoreApplication::processEvents() now and then
3. do not use a thread
4. use a plain callback (do not forget to synchronize access! and don't forget you must not call gui code from another thread!)

HTH

What happen when You don't emit signal but You call in.pos() ?

Code:

---

#include "openner.h"
#include <QFile>
#include <QTextStream>
openner::openner(QString f)
	: QThread(0)
{
	file=f;
}
void openner::run()
{
	QString str;
	QFile f(file);	
	f.open(QIODevice::ReadOnly | QIODevice::Text);		
	QTextStream in(&f);
	emit onStart(f.size());
	while(!in.atEnd())
	{
		str=in.readLine();		
		emit on(in.pos());
 
               	QApplication::processEvents();
 
	}
	emit onEnd(f.size());
	f.close();
}
openner::~openner()
{
 
}

---

Try the processEvents() function. I think that u emit too much signals, so the GUI its not able to process them during an intensive while loop.

OPPS! Sorry for the mistake

use QCoreApplication::processEvents();